Dominance hierarchy limits resilience in the endangered queenless ant Dinoponera lucida

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However, species differ widely in the specific mechanisms associated with division of labour. Often, social groups have to cope with severe perturbations and resume normal functioning as quickly as possible. How well they do so depends on the behavioural mechanisms involved and on species life-history traits. Here, we studied the division of labour in D. lucida , a threatened species of native Brazilian queenless ants with small colony sizes, to assess whether colonies facing a drastic perturbation of the established task allocation are resilient, and through which potential mechanisms. We first separated the colonies into two sub-colonies, one with the foragers and the other with the nurses. As this is an important modification of colony structure, we expected workers to respond quickly by switching tasks. Our experiment showed that, contrary to our hypotheses, workers showed little plasticity in switching tasks, and colonies did show very limited resilience. Foragers, when isolated from nurses, show a certain plasticity in their behavioural repertoire, performing both tasks (foraging and nursing). However, groups of nurses facing the absence of foragers kept almost exclusively to nursing tasks. Only a few performed episodic outside activities. When workers were returned to their original colonies, foragers switched back to foraging. However, the effect of the manipulation could still be observed 20 days after reintroduction, with workers showing lower general activity, ingesting larvae and reproductive workers losing their dominance. Considering our current knowledge about the regulation of both division of labour and reproductive hierarchies in Dinoponera and other ponerine ants, we propose that this lack of resilience is due to the reproductive conflict between nurses, which delays behavioural maturation and motivation to engage in outside tasks. The existence of individual strategies thus imposes severe costs on group functioning. This could be an additional issue when considering the conservation of this endangered species. division of labour behavioural flexibility plasticity task allocation conservation Ponerinae Figures Figure 1 Figure 2 Figure 3 Introduction One of the main reasons for the ecological dominance of social insects across the globe is division of labour, also known as task allocation (Hölldobler and Wilson 1990 ). It relies on the temporary or permanent specialisation of group members in the execution of specific sets of tasks. Division of labour allows the efficient and simultaneous execution of all the tasks necessary for colony maintenance in self-organised groups without central control (Robinson et al. 2009 ). Task choice and degree of specialisation can be influenced by many factors and the process of division of labour is not to this day fully understood (review in Beshers and Fewell 2001 ). Genetic (Kohlmeier et al. 2019 ), physiological (Leitner and Dornhaus 2019 ; Robinson 2009 ) and social/environmental factors (Tripet and Nonacs 2004 ; Ravary et al. 2007 ; Tanaka et al. 2022 ), as well as age (Wakano et al. 1998 ; Hölldobler and Wilson 1990 ) and morphology (Grzes et al. 2016 ; Kamhi et al. 2015 ) influence division of labour. Many of these factors are interconnected, with nurses being the youngest, most corpulent and most fertile when compared with foragers (Féneron et al. 1996 ; Robinson et al. 2009 ; Tanaka et al. 2022 ). These ants have a high work potential and/or reproductive value for the colony and generally begin their lives in low-risk tasks, transitioning to more risky tasks as they age (Beshers and Fewell 2001 ). Task specialisation and work organisation are not however inflexible and stereotyped processes. The immediate needs of the colonies are perceived by colony members, leading to task shifting when the social group has a limited workforce to perform competing tasks (Gordon, 1996 ). This ability to maintain colony homeostasis or to return to a pre-disturbance performance state after perturbation characterises group resilience (Middleton and Latty 2016 ). For example, according to seasonal variations, colonies may need more nurses when producing more immature (in the reproductive phase, for example) or need more foragers during food abundance periods or when foragers longevity decreases due to abiotic (e.g., desiccation) or biotic (e.g., competition or predation) reasons (Wilson 1984 ). Thus, behavioural plasticity is likely a critical component of colony resilience. This process acts as a buffer for colony loss in fitness (i.e. loss of immature) until the initial task ratio slowly recovers (Kwapich and Tschinkel 2013 ), even when the original efficiency is committed due to developmental limitations (Calderone 1995 ). Workers' ability to express behavioural plasticity in executing tasks is well-known for ants (Seid and Traniello 2006 ; Robinson et al. 2009 ; Bernadou et al., 2015 ;Tanaka et al. 2022 ). The probability of switching tasks varies across species and between behavioural subcastes. For example, for Pheidole dentata , older individuals acquire a larger behavioural repertory and are more prone to switch roles as changes in colony needs arise (Seid and Traniello 2006 ). In Temnothorax albipennis , less corpulent individuals act as 'elite' and fulfil the need for more brood care and foraging (Robinson et al., 2009 ). In Temnothorax rugatulus , inactive ants serve as an important resilience element for being a ‘reserve’ labour force. The removal of most active ants doesn’t affect colony efficiency since previous inactive ants increased their activity and occupied the gaps (Charbonneau et al. 2017 ). Task plasticity or lack thereof is usually explained by the response threshold model. The model proposes that when the intensity of a given stimulus for a task exceeds the individual response threshold of a worker, this worker is more likely to engage in the execution of this task; in turn, the conclusion of the task reduces the stimulus intensity, limiting the number of workers engaged in the task (Bonabeau et al. 1996 ). Workers with different thresholds thus commit to different tasks, leading to different task allocations. However, considering the response threshold as fixed in time could lead to limitations, due to the fixed threshold models needing to account for factors such as changes associated with time and age, physiology, hormones, learning, among others (Theraulaz et al. 1998 ). In the logic of response threshold, Jeanson ( 2019 ) points out two mechanisms that can lead to task plasticity: large fluctuations in task-related stimuli and internal changes to the stimuli responsiveness. The responsiveness variation may be due to stochastic changes in perception and motor execution, but also to learning, maturation and environmental changes. However, there are cases where task plasticity was absent and workers were unable to shift tasks (Johnson, 2003 ; McGregor et al., 2024 ; Schmid-Hempel, 1992 ), especially to fill a lack of foragers (Kwapich & Tschinkel, 2013 , 2016 ). In Pogonomyrmex badius , the experimental removal of foragers leads to the death of larvae in the same proportion (Kwapich & Tschinkel, 2013 ), even in the presence of seed storages and other colony members (Kwapich & Tschinkel, 2016 ). Although the benefits of behavioural plasticity are well discussed, the possible benefits of limited plasticity have not been well documented. According to Jeanson ( 2019 ), there is a trade-off between behavioural plasticity (within-individual behavioural variation) and behavioural consistency. Higher specialisation favours the colony's homeostasis by reducing task-switching costs, while higher plasticity allows colonies to respond to sudden fluctuations in task needs. Jeanson ( 2019 ) also proposes a positive relation between group size and task specialisation, in that more populous colonies tend to have a more specialised workforce compared to a less populous colony. In those populous colonies, plasticity emerges at the colonial level by auto-organised processes. Such processes however need a large number of individuals to interact to be effective (Beekman et al. 2001 ). In Ponerine ants, which have small colonies and usually do not have polymorphic workers, behavioural plasticity is expected to be higher, and this has been shown in some species (Lachaud & Fresneau, 1987 ; Tanaka et al., 2022 ). This supposed plasticity becomes crucial when colonies are exposed to repeated perturbations, as can be the case for species occurring in areas with anthropic activities that lead to habitat fragmentation and heavy traffic. Ultimately, the impact of habitat fragmentation is more serious with species that have small colony size or reproduction by fission because it limits dispersion (Peixoto et al., 2008 ). It is thus important to evaluate across species what are the characteristics of task allocation and resilience after perturbation. In some species of ants (Peeters, 1993 ) the female reproductive caste (queens) has been lost and colonies are composed of totipotent workers who are all potentially fertile and able to mate. This adds another level of complexity to the division of labour since workers can be reproducers or non-reproducers, and also assume different tasks, such as nurses and foragers. In most queenless ant species, younger workers interact through agonistic interactions and establish a dominance hierarchy based on ovarian activity and behavioural dominance (Peixoto et al., 2008 ; Monnin and Peeters, 1999 ). Hopeful reproducers thus stay in the nest, monitoring the gamergate’s fertility (the dominant mated worker; Peeters and Crewe, 1984 ), and other potentially fertile workers through chemical signalling and typical agonistic behavioural interactions (reviewed in Peeters, 1993 ; Monnin & Peeters, 1998 ; Monnin and Peeters, 1999 ). This leads these hopeful workers and the gamergate to stay close to the brood, where they assume the role of nurses (brood tending, brood carrying, larval feeding). This also allows monitoring of the egg piles for eggs laid by subordinate workers, and oophagy by the gamergate (Monnin & Peeters, 1999 ). Therefore, in these cases, it is also expected that the least fertile workers are the most likely to abandon brood care (Tanaka et al., 2022 ). This superposition of the hopeful reproducers/nurses task in queenless ants can have implications for task allocation and its plasticity because totipotent workers can opt for reproductive or ergonomic tasks as well as for the different tasks at hand. Here we investigate the degree of plasticity in task allocation in Dinoponera lucida (Emery, 1901), a threatened ant species endemic to Brazil, that is suffering from human-induced rapid environmental changes (Delabie, 2018 ). We separated the workers of two colonies according to task (sociotomy) and later reunited them to explore task switching and resilience (Lachaud & Fresneau, 1987 ; McGregor et al., 2024 ; Tanaka et al., 2022 ). In this species, life history traits such as very small colony size, the foundation of new colonies by fission and multiple foragers' deaths by human activity can cause the colony to face task-biased segregation. By doing so, we aim to understand how colonies react to drastic modifications of immediate needs in task allocation. Ultimately, our findings can support the hypothesis that fissioning should respect some proportions for each task-related worker and lead to new possibilities of mitigation strategies for human impact on a threatened native ant species. Material and Methods 1. Study Model D. lucida occurs in hot and humid forests and is endemic to the Brazilian Atlantic Rainforest (Peixoto et al. 2010 ; Delabie 2018 ), with its occurrence records including the states of São Paulo, Minas Gerais, Espírito Santo and Bahia (Dias and Lattke 2021 ). This species is currently classified as endangered, which is aggravated by its method of founding new colonies (Delabie 2018 ). That is, by the process of fission which reduces its dispersion abilities when compared with species which disperse through flying queens (Peixoto et al. 2010 ). The females’ body length ranges from 2.5 cm to 2.9 cm (Dias and Lattke 2021 ), and the number of workers in a colony can range from 22 to 106 (Peixoto 2010). Since D. lucida is an endangered species, we chose to reduce the number of collected colonies. Two colonies were collected in the Reserva Biológica de Sooretama nature reserve, Espírito Santo, Brazil (-19.0034543, -40.156555). Colony 1 had 18 workers, 19 eggs, 13 larvae and 2 pupae at the beginning of the experiments while Colony 2 had 25 workers, 24 eggs and 22 larvae. They were then transferred to the laboratory where they were maintained at stable temperature (25 ± 2°C) and humidity (67 ± 3%) conditions. The colonies were installed in artificial plaster nests (50 cm x 50 cm x 50 cm) subdivided into five chambers, connected by a tube to a plastic box serving as a foraging area (50 cm x 50 cm x 50 cm). The colonies were fed at least three times per week with Tenebrio molitor larvae, a mix of apple and honey and water ad libitum . The foraging areas were covered with moistened paper to prevent dryness and contained pieces of wood, small rocks and soil from the collection site to offer a less homogeneous environment. To permit individual identification of all workers they were marked with plastic tags fixed in the back of their thorax (Corbara et al. 1986 ). Each colony had tags of different colours, and each ant had a different letter printed on the tag. 2. Experimental Methods We adapted the three-phase protocol used by Tanaka et al. ( 2022 ) to meet the restrictions imposed by D. lucida . As such, to compare social organisation before, during and after an event of task segregation, we divided our experiment into three phases: original colonies, biased colonies (i.e., colonies splitted according to workers subcastes) and reunited colonies (Tanaka et al., 2022 ). For the behavioural observations during the whole experiment, we performed scan sampling at 30-minute intervals, using a webcam (model Logitech C922 Pro HD Stream, resolution 2560 x 1440 px) attached to a tripod and connected to a computer. To register which ants were acting as nurses, foragers or were indeterminate (performing both tasks or none), in each sampling bout, we took photos of the nests and foraging areas. To identify the gamergate, at the beginning of every phase and after the scan sampling period, we recorded the nest of each colony for 30 minutes on two different days. We also used chance observations during colony maintenance and experiment setup to confirm the gamergates identities. This identification was based on the observation of the very recognizable dominance agonistic behaviours and egg laying, as in the ethogram proposed by Monnin and Peeters ( 1999 ) for Dinoponera quadriceps . Like Peixoto et al. ( 2008 ), we did not observe in D. lucida the specific behaviours of blocking or gaster rubbing described in Monnin and Peeters ( 1999 ), two behaviours which are the most frequently expressed by gamergates of D. quadriceps . The behaviours that were expressed by workers of D. lucida , and most expressed by the putative gamergate, were gaster curling, antennal boxing and egg laying. These behaviours are also expressed by gamergates of D. quadriceps and were used to determine the gamergates in our colonies. We chose not to euthanize the ants to confirm insemination and ovarian activity for ethical reasons and because of their conservation status. For the first phase of the experiment, we observed the unmanipulated colonies to identify the original tasks of the workers. We performed 10 scans per day, separated by at least 30 minutes, for 4 consecutive days (Tanaka et al., 2022 ). We considered nurses the ants that were observed in contact with the brood or standing atop it at least once and that never left the nest. For foragers, we considered the ants that were observed at least once exploring the foraging area and did not interact with the brood. We chose to maintain the same terminology as Tanaka et al. ( 2022 ). Stable nurses and foragers were workers that exclusively kept doing the same task during the separation period. Precocious foragers are nurses that change to exclusively assume foraging associated tasks in the nurse biased subcolonies. Reversed nurses are foragers that switch to perform exclusively nursing tasks in the forager biased subcolonies. Finally, the indeterminate ants were classified into two groups: ‘both tasks’, the ones that were observed acting as both forager and nurse or ‘non-task’ those that have not been observed performing any of them. Finally, the ants' nursing propensity index was defined on a scale of 0 to 1 where 0 were exclusive foragers and 1 were exclusive nurses by dividing the number of times a worker performed brood related tasks divided by the total number of behaviours. Similarly, the activity level of workers was calculated on a 0 to 1 scale where zero was inactive in all the scans (non-task) and 1 was the ants that were seen active (foraging or caring) in all the scans. In the second phase of the experiment, we moved the ants classified as nurses to nurse-biased colonies and foragers to forager-biased colonies. All subcolonies were moved to new plaster nests to prevent the colony smell from biasing this experimental phase. The eggs, pupae and larvae of the original colonies were equally distributed between the biased colonies. Unlike Tanaka et al. ( 2022 ), we did not remove the indeterminate ants from the experiment, as they were too few to be kept in isolation. Instead, we also equally distributed them between the biased colonies. As in Tanaka et al. ( 2022 ), the identified gamergates were also moved to the foraged-biased colonies. Maintaining the gamergates in the experimental colonies was important to make sure the colonies kept their cohesion and to limit physiological and behavioural changes in workers. The choice to keep them with foragers was because this would ensure group cohesion. This was not as important in the nurse-biased colonies because dominant ants also perform nursing behaviour (Smith et al., 2011 ; Shimoji et al., 2020 ), meaning that fertile ants were present in these colonies. Our choice means that the dominant ants in the nurse-biased colonies could exhibit agonistic behaviours in order to select a new alpha (Monnin & Peeters, 1999 ). However, considering D. lucida colony size, the conflict should be limited to 2 or 3 workers (Monnin et al., 2003 ). This second phase lasted seven days, being the initial three days for the colonies’ habituation and the last four for the behavioural observations, with the same sampling methods as used in the first phase. For the third and final phase, we returned both nurse- and forager-biased colonies to the original nest, reuniting the ants of each colony. The ants were put in the foraging area and left to enter the nest spontaneously. The brood was counted before reunion. After a one-day interval when the ants settled in their original nest, we resumed the sampling for four days with the same methods as before. As Tanaka et al. ( 2022 ), we observed the ants for two days, one week after the conclusion of the observations, and two more days a week later. In both two-day samplings, we filmed interactions in the nests for 30 minutes each day after the scan samplings were done. Statistical analysis To test the propensity of nurses and foragers to change tasks, we compared the transition rates using a chi-square test. To compare activity ratios and task proportion between phases we performed a Friedman test. To investigate the relationship between the activity in original colonies and the propensity to change tasks we constructed generalised linear mixed models (GLMMs) with a binomial distribution. We used the ants' nursing propensity index as the response variable. The proportion of foragers or nurses over the total number of workers across the total observation period (40 observations) in the original colony was the fixed effect, and colony ID was the random effect. We performed all statistical tests using the open-source software R (R Core Team, 2022 ). Results We performed 160 observations of 43 workers. In the original colonies, more ants were nurses and they mostly stayed stable nurses during the whole experiment (Table S1 ). In both forager-biased colonies, none of the original foragers were able to fully revert to nurse and in the nurse-biased colonies, only one nurse became a precocious forager. In the forager-biased colony, only 3 out of 13 (23%) foragers remained stable in this task. In stark contrast, a total of 15 out of 22 (68,1%) nurses remained stable in nurse biased colonies. We also observed that 4 out of 22 (18,1%) nurses transitioned to both tasks in that phase, and 8 out 13 (61,5%) foragers made this same task transition. Analysing the conversion rate of nurses and foragers, we found foragers to be more likely to change tasks. These ants showed more flexible behaviour, performing both tasks when most nurses remained exclusive nurses during the biased colony phase (X² test; X² = 8.4311, df = 2, p = 0.01, Fig. 1 ). Besides, there was no relation between workers' activity level (i.e. the intensity of work as a forager or nurse) in the original colony and their propensity to change tasks in the biased colony period (GLMM; nurses: df = 17, Z = 1.586, p = 0.113; foragers: df = 8, Z = -1.55, p = 0.121). Table 1 Number of workers in each task group during the three phases of the experiment. Original task Task in the biased colony* Task in the reintroduced colony (week 1) Forager 13 Stable forager 3 Forager 10 Nurse 22 Precocious forager 1 Nurse 23 Both tasks 1 Stable nurse 15 Both tasks 4 Non-task 5 Reverted nurse 0 Non-task 2 Both tasks 14 Non-task 2 *Changes between non-task/both tasks and the other categories were omitted for clarity (i.e. forager to both tasks, forager to non-task, etc) Table 2 Number of workers of each original and biased subcolonies task groups assuming different tasks in the reunited colonies (week 1) of the experiment. Original task Task in the biased colony Categorized task in the reintroduced colony (week 1) Forager Nurse Both tasks Non-task Forager Partially reverted nurse* 5 1 1 1 Stable forager 3 0 0 0 Nurse Precocious forager 0 0 1 0 Partially precocious forager* 0 3 1 0 Stable nurse 0 15 0 0 *performed both-tasks In the first week of the reintroduced colony, most foragers that partially reverted to nurses (i.e., performed both tasks) returned exclusively to foraging (n = 5/8; Fig. 1 and Table 2 ), only one of them became an exclusive nurse. In the second and third week of the reintroduction phase, we observed a radical change in the behaviour of the experimental colonies. The colonies as a whole significantly decreased their nursing and foraging activities during this period compared to the other phases (Friedman test: X² = 62.937, df = 4, p < 0.001; Fig. 2 ). However, there was no significant difference in the proportion of tasks during the experiment (Friedman test: X² = 7.4, df = 4, p = 0.12, Fig. 3 ). That is, the number of workers involved in one task was not transferred to another, despite an increase of 'both-tasks' workers in the biased phase and 'non-tasks' in the reintroduction phase (Fig. 3 , Table S1 ). These modifications seem to be associated with the expression of reproductive conflict. The reproductive workers of both colonies lost their rank as gamergates and all larvae had been eaten in both colonies when the third phase ended (colony 1 and 2 respectively had 5 and 18 larvae in the beginning of the reintroduction phase). In colony 1, the original gamergate was not attacked but her role as a nurse and her proximity to the brood decreased (activity in the original colony vs. activity in the third week of the reintroduced colony: 0.425 vs. 0.025). Other workers started to interact mildly aggressively on top of the brood pile (antennal boxing). In colony 2, the gamergate was immobilised almost permanently by two to eight workers (Figure S1 ), and on week 2 was actively maintained outside the nest. Twenty days later, she was observed inside the nest but still with a worker holding its antennae. Discussion In this study, we studied the division of labour (DOL) of the queenless ant D. lucida in an experimental sociotomy (i.e., the colony division in task-biased subcolonies). We found that foragers were more prone to show behavioural plasticity and assume nursing activities when facing a lack of nurses. Nurses, on the contrary, were unable to behave the same way, maintaining exclusively nursing activities when there were no foragers, and this despite worker and larvae starvation. Then, when colonies were reunited again, foragers returned to their original activity while nurses exhibited increased conflict related behaviours and consumed the brood. Our results bring important elements to the understanding of the organisation of the DOL in a queenless species with small colonies, and about which mechanisms could be involved in this complex phenomenon. Besides, it is interesting to investigate in which scenarios colony resilience is not expected to occur. In D. lucida original colonies, most ants were specialised in foraging or nurse activities. By generating separate groups of workers allocated to different tasks, DOL allows an efficient colony functioning with parallel processing of the different colony needs (Hölldobler & Wilson, 1990 ). Thus, DOL is thought to be an element of ecological success in insect societies (Oster & Wilson, 1978 ). However, DOL also can expose species with small colony sizes or frequent mortality of some categories of workers to prolonged perturbation (Waibel et al., 2006 ). The disturbance of colony organisation can lead to fitness losses and ultimately to colony decline. Several mechanisms are thought to alleviate these potential deleterious effects. For example, the rapid reallocation of workers from one task to the other, or a less pronounced specialisation (Karsai & Wenzel, 1998 ; Jongepier & Foitzik, 2016 ). This plasticity that restores colony homeostasis represents the group's resilience to perturbation. Colony resilience correlates positively with colony size because the loss of some workers will affect small colonies more drastically (Jeanson, 2019 ). This tendency has already been observed in several cases (Seid and Traniello, 2006 ; Robinson et al., 2009 ; Tanaka et al., 2022 ). Our results show that foragers indeed presented immediate group resilience when in forager-biased subcolonies since these workers partially reverted to nurses, that is, they were capable of diversifying their behavioural repertoire and started to perform both tasks, foraging and nursing. Once the ants experimentally removed are reintroduced in the original colonies, foragers mainly return exclusively to foraging. The foragers are the oldest and least fertile workers in Dinoponera (Peixoto et al., 2008 ; Monnin & Peeters, 1999 ). Because of age polyethism, they also had experience in nursing during their first months as adults. Thus, behavioural plasticity here is facilitated by workers’ previous experience, direct feeding of the larvae and by the fact that colonies are small and that there’s no morphological difference between workers. Other ant studies found similar results with foragers showing greater behavioural plasticity, whether due to age, experience or reduced fertility (Tanaka et al., 2022 ) and corpulence (Robinson et al., 2009 ). In another ant of the same genus, D. quadriceps , foragers were also segregated from nurses and they showed task plasticity (Medeiros, 2016 ). Finally the return of foragers to their initial task in colonies reintroduction is in accordance with the model based on thresholds and similar results are found in other ant species (Seid & Traniello, 2006 ; Jeanson, 2019 ). For example, in the Ponerine ant, Neoponera apicalis , workers are capable of assuming the missing task behaviour, but, when recombined with their parent nest, they resume their previous age-specific tasks (Lachaud and Fresneau, 1987 ). One of the most striking results is the lack of plasticity in nurses. When divided in nurse-biased colonies, despite the need of foragers, most of these ants remained exclusively performing in-nest behaviours. This is counterintuitive since it led to larvae and worker starvation during the subcolonies phase. The response threshold model predicts that higher levels of a signal, such as brood hunger pheromone, lead to more workers being stimulated as the signal surpasses their threshold to respond to the task (Beshers & Fewell, 2001 ). Here, it seems that nurses were not able to respond to increased stimulus by changing their behavioural repertoire. It is unlikely that workers did not perceive the signal, since in original colonies nurses fed the larvae with the food brought by foragers.The absence of resilience could happen because Dinoponera nurses are invariably the more corpulent, fertile and young workers in the colony (Monnin & Peeters, 1999 ; Smith et al., 2011 ). Nurses/reproductive workers also have lower JH titers, a hormone associated with behavioural maturation and foraging tasks in the genus and other genera (Norman et al., 2019 ; Pamminger et al., 2016). These characteristics probably cause nurses to have a higher response threshold for foraging-related stimuli and to not engage in risky tasks, such as foraging (Asher et al., 2013 ), since they are the ones that make them hopeful reproductives in this reproductive hierarchy based species. Because of this, we propose that in queenless ant the conflict for reproduction associated with queuing for the alpha position reduces the ability of in-nest workers to express foraging behaviour, since the traits associated with foraging (lower fat, higher JH titers), reduces their competitive ability. Another experiment of split colonies in D. quadriceps gave similar results (Medeiros 2016 ). In this study, the proportion of behaviour performed by workers (foraging and nursing) was recorded, and the workers were assigned to subcastes not on an all-or-nothing criteria, but based on the proportion of nursing and foraging related behaviours. The colonies were split according to these categories. In the forager biased colonies, nursing activity increased significantly among foragers. After reunion, inactivity increased and both foraging and nursing were reduced. The isolated nurses also had reduced activities. In the nurse biased colonies, very little foraging was observed As workers lose fertility and gain foraging experience with age this could be another factor driving nurses to continue doing exclusively this task, similar to our study. The tendency to remain as a stable nurse could be also explained by the fact these ants were separated from their original gamergate. A similar situation happens in nature when the gamergate loses fertility or dies. In this case, another high fertility worker (usually beta in the hierarchy) occupies her place (Monnin and Peeters 1999 ). Thus, it is also important to remain performing nurse activities to monitor changes in the dominance hierarchy (Peixoto et al., 2008 ; Monnin & Peeters, 1999 ). In Diacamma cf. indicum , another queenless ant (Tanaka et al., 2022 ), the dominance hierarchy presents very remarkable differences. The gamergate cuts other workers' gemmae preventing them from ever occupying the gamergate position, making it more likely for nurses to perform riskier tasks (Fukumoto et al., 1989 ; Peeters & Higashi, 1989 ; reviewed in Tsuji, 2021 ). Therefore, in this species, a great number of nurses become precocious foragers when living in a nurse-biased colony (Tanaka et al., 2022 ). This, although, comes with a disadvantage since nurses that became precocious foragers showed lower ovarian activity than matched stable nurses (Tanaka et al., 2024 ). In conclusion, even in the absence of foragers, a situation that can happen in nature due to the death or disappearance of foragers, for example, D. lucida nurses are not motivated to start foraging. As they have an opportunity to assume the reproductive role, hopeful nurses invest in the reproductive competition and are unable to compensate for past distress (i.e., the great loss of foragers). This is probably also linked with the probability of gamergate turnover, which may be high in species with small colony sizes such as D. lucida (Monnin et al., 2003 ). It is thus probable that the threshold model does not correspond well to what happens in D. lucida , or that reproductive competition increases the threshold too much for workers to switch tasks efficiently. The association of fertility with task performance is not unusual, mainly because hormones such as JH and vitellogenin are known to influence DoL, in particular in species where workers lay trophic or fertile eggs regularly (de Souza & Hartfelder, 2023 ). From the second week on after reintroduction, colonies showed decreased activity, larvae were eaten and the gamergates lost their alpha position in the dominance hierarchy. The absence of larvae caused a general colony desorganisation, which is expected since larvae are known to be an important stimulus for colony functioning and DoL. The absence of larvae caused a general colony desorganisation, which is expected since larvae are known to be an important stimulus for colony functioning and DoL. The replacement of the gamergates may have several causes. First, starvation can have created a loss of fertility in the reproductive workers. Second the absence of the gamergate from the nurse biased colonies, even if short, can have heightened conflict and caused potentially reproductive nurses to aggress the gamergate and to immobilise her in Colony 2. This behaviour, described originally for D. quadriceps (Monnin and Peeters 1999 ) has been also observed in D. lucida (Peixoto et al., 2008 ). Thus, our manipulation led to drastic changes in colony organisation which had detrimental effects on their functioning. Independent of the initial task, total reversions (i.e., a complete change between nurse to forager and forager to nurse tasks) are rare in D. lucida . In many species, the mechanisms associated with division of labour, and especially the transition from inside to outside tasks are thought to be age, morphology, and to a lesser degree physiology and experience (Beshers & Fewell, 2001 ). Many experiments, inspired by historical work on honey bees, have shown general plasticity in task specialisation, both in the reversion of foragers to nurses and the acceleration of development towards external tasks (Seid and Traniello, 2006 ; Robinson et al., 2009 ; Leitner & Dornhaus, 2019 ; Tanaka et al., 2022 ). These changes are labile and transient physiological modifications are observed (Toth & Robinson, 2005 ). Most of these studies however used models with short lived workers. Indeed, most species, like honey bees, seem to have a worker lifespan of months at the maximum. Maturation of workers is often a matter of weeks. In stark contrast, Dinoponera non-reproductive workers can live more than two years and the maturation of workers from inside to outside tasks is a slow process, often requiring months (Medeiros, 2016 ). This could explain why nurses are not able to switch quickly from inside to outside tasks, since foraging is associated with profound changes in many aspects of the ants physiology and behaviour. This can also explain why foragers do not completely switch back to nursing, since they probably are much older than usual nurses, and have an extended experience of outside tasks. More than age, this finding suggests that physiological (i.e., fertility, fat content and hormone titers), behavioural (boldness and aggression), cognitive (experience, motivation), adaptive (the permanence in the queue for potential reproduction), and evolutionary (the loss of the queen morph) mechanisms also regulate division of labour, making workers less flexible in this long-lived species. The transition between nurses to foragers does seem to be a complex process of maturation (Féneron et al., 1996 ). In a situation when workers can opt for individual strategies, our results show that the group is susceptible to loss of cohesion and fitness, and resilience is weak (Bourke, 2011 ). In conclusion, our results suggest that, under disturbed conditions, colonies of D. lucida do not efficiently reallocate workers to the different tasks. Dominance hierarchy and the competition for reproduction seem to be elements that prevent resilience, making nurses less flexible. When the disturbance disappears, the ants return to or maintain their previous task. D. lucida is thought to be threatened because of the destruction of its habitat combined with reduced reproductive and dispersion ability (Peixoto et al., 2010 ). In our study, we also show that in situations when forager mortality increases, the lack of resilience we observed could also impair colonies' survival. Although our study is based on a limited number of colonies of these endangered ants, they are in line with published literature and bring interesting elements on the potential threats that could make conservation efforts difficult. Understanding the mechanisms of division of labour in ponerine ants such as D. lucida can be useful to elucidate how division of labour mechanisms change, interact and evolve in the Formicidae clade. It can also be an important factor to take into account in species conservation issues. Declarations Funding MELV received a funding grant from the Brazilian Science Ministry (Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq), MCTI/CNPq/Universal PQ 311790/2021-8 and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), CAPES/PRInt 88887.916823/2023-00. NC received funding from CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) process CAPES/PRInt 88887.915491/2023-00. DHT received a funding grant from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), process CAPES/Proex 88887.875303/2023-00. TRBM received a funding grant from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), process CAPES/Proex 88887.702947/2022-00 Declaration of interest We declare no competing interests. Acknowledgements We thank the team at the Reserva Biológica de Sooretama for their help in collecting the colonies and Igor Eloi for the assistance in the statistics. We also thank Stéphane Chameron for his helpful comments. This paper is a result of the practical classes of the course taught by NC: PSE5929, promotion 2023, “Etologia dos Insetos Sociais” of the Psicologia Experimental graduate course at the Institute of Psychology, Universidade de São Paulo, Brazil. 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Supplementary Files Supplementary.docx DLucDOL.rproj Dadosgeral.xlsx General.csv Initial.foragers.csv Initial.nurses.csv Script.r dt1.csv x2.csv Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Major Revisions Needed 16 Jun, 2024 Reviewers agreed at journal 12 May, 2024 Reviewers invited by journal 12 May, 2024 Editor assigned by journal 20 Apr, 2024 First submitted to journal 13 Apr, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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It relies on the temporary or permanent specialisation of group members in the execution of specific sets of tasks. Division of labour allows the efficient and simultaneous execution of all the tasks necessary for colony maintenance in self-organised groups without central control (Robinson et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Task choice and degree of specialisation can be influenced by many factors and the process of division of labour is not to this day fully understood (review in Beshers and Fewell \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Genetic (Kohlmeier et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), physiological (Leitner and Dornhaus \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Robinson \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) and social/environmental factors (Tripet and Nonacs \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Ravary et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Tanaka et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), as well as age (Wakano et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; H\u0026ouml;lldobler and Wilson \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) and morphology (Grzes et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Kamhi et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) influence division of labour. Many of these factors are interconnected, with nurses being the youngest, most corpulent and most fertile when compared with foragers (F\u0026eacute;neron et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Robinson et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Tanaka et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These ants have a high work potential and/or reproductive value for the colony and generally begin their lives in low-risk tasks, transitioning to more risky tasks as they age (Beshers and Fewell \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTask specialisation and work organisation are not however inflexible and stereotyped processes. The immediate needs of the colonies are perceived by colony members, leading to task shifting when the social group has a limited workforce to perform competing tasks (Gordon, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). This ability to maintain colony homeostasis or to return to a pre-disturbance performance state after perturbation characterises group resilience (Middleton and Latty \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). For example, according to seasonal variations, colonies may need more nurses when producing more immature (in the reproductive phase, for example) or need more foragers during food abundance periods or when foragers longevity decreases due to abiotic (e.g., desiccation) or biotic (e.g., competition or predation) reasons (Wilson \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). Thus, behavioural plasticity is likely a critical component of colony resilience. This process acts as a buffer for colony loss in fitness (i.e. loss of immature) until the initial task ratio slowly recovers (Kwapich and Tschinkel \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), even when the original efficiency is committed due to developmental limitations (Calderone \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1995\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWorkers' ability to express behavioural plasticity in executing tasks is well-known for ants (Seid and Traniello \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Robinson et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Bernadou et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2015\u003c/span\u003e;Tanaka et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The probability of switching tasks varies across species and between behavioural subcastes. For example, for \u003cem\u003ePheidole dentata\u003c/em\u003e, older individuals acquire a larger behavioural repertory and are more prone to switch roles as changes in colony needs arise (Seid and Traniello \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). In \u003cem\u003eTemnothorax albipennis\u003c/em\u003e, less corpulent individuals act as 'elite' and fulfil the need for more brood care and foraging (Robinson et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In \u003cem\u003eTemnothorax rugatulus\u003c/em\u003e, inactive ants serve as an important resilience element for being a \u0026lsquo;reserve\u0026rsquo; labour force. The removal of most active ants doesn\u0026rsquo;t affect colony efficiency since previous inactive ants increased their activity and occupied the gaps (Charbonneau et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Task plasticity or lack thereof is usually explained by the response threshold model. The model proposes that when the intensity of a given stimulus for a task exceeds the individual response threshold of a worker, this worker is more likely to engage in the execution of this task; in turn, the conclusion of the task reduces the stimulus intensity, limiting the number of workers engaged in the task (Bonabeau et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Workers with different thresholds thus commit to different tasks, leading to different task allocations. However, considering the response threshold as fixed in time could lead to limitations, due to the fixed threshold models needing to account for factors such as changes associated with time and age, physiology, hormones, learning, among others (Theraulaz et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). In the logic of response threshold, Jeanson (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) points out two mechanisms that can lead to task plasticity: large fluctuations in task-related stimuli and internal changes to the stimuli responsiveness. The responsiveness variation may be due to stochastic changes in perception and motor execution, but also to learning, maturation and environmental changes.\u003c/p\u003e \u003cp\u003eHowever, there are cases where task plasticity was absent and workers were unable to shift tasks (Johnson, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; McGregor et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Schmid-Hempel, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), especially to fill a lack of foragers (Kwapich \u0026amp; Tschinkel, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In \u003cem\u003ePogonomyrmex badius\u003c/em\u003e, the experimental removal of foragers leads to the death of larvae in the same proportion (Kwapich \u0026amp; Tschinkel, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), even in the presence of seed storages and other colony members (Kwapich \u0026amp; Tschinkel, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Although the benefits of behavioural plasticity are well discussed, the possible benefits of limited plasticity have not been well documented. According to Jeanson (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), there is a trade-off between behavioural plasticity (within-individual behavioural variation) and behavioural consistency. Higher specialisation favours the colony's homeostasis by reducing task-switching costs, while higher plasticity allows colonies to respond to sudden fluctuations in task needs. Jeanson (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) also proposes a positive relation between group size and task specialisation, in that more populous colonies tend to have a more specialised workforce compared to a less populous colony. In those populous colonies, plasticity emerges at the colonial level by auto-organised processes. Such processes however need a large number of individuals to interact to be effective (Beekman et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Ponerine ants, which have small colonies and usually do not have polymorphic workers, behavioural plasticity is expected to be higher, and this has been shown in some species (Lachaud \u0026amp; Fresneau, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This supposed plasticity becomes crucial when colonies are exposed to repeated perturbations, as can be the case for species occurring in areas with anthropic activities that lead to habitat fragmentation and heavy traffic. Ultimately, the impact of habitat fragmentation is more serious with species that have small colony size or reproduction by fission because it limits dispersion (Peixoto et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). It is thus important to evaluate across species what are the characteristics of task allocation and resilience after perturbation.\u003c/p\u003e \u003cp\u003eIn some species of ants (Peeters, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1993\u003c/span\u003e) the female reproductive caste (queens) has been lost and colonies are composed of totipotent workers who are all potentially fertile and able to mate. This adds another level of complexity to the division of labour since workers can be reproducers or non-reproducers, and also assume different tasks, such as nurses and foragers. In most queenless ant species, younger workers interact through agonistic interactions and establish a dominance hierarchy based on ovarian activity and behavioural dominance (Peixoto et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Monnin and Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Hopeful reproducers thus stay in the nest, monitoring the gamergate\u0026rsquo;s fertility (the dominant mated worker; Peeters and Crewe, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1984\u003c/span\u003e), and other potentially fertile workers through chemical signalling and typical agonistic behavioural interactions (reviewed in Peeters, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Monnin \u0026amp; Peeters, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Monnin and Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). This leads these hopeful workers and the gamergate to stay close to the brood, where they assume the role of nurses (brood tending, brood carrying, larval feeding). This also allows monitoring of the egg piles for eggs laid by subordinate workers, and oophagy by the gamergate (Monnin \u0026amp; Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Therefore, in these cases, it is also expected that the least fertile workers are the most likely to abandon brood care (Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This superposition of the hopeful reproducers/nurses task in queenless ants can have implications for task allocation and its plasticity because totipotent workers can opt for reproductive or ergonomic tasks as well as for the different tasks at hand.\u003c/p\u003e \u003cp\u003eHere we investigate the degree of plasticity in task allocation in \u003cem\u003eDinoponera lucida\u003c/em\u003e (Emery, 1901), a threatened ant species endemic to Brazil, that is suffering from human-induced rapid environmental changes (Delabie, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). We separated the workers of two colonies according to task (sociotomy) and later reunited them to explore task switching and resilience (Lachaud \u0026amp; Fresneau, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; McGregor et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this species, life history traits such as very small colony size, the foundation of new colonies by fission and multiple foragers' deaths by human activity can cause the colony to face task-biased segregation. By doing so, we aim to understand how colonies react to drastic modifications of immediate needs in task allocation. Ultimately, our findings can support the hypothesis that fissioning should respect some proportions for each task-related worker and lead to new possibilities of mitigation strategies for human impact on a threatened native ant species.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1. Study Model\u003c/h2\u003e \u003cp\u003e \u003cem\u003eD. lucida\u003c/em\u003e occurs in hot and humid forests and is endemic to the Brazilian Atlantic Rainforest (Peixoto et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Delabie \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), with its occurrence records including the states of S\u0026atilde;o Paulo, Minas Gerais, Esp\u0026iacute;rito Santo and Bahia (Dias and Lattke \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This species is currently classified as endangered, which is aggravated by its method of founding new colonies (Delabie \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). That is, by the process of fission which reduces its dispersion abilities when compared with species which disperse through flying queens (Peixoto et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). The females\u0026rsquo; body length ranges from 2.5 cm to 2.9 cm (Dias and Lattke \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and the number of workers in a colony can range from 22 to 106 (Peixoto 2010). Since \u003cem\u003eD. lucida\u003c/em\u003e is an endangered species, we chose to reduce the number of collected colonies. Two colonies were collected in the Reserva Biol\u0026oacute;gica de Sooretama nature reserve, Esp\u0026iacute;rito Santo, Brazil (-19.0034543, -40.156555). Colony 1 had 18 workers, 19 eggs, 13 larvae and 2 pupae at the beginning of the experiments while Colony 2 had 25 workers, 24 eggs and 22 larvae. They were then transferred to the laboratory where they were maintained at stable temperature (25\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C) and humidity (67\u0026thinsp;\u0026plusmn;\u0026thinsp;3%) conditions. The colonies were installed in artificial plaster nests (50 cm x 50 cm x 50 cm) subdivided into five chambers, connected by a tube to a plastic box serving as a foraging area (50 cm x 50 cm x 50 cm). The colonies were fed at least three times per week with \u003cem\u003eTenebrio molitor\u003c/em\u003e larvae, a mix of apple and honey and water \u003cem\u003ead libitum\u003c/em\u003e. The foraging areas were covered with moistened paper to prevent dryness and contained pieces of wood, small rocks and soil from the collection site to offer a less homogeneous environment. To permit individual identification of all workers they were marked with plastic tags fixed in the back of their thorax (Corbara et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Each colony had tags of different colours, and each ant had a different letter printed on the tag.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2. Experimental Methods\u003c/h2\u003e \u003cp\u003eWe adapted the three-phase protocol used by Tanaka et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) to meet the restrictions imposed by \u003cem\u003eD. lucida\u003c/em\u003e. As such, to compare social organisation before, during and after an event of task segregation, we divided our experiment into three phases: original colonies, biased colonies (i.e., colonies splitted according to workers subcastes) and reunited colonies (Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For the behavioural observations during the whole experiment, we performed scan sampling at 30-minute intervals, using a webcam (model Logitech C922 Pro HD Stream, resolution 2560 x 1440 px) attached to a tripod and connected to a computer. To register which ants were acting as nurses, foragers or were indeterminate (performing both tasks or none), in each sampling bout, we took photos of the nests and foraging areas. To identify the gamergate, at the beginning of every phase and after the scan sampling period, we recorded the nest of each colony for 30 minutes on two different days. We also used chance observations during colony maintenance and experiment setup to confirm the gamergates identities. This identification was based on the observation of the very recognizable dominance agonistic behaviours and egg laying, as in the ethogram proposed by Monnin and Peeters (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) for \u003cem\u003eDinoponera quadriceps\u003c/em\u003e. Like Peixoto et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), we did not observe in \u003cem\u003eD. lucida\u003c/em\u003e the specific behaviours of blocking or gaster rubbing described in Monnin and Peeters (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), two behaviours which are the most frequently expressed by gamergates of \u003cem\u003eD. quadriceps\u003c/em\u003e. The behaviours that were expressed by workers of \u003cem\u003eD. lucida\u003c/em\u003e, and most expressed by the putative gamergate, were gaster curling, antennal boxing and egg laying. These behaviours are also expressed by gamergates of \u003cem\u003eD. quadriceps\u003c/em\u003e and were used to determine the gamergates in our colonies. We chose not to euthanize the ants to confirm insemination and ovarian activity for ethical reasons and because of their conservation status.\u003c/p\u003e \u003cp\u003eFor the first phase of the experiment, we observed the unmanipulated colonies to identify the original tasks of the workers. We performed 10 scans per day, separated by at least 30 minutes, for 4 consecutive days (Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). We considered nurses the ants that were observed in contact with the brood or standing atop it at least once and that never left the nest. For foragers, we considered the ants that were observed at least once exploring the foraging area and did not interact with the brood. We chose to maintain the same terminology as Tanaka et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Stable nurses and foragers were workers that exclusively kept doing the same task during the separation period. Precocious foragers are nurses that change to exclusively assume foraging associated tasks in the nurse biased subcolonies. Reversed nurses are foragers that switch to perform exclusively nursing tasks in the forager biased subcolonies. Finally, the indeterminate ants were classified into two groups: \u0026lsquo;both tasks\u0026rsquo;, the ones that were observed acting as both forager and nurse or \u0026lsquo;non-task\u0026rsquo; those that have not been observed performing any of them. Finally, the ants' nursing propensity index was defined on a scale of 0 to 1 where 0 were exclusive foragers and 1 were exclusive nurses by dividing the number of times a worker performed brood related tasks divided by the total number of behaviours. Similarly, the activity level of workers was calculated on a 0 to 1 scale where zero was inactive in all the scans (non-task) and 1 was the ants that were seen active (foraging or caring) in all the scans.\u003c/p\u003e \u003cp\u003eIn the second phase of the experiment, we moved the ants classified as nurses to nurse-biased colonies and foragers to forager-biased colonies. All subcolonies were moved to new plaster nests to prevent the colony smell from biasing this experimental phase. The eggs, pupae and larvae of the original colonies were equally distributed between the biased colonies. Unlike Tanaka et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), we did not remove the indeterminate ants from the experiment, as they were too few to be kept in isolation. Instead, we also equally distributed them between the biased colonies. As in Tanaka et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), the identified gamergates were also moved to the foraged-biased colonies. Maintaining the gamergates in the experimental colonies was important to make sure the colonies kept their cohesion and to limit physiological and behavioural changes in workers. The choice to keep them with foragers was because this would ensure group cohesion. This was not as important in the nurse-biased colonies because dominant ants also perform nursing behaviour (Smith et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Shimoji et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), meaning that fertile ants were present in these colonies. Our choice means that the dominant ants in the nurse-biased colonies could exhibit agonistic behaviours in order to select a new alpha (Monnin \u0026amp; Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). However, considering \u003cem\u003eD. lucida\u003c/em\u003e colony size, the conflict should be limited to 2 or 3 workers (Monnin et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). This second phase lasted seven days, being the initial three days for the colonies\u0026rsquo; habituation and the last four for the behavioural observations, with the same sampling methods as used in the first phase.\u003c/p\u003e \u003cp\u003eFor the third and final phase, we returned both nurse- and forager-biased colonies to the original nest, reuniting the ants of each colony. The ants were put in the foraging area and left to enter the nest spontaneously. The brood was counted before reunion. After a one-day interval when the ants settled in their original nest, we resumed the sampling for four days with the same methods as before. As Tanaka et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), we observed the ants for two days, one week after the conclusion of the observations, and two more days a week later. In both two-day samplings, we filmed interactions in the nests for 30 minutes each day after the scan samplings were done.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eTo test the propensity of nurses and foragers to change tasks, we compared the transition rates using a chi-square test. To compare activity ratios and task proportion between phases we performed a Friedman test. To investigate the relationship between the activity in original colonies and the propensity to change tasks we constructed generalised linear mixed models (GLMMs) with a binomial distribution. We used the ants' nursing propensity index as the response variable. The proportion of foragers or nurses over the total number of workers across the total observation period (40 observations) in the original colony was the fixed effect, and colony ID was the random effect. We performed all statistical tests using the open-source software R (R Core Team, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eWe performed 160 observations of 43 workers. In the original colonies, more ants were nurses and they mostly stayed stable nurses during the whole experiment (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). In both forager-biased colonies, none of the original foragers were able to fully revert to nurse and in the nurse-biased colonies, only one nurse became a precocious forager. In the forager-biased colony, only 3 out of 13 (23%) foragers remained stable in this task. In stark contrast, a total of 15 out of 22 (68,1%) nurses remained stable in nurse biased colonies. We also observed that 4 out of 22 (18,1%) nurses transitioned to both tasks in that phase, and 8 out 13 (61,5%) foragers made this same task transition. Analysing the conversion rate of nurses and foragers, we found foragers to be more likely to change tasks. These ants showed more flexible behaviour, performing both tasks when most nurses remained exclusive nurses during the biased colony phase (X\u0026sup2; test; X\u0026sup2; = 8.4311, df\u0026thinsp;=\u0026thinsp;2, p\u0026thinsp;=\u0026thinsp;0.01, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Besides, there was no relation between workers' activity level (i.e. the intensity of work as a forager or nurse) in the original colony and their propensity to change tasks in the biased colony period (GLMM; nurses: df\u0026thinsp;=\u0026thinsp;17, Z\u0026thinsp;=\u0026thinsp;1.586, p\u0026thinsp;=\u0026thinsp;0.113; foragers: df\u0026thinsp;=\u0026thinsp;8, Z = -1.55, p\u0026thinsp;=\u0026thinsp;0.121).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eNumber of workers in each task group during the three phases of the experiment.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eOriginal task\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eTask in the biased colony*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eTask in the reintroduced colony (week 1)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eForager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStable forager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eForager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNurse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePrecocious forager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNurse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBoth tasks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStable nurse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBoth tasks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNon-task\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReverted nurse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNon-task\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBoth tasks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNon-task\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e*Changes between non-task/both tasks and the other categories were omitted for clarity (i.e. forager to both tasks, forager to non-task, etc)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eNumber of workers of each original and biased subcolonies task groups assuming different tasks in the reunited colonies (week 1) of the experiment.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eOriginal task\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTask in the biased colony\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c6\" namest=\"c3\"\u003e \u003cp\u003eCategorized task in the reintroduced colony (week 1)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eForager\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNurse\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBoth tasks\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNon-task\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eForager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePartially reverted nurse*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStable forager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eNurse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePrecocious forager\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePartially precocious forager*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStable nurse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e*performed both-tasks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the first week of the reintroduced colony, most foragers that partially reverted to nurses (i.e., performed both tasks) returned exclusively to foraging (n\u0026thinsp;=\u0026thinsp;5/8; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), only one of them became an exclusive nurse. In the second and third week of the reintroduction phase, we observed a radical change in the behaviour of the experimental colonies. The colonies as a whole significantly decreased their nursing and foraging activities during this period compared to the other phases (Friedman test: X\u0026sup2; = 62.937, df\u0026thinsp;=\u0026thinsp;4, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). However, there was no significant difference in the proportion of tasks during the experiment (Friedman test: X\u0026sup2; = 7.4, df\u0026thinsp;=\u0026thinsp;4, p\u0026thinsp;=\u0026thinsp;0.12, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). That is, the number of workers involved in one task was not transferred to another, despite an increase of 'both-tasks' workers in the biased phase and 'non-tasks' in the reintroduction phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). These modifications seem to be associated with the expression of reproductive conflict. The reproductive workers of both colonies lost their rank as gamergates and all larvae had been eaten in both colonies when the third phase ended (colony 1 and 2 respectively had 5 and 18 larvae in the beginning of the reintroduction phase). In colony 1, the original gamergate was not attacked but her role as a nurse and her proximity to the brood decreased (activity in the original colony vs. activity in the third week of the reintroduced colony: 0.425 vs. 0.025). Other workers started to interact mildly aggressively on top of the brood pile (antennal boxing). In colony 2, the gamergate was immobilised almost permanently by two to eight workers (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), and on week 2 was actively maintained outside the nest. Twenty days later, she was observed inside the nest but still with a worker holding its antennae.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we studied the division of labour (DOL) of the queenless ant \u003cem\u003eD. lucida\u003c/em\u003e in an experimental sociotomy (i.e., the colony division in task-biased subcolonies). We found that foragers were more prone to show behavioural plasticity and assume nursing activities when facing a lack of nurses. Nurses, on the contrary, were unable to behave the same way, maintaining exclusively nursing activities when there were no foragers, and this despite worker and larvae starvation. Then, when colonies were reunited again, foragers returned to their original activity while nurses exhibited increased conflict related behaviours and consumed the brood. Our results bring important elements to the understanding of the organisation of the DOL in a queenless species with small colonies, and about which mechanisms could be involved in this complex phenomenon. Besides, it is interesting to investigate in which scenarios colony resilience is not expected to occur.\u003c/p\u003e \u003cp\u003eIn \u003cem\u003eD. lucida\u003c/em\u003e original colonies, most ants were specialised in foraging or nurse activities. By generating separate groups of workers allocated to different tasks, DOL allows an efficient colony functioning with parallel processing of the different colony needs (H\u0026ouml;lldobler \u0026amp; Wilson, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). Thus, DOL is thought to be an element of ecological success in insect societies (Oster \u0026amp; Wilson, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1978\u003c/span\u003e). However, DOL also can expose species with small colony sizes or frequent mortality of some categories of workers to prolonged perturbation (Waibel et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The disturbance of colony organisation can lead to fitness losses and ultimately to colony decline. Several mechanisms are thought to alleviate these potential deleterious effects. For example, the rapid reallocation of workers from one task to the other, or a less pronounced specialisation (Karsai \u0026amp; Wenzel, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Jongepier \u0026amp; Foitzik, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). This plasticity that restores colony homeostasis represents the group's resilience to perturbation. Colony resilience correlates positively with colony size because the loss of some workers will affect small colonies more drastically (Jeanson, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This tendency has already been observed in several cases (Seid and Traniello, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Robinson et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOur results show that foragers indeed presented immediate group resilience when in forager-biased subcolonies since these workers partially reverted to nurses, that is, they were capable of diversifying their behavioural repertoire and started to perform both tasks, foraging and nursing. Once the ants experimentally removed are reintroduced in the original colonies, foragers mainly return exclusively to foraging. The foragers are the oldest and least fertile workers in \u003cem\u003eDinoponera\u003c/em\u003e (Peixoto et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Monnin \u0026amp; Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Because of age polyethism, they also had experience in nursing during their first months as adults. Thus, behavioural plasticity here is facilitated by workers\u0026rsquo; previous experience, direct feeding of the larvae and by the fact that colonies are small and that there\u0026rsquo;s no morphological difference between workers. Other ant studies found similar results with foragers showing greater behavioural plasticity, whether due to age, experience or reduced fertility (Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) and corpulence (Robinson et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In another ant of the same genus, \u003cem\u003eD. quadriceps\u003c/em\u003e, foragers were also segregated from nurses and they showed task plasticity (Medeiros, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Finally the return of foragers to their initial task in colonies reintroduction is in accordance with the model based on thresholds and similar results are found in other ant species (Seid \u0026amp; Traniello, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Jeanson, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). For example, in the Ponerine ant, \u003cem\u003eNeoponera apicalis\u003c/em\u003e, workers are capable of assuming the missing task behaviour, but, when recombined with their parent nest, they resume their previous age-specific tasks (Lachaud and Fresneau, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1987\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOne of the most striking results is the lack of plasticity in nurses. When divided in nurse-biased colonies, despite the need of foragers, most of these ants remained exclusively performing in-nest behaviours. This is counterintuitive since it led to larvae and worker starvation during the subcolonies phase. The response threshold model predicts that higher levels of a signal, such as brood hunger pheromone, lead to more workers being stimulated as the signal surpasses their threshold to respond to the task (Beshers \u0026amp; Fewell, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Here, it seems that nurses were not able to respond to increased stimulus by changing their behavioural repertoire. It is unlikely that workers did not perceive the signal, since in original colonies nurses fed the larvae with the food brought by foragers.The absence of resilience could happen because \u003cem\u003eDinoponera\u003c/em\u003e nurses are invariably the more corpulent, fertile and young workers in the colony (Monnin \u0026amp; Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Smith et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Nurses/reproductive workers also have lower JH titers, a hormone associated with behavioural maturation and foraging tasks in the genus and other genera (Norman et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Pamminger et al., 2016). These characteristics probably cause nurses to have a higher response threshold for foraging-related stimuli and to not engage in risky tasks, such as foraging (Asher et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), since they are the ones that make them hopeful reproductives in this reproductive hierarchy based species. Because of this, we propose that in queenless ant the conflict for reproduction associated with queuing for the alpha position reduces the ability of in-nest workers to express foraging behaviour, since the traits associated with foraging (lower fat, higher JH titers), reduces their competitive ability. Another experiment of split colonies in \u003cem\u003eD. quadriceps\u003c/em\u003e gave similar results (Medeiros \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In this study, the proportion of behaviour performed by workers (foraging and nursing) was recorded, and the workers were assigned to subcastes not on an all-or-nothing criteria, but based on the proportion of nursing and foraging related behaviours. The colonies were split according to these categories. In the forager biased colonies, nursing activity increased significantly among foragers. After reunion, inactivity increased and both foraging and nursing were reduced. The isolated nurses also had reduced activities. In the nurse biased colonies, very little foraging was observed As workers lose fertility and gain foraging experience with age this could be another factor driving nurses to continue doing exclusively this task, similar to our study.\u003c/p\u003e \u003cp\u003eThe tendency to remain as a stable nurse could be also explained by the fact these ants were separated from their original gamergate. A similar situation happens in nature when the gamergate loses fertility or dies. In this case, another high fertility worker (usually beta in the hierarchy) occupies her place (Monnin and Peeters \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Thus, it is also important to remain performing nurse activities to monitor changes in the dominance hierarchy (Peixoto et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Monnin \u0026amp; Peeters, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). In \u003cem\u003eDiacamma cf. indicum\u003c/em\u003e, another queenless ant (Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), the dominance hierarchy presents very remarkable differences. The gamergate cuts other workers' gemmae preventing them from ever occupying the gamergate position, making it more likely for nurses to perform riskier tasks (Fukumoto et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Peeters \u0026amp; Higashi, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; reviewed in Tsuji, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, in this species, a great number of nurses become precocious foragers when living in a nurse-biased colony (Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This, although, comes with a disadvantage since nurses that became precocious foragers showed lower ovarian activity than matched stable nurses (Tanaka et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In conclusion, even in the absence of foragers, a situation that can happen in nature due to the death or disappearance of foragers, for example, \u003cem\u003eD. lucida\u003c/em\u003e nurses are not motivated to start foraging. As they have an opportunity to assume the reproductive role, hopeful nurses invest in the reproductive competition and are unable to compensate for past distress (i.e., the great loss of foragers). This is probably also linked with the probability of gamergate turnover, which may be high in species with small colony sizes such as \u003cem\u003eD. lucida\u003c/em\u003e (Monnin et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). It is thus probable that the threshold model does not correspond well to what happens in \u003cem\u003eD. lucida\u003c/em\u003e, or that reproductive competition increases the threshold too much for workers to switch tasks efficiently. The association of fertility with task performance is not unusual, mainly because hormones such as JH and vitellogenin are known to influence DoL, in particular in species where workers lay trophic or fertile eggs regularly (de Souza \u0026amp; Hartfelder, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFrom the second week on after reintroduction, colonies showed decreased activity, larvae were eaten and the gamergates lost their alpha position in the dominance hierarchy. The absence of larvae caused a general colony desorganisation, which is expected since larvae are known to be an important stimulus for colony functioning and DoL. The absence of larvae caused a general colony desorganisation, which is expected since larvae are known to be an important stimulus for colony functioning and DoL. The replacement of the gamergates may have several causes. First, starvation can have created a loss of fertility in the reproductive workers. Second the absence of the gamergate from the nurse biased colonies, even if short, can have heightened conflict and caused potentially reproductive nurses to aggress the gamergate and to immobilise her in Colony 2. This behaviour, described originally for \u003cem\u003eD. quadriceps\u003c/em\u003e (Monnin and Peeters \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) has been also observed in \u003cem\u003eD. lucida\u003c/em\u003e (Peixoto et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Thus, our manipulation led to drastic changes in colony organisation which had detrimental effects on their functioning.\u003c/p\u003e \u003cp\u003eIndependent of the initial task, total reversions (i.e., a complete change between nurse to forager and forager to nurse tasks) are rare in \u003cem\u003eD. lucida\u003c/em\u003e. In many species, the mechanisms associated with division of labour, and especially the transition from inside to outside tasks are thought to be age, morphology, and to a lesser degree physiology and experience (Beshers \u0026amp; Fewell, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Many experiments, inspired by historical work on honey bees, have shown general plasticity in task specialisation, both in the reversion of foragers to nurses and the acceleration of development towards external tasks (Seid and Traniello, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Robinson et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Leitner \u0026amp; Dornhaus, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tanaka et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These changes are labile and transient physiological modifications are observed (Toth \u0026amp; Robinson, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Most of these studies however used models with short lived workers. Indeed, most species, like honey bees, seem to have a worker lifespan of months at the maximum. Maturation of workers is often a matter of weeks. In stark contrast, \u003cem\u003eDinoponera\u003c/em\u003e non-reproductive workers can live more than two years and the maturation of workers from inside to outside tasks is a slow process, often requiring months (Medeiros, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). This could explain why nurses are not able to switch quickly from inside to outside tasks, since foraging is associated with profound changes in many aspects of the ants physiology and behaviour. This can also explain why foragers do not completely switch back to nursing, since they probably are much older than usual nurses, and have an extended experience of outside tasks. More than age, this finding suggests that physiological (i.e., fertility, fat content and hormone titers), behavioural (boldness and aggression), cognitive (experience, motivation), adaptive (the permanence in the queue for potential reproduction), and evolutionary (the loss of the queen morph) mechanisms also regulate division of labour, making workers less flexible in this long-lived species. The transition between nurses to foragers does seem to be a complex process of maturation (F\u0026eacute;neron et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). In a situation when workers can opt for individual strategies, our results show that the group is susceptible to loss of cohesion and fitness, and resilience is weak (Bourke, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn conclusion, our results suggest that, under disturbed conditions, colonies of \u003cem\u003eD. lucida\u003c/em\u003e do not efficiently reallocate workers to the different tasks. Dominance hierarchy and the competition for reproduction seem to be elements that prevent resilience, making nurses less flexible. When the disturbance disappears, the ants return to or maintain their previous task. \u003cem\u003eD. lucida\u003c/em\u003e is thought to be threatened because of the destruction of its habitat combined with reduced reproductive and dispersion ability (Peixoto et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). In our study, we also show that in situations when forager mortality increases, the lack of resilience we observed could also impair colonies' survival. Although our study is based on a limited number of colonies of these endangered ants, they are in line with published literature and bring interesting elements on the potential threats that could make conservation efforts difficult. Understanding the mechanisms of division of labour in ponerine ants such as \u003cem\u003eD. lucida\u003c/em\u003e can be useful to elucidate how division of labour mechanisms change, interact and evolve in the Formicidae clade. It can also be an important factor to take into account in species conservation issues.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cu\u003eFunding\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eMELV received a funding grant from the Brazilian Science Ministry (Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq), MCTI/CNPq/Universal PQ 311790/2021-8 and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), CAPES/PRInt 88887.916823/2023-00. NC received funding from CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) process CAPES/PRInt 88887.915491/2023-00. DHT received a funding grant from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), process CAPES/Proex 88887.875303/2023-00. TRBM\u0026nbsp;received a funding grant from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), process CAPES/Proex 88887.702947/2022-00\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eDeclaration of interest\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eWe declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAcknowledgements\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eWe thank the team at the Reserva Biológica de Sooretama for their help in collecting the colonies and Igor Eloi for the assistance in the statistics. We also thank Stéphane Chameron for his helpful comments. This paper is a result of the practical classes of the course taught by NC: PSE5929, promotion 2023, “Etologia dos Insetos Sociais” of the Psicologia Experimental graduate course at the Institute of Psychology, Universidade de São Paulo, Brazil.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAuthor contributions\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: MELV, DHT, TRBM; Methodology: MELV, DHT, TRBM, NC; Formal analysis and investigation: MELV; Writing - original draft preparation: MELV, DHT, NC; Writing - review and editing: MELV, DHT, NC; Resources: NC; Supervision: NC.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eEthics approval\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe study was submitted to Sistema de Autorização e Informação em Biodiversidade (SISBIO) of Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and approved by permission nº 47615. Because our experimental animal is an invertebrate, according to the law Arouca, nº 11.794/2008, there was no need for submission to Comissão de Ética no Uso de Animais (CEUA/USP). We also consider the recommendations made in the Guidelines for the Use of Animals (ASAB Ethical Committee/ABS Animal Care Committee, 2023).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAsher, C. L., Nascimento, F. S., Sumner, S., \u0026amp; Hughes, W. O. (2013). Division of labour and risk taking in the dinosaur ant, Dinoponera quadriceps (Hymenoptera: Formicidae). Myrmecol News, 18, 121-129.\u003c/li\u003e\n\u003cli\u003eBeekman, M., Sumpter, D. J., \u0026amp; Ratnieks, F. L. (2001). Phase transition between disordered and ordered foraging in Pharaoh\u0026apos;s ants. Proceedings of the National Academy of Sciences, 98(17), 9703-9706.\u003c/li\u003e\n\u003cli\u003eBernadou, A., Busch, J., \u0026amp; Heinze, J. (2015). 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Behav Ecol Sociobiol.,16, 89\u0026ndash;98.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"insectes-sociaux","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"inso","sideBox":"Learn more about [Insectes Sociaux](http://link.springer.com/journal/40)","snPcode":"40","submissionUrl":"https://www.editorialmanager.com/inso/default2.aspx","title":"Insectes Sociaux","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"division of labour, behavioural flexibility, plasticity, task allocation, conservation, Ponerinae","lastPublishedDoi":"10.21203/rs.3.rs-4261997/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4261997/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDivision of labour is an important factor of social insect ecological success. However, species differ widely in the specific mechanisms associated with division of labour. Often, social groups have to cope with severe perturbations and resume normal functioning as quickly as possible. How well they do so depends on the behavioural mechanisms involved and on species life-history traits. Here, we studied the division of labour in \u003cem\u003eD. lucida\u003c/em\u003e, a threatened species of native Brazilian queenless ants with small colony sizes, to assess whether colonies facing a drastic perturbation of the established task allocation are resilient, and through which potential mechanisms. We first separated the colonies into two sub-colonies, one with the foragers and the other with the nurses. As this is an important modification of colony structure, we expected workers to respond quickly by switching tasks. Our experiment showed that, contrary to our hypotheses, workers showed little plasticity in switching tasks, and colonies did show very limited resilience. Foragers, when isolated from nurses, show a certain plasticity in their behavioural repertoire, performing both tasks (foraging and nursing). However, groups of nurses facing the absence of foragers kept almost exclusively to nursing tasks. Only a few performed episodic outside activities. When workers were returned to their original colonies, foragers switched back to foraging. However, the effect of the manipulation could still be observed 20 days after reintroduction, with workers showing lower general activity, ingesting larvae and reproductive workers losing their dominance. Considering our current knowledge about the regulation of both division of labour and reproductive hierarchies in \u003cem\u003eDinoponera\u003c/em\u003e and other ponerine ants, we propose that this lack of resilience is due to the reproductive conflict between nurses, which delays behavioural maturation and motivation to engage in outside tasks. The existence of individual strategies thus imposes severe costs on group functioning. This could be an additional issue when considering the conservation of this endangered species.\u003c/p\u003e","manuscriptTitle":"Dominance hierarchy limits resilience in the endangered queenless ant Dinoponera lucida","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-28 20:28:13","doi":"10.21203/rs.3.rs-4261997/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2024-06-16T22:02:38+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-05-12T18:00:23+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-12T05:59:20+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-20T11:43:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Insectes Sociaux","date":"2024-04-13T09:53:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"insectes-sociaux","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"inso","sideBox":"Learn more about [Insectes Sociaux](http://link.springer.com/journal/40)","snPcode":"40","submissionUrl":"https://www.editorialmanager.com/inso/default2.aspx","title":"Insectes Sociaux","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a37f2e82-3034-4739-acf7-681829fc9a9c","owner":[],"postedDate":"May 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-06-30T23:59:27+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-28 20:28:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4261997","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4261997","identity":"rs-4261997","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}