Length of activity season drives geographic variation in body size of a widely distributed lizard

Terézia Horváthová,Dušan Jelić,Ioan Ghira,Patrick S Fitze,Tobias Uller,Tuula A Oksanen,Christopher R Cooney,David Jandzik

doi:10.1002/ece3.613

Abstract

AbstractUnderstanding the factors that drive geographic variation in life history is an important challenge in evolutionary ecology. Here, we analyze what predicts geographic variation in life‐history traits of the common lizard,Zootoca vivipara, which has the globally largest distribution range of all terrestrial reptile species. Variation in body size was predicted by differences in the length of activity season, while we found no effects of environmental temperature per se. Females experiencing relatively short activity season mature at a larger size and remain larger on average than females in populations with relatively long activity seasons. Interpopulation variation in fecundity was largely explained by mean body size of females and reproductive mode, with viviparous populations having larger clutch size than oviparous populations. Finally, body size‐fecundity relationship differs between viviparous and oviparous populations, with relatively lower reproductive investment for a given body size in oviparous populations. While the phylogenetic signal was weak overall, the patterns of variation showed spatial effects, perhaps reflecting genetic divergence or geographic variation in additional biotic and abiotic factors. Our findings emphasize that time constraints imposed by the environment rather than ambient temperature play a major role in shaping life histories in the common lizard. This might be attributed to the fact that lizards can attain their preferred body temperature via behavioral thermoregulation across different thermal environments. Length of activity season, defining the maximum time available for lizards to maintain optimal performance, is thus the main environmental factor constraining growth rate and annual rates of mortality. Our results suggest that this factor may partly explain variation in the extent to which different taxa follow ecogeographic rules.

Highlights

Variation in body size was predicted by differences in the length of activity season, while we found no effects of environmental temperature per se
Species distributed across broad geographic ranges often exhibit extensive variation in life-history traits, and understanding the causes and consequences of this variation has been a central topic in evolutionary ecology for decades
We focused on testing whether (1) differences in seasonal activity better explain variation in body size than differences in mean ambient temperature experienced during activity; (2) costs associated with higher growth rates are offset by some benefits; (3) other abiotic factors which have an effect on growth rate significantly contribute to variation in body size; (4) the potential costs of higher growth rate are offset by benefits in terms of fecundity or survival at the population level

Summary

Introduction

Species distributed across broad geographic ranges often exhibit extensive variation in life-history traits, and understanding the causes and consequences of this variation has been a central topic in evolutionary ecology for decades. The selective regimes that drive these patterns are not fully understood and may include other aspects of the environment than ambient temperature. This is relevant for studies that rely on latitude as a proxy for temperature As most ectotherms grow larger when reared at lower temperatures (Atkinson 1994; Partridge et al 1994; Van Voorhies 1996; Angilletta and Dunham 2003), Bergmann clines may at least partially arise as a result of general plastic response in cell size (Van Voorhies 1996)

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