Sexual dimorphism in the mountain dragon (Diploderma vela) from the upper Lancang River Basin: Integrated analysis of morphology, coloration, and bite force

Sexual dimorphism in the mountain dragon (Diploderma vela) from the upper Lancang River Basin: Integrated analysis of morphology, coloration, and bite force | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Ecology and Evolution This is a preprint and has not been peer reviewed. Data may be preliminary. 20 August 2025 V1 Latest version Share on Sexual dimorphism in the mountain dragon (Diploderma vela) from the upper Lancang River Basin: Integrated analysis of morphology, coloration, and bite force Authors : Songwen Tan 0009-0009-1461-6328 , Ling Li , Wei Gao , Guocheng Shu , Peng Guo 0000-0001-5585-292X , and Yayong Wu 0000-0003-2752-4085 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175567696.68305850/v1 296 views 154 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Sexual dimorphism in lizards arises from the dynamic interplay between natural and sexual selection, manifesting in divergent morphological, chromatic, and functional traits across taxa. This study investigated the extent and structure of sexual dimorphism in the mountain dragon (Diploderma vela), a protected species endemic to the arid river valleys of the upper Lancang River basin in southwestern China. A total of 94 individuals were assessed for nine morphological parameters, maximum bite force capacity, and body coloration across 15 anatomical regions. Results revealed pronounced male-biased dimorphism was present in this lizard, with males exhibiting larger head dimensions, elongated limbs and tails, and stronger bite force capacity than females, consistent with patterns driven by intrasexual selection. Marked sexual dichromatism was observed in the throat, lateral body surfaces, and dorsal markings (both light and dark). Bite force scaled positively with head dimensions but exhibited distinct sex-specific predictors, revealing divergent selective trajectories. In males, bite capacity was most significantly associated with head width, whereas in females, head length emerged as the primary determinant. This sexually differentiated architecture underscores the complex interplay between sexual and natural selection in shaping functional traits. These findings offer a mechanistic framework for understanding trait evolution in D. vela and provide a critical empirical foundation for conservation strategies tailored to the ecological and evolutionary dynamics of this restricted-range species. Sexual dimorphism in the mountain dragon ( Diploderma vela ) from the upper Lancang River Basin: Integrated analysis of morphology, coloration, and bite force Songwen TAN 1 , Ling LI 1,2 , Wei GAO 2 , Guocheng SHU 1 , Peng GUO 1 , Yayong WU 1，2* 1 Faculty of Agriculture , Forestry and Food Engineering , Yibin University , Yibin , Sichuan 644000 , China 2 State Key Laboratory of Genetic Resource and Evolution & Yunnan Key Laboratory of Biodiversity and Ecological Security of Gaoligong Mountain , Kunming Institute of Zoology , Chinese Academy of Sciences , Kunming 650000 , Yunnan , China * Corresponding author: Yayong WU, Faculty of Agriculture, Forestry and Food Engineering, Yibin University, Yibin 644000, Sichuan, China. E-mail: [email protected] (Yayong WU) Abstract Sexual dimorphism in lizards arises from the dynamic interplay between natural and sexual selection, manifesting in divergent morphological, chromatic, and functional traits across taxa. This study investigated the extent and structure of sexual dimorphism in the mountain dragon ( Diploderma vela ), a protected species endemic to the arid river valleys of the upper Lancang River basin in southwestern China. A total of 94 individuals were assessed for nine morphological parameters, maximum bite force capacity, and body coloration across 15 anatomical regions. Results revealed pronounced male-biased dimorphism was present in this lizard, with males exhibiting larger head dimensions, elongated limbs and tails, and stronger bite force capacity than females, consistent with patterns driven by intrasexual selection. Marked sexual dichromatism was observed in the throat, lateral body surfaces, and dorsal markings (both light and dark). Bite force scaled positively with head dimensions but exhibited distinct sex-specific predictors, revealing divergent selective trajectories. In males, bite capacity was most significantly associated with head width, whereas in females, head length emerged as the primary determinant. This sexually differentiated architecture underscores the complex interplay between sexual and natural selection in shaping functional traits. These findings offer a mechanistic framework for understanding trait evolution in D. vela and provide a critical empirical foundation for conservation strategies tailored to the ecological and evolutionary dynamics of this restricted-range species. Keywords Sexual dimorphism; Bite force performance; Body coloration; Mountain dragon; Sexual selection 1. Introduction Sexual dimorphism, defined by divergent phenotypic traits between males and females of the same species, is a widespread evolutionary outcome observed across diverse animal taxa, including invertebrates, amphibians, reptiles, birds, and mammals (Pinto et al ., 2005; Andre et al ., 2018; Pincheira-Donoso et al. , 2020; Zhong et al ., 2017; Jozet-Alves et al ., 2008). Despite its ubiquity, the expression of dimorphic traits is remarkably heterogeneous, with patterns varying not only across higher taxonomic levels but also within families and genera, particularly in reptilian clades (Cox et al ., 2009; Cruz-Elizalde et al ., 2021). These dimorphic patterns are manifested through multiple phenotypic dimensions, including morphology, coloration, and bite force performance in reptiles (Herrel et al ., 2018; Pincheira-Donoso et al. , 2020; Stuart-Fox et al ., 2020). Body size is commonly employed as a principal indicator of sexual dimorphism, with sexual size dimorphism (SSD) representing one of the most pervasive signatures of sex-specific adaptive divergence across the reptiles (Fairbairn et al ., 2007; Pincheira-Donoso et al. , 2020). Three primary SSD patterns have been identified within reptiles (Cruz-Elizalde et al ., 2021), including male-biased (Herrel et al ., 2010), female-biased (Cox et al ., 2009), and unbiased (Schwarzkopf, 2005). Several evolutionary hypotheses have been proposed to explain these patterns. The sexual selection hypothesis attributes male-biased SSD to advantages conferred by larger size in territoriality, resource competition, and mate acquisition (Rosenthal, 2017; Cruz-Elizalde et al ., 2021). Conversely, the fecundity advantage hypothesis suggests that larger female body size enhances reproductive output through increased offspring number or size (Nali et al ., 2014; Pincheira‐Donoso & Hunt, 2017). Furthermore, the intraspecific niche divergence hypothesis proposes that competition between males and females for ecological resources leads to niche divergence, ultimately resulting in SSD (Bolnick & Doebeli, 2003; Pincheira-Donoso et al ., 2018). However, reliance on size metrics alone may obscure finer-scale phenotypic differentiation. Morphological traits such as cephalic proportions and appendicular dimensions often yield finer resolution in characterizing sex-specific divergence (Cruz-Elizalde et al ., 2020). In addition, growing evidence has highlighted the ontogenetic mechanisms underlying sexual size dimorphism (SSD), emphasizing the pivotal roles of sex-specific growth rates, survival strategies, energy allocation patterns, trophic niche differentiation, and life-history trajectories in driving dimorphic outcomes (Cox et al ., 2009; Johnston, 2011; Zhang et al ., 2018). Consequently, integrative analyses of finer-scale phenotypic differentiation and growth dynamics are critical to elucidate the multifaceted origins and evolution of sexual dimorphism (Zhang et al ., 2018). The recurrent and phylogenetically independent evolution of conspicuous sexual coloration in reptiles suggests that coloration plays important adaptive roles (Stuart-Fox et al ., 2020). These include background matching for crypsis (Bu et al ., 2020; Perez-Martinez et al ., 2020), predator deterrence via intimidation or confusion (Perez-Martinez et al ., 2020), thermoregulation through light absorption modulation (Smith et al ., 2016; Norris, 1967), and intraspecific signaling in both social and reproductive contexts (Hamilton & Sullivan, 2005; Salvador et al ., 2008; Whiting et al ., 2006; Protas & Patel, 2008). These functions, however, often involve functional trade-offs that can give rise to color polymorphism and sex-specific divergence in coloration patterns (Smith et al ., 2016). For example, in many lizard species, males exhibit brighter and more variable throat coloration, often displaying marked intraspecific polymorphism, while females typically remain more cryptically pigmented (Stuart-Fox et al ., 2020). Such patterns underscore the influence of sexual selection, wherein male throat coloration acts as a condition-dependent signal of individual fitness, conferring advantages in male-male competition and female mate choice (Pérez I de Lanuza et al ., 2013). Accordingly, investigating sexually dimorphic coloration provides critical insight into reptilian adaptation to ecological conditions while also advancing understanding of behavioral ecology through the lens of interactions between sexual selection and adaptive evolutionary processes. Bite force also exhibits pronounced sexual dimorphism across the reptilian, reflecting divergent selective pressures on functional performance traits. As an important indicator of whole-organism performance, bite force plays a pivotal role in a range of ecologically and behaviorally relevant functions, including prey processing, territorial defense, agonistic interactions, and reproductive competition (Huyghe et al ., 2005; Kaliontzopoulou et al ., 2012; Naretto et al ., 2022). Its magnitude is strongly shaped by cranial morphology, with head size and shape critically influencing mechanical output through their effects on skeletal leverage and muscular architecture (Herrel et al ., 2007; Sagonas et al ., 2014; Naretto et al ., 2022; McBrayer & Anderson, 2007). As a biomechanical trait closely tied to ecological function, the relationship between head morphology and bite performance carries significant evolutionary relevance. Bite force dimorphism is shaped by the combined influences of sexual selection and intersexual ecological divergence (McBrayer & Anderson, 2007). For example，in many lizard species, male-male competition exerts strong selective pressure for enlarged cranial morphology, which enhances bite capacity and confers advantages in physical contests and mate acquisition (Lappin et al ., 2010). Simultaneously, sex-specific competition for ecological resources can drive trophic niche differentiation, further reinforcing divergence in bite performance (Verwaijen et al ., 2010). Studying bite force dimorphism and the morphological correlates offers critical insight into the evolutionary pressures driving functional specialization and the adaptive significance of performance traits in sexually dimorphic systems. Diploderma vela , an agamid lizard described in 2015, is endemic to the arid upper Lancang River valley of southwestern China, where it occupies rocky outcrops and xeric shrublands, and feeds primarily on insects and spiders (Wang et al ., 2015). Due to its restricted distribution and strong habitat specificity, the species was designated a National Second-level Protected Wild Animal in China in 2021. However, ongoing hydropower development has resulted in extensive habitat degradation, driving severe population declines. Despite its conservation priority, core biological and ecological data for D. vela remain limited. This study investigated sexual dimorphism in the mountain dragon across three major functional domains, including external morphology, body coloration, and bite force performance. By establishing foundational data on functional morphology, this study enhances the biological profile of the species and provides valuable insights for conservation strategies. Furthermore, the analytical framework developed here may inform studies of sexual dimorphism in other habitat-specialized reptiles. 2. Materials and Methods 2.1. Study site Fieldwork was conducted in Quzika Township (29°05′ N, 98°36′ E; 2 350 m a.s.l.), located in the upper Lancang River valley of Mekong County on the eastern Tibetan Plateau, China (Fig. 1). This site represents the type locality of D. vela and harbors the highest known population density. Individuals were primarily observed inhabiting rock crevices and shrub-steppe vegetation along valley slopes adjacent to the Lancang River. The region has a continental monsoon climate, typified by hot, humid summers and cold, dry winters. Annual precipitation ranges from 350 to 450 mm, with most rainfall occurring between June and September. A brief frost-free period of approximately 95 days, coupled with pronounced seasonality, defines a habitat that also sustains potential predators such as the copperhead racer ( Elaphe taeniura ) and common kestrel ( Falco tinnunculus ) (Wang et al ., 2015) . 2.2. Animal sampling A total of 94 D. vela individuals (57 males and 37 females) were captured in June 2020 using manual and noose techniques during peak diurnal periods (10:00 AM–17:00 PM). Each specimen was assigned a unique identification code, with sex and precise geographical coordinates recorded at the time of capture. Sex determination was based on dorsal coloration pattern and the presence or absence of hemipenal bulges. Cloacal body temperature (BT) and maximum voluntary bite force were measured in the field immediately following capture. Morphological traits were recorded on-site, and all individuals were released unharmed at their original capture locations within two hours. All procedures were conducted in accordance with ethical guidelines approved by the Animal Care Committee of Yibin University (License No. YBU2020008), ensuring animal welfare and ecological integrity. 2.3. Measurement of morphology traits, bite force, and body coloration Morphological traits were quantified using a precision digital caliper (Deli DL91200, Ningbo, China; accuracy ±0.01 mm) and an electronic balance (Mengfu I-2000, Dongguan, China; accuracy ±0.01 g). Nine linear variables were measured following established protocols (Cruz-Elizalde et al ., 2020), including snout-vent length (SVL), tail length (TL), abdomen length (AL), head length (HL), head width (HW), head height (HH), mouth length (ML), forelimb length (FLL), and hindlimb length (HLL). All measurements were performed by a single investigator to avoid errors, with three replicates per trait used to calculate means. Cloacal body temperature was recorded using an ultra-thin catheter electronic thermocouple (Victor UT323, Shenzhen, China; resolution +0.01 ℃), inserted 5 mm into the cloaca. Bite force was assessed using a piezoelectric force transducer (Viste VXT500, Shenzhen, China; 0–50 N), composed of a pair of 2-mm-thick steel bite plates (resolution 0.1 N), a hand-operated amplifier, and a digital output display. To prevent dental injury, each bite plate was fitted with a layer of non-toxic rubber. Prior to each session, the system was calibrated using certified weights. During trials, lizards were gently restrained and positioned with the rostrum aligned perpendicularly to the sensor surface to ensure full jaw engagement. Six bite trials (three in the field and three in the laboratory) were performed under controlled thermal conditions. Following standard protocols (McBrayer & Anderson, 2007), the maximum bite force across all trials, along with its corresponding body temperature, was used for analysis. Body coloration was measured using an AVASPEC-2048 fiber-optic spectrometer (Ocean Insight, USA) equipped with a halogen light source and a reflection probe. Spectral measurements were taken from 15 points distributed across five anatomical regions: throat (3 points), abdomen (2 points), lateral torso (4 points), dorsal light markings (4 points), and dorsal dark markings (3 points) (Fig. 2). The probe was held perpendicular to the skin surface at a fixed distance of 2 mm, with reflectance spectra (300–700 nm) acquired at a 100 ms integration time using SpectraSuite software. Spectral data were categorized into biologically relevant wavelength bands: ultraviolet (UV, 300–400 nm), blue (400–475 nm), green (475–550 nm), yellow (550–625 nm), and red (625–700 nm). Triplicate measurements were taken at each point to ensure reproducibility, with irradiance calibration performed to reduce environmental variability. 2.4. Coloration parameter calculation To facilitate body coloration analysis, reflectance spectra, including luminance, chroma, and hue components, were collected. The formula for luminance is as follows: Qt = \(\sum\) R(λ) Where R is reflectance at specific wavelength λ and Qt represents total reflectance from 300 to 700 nm. Relative luminance for each color band was subsequently calculated using the following formulae: U = Quv/Qt B = Qb/Qt G = Qg/Qt Y = Qy/Qt R = Qr/Qt Where U , B , G , Y , and R represent the relative luminance of UV, blue, green, yellow, and red light, respectively, and Quv , Qb , Qg , Qy , and Qr represent the reflectance ratio of UV, blue, green, yellow, and red light, respectively. Chroma ( C ) was then calculated as: C =\(\sqrt{{(R-G)}^{2}+{(Y-B)}^{2}}\ \)=\(\ \sqrt{\text{LM}^{2}+\text{MS}^{2}}\) Where LM represents the relative difference in reflectance between red and green light, and MS represents the relative difference in reflectance between yellow and green light. 2.5. Statistical analysis All data were logarithmically transformed to approximate normality, with missing values imputed using multiple imputation by chained equations (MICE). Assumptions of normality (Shapiro-Wilk test) and homoscedasticity (Levene’s test) were verified, applying Box-Cox transformation when violations occurred. Sex-based differences in morphological traits and bite force were initially evaluated using one-way analysis of variance (ANOVA). Pearson correlation analyses were then conducted between SVL and other morphological traits for males and females. If significant positive correlations with SVL were observed across traits, multivariate ANOVA (MANCOVA) was employed to assess sex differences in morphology and bite force, using SVL as a covariate. Covariance analyses were additionally applied to evaluate variation in morphological traits between sexes relative to SVL. For body coloration, mean spectral reflectance was calculated for each anatomical region, and reflectance curves were generated accordingly. Sex-specific differences in luminance and chroma across anatomical regions were tested using independent samples t -tests. To identify morphological drivers of bite force dimorphism, univariate linear regressions were first performed to examine the sex-specific relationships between bite force and individual cranial dimensions (length, width, and height). Significant predictors ( P < 0.05) were then incorporated into stepwise multiple regression models, with model selection based on Akaike’s Information Criterion (AIC), to determine the optimal set of variables explaining variation in bite force. All statistical analyses were conducted using R v4.2.2 and SPSS v27.0. Visualizations were generated using the R package “ggplot2” and Origin 2024. Statistical significance was set at P < 0.05. 3. Results 3.1. Sexual dimorphism in morphology Significant sexual dimorphism was observed between males and females across multiple morphological traits (Table 1). Although one-way ANOVA revealed no significant differences in SVL ( F = 2.502, P = 0.117) and AL ( F = 2.004, P = 0.160), MANCOVA revealed that males possessed significantly larger trait values than females for TL ( F = 155.361, P < 0.001), HL ( F = 46.235, P < 0.001), HW ( F = 28.813, P < 0.001), HH ( F = 39.047, P < 0.001), ML ( F = 12.892, P < 0.001), FLL ( F = 40.312, P < 0.001), and HLL ( F = 39.052, P < 0.001). In contrast, abdomen length was significantly greater in females ( F = 52.410, P < 0.001). Regarding growth rates, TL exhibited allometric growth between sexes ( F = 3.993, P = 0.049), whereas other traits conformed to isometric growth patterns (Fig. 3). 3.2. Sexual dimorphism in body coloration Distinct sex-based differences in body coloration were evident in D. vela (Fig. 4). Males exhibited significantly higher luminance in dorsal light markings ( t = −5.619, P < 0.001), indicating brighter pigmentation in these regions. Conversely, females displayed significantly higher luminance in dorsal dark markings ( t = −5.619, P < 0.001), as well as greater chroma values in both the throat ( t = −2.623, P = 0.012) and lateral torso ( t = −3.324, P = 0.002), suggesting more saturated coloration. No significant sex differences were observed in abdominal coloration. 3.3. Sexual dimorphism in bite force and its determinants Diploderma vela exhibited pronounced male-biased bite force. Males generated significantly higher absolute bite force than females (ANOVA, F = 7.214, P = 0.009, Fig. 5a). This sex difference remained significant after controlling for SVL, with males maintaining greater bite force (MANCOVA, F = 15.233, P < 0.001, Fig. 5b). Stepwise multiple regression analysis identified HW as the strongest predictor of bite force in males ( R 2 = 0.610, P < 0.001), whereas HL emerged as the primary determinant in females ( R 2 = 0.704, P < 0.001) (Table 2). Univariate linear regression analysis revealed significant positive correlations between bite force and HL, HW, HH, and ML (Table 2). Additionally, bite force in both sexes exhibited isometric growth with increasing morphological traits (HL: F = 1.474, P = 0.228; HW: F = 0.098, P = 0.755; HH: F = 0.375, P = 0.542; ML: F = 0.237, P = 0.627; Fig. 6). 4. Discussion SSD in lizards reflects a complex interplay of evolutionary forces, with documented patterns ranging from male-biased to female-biased or phenotypically monomorphic across taxa (Herrel et al ., 2010; Cox et al ., 2009; Schwarzkopf, 2005). Within the genus Diploderma , SSD appears to be predominantly male-biased (Kuo et al ., 2009; Xiong et al ., 2022), as evident in species such as D. swinhonis and D. micangshanensis , where males consistently exhibit larger body sizes than females (Kuo, 2009; Xiong et al ., 2022). This study revealed a similar pattern in D. vela , with males exhibiting significantly larger dimensions in most morphological traits. Notably, multivariate analyses controlling for SVL confirmed robust male-biased across all measured traits except abdomen length, suggesting that body size alone underrepresents the extent of morphological divergence. Despite exhibiting comparable SVL, females possessed significantly longer AL, consistent with the fecundity advantage hypothesis, which posits that increased abdominal volume enhances reproductive capacity by accommodating larger clutch size (Pincheira‐Donoso & Hunt, 2017). In contrast, males displayed enlarged dimensions in multiple morphological traits, which likely reflects intensified sexual selection on locomotor and cranial traits in arid montane habitats. Such environments may impose ecological constraints that amplify male-male competition, thereby favoring enhanced body structure for intrasexual competition, territorial defense and reproductive success (Kaliontzopoulou et al ., 2012; Rosenthal, 2017). These advantages are expressed through well-developed cranial and appendicular structures, including robust heads and limbs, which are functionally linked to physical dominance, coercive mating strategies, and resource monopolization (Herrel et al ., 2010; Hierlihy et al ., 2013). Such male-biased dimorphism is broadly conserved across lizard lineages (Liang et al ., 2025), with parallel patterns reported in Tropidurus (Tropiduridae), Anolis (Dactyloidae), Varanus (Varanidae), Sceloporus (Phrynosomatidae), and other Diploderma (Agamidae) species (Cox et al ., 2009; Kuo et al ., 2009; Jiménez-Arcos et al ., 2017). Additionally, the accelerated TL growth rates in males suggests that this appendage may play a more significant role in visual communication for males. As observed in Phrynocephalus vlangalii , where tail displays mediate territorial and reproductive communication (Peters et al ., 2016; Wu et al ., 2018), the elongated tails of male D. vela may similarly function in dual contexts—enhancing mate attraction while serving as a deterrent in male-male contests. Coloration and ornamentation are critical phenotypic traits that mediate ecological communication, with their evolution shaped by competing selective pressures, including sexual selection, thermoregulation, predator avoidance, and physiological trade-offs (Bu et al ., 2020; Perez-Martinez et al ., 2020). While chromatic signals often convey complex, multimodal information—as seen in Lacerta schreiberi , where male dorsal coloration simultaneously reflects dominance and immune status (Martín & López, 2009)—their functional outcomes exhibit taxon-specific and context-dependent complexity. Intraspecific divergence in coloration is further intensified by sex-specific selection pressures and differential resource demands. This complexity is exemplified in D. vela , which displays an atypical pattern of sexual dichromatism. Unlike other mountain dragons where males bear vividly pigmented throats that function as dominance signals in competitive encounters (Pérez I de Lanuza et al ., 2013; Wang et al ., 2021), male D. vela lizards showed subdued throat coloration and reduced chromatic contrast relative to females. This reversed pattern of sexual dimorphism is rare among lizards and has only been reported in a few species, such as Shinisaurus crocodilurus (Qiu et al ., 2022). However, in contrast to the functionally rich throat coloration of Shinisaurus crocodilurus , throat color in D. vela showed no significant association with body size or other performance-related traits (Appendix 1). Instead, the most prominent sex-linked color difference in D. vela occurred on the dorsum, where dorsal light markings in males were correlated with body size (Appendix 1). By displaying dorsal light markings, males achieve the same signaling effect as the brightly colored throats of other mountain dragons. This unique phenotypic pattern may be closely related to adaptation to specific habitats and the differential evolution between neighboring species. Bite force represents a key functional trait in lizards, directly mediating ecological performance across multiple behavioral contexts, including prey capture, territorial aggression, and mating competition (Lailvaux et al ., 2004; Chazeau et al ., 2013; Sagonas et al ., 2014; Herrel et al ., 2018). Although cranial morphology—particularly head size and shape—typically governs bite force through biomechanical optimization such as enhanced muscle leverage and expanded cross-sectional area (Deeming et al ., 2022; Naretto et al ., 2022), the strength of this relationship varies across taxa. In D. vela , males exhibited significantly greater head dimensions (HW) and bite force compared to females, a pattern consistent with musculoskeletal adaptations described in other sexually dimorphic reptiles, including Malaclemys terrapin (Herrel et al ., 2018). An expanded HW in males likely accommodates enlarged temporalis muscle attachment, increasing occlusal force for effective prey immobilization and performance in male-male combat (Herrel et al ., 2005). However, head size alone does not universally predict bite performance. In species such as Crotaphytus collaris , weak correlations between head dimensions and bite force emphasize the functional relevance of internal cranial architecture (Lappin & Husak, 2005). In D. vela , the observed dimorphism reflects the combined influence of sexual and natural selection. Male-specific cranial enlargement likely facilitates coercive mating behaviors and dominance in intrasexual contests (McBrayer et al ., 2007), whereas dietary niche partitioning may further reduce competition between sexes by favoring size-based prey specialization (Verwaijen et al ., 2010). Importantly, the morphological predictors of bite force differed between the sexes; in males, performance was correlated with HW, reflecting competition-driven selection for larger prey; in females, bite force was associated with HL, suggesting optimization for routine feeding efficiency (Herrel et al ., 2001). These divergent trajectories underscore sex-specific functional trade-offs in cranial evolution, with males evolving structural weaponization and females maximizing resource-processing capacity. In summary, D. vela exhibited pronounced sexual divergence in morphological traits, bite force, and body coloration, shaped by the interplay of three evolutionary mechanisms: sexual selection, fecundity advantage, and intraspecific niche divergence. These complementary, non-exclusive processes collectively enhance adaptive fitness in the hot, dry river valley ecosystems. By enabling flexible phenotypic responses to both reproductive and ecological pressures, this trait modularity may bolster population persistence under intensifying climate-driven aridification and environmental stochasticity. Acknowledgements We would like to thank YH Xiang, YH Wen, BL Lu, F Liu, and XP Wu for their assistance in field. This work was supported by the National Natural Science Foundation of China (32130015, 31801980) and the Ph.D. Fund Project of Yibin University (2019QD13, 2020QH07). CONFLICTS OF INTEREST The authors declare no conflicts of interest. AUTHORS’ CONTRIBUTIONS Song-Wen Tan: Conceptualization (lead); Data curation (lead); Formal analysis (supporting); Methodology (equal); Validation (equal); Visualization (supporting); Writing-original draft (equal); Writing-review & editing (equal). Ling Li : Conceptualization (supporting); Data curation (supporting); Formal analysis (lead); Methodology (equal); Software (lead); Validation (equal); Writing-review & editing (equal). Wei Gao : Conceptualization (supporting); Data curation (supporting); Formal analysis (lead); Investigation (equal). Guo-Cheng Shu : Conceptualization (supporting); Data curation (supporting); Validation (equal); Writing-review & editing (equal). Peng Guo : Formal analysis (supporting); Investigation (supporting); Writing-review & editing (equal). Ya-Yong Wu : Conceptualization (lead); Data curation (lead); Formal analysis (supporting); Investigation (supporting); Methodology (supporting); Software (supporting); Visualization (supporting); Writing-original draft (equal); Writing-review & editing (supporting)；Funding acquisition (supporting)；Project administration (lead). DATA AVAILABILITY STATEMENT The raw data are provided in the form of supplementary files. References 1. Andre C. B., Peterson T. L., Gabriel C. C. 2018. Characterisation of sexual dimorphism and male colour morphs of Tropidurus semitaeniatus (Spix, 1825) in three populations from northeast of Brazil. Herpetology Notes, 11: 755-760 2. Bolnick D. I., Doebeli M. 2003. Sexual dimorphism and adaptive speciation: two sides of the same ecological coin. Evolution, 57(11): 2433-2449 3. Bu R. P., Xiao F. R., Lovell P. G., Ye Z. H., Shi H. T. 2020. 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Asian Herpetological Research, 8(2): 118-122 Supplementary Material File (appendix 1.docx) Download 18.87 KB File (table 1.docx) Download 18.54 KB File (table 2.docx) Download 17.29 KB Information & Authors Information Version history V1 Version 1 20 August 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Ecology and Evolution Keywords comparative description evolutionary ecology statistical terrestrial vertebrate Authors Affiliations Songwen Tan 0009-0009-1461-6328 Yibin University View all articles by this author Ling Li Yibin University View all articles by this author Wei Gao Kunming Institute of Zoology Chinese Academy of Sciences View all articles by this author Guocheng Shu Yibin University View all articles by this author Peng Guo 0000-0001-5585-292X Yibin University View all articles by this author Yayong Wu 0000-0003-2752-4085 [email protected] Yibin University View all articles by this author Metrics & Citations Metrics Article Usage 296 views 154 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Songwen Tan, Ling Li, Wei Gao, et al. Sexual dimorphism in the mountain dragon (Diploderma vela) from the upper Lancang River Basin: Integrated analysis of morphology, coloration, and bite force. Authorea . 20 August 2025. 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