Influence of biogeographic realm on global body size and reproductive variation in squamate reptiles.

Aim: Body size and clutch size are key life-history traits that shape ecological strategies and evolutionary patterns across reptiles. However, the extent to which these traits vary among major biogeographic realms remains unclear for squamates. Because prolonged evolutionary isolation and adaptation to distinct regional environments can influence morphology and reproduction, we tested whether body size (SVL) and clutch size exhibit significant biogeographic structuring across the world’s principal realms. Location: Global. Taxon: Squamata (lizards and snakes). Methods: We compiled data for approximately 6,400 squamate species representing all eight major terrestrial biogeographic realms: Afrotropic, Australasia, Madagascar, Nearctic, Neotropic, Oceania, Oriental, and Palearctic. We assessed morphological variation using Welch’s ANOVA with Games–Howell post hoc comparisons to test differences in mean body size among realms, and Kruskal–Wallis non parametric ANOVA with Dunn’s tests to examine clutchsize variation. Relationships between body size and clutch size were evaluated using linear regression models. Results: Statistical analyses revealed significant realm-level differences in body size (Welch’s ANOVA, p < 0.001) and clutch size (Kruskal–Wallis, p < 0.001), yet effect sizes were small, indicating weak explanatory power of realm identity (partial η2 ≈ 0.01; R2 ≈ 0.016). No biologically meaningful association was detected between body size and realm, although Nearctic species exhibited slightly smaller mean body sizes than species from other realms. Main conclusions: Our results demonstrate that large-scale biogeographic divisions exert only a minor influence on squamate morphological and reproductive variation. Despite statistically significant realm differences, the effect magnitudes were negligible, suggesting that local ecological, phylogenetic, and evolutionary factors override continental-scale biogeographic structuring. These findings highlight the complexity of macroecological drivers underlying trait evolution in squamate reptiles.