A male brown anole basking on a tree.

A male brown anole basking on a tree.

Theory predicts that as environmental temperatures change, animals that function better at the new temperatures will be favored by natural selection. Thus, we might expect that climate warming will select for animals with higher thermal optimums (Topt). In addition, thermal performance curves are also characterized by the breadth of temperatures that animals can function. Theory predicts that increases in environmental temperature variation will select for animals with larger thermal breadths (Tbr). Previous work has shown that brown anoles transplanted to a warmer environment experienced strong directional selection favoring individuals with higher Topt and Tbr (Logan et al. 2014). However, it is unclear if selection acts on these two traits independently or if they might be genetically constrained.

Mike Logan, an NSF postdoctoral fellow at Stellenbosch University, gave a talk on a study that he and coauthors (John Curlis, Ingrid Minnaar, Joel McGlothlin, Susana Clusella-Trullas, and Bob Cox) conducted to test this question. They brought brown anoles into the lab and found a significant negative correlation between Topt and Tbr, suggesting that increases in one trait lead to reduction in the other. To test the generality of their findings, they brought ladybugs into the lab and conducted similar trials. Interestingly, they found the same results for ladybugs. This study suggests that these thermal adaptations are evolutionarily constrained in two very distant relatives.

Logan, M. L., Cox, R. M., & Calsbeek, R. 2014. Natural selection on thermal performance in a novel thermal environment. Proceedings of the National Academy of Sciences 111(39):14165-14169.

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