Latitudinal and climatic variation in body size and dorsal scale counts in Sceloporus lizards:a phylogenetic perspective

Abstract

Squamates often follow an inverse Bergmann's rule, with larger-bodied animals occurring in warmer areas or at lower latitudes. The size of dorsal scales in lizards has also been proposed to vary along climatic gradients, with species in warmer areas exhibiting larger scales, putatively to reduce heat load. We tested for these patterns in the diverse and widespread lizard genus Sceloporus. Among 106 species or populations, body size was associated positively with maximum temperature (consistent with the inverse of Bergmann's rule) and aridity, but did not covary with latitude. Scale size (inferred from the inverse relation with numbers of scales) was positively related to body size. Controlling for body size via multiple regression, scale size was associated negatively with latitude (best predictor), positively with minimum temperature, and negatively with aridity (similar results were obtained using scores from a principal components analysis of latitude and climatic indicators). Thus, lizards with larger scales are not necessarily found in areas with higher temperatures. Univariate analyses indicated phylogenetic signal for body size, scale counts, latitude, and all climate indicators. In all cases, phylogenetic regression models fit the data significantly better than nonphylogenetic models; thus, residuals for log(10) number of dorsal scale rows exhibited phylogenetic signal.