On dwarf males in the deep-sea acorn barnacle Bathylasma hirsutum (Thoracica: Bathylasmatidae)

On dwarf males in the deep-sea acorn barnacle Bathylasma hirsutum (Thoracica: Bathylasmatidae) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Help Center Sign In Submit a Preprint Cite Share Download PDF Short Report On dwarf males in the deep-sea acorn barnacle Bathylasma hirsutum (Thoracica: Bathylasmatidae) Jenny Neuhaus This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5178867/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2025 Read the published version in Marine Biodiversity → Version 1 posted 6 You are reading this latest preprint version Abstract The sessile lifestyle of thoracican barnacles has driven the evolution of a mating behavior that maximizes reproductive success by increasing the reach and number of potential mating partners. While most species are simultaneous hermaphrodites, possessing both male and female reproductive structures, some have evolved an androdioecious system in which hermaphrodites and dwarf males coexist. These dwarf males allocate more resources to male function than growth and typically settle near the orifice of their conspecifics. Environmental factors such as food availability and the number of potential mates influence mating group size in barnacle populations, which is generally lower in deep-sea habitats compared to nutrient-rich shallow-water environments. Evolution is likely to favor the presence of dwarf males in deep-sea barnacles to facilitate mating success in such challenging conditions. The genus Bathylasma Newman & Ross, 1971 currently comprises four extant species, two of which are known to exhibit an androdioecious sexual system. Bathylasma hirsutum (Hoek, 1883) is the sole representative of this genus at northern latitudes, inhabiting hard-bottom habitats down to 1829 meters depth. This study reports on two specimens from the Reykjanes Ridge axis, where minute individuals were found apically attached in the tergal furrow, hypothesized to function as dwarf males. This suggests B. hirsutum as the third species within the genus to exhibit an androdioecious sexual system. These findings offer new insights into the reproductive diversity and sex allocation strategies of deep-sea thoracican barnacles, for which a complete understanding has yet to be achieved. androdioecy sexual system resource allocation Reykjanes Ridge Figures Figure 1 Figure 2 Introduction Thoracican barnacles, which include pedunculate and sessile forms, exhibit diverse sexuality patterns and life history strategies despite their immobility after larval settlement (Darwin 1851 ; Charnov 1987 ; Lin et al. 2015 ). Their sexual systems include simultaneous hermaphroditism (concomitant male and female sexual behavior), androdioecy (occurrence of males and hermaphrodites), and dioecy (occurrence of males and females). The sessile lifestyle of barnacles has favoured the evolution of a mating behaviour that maximizes reproductive success by increasing the reach and number of potential mating partners through copulation with an elongated penis (Darwin 1851 ; Anderson 1994 ). The mating group size (MGS) is addressed as one of the major drivers in the evolution of reproductive life histories and sex allocation and has been subject to many evolutionary studies (Charnov 1987 ; Pérez-Losada et al. 2008 ; Yamaguchi et al. 2008 , 2012 , 2013 ; Urano et al. 2009 ; Kelly and Sanford 2010 ; Yusa et al. 2012 ; Lin et al. 2015 ). Food availability through MGS is one of the most important environmental factors regulating sexuality patterns, driven by optimal resource allocation to growth and reproductive success (Yamaguchi et al. 2008 ). Overall, food-rich environments tend to favour high population densities (large MGS) and the occurrence of simultaneous hermaphrodites in close mating distance. With a lowered influx of organic matter, MGS decreases and induces an extended mating distance between conspecifics, limiting the opportunity to copulate. Although sex determination in barnacles is not fully understood (Charnov 1982 , 1987 ; Yamaguchi et al. 2008 ; Urano et al. 2009 ), sex allocation theories suggest genetically determined strategies which, at a decreasing MGS, favour the development of dwarf males (androdioecy). The presence of minute males was first reported by Darwin ( 1852 , 1854 ) where he differentiated between complemental males (attached to hermaphrodites) and dwarf males (attached to true females). Although highlighting an important sexual difference, this literal distinction was suggested to be put aside, proposing the term “dwarf male” for any minute male that matures at much smaller size than conspecific hermaphrodites or females, irrespective of its morphology, functionality, and positioning on the specimen it is associated with (Spremberg et al. 2012 ; Yusa et al. 2012 ; Lin et al. 2015 ). Accordingly, this terminology is used herein. Dwarf males distinguish from hermaphrodites by being settled close to the fertilisation site of conspecifics and by allocating more resources to male function than growth (Charlesworth, 1984 ; Klepal, 1987 ; Yamaguchi et al., 2013 ). This way, dwarf males bypass the need to compete with male function and thus have a potential mating advantage towards hermaphrodites. Nevertheless, dwarf males remain in competition with hermaphrodites for egg fertilisation, resulting in a comparable fitness for both forms (Yamaguchi et al. 2008 ; Yusa et al. 2012 ; Chan and Høeg 2015 ). To simulate this competition, Urano et al. ( 2009 ) developed a model on the life history of androdioecious barnacles which showed an increased evolutionary stable proportion of larvae developing into dwarf males in populations with a lowered MGS, but never exceeding a ratio of 50%. As deep-sea thoracican barnacles are mainly represented by a lower MGS compared to species found in shallow-water habitats, evolution is expected to favour the presence of dwarf males (Chan and Høeg 2015 ; Lin et al. 2015 ). The deep-sea acorn barnacle Bathylasma hirsutum (Hoek, 1883) represents one of four extant species which are nested within the family Bathylasmatidae Newman & Ross, 1971. In common with other thoracican barnacles, B. hirsutum is of gregarious nature as it tends to settle crowded and exhibits epizoic growth where one established animal has one or several specimens laterally attached (Anderson 1994 ). The species populates hard-bottom habitats between 384–1829 m depth in the North-east Atlantic Ocean and is a sole representative of Bathylasma at northern latitudes. Previous studies on the sister species B. alearum (Foster, 1978) from New-Zealand and B. corolliforme (Hoek, 1883) from the Antarctic Peninsula have reported on dwarf males apically attached to the articular ridges of scuta, terga or the longitudinal carinal sheath, attesting an androdioecious sexual system (Dayton et al. 1982 ; Foster 1983 ; Kelly and Sanford 2010 ). This study reports on the presence of minute individuals in the tergal furrow of mature specimens of B. hirsutum which are hypothesized to function as dwarf males. Bathylasma hirsutum is suggested as the third bathylasmatid species with an androdioecious sexual system. Material and methods Specimens of B. hirsutum ( n = 29) were collected along the Reykjanes Ridge axis south of Iceland (station 31; 60°14.274’N 029°08.138‘W) from a field of pillow lava at 719 m depth (Fig. 1 ). Sampling was conducted with the Remotely Operated Vehicle (ROV) Phoca , using the operational arm and net, onboard the RV Maria S. Merian (MSM75) during the IceAGE_RR expedition (Devey et al. 2018 ). At the sampled site, barnacle abundances varied from small patches with few specimens to larger fields with high individual counts. In situ video footage of the sampled habitat (site B in Neuhaus et al., 2024 ) is accessible via https://zenodo.org/records/10220154 . Upon sampling, the material was stored on 96% undenatured ethanol in sealed plastic bags and kept on -20°C. Morphological examinations and measurements of the two minute individuals, each apically attached to each one adult specimen (DZMB-HH-71486, DZMB-HH-71491), were done using a Leica stereomicroscope and a digital vernier calliper. Specimens were photographed with a Canon EOS 2000D. Further Information on the respective specimens can be accessed in the Barcode of Life Data Systems (BOLD) via: https://doi.org/10.5883/DS-IACIR . Results and Discussion Upon collection and morphological examination of 29 barnacles from the Reykjanes Ridge axis, two specimens of B. hirsutum were found with each one minute individual situated apically in the tergal articular furrow (Fig. 2 ). The habitus of these minute specimens is laterally compressed and shows deformed terga and scuta (opercula). They measure carino-rostral diameters of 2.42 mm (Fig. 2 b) and 2.98 mm (Fig. 2 d). The positioning, habitus and size measurements of the herein presented minute individuals on B. hirsutum correspond with the characteristics of dwarf males found in the sister species B. alearum and B. corolliforme (Dayton et al. 1982 ; Foster 1983 ). Foster ( 1983 ) discovered a total of 35 dwarf males in 21 adult specimens of B. alearum , positioned with their carino-rostral axis aligned to the tergal and scutal furrows or the longitudinal carinal sheath. He observed the laterally compressed males to range from one to four mm in carino-rostral diameter, often with deformed opercula. Based on these observations, Dayton et al. ( 1982 ) re-examined what they believed were juveniles of B. corolliforme and found 19 out of 35 pre-defined juveniles to be functional dwarf males instead. Over a 2-year experimental period, they succeeded to observe recruitment of dwarf males on B. corolliforme , settling in the orifical region only. As this narrow region gives almost no room for growth, barnacle larvae that settle and metamorphose here remain dwarfed. Main resources are allocated to sperm production instead of growth, resulting in testes occupying most of the prosoma, charged seminal vesicles and a well-developed penis longer than cirrus VI (Dayton et al. 1982 ; Foster 1983 ). Due to time constraints and technological limitations, detailed morpho-anatomical examinations of the herein reported minute individuals of B. hirsutum are yet to be completed. Specialists are highly encouraged to perform histological examinations of the present material, which is expected to reveal anatomical features analogous to the dwarf males of B. alearum and B. corolliforme . Compared to other sampled sites along the Reykjanes Ridge axis (Narayanaswamy et al. 2006 , 2013 ; Neuhaus et al. 2024 ), the specimens studied herein were collected from a patch of pillow lava with moderate barnacle abundance (Fig. 1 ). Reflected in morphometric measurements of parietal plates, specimens inhabiting this site showed a large size span, indicating a vital population with successful recruitment of juveniles (Neuhaus et al. 2024 ). The two specimens that carry potential dwarf males were likely collected from the edge of the pillow lava, where barnacle densities decline (Fig. 1 ). MGS at this particular site is lower compared to the centre of the populated area and might thus have had an effect on larval settlement, which happened to be in the narrow orifical region of two mature specimens studied herein (Fig. 2 ). As merely two potential dwarf males were found, the population of B. hirsutum at this site is likely not affected by a low MGS in general. However, the overall presence of dwarf males, despite of being a potential local adaptation to a low MGS at the edge of a populated habitat, would prove B. hirsutum to be capable of adapting an androdioecious sexual system which accelerates the reproductive success of mature hermaphrodites and might facilitate population expansion over time. Declarations Compliance with Ethical Standards No specific ethical approval was required for this research. Funding This research was made possible with the funding support of the German Science Foundation (IceAGE_RR: grant BR3843/5 − 1) and the Federal Ministry of Education and Research. The author was supported through the grant GPF 21 − 2_052 (SO286) as part of the IceDivA project which is a contribution to the iAtlantic project, funded by EU/HORIZON 2020, Blue Growth (grant agreement No 818123). Acknowledgements The crew of RV Maria S. Merian, MSM75 chief scientist Colin Devey, technical staff and fellow scientists are acknowledged for their support during the expedition. Special thanks to the crew of ROV Phoca from the GEOMAR Helmholtz Centre for Ocean Research, Kiel for obtaining imagery data and biological material. Karen Jeskulke, Nicole Gatzemeier and Clara Bachmann are thanked for their assistance in sample management and processing. This research has greatly benefited from the support of Saskia Brix and Katrin Linse. Data availability statement Voucher specimens are deposited at the German Centre for Marine Biodiversity Research in Hamburg, Germany to ensure availability for future research. All data is publicly available in the Barcode of Life Data Systems (BOLD) via https://doi.org/10.5883/DS-IACIR . In situ video records are deposited at https://zenodo.org/records/10220154 . References Anderson DT (1994) Barnacles. Structure, function, development and evolution. Chapman & Hall, London Chan BKK, Høeg JT (2015) Diversity of Lifestyles, Sexual Systems, and Larval Development Patterns in Sessile Crustaceans. In: Thiel M, Watling L (eds) The Natural History of the Crustacea. Lifestyles and Feeding Biology, Volume 2. Oxford University Press, Oxford, pp 14–34 Charlesworth D (1984) Androdioecy and the evolution of dioecy. Biol J Linn Soc 22:333–348 Charnov EL (1987) Sexuality and hermaphroditism in barnacles: A natural selection approach. In: Southward A (ed) Barnacle Biology. A. A. Balkema, Rotterdam, pp 89–103 Charnov EL (1982) The Theory of Sex Allocation. Princeton University Press, Princeton Darwin C (1851) A Monograph on the Sub-class Cirripedia, with Figures of All the Species. Ray Society Publications, London Darwin C (1852) A monograph of the Sub-class Cirripedia, with Figures of All the Species. The Lepadidae; or, pedunculated cirripedes. Ray Society Publications, London Darwin C (1854) A monograph of the Sub-class Cirripedia, with figures of all the species. The Balanidae, Verrucidae etc. Ray Society Publications, London Dayton PK, Newman WA, Oliver J (1982) The Vertical Zonation of the Deep-Sea Antarctic Acorn Barnacle, Bathylasma corolliforme (Hoek): Experimental Transplants from the Shelf into Shallow Water. J Biogeogr 9:95–109. https://doi.org/10.2307/2844695 Devey C, Brix S, Barua A, et al (2018) Detailed Mapping and Sampling of the Reykjanes Ridge, Cruise No. MSM75, 29 June 2018 - 8 August 2018, Reykjavik-Reykjavik Foster BA (1983) Complemental males in the barnacle Bathylasma alearum (Cirripedia: Pachylasmidae). In: Lowry JK (ed) Papers from the Conference on the Biology and Evolution of Crustacea, Australian Museum Memoir Vol. 18. The Australian Museum, Sydney, New South Wales, pp 133–139 Kelly MW, Sanford E (2010) The evolution of mating systems in barnacles. J Exp Mar Bio Ecol 392:37–45. https://doi.org/10.1016/j.jembe.2010.04.009 Klepal W (1987) A Review of the Comparative Anatomy of the Males in Cirripedes. In: Barnes H, Barnes M (eds) Oceanography and Marine Biology: An Annual Review. Aberdeen University Press, pp 250–304 Lin HC, Høeg JT, Yusa Y, Chan BKK (2015) The origins and evolution of dwarf males and habitat use in thoracican barnacles. Mol Phylogenet Evol 91:1–11. https://doi.org/10.1016/j.ympev.2015.04.026 Narayanaswamy BE, Howell KL, Hughes DJ, et al (2006) Strategic Environmental Assessment Area 7 Photographic Analysis Report. London Narayanaswamy BE, Hughes DJ, Howell KL, et al (2013) First observations of megafaunal communities inhabiting George Bligh Bank, Northeast Atlantic. Deep Res II 92:79–86. https://doi.org/10.1016/j.dsr2.2013.03.004 Neuhaus J, Linse K, Brix S, et al (2024) Population Genetics of the Deep-sea Acorn Barnacle Bathylasma hirsutum (Hoek, 1883) and the First Report of its Affiliation with a Hydrothermal Vent Field. Zool Stud 25:1–23. https://doi.org/10.6620/ZS.2024.63-25 Pérez-Losada M, Harp M, Høeg JT, et al (2008) The tempo and mode of barnacle evolution. Mol Phylogenet Evol 46:328–346. https://doi.org/10.1016/j.ympev.2007.10.004 Spremberg U, Høeg JT, Buhl-Mortensen L, Yusa Y (2012) Cypris settlement and dwarf male formation in the barnacle Scalpellum scalpellum : a model for an androdioecious reproductive system. J Exp Mar Bio Ecol 422–423:39–47. https://doi.org/10.1016/J.JEMBE.2012.04.004 Urano S, Yamaguchi S, Yamato S, et al (2009) Evolution of dwarf males and a variety of sexual modes in barnacles: an ESS approach. Evol Ecol Res 11:713–729 Yamaguchi S, Charnov EL, Sawada K, Yusa Y (2012) Sexual Systems and Life History of Barnacles: A Theoretical Perspective. Integr Comp Biol 52:356–365. https://doi.org/10.1093/icb/ics046 Yamaguchi S, Yusa Y, Sawada K, Takahashi S (2013) Sexual systems and dwarf males in barnacles: Integrating life history and sex allocation theories. J Theor Biol 320:1–9. https://doi.org/10.1016/j.jtbi.2012.12.001 Yamaguchi S, Yusa Y, Yamato S, et al (2008) Mating group size and evolutionarily stable pattern of sexuality in barnacles. J Theor Biol 253:61–73. https://doi.org/10.1016/j.jtbi.2008.01.025 Yusa Y, Yoshikawa M, Kitaura J, et al (2012) Adaptive evolution of sexual systems in pedunculate barnacles. Proc R Soc B Biol Sci 279:959–966. https://doi.org/10.1098/rspb.2011.1554 Cite Share Download PDF Status: Published Journal Publication published 06 Mar, 2025 Read the published version in Marine Biodiversity → Version 1 posted Editorial decision: Minor Revisions Needed 09 Dec, 2024 Reviewers agreed at journal 14 Nov, 2024 Reviewers invited by journal 10 Nov, 2024 Editor invited by journal 09 Nov, 2024 Editor assigned by journal 01 Oct, 2024 First submitted to journal 30 Sep, 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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Also discoverable on Platform About Our Team In Review Editorial Policies Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5178867","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":376276834,"identity":"2ea5b520-dcf1-4092-98af-fb8bafe16211","order_by":0,"name":"Jenny Neuhaus","email":"data:image/png;base64,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","orcid":"https://orcid.org/0009-0000-7570-4094","institution":"Senckenberg Society for Nature Research: Senckenberg Gesellschaft fur Naturforschung","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Jenny","middleName":"","lastName":"Neuhaus","suffix":""}],"badges":[],"createdAt":"2024-09-30 08:05:01","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5178867/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5178867/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12526-025-01509-0","type":"published","date":"2025-03-06T15:58:44+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":70086775,"identity":"5a149a05-d83f-4dff-99dc-1e0a948d7e47","added_by":"auto","created_at":"2024-11-28 08:21:17","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2967887,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eIn situ\u003c/em\u003e footage of a population of \u003cem\u003eB. hirsutum\u003c/em\u003e prior to sampling. The habitat is situated along the Reykjanes Ridge axis and is composed of lobes of pillow lava. ROV station 31. Image courtesy: GEOMAR, Kiel.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5178867/v1/0b0e36c62703ea57c96ec3aa.jpg"},{"id":70086774,"identity":"c4249a9f-330d-4468-a0d5-652b4139519a","added_by":"auto","created_at":"2024-11-28 08:21:17","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1494192,"visible":true,"origin":"","legend":"\u003cp\u003eTwo specimens of \u003cem\u003eBathylasma hirsutum\u003c/em\u003ewith each one dwarf male situated apically in the tergal furrow (indicated by arrows) \u003cstrong\u003ea\u003c/strong\u003e, \u003cstrong\u003eb\u003c/strong\u003e Top view and detailed view of specimen (DZMB-HH-71485) with dwarf male in right tergal furrow \u003cstrong\u003ec, d\u003c/strong\u003e Top view and detailed view of specimen (DZMB-HH-71491) with dwarf male in left tergal furrow. Scale bars: \u003cstrong\u003ea\u003c/strong\u003e: 3 cm, \u003cstrong\u003eb\u003c/strong\u003e: 2.42 mm, \u003cstrong\u003ec\u003c/strong\u003e: 3 cm, \u003cstrong\u003ed\u003c/strong\u003e: 2.98 mm\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5178867/v1/565233de52330cc9161df1a0.jpg"},{"id":78190904,"identity":"4e92bfc3-10dd-4f50-89f3-4f6a085c929f","added_by":"auto","created_at":"2025-03-10 19:51:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4790290,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5178867/v1/ff4aeed3-752f-418e-a341-608b88c85b2b.pdf"}],"financialInterests":"","formattedTitle":"On dwarf males in the deep-sea acorn barnacle Bathylasma hirsutum (Thoracica: Bathylasmatidae)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThoracican barnacles, which include pedunculate and sessile forms, exhibit diverse sexuality patterns and life history strategies despite their immobility after larval settlement (Darwin \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1851\u003c/span\u003e; Charnov \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Lin et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Their sexual systems include simultaneous hermaphroditism (concomitant male and female sexual behavior), androdioecy (occurrence of males and hermaphrodites), and dioecy (occurrence of males and females). The sessile lifestyle of barnacles has favoured the evolution of a mating behaviour that maximizes reproductive success by increasing the reach and number of potential mating partners through copulation with an elongated penis (Darwin \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1851\u003c/span\u003e; Anderson \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). The mating group size (MGS) is addressed as one of the major drivers in the evolution of reproductive life histories and sex allocation and has been subject to many evolutionary studies (Charnov \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; P\u0026eacute;rez-Losada et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Yamaguchi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2012\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Urano et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Kelly and Sanford \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Yusa et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Lin et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Food availability through MGS is one of the most important environmental factors regulating sexuality patterns, driven by optimal resource allocation to growth and reproductive success (Yamaguchi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Overall, food-rich environments tend to favour high population densities (large MGS) and the occurrence of simultaneous hermaphrodites in close mating distance. With a lowered influx of organic matter, MGS decreases and induces an extended mating distance between conspecifics, limiting the opportunity to copulate. Although sex determination in barnacles is not fully understood (Charnov \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1982\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Yamaguchi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Urano et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), sex allocation theories suggest genetically determined strategies which, at a decreasing MGS, favour the development of dwarf males (androdioecy).\u003c/p\u003e \u003cp\u003eThe presence of minute males was first reported by Darwin (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1852\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1854\u003c/span\u003e) where he differentiated between complemental males (attached to hermaphrodites) and dwarf males (attached to true females). Although highlighting an important sexual difference, this literal distinction was suggested to be put aside, proposing the term \u0026ldquo;dwarf male\u0026rdquo; for any minute male that matures at much smaller size than conspecific hermaphrodites or females, irrespective of its morphology, functionality, and positioning on the specimen it is associated with (Spremberg et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Yusa et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Lin et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Accordingly, this terminology is used herein.\u003c/p\u003e \u003cp\u003eDwarf males distinguish from hermaphrodites by being settled close to the fertilisation site of conspecifics and by allocating more resources to male function than growth (Charlesworth, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1984\u003c/span\u003e; Klepal, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Yamaguchi et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). This way, dwarf males bypass the need to compete with male function and thus have a potential mating advantage towards hermaphrodites. Nevertheless, dwarf males remain in competition with hermaphrodites for egg fertilisation, resulting in a comparable fitness for both forms (Yamaguchi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Yusa et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Chan and H\u0026oslash;eg \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). To simulate this competition, Urano et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) developed a model on the life history of androdioecious barnacles which showed an increased evolutionary stable proportion of larvae developing into dwarf males in populations with a lowered MGS, but never exceeding a ratio of 50%. As deep-sea thoracican barnacles are mainly represented by a lower MGS compared to species found in shallow-water habitats, evolution is expected to favour the presence of dwarf males (Chan and H\u0026oslash;eg \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Lin et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe deep-sea acorn barnacle \u003cem\u003eBathylasma hirsutum\u003c/em\u003e (Hoek, 1883) represents one of four extant species which are nested within the family Bathylasmatidae Newman \u0026amp; Ross, 1971. In common with other thoracican barnacles, \u003cem\u003eB. hirsutum\u003c/em\u003e is of gregarious nature as it tends to settle crowded and exhibits epizoic growth where one established animal has one or several specimens laterally attached (Anderson \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). The species populates hard-bottom habitats between 384\u0026ndash;1829 m depth in the North-east Atlantic Ocean and is a sole representative of \u003cem\u003eBathylasma\u003c/em\u003e at northern latitudes. Previous studies on the sister species \u003cem\u003eB. alearum\u003c/em\u003e (Foster, 1978) from New-Zealand and \u003cem\u003eB. corolliforme\u003c/em\u003e (Hoek, 1883) from the Antarctic Peninsula have reported on dwarf males apically attached to the articular ridges of scuta, terga or the longitudinal carinal sheath, attesting an androdioecious sexual system (Dayton et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Foster \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Kelly and Sanford \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). This study reports on the presence of minute individuals in the tergal furrow of mature specimens of \u003cem\u003eB. hirsutum\u003c/em\u003e which are hypothesized to function as dwarf males. \u003cem\u003eBathylasma hirsutum\u003c/em\u003e is suggested as the third bathylasmatid species with an androdioecious sexual system.\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cp\u003eSpecimens of \u003cem\u003eB. hirsutum\u003c/em\u003e (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;29) were collected along the Reykjanes Ridge axis south of Iceland (station 31; 60\u0026deg;14.274\u0026rsquo;N 029\u0026deg;08.138\u0026lsquo;W) from a field of pillow lava at 719 m depth (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Sampling was conducted with the Remotely Operated Vehicle (ROV) \u003cem\u003ePhoca\u003c/em\u003e, using the operational arm and net, onboard the RV \u003cem\u003eMaria S. Merian\u003c/em\u003e (MSM75) during the IceAGE_RR expedition (Devey et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). At the sampled site, barnacle abundances varied from small patches with few specimens to larger fields with high individual counts. \u003cem\u003eIn situ\u003c/em\u003e video footage of the sampled habitat (site B in Neuhaus et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) is accessible via \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://zenodo.org/records/10220154\u003c/span\u003e\u003cspan address=\"https://zenodo.org/records/10220154\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Upon sampling, the material was stored on 96% undenatured ethanol in sealed plastic bags and kept on -20\u0026deg;C. Morphological examinations and measurements of the two minute individuals, each apically attached to each one adult specimen (DZMB-HH-71486, DZMB-HH-71491), were done using a Leica stereomicroscope and a digital vernier calliper. Specimens were photographed with a Canon EOS 2000D. Further Information on the respective specimens can be accessed in the Barcode of Life Data Systems (BOLD) via: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5883/DS-IACIR\u003c/span\u003e\u003cspan address=\"10.5883/DS-IACIR\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eUpon collection and morphological examination of 29 barnacles from the Reykjanes Ridge axis, two specimens of \u003cem\u003eB. hirsutum\u003c/em\u003e were found with each one minute individual situated apically in the tergal articular furrow (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The habitus of these minute specimens is laterally compressed and shows deformed terga and scuta (opercula). They measure carino-rostral diameters of 2.42 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) and 2.98 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003eThe positioning, habitus and size measurements of the herein presented minute individuals on \u003cem\u003eB. hirsutum\u003c/em\u003e correspond with the characteristics of dwarf males found in the sister species \u003cem\u003eB. alearum\u003c/em\u003e and \u003cem\u003eB. corolliforme\u003c/em\u003e (Dayton et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Foster \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1983\u003c/span\u003e). Foster (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1983\u003c/span\u003e) discovered a total of 35 dwarf males in 21 adult specimens of \u003cem\u003eB. alearum\u003c/em\u003e, positioned with their carino-rostral axis aligned to the tergal and scutal furrows or the longitudinal carinal sheath. He observed the laterally compressed males to range from one to four mm in carino-rostral diameter, often with deformed opercula. Based on these observations, Dayton et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1982\u003c/span\u003e) re-examined what they believed were juveniles of \u003cem\u003eB. corolliforme\u003c/em\u003e and found 19 out of 35 pre-defined juveniles to be functional dwarf males instead. Over a 2-year experimental period, they succeeded to observe recruitment of dwarf males on \u003cem\u003eB. corolliforme\u003c/em\u003e, settling in the orifical region only. As this narrow region gives almost no room for growth, barnacle larvae that settle and metamorphose here remain dwarfed. Main resources are allocated to sperm production instead of growth, resulting in testes occupying most of the prosoma, charged seminal vesicles and a well-developed penis longer than cirrus VI (Dayton et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Foster \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1983\u003c/span\u003e). Due to time constraints and technological limitations, detailed morpho-anatomical examinations of the herein reported minute individuals of \u003cem\u003eB. hirsutum\u003c/em\u003e are yet to be completed. Specialists are highly encouraged to perform histological examinations of the present material, which is expected to reveal anatomical features analogous to the dwarf males of \u003cem\u003eB. alearum\u003c/em\u003e and \u003cem\u003eB. corolliforme\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eCompared to other sampled sites along the Reykjanes Ridge axis (Narayanaswamy et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Neuhaus et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), the specimens studied herein were collected from a patch of pillow lava with moderate barnacle abundance (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Reflected in morphometric measurements of parietal plates, specimens inhabiting this site showed a large size span, indicating a vital population with successful recruitment of juveniles (Neuhaus et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The two specimens that carry potential dwarf males were likely collected from the edge of the pillow lava, where barnacle densities decline (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). MGS at this particular site is lower compared to the centre of the populated area and might thus have had an effect on larval settlement, which happened to be in the narrow orifical region of two mature specimens studied herein (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). As merely two potential dwarf males were found, the population of \u003cem\u003eB. hirsutum\u003c/em\u003e at this site is likely not affected by a low MGS in general. However, the overall presence of dwarf males, despite of being a potential local adaptation to a low MGS at the edge of a populated habitat, would prove \u003cem\u003eB. hirsutum\u003c/em\u003e to be capable of adapting an androdioecious sexual system which accelerates the reproductive success of mature hermaphrodites and might facilitate population expansion over time.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompliance with Ethical Standards\u003c/h2\u003e \u003cp\u003eNo specific ethical approval was required for this research.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research was made possible with the funding support of the German Science Foundation (IceAGE_RR: grant BR3843/5\u0026thinsp;\u0026minus;\u0026thinsp;1) and the Federal Ministry of Education and Research. The author was supported through the grant GPF 21\u0026thinsp;\u0026minus;\u0026thinsp;2_052 (SO286) as part of the IceDivA project which is a contribution to the iAtlantic project, funded by EU/HORIZON 2020, Blue Growth (grant agreement No 818123).\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe crew of RV Maria S. Merian, MSM75 chief scientist Colin Devey, technical staff and fellow scientists are acknowledged for their support during the expedition. Special thanks to the crew of ROV Phoca from the GEOMAR Helmholtz Centre for Ocean Research, Kiel for obtaining imagery data and biological material. Karen Jeskulke, Nicole Gatzemeier and Clara Bachmann are thanked for their assistance in sample management and processing. This research has greatly benefited from the support of Saskia Brix and Katrin Linse.\u003c/p\u003e\u003ch2\u003eData availability statement\u003c/h2\u003e \u003cp\u003eVoucher specimens are deposited at the German Centre for Marine Biodiversity Research in Hamburg, Germany to ensure availability for future research. All data is publicly available in the Barcode of Life Data Systems (BOLD) via \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5883/DS-IACIR\u003c/span\u003e\u003cspan address=\"10.5883/DS-IACIR\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. In situ video records are deposited at \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://zenodo.org/records/10220154\u003c/span\u003e\u003cspan address=\"https://zenodo.org/records/10220154\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnderson DT (1994) Barnacles. Structure, function, development and evolution. Chapman \u0026amp; Hall, London\u003c/li\u003e\n\u003cli\u003eChan BKK, H\u0026oslash;eg JT (2015) Diversity of Lifestyles, Sexual Systems, and Larval Development Patterns in Sessile Crustaceans. In: Thiel M, Watling L (eds) The Natural History of the Crustacea. Lifestyles and Feeding Biology, Volume 2. Oxford University Press, Oxford, pp 14\u0026ndash;34\u003c/li\u003e\n\u003cli\u003eCharlesworth D (1984) Androdioecy and the evolution of dioecy. Biol J Linn Soc 22:333\u0026ndash;348\u003c/li\u003e\n\u003cli\u003eCharnov EL (1987) Sexuality and hermaphroditism in barnacles: A natural selection approach. In: Southward A (ed) Barnacle Biology. A. A. Balkema, Rotterdam, pp 89\u0026ndash;103\u003c/li\u003e\n\u003cli\u003eCharnov EL (1982) The Theory of Sex Allocation. Princeton University Press, Princeton\u003c/li\u003e\n\u003cli\u003eDarwin C (1851) A Monograph on the Sub-class Cirripedia, with Figures of All the Species. Ray Society Publications, London\u003c/li\u003e\n\u003cli\u003eDarwin C (1852) A monograph of the Sub-class Cirripedia, with Figures of All the Species. The Lepadidae; or, pedunculated cirripedes. Ray Society Publications, London\u003c/li\u003e\n\u003cli\u003eDarwin C (1854) A monograph of the Sub-class Cirripedia, with figures of all the species. The Balanidae, Verrucidae etc. Ray Society Publications, London\u003c/li\u003e\n\u003cli\u003eDayton PK, Newman WA, Oliver J (1982) The Vertical Zonation of the Deep-Sea Antarctic Acorn Barnacle, \u003cem\u003eBathylasma corolliforme\u003c/em\u003e (Hoek): Experimental Transplants from the Shelf into Shallow Water. J Biogeogr 9:95\u0026ndash;109. https://doi.org/10.2307/2844695\u003c/li\u003e\n\u003cli\u003eDevey C, Brix S, Barua A, et al (2018) Detailed Mapping and Sampling of the Reykjanes Ridge, Cruise No. MSM75, 29 June 2018 - 8 August 2018, Reykjavik-Reykjavik\u003c/li\u003e\n\u003cli\u003eFoster BA (1983) Complemental males in the barnacle \u003cem\u003eBathylasma alearum\u003c/em\u003e (Cirripedia: Pachylasmidae). In: Lowry JK (ed) Papers from the Conference on the Biology and Evolution of Crustacea, Australian Museum Memoir Vol. 18. The Australian Museum, Sydney, New South Wales, pp 133\u0026ndash;139\u003c/li\u003e\n\u003cli\u003eKelly MW, Sanford E (2010) The evolution of mating systems in barnacles. J Exp Mar Bio Ecol 392:37\u0026ndash;45. https://doi.org/10.1016/j.jembe.2010.04.009\u003c/li\u003e\n\u003cli\u003eKlepal W (1987) A Review of the Comparative Anatomy of the Males in Cirripedes. In: Barnes H, Barnes M (eds) Oceanography and Marine Biology: An Annual Review. Aberdeen University Press, pp 250\u0026ndash;304\u003c/li\u003e\n\u003cli\u003eLin HC, H\u0026oslash;eg JT, Yusa Y, Chan BKK (2015) The origins and evolution of dwarf males and habitat use in thoracican barnacles. Mol Phylogenet Evol 91:1\u0026ndash;11. https://doi.org/10.1016/j.ympev.2015.04.026\u003c/li\u003e\n\u003cli\u003eNarayanaswamy BE, Howell KL, Hughes DJ, et al (2006) Strategic Environmental Assessment Area 7 Photographic Analysis Report. London\u003c/li\u003e\n\u003cli\u003eNarayanaswamy BE, Hughes DJ, Howell KL, et al (2013) First observations of megafaunal communities inhabiting George Bligh Bank, Northeast Atlantic. Deep Res II 92:79\u0026ndash;86. https://doi.org/10.1016/j.dsr2.2013.03.004\u003c/li\u003e\n\u003cli\u003eNeuhaus J, Linse K, Brix S, et al (2024) Population Genetics of the Deep-sea Acorn Barnacle \u003cem\u003eBathylasma hirsutum \u003c/em\u003e(Hoek, 1883) and the First Report of its Affiliation with a Hydrothermal Vent Field. Zool Stud 25:1\u0026ndash;23. https://doi.org/10.6620/ZS.2024.63-25\u003c/li\u003e\n\u003cli\u003eP\u0026eacute;rez-Losada M, Harp M, H\u0026oslash;eg JT, et al (2008) The tempo and mode of barnacle evolution. Mol Phylogenet Evol 46:328\u0026ndash;346. https://doi.org/10.1016/j.ympev.2007.10.004\u003c/li\u003e\n\u003cli\u003eSpremberg U, H\u0026oslash;eg JT, Buhl-Mortensen L, Yusa Y (2012) Cypris settlement and dwarf male formation in the barnacle \u003cem\u003eScalpellum scalpellum\u003c/em\u003e: a model for an androdioecious reproductive system. J Exp Mar Bio Ecol 422\u0026ndash;423:39\u0026ndash;47. https://doi.org/10.1016/J.JEMBE.2012.04.004\u003c/li\u003e\n\u003cli\u003eUrano S, Yamaguchi S, Yamato S, et al (2009) Evolution of dwarf males and a variety of sexual modes in barnacles: an ESS approach. Evol Ecol Res 11:713\u0026ndash;729\u003c/li\u003e\n\u003cli\u003eYamaguchi S, Charnov EL, Sawada K, Yusa Y (2012) Sexual Systems and Life History of Barnacles: A Theoretical Perspective. Integr Comp Biol 52:356\u0026ndash;365. https://doi.org/10.1093/icb/ics046\u003c/li\u003e\n\u003cli\u003eYamaguchi S, Yusa Y, Sawada K, Takahashi S (2013) Sexual systems and dwarf males in barnacles: Integrating life history and sex allocation theories. J Theor Biol 320:1\u0026ndash;9. https://doi.org/10.1016/j.jtbi.2012.12.001\u003c/li\u003e\n\u003cli\u003eYamaguchi S, Yusa Y, Yamato S, et al (2008) Mating group size and evolutionarily stable pattern of sexuality in barnacles. J Theor Biol 253:61\u0026ndash;73. https://doi.org/10.1016/j.jtbi.2008.01.025\u003c/li\u003e\n\u003cli\u003eYusa Y, Yoshikawa M, Kitaura J, et al (2012) Adaptive evolution of sexual systems in pedunculate barnacles. Proc R Soc B Biol Sci 279:959\u0026ndash;966. https://doi.org/10.1098/rspb.2011.1554\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":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"marine-biodiversity","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"marb","sideBox":"Learn more about [Marine Biodiversity](http://link.springer.com/journal/12526)","snPcode":"12526","submissionUrl":"https://www.editorialmanager.com/marb/default2.aspx","title":"Marine Biodiversity","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"androdioecy, sexual system, resource allocation, Reykjanes Ridge","lastPublishedDoi":"10.21203/rs.3.rs-5178867/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5178867/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe sessile lifestyle of thoracican barnacles has driven the evolution of a mating behavior that maximizes reproductive success by increasing the reach and number of potential mating partners. While most species are simultaneous hermaphrodites, possessing both male and female reproductive structures, some have evolved an androdioecious system in which hermaphrodites and dwarf males coexist. These dwarf males allocate more resources to male function than growth and typically settle near the orifice of their conspecifics. Environmental factors such as food availability and the number of potential mates influence mating group size in barnacle populations, which is generally lower in deep-sea habitats compared to nutrient-rich shallow-water environments. Evolution is likely to favor the presence of dwarf males in deep-sea barnacles to facilitate mating success in such challenging conditions. The genus \u003cem\u003eBathylasma\u003c/em\u003e Newman \u0026amp; Ross, 1971 currently comprises four extant species, two of which are known to exhibit an androdioecious sexual system. \u003cem\u003eBathylasma hirsutum\u003c/em\u003e (Hoek, 1883) is the sole representative of this genus at northern latitudes, inhabiting hard-bottom habitats down to 1829 meters depth. This study reports on two specimens from the Reykjanes Ridge axis, where minute individuals were found apically attached in the tergal furrow, hypothesized to function as dwarf males. This suggests \u003cem\u003eB. hirsutum\u003c/em\u003e as the third species within the genus to exhibit an androdioecious sexual system. These findings offer new insights into the reproductive diversity and sex allocation strategies of deep-sea thoracican barnacles, for which a complete understanding has yet to be achieved.\u003c/p\u003e","manuscriptTitle":"On dwarf males in the deep-sea acorn barnacle Bathylasma hirsutum (Thoracica: Bathylasmatidae)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-28 08:21:12","doi":"10.21203/rs.3.rs-5178867/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Minor Revisions Needed","date":"2024-12-09T13:33:55+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-11-14T18:10:47+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-10T16:21:32+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Marine Biodiversity","date":"2024-11-09T23:08:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-02T02:24:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Marine Biodiversity","date":"2024-09-30T04:02:24+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"marine-biodiversity","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"marb","sideBox":"Learn more about [Marine Biodiversity](http://link.springer.com/journal/12526)","snPcode":"12526","submissionUrl":"https://www.editorialmanager.com/marb/default2.aspx","title":"Marine Biodiversity","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"390ef533-59df-4060-bf72-0456c9b77658","owner":[],"postedDate":"November 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-03-10T19:50:32+00:00","versionOfRecord":{"articleIdentity":"rs-5178867","link":"https://doi.org/10.1007/s12526-025-01509-0","journal":{"identity":"marine-biodiversity","isVorOnly":false,"title":"Marine Biodiversity"},"publishedOn":"2025-03-06 15:58:44","publishedOnDateReadable":"March 6th, 2025"},"versionCreatedAt":"2024-11-28 08:21:12","video":"","vorDoi":"10.1007/s12526-025-01509-0","vorDoiUrl":"https://doi.org/10.1007/s12526-025-01509-0","workflowStages":[]},"version":"v1","identity":"rs-5178867","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5178867","identity":"rs-5178867","version":["v1"]},"buildId":"zQwnuV7TCBrMSSSToR1PI","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}