Projecting responses to climate change: a view from the underground

Sears, Michael W.

Carlo, Michael A.

Department of Biological Sciences

Clemson University

Clemson, SC

Predictive models are necessary to assess the vulnerability of lizard populations to changing climates. Most attempts to predict responses to changing climates have largely depended on the thermal ecology of adults, focussing on the energetic consequences of aboveground activity. Though powerful, this approach can be misleading because it often ignores embryonic stages, where animals lack the ability to modify behaviors in response to changing environmental conditions. Over the past five years, we have conducted a series of laboratory and field studies to assess the potential responses of embryos to environmental warming across a latitudinal gradient in the Eastern fence lizard, Sceloporus undulatus. We have characterized the thermal conditions of nests chosen by females, characterized the phenotypic effects of sublethal warming of nests and embryos, and performed a lab-based reciprocal transplant study, leveraging a space for time substitution to understand the adaptive potential of embryos to tolerate warming climates. Further, many of these responses have been incorporated into a mechanistic species range model. Our findings suggest that 1) mortality and reduced post-hatching growth induced by sublethal temperatures can greatly reduce population growth, 2) due to the behavior of mothers, nesting environments are actually warmer in northern populations, 3) warming will likely lead to cooler nests in northern populations and warmer nests in southern populations, and 4) developmental rates are fairly insensitive to environmental conditions despite local adaptation in other life history traits. In combination, these results suggest that climate warming will benefit northern populations (across all life stages) and harm southern populations, and the magnitudes of these effects are predicted to be more extreme than if only considering the biology of adults.