Thermal and fitness-related consequences of nest location in Painted Turtles (Chrysemys picta)

Abstract

1. Laboratory experiments have documented substantial temperature effects on the physiological ecology of reptilian eggs, embryos and offspring. However, functional links between important habitat characteristics, nest microenvironments and fitness-related traits of neonates in natural nests have rarely been studied. 2. A field study of 11 Painted Turtle (Chrysemys picta) nests was conducted to quantify the relationships between a habitat characteristic (i.e. vegetational cover around nests at oviposition) and (1) developmental temperature and its effect on offspring sex ratio and (2) hibernation temperature and its effect on offspring survivorship. 3. Vegetational cover was negatively correlated with nest temperatures in July, the period when offspring sex is determined. However, neither vegetational cover nor mean nest temperature predicted nest sex ratios, although correlations among these variables were consistent with causal relationships derived from laboratory studies. 4. Summer vegetational cover was also negatively correlated with measures of winter nest temperatures. Of the three nests exhibiting overwinter mortality, two were surrounded by thick vegetation and all experienced temperatures below - 8 °C. The remaining nests reached temperatures as low as - 6 °C without mortality, indicating that hatchlings in these nests exhibited remarkable supercooling ability. 5. The results suggest that habitat characteristics and nest microenvironments are functionally linked and have fitness consequences for both embryos and offspring, implying that nest-site choice by female turtles could have considerable utility.