Sex‐Specific Phenotype‐Performance Links: Divergent Correlations Between Morphology, Coloration, and Bite Force in the Mountain Dragon (Diploderma vela)

TL;DR

The study explores how male and female mountain dragons differ in traits like body shape and coloration, and how these traits relate to bite force, revealing sex-specific adaptations.

Contribution

The paper demonstrates sex-specific correlations between morphology and bite force in Diploderma vela, extending understanding of sexual dimorphism beyond trait means.

Findings

Male mountain dragons show male-biased dimorphism in most morphological traits, while females have longer abdomens.

Morphology-bite force relationships differ between sexes, but coloration does not correlate with bite force in either sex.

Sexual dimorphism in D. vela is shaped by sexual selection, fecundity advantage, and niche divergence, enhancing adaptive fitness.

Abstract

Sexual dimorphism in lizards arises from the dynamic interplay between natural and sexual selection, manifesting in divergent phenotypic traits across taxa. A key unresolved question is whether the relationship between such sexually dimorphic traits and functional performance also differs between the sexes. This study investigated this question in the mountain dragon (Diploderma vela), a protected species endemic to the upper Lancang River basin in southwestern China, by quantifying its sexual dimorphism in morphology and coloration and assessing their sex‐specific correlations with bite force. A total of 94 individuals were assessed for nine morphological traits, maximum bite force capacity, and body coloration across 15 anatomical regions. After controlling for body size, significant male‐biased dimorphism was detected in most morphological traits, whereas abdomen length was female‐biased. Coloration also differed between sexes across all measured regions except the abdomen. Crucially, the relationship between morphology and bite force was sex‐specific; different suites of traits predicted bite force in males versus females. In contrast, no correlation was found between coloration and bite force in either sex. These divergences reflect the species' flexible phenotypic responses to varying reproductive and ecological pressures. These findings demonstrate that sexual dimorphism extends beyond trait means to encompass sex‐specific phenotype‐performance relationships, highlighting differential adaptive responses. This work provides a functional framework for understanding trait evolution in D. vela and underscores the need for sex‐specific considerations in its conservation.

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.

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