Phenotypic Decoupling Along Environmental Gradients: Somatic Plasticity versus Reproductive Stability in Lacerta strigata (Reptilia: Lacertidae)

Environmental gradients are among the most powerful forces shaping phenotypic diversity in ectothermic vertebrates, yet different life-history traits often respond unequally to spatial heterogeneity. Here, we investigate how morphology, body condition, reproductive investment, and parasite burden vary across a pronounced climatic and elevational gradient in Lacerta strigata (Eichwald, 1831). A total of 148 individuals were sampled from six ecologically contrasting regions of Azerbaijan, spanning arid coastal lowlands, xeric foothills, and humid montane forest-edge habitats. Snout–vent length and body mass showed clear spatial structuring, with larger individuals generally occurring in cooler and more productive montane environments, whereas arid lowland populations exhibited reduced body size and mass. Body condition index displayed moderate geographic variation, reaching its highest values in the Lesser Caucasus populations. In contrast, reproductive traits were comparatively conserved: egg dimensions and volume did not differ significantly among populations along the environmental gradient (one-way ANOVA: F (5, 38) =0.66, p=0.655), indicating developmental stability of reproductive allocation despite ecological variation. Digestive tract parasite helminth abundance increased toward humid and forest-associated habitats, highlighting strong environmental influences on host–parasite interactions. Together, these results reveal a decoupling between environmentally responsive somatic traits and relatively stable reproductive parameters, suggesting that environmental gradients in the Caucasus promote phenotypic flexibility in somatic traits while maintaining reproductive stability in widespread lacertid lizards. Our findings provide a gradient-based ecological framework for understanding how widespread reptile species balance phenotypic flexibility and reproductive stability across heterogeneous landscapes. We hypothesized that somatic traits would vary along environmental gradients, whereas reproductive investment would remain relatively conserved.

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