6533b824fe1ef96bd1281674

RESEARCH PRODUCT

The genomic footprint of climate adaptation inChironomus riparius

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The gradual heterogeneity of climatic factors produces continuously varying selection pressures across geographic distances that leave signatures of clinal variation in the genome. Separating signatures of clinal adaptation from signatures of other evolutionary forces, such as demographic processes, genetic drift, and adaptation to specific non-clinal conditions of the immediate local environment is a major challenge. Here, we examine climate adaptation in five natural populations of the non-biting midge Chironomus riparius sampled along a climatic gradient across Europe. Our study integrates experimental data, individual genome resequencing, Pool-Seq data, and population genetic modelling. Common-garden experiments revealed a positive correlation of population growth rates corresponding to the population origin along the climate gradient, suggesting thermal adaptation on the phenotypic level. In a population genomic analysis, we derived empirical estimates of historical demography and migration as parameters for species-specific models to simulate neutral divergence among populations. Despite this effort, the modelling approach consistently underestimated the empirical population differentiation. This might be due to special evolutionary dynamics in multivoltine ectotherms and we highlight important challenges and pitfalls for such population genetic modelling. We instead used a more conservative statistical F ST outlier threshold based on empirical data to infer positive selection across the climate gradient, and combined the results with an environmental association analysis. Through this integration, we disentangled 162 candidate genes for climate adaptation from 999 candidate genes for (non-clinal) local adaptation. GO term enrichment analysis revealed that the functional basis of climate adaptation involves the apoptotic process and molecular response to heat.