Heightened among-individual variation in life history but not morphology is related to developmental temperature in reptiles.

Increases in phenotypic variation under extreme (e.g. novel or stressful) environmental conditions is emerging as a crucial process through which evolutionary adaptation can occur. Lack of prior stabilising selection, as well as potential instability of developmental processes in these environments, may lead to a release of phenotypic variation that can have important evolutionary consequences. While such patterns have been shown in model study organisms, we know little about the generality of trait variance across environments for non-model organisms. Here, we test whether extreme developmental temperatures increase phenotypic variation across diverse reptile taxa. We find that among-individual variation in a key life-history trait (post-hatching growth) increases at extreme cold and hot temperatures. However, variation in two measures of hatchlings morphology and in hatchling performance were not related to developmental temperature. While extreme developmental temperatures may increase variation in growth, our results suggest that plastic responses to stressful incubation conditions do not generally make more extreme phenotypes available to selection. We discuss the reasons for the general lack of increased variability at extreme incubation temperatures and the implications this has for local adaptation in hatchling morphology and physiology.