Climate change isn’t just leading to greater average environmental temperatures – it’s also leading to an increase in the frequency and severity of extreme weather events, such as heat waves and hurricanes. Of interest to Shane Campbell-Staton, a post-doctoral researcher in the Cheviron Lab and a recent graduate from the Losos Lab at Harvard, is understanding how the recent polar vortex in North America impacted the native green anole, Anolis carolinensis. The polar vortex of winter 2013/2014 set several records in snow fall and in all-time low temperatures in the south, and also led to severe weather in the midwest and east.
Shane found that, immediately following the polar vortex event, cold tolerance (CTmin) was significantly lower in lizards from southern Texas, as low as in lizards from much higher latitudes. He suggested that this result stems from differential survivorship during the event – lizards in south Texas that were more cold tolerant (i.e., had a lower CTmin) were more likely to survive the winter vortex than less cold tolerant individuals. He then returned to south Texas a few months later and sampled both the survivors and their offspring and found that the decrease in CTmin persisted, indicating a potential evolutionary shift in cold tolerance. He put the final nail in the coffin by running a common garden experiment, where he demonstrated that, even when reared under common laboratory conditions, offspring exhibited cold tolerance similar to their parents, indicating high heritability in this trait and that the shift observed in nature was evolved rather than due to plasticity.
Shane then examined the response to the weather event at the genetic level by sequencing liver transcriptomes. Transcriptomes quantify patterns of gene expression levels for all genes regulated in a tissue; hence, by examining what genes are differentially expressed following cold stress, we can figure out the molecular underpinnings to cold adaptation and acclimation. He found that gene expression in survivors from the south closely resembled expression patterns in northern lizards, indicating a shared molecular pathway to cold tolerance adaptation in lizards from both habitats. The gene expression modules (or groups of genes) that exhibited a strong statistical association with CTmin variation were overrepresented for genes associated with oxidative phosphorylation. Oxygen consumption, which feeds oxidative phosphorylation, is directly related to CTmin: Animals that are more cold tolerant consume less oxygen during cooling. Hence, the expression differences in oxidative phosphorylation may pinpoint a proximate mechanism for cold tolerance adaptation.
You can learn more about Shane’s work on adaptation following the polar vortex in his recent Harvard Horizons talk.