The genomics of adaptation to climate in European great tit (Parus major) populations

The recognition that climate change is occurring at an unprecedented rate means that there is increased urgency in understanding how organisms can adapt to a changing environment. Wild great tit (Parus major) populations represent an attractive ecological model system to understand the genomics of climate adaptation. They are widely distributed across Eurasia and they have been documented to respond to climate change. We performed a Bayesian genome-environment analysis, by combining local climate data with single nucleotide polymorphisms genotype data from 20 European populations (broadly spanning the species' continental range). We found 36 genes putatively linked to adaptation to climate. Following an enrichment analysis of biological process Gene Ontology (GO) terms, we identified over-represented terms and pathways among the candidate genes. Because many different genes and GO terms are associated with climate variables, it seems likely that climate adaptation is polygenic and genetically complex. Our findings also suggest that geographical climate adaptation has been occurring since great tits left their Southern European refugia at the end of the last ice age. Finally, we show that substantial climate-associated genetic variation remains, which will be essential for adaptation to future changes. Whether and how organisms adapt to variations in climate remains a challenging question. However, advances in ecological genomics tools and statistical genetics methods have made it feasible to identify genomic regions that have possibly responded to selection. Here we study pan-European populations of the ecological model species, the great tit (Parus major ), to try to identify genes and genetic pathways that have possibly enabled different populations to adapt to past and present climate conditions. By: (i) genotyping 20 different great tit populations at 479,590 single nucleotide polymorphisms, and looking for associations with climate data collected from each location between the 1970s and 2000s, and (ii) using Gene Ontology enrichment analysis to infer the biological roles of climate-associated genes, we aimed to better understand the genetics of climate adaptation. Up to 36 different genes were found to be significantly associated with adaptation to climate, and several different biological processes were over-represented among these genes. Our findings suggest that adaptation to multiple climate variables has occurred, with many genes enabling different populations to adapt to their current and past environmental climatic conditions. It is likely that adaptive genetic variation persists in contemporary great tit populations.