Recent theory on the genetic basis of local adaptation predicts that X-linked genes should nearly always make a larger contribution to local adaptation than autosomal genes. To test this prediction, we expanded upon a widely-used reciprocal cross method for estimating the influence of the X-chromosome on phenotypic divergence between populations (captured by the X-linked divergence metric, IX, from Reinhold 1998). In the present study, we developed indices for estimating the contributions of the X-chromosome (IX), the autosomes (IA), and cytoplasmic and Y-linked genes (ICY) to phenotypic divergence between populations. We used reciprocal crosses from two geographically distinct populations of Drosophila melanogaster collected from along a latitudinal gradient to generate F1 and F2 males that were then phenotyped for a series of four ecologically important and clinally variable traits: heat resistance, desiccation and starvation resistance, and wing size (a proxy for body size). In contrast to the theoretical predictions, we find that divergence is dominated by autosomal genes, and genes with uniparental inheritance (e.g., mitochondria, Y). We discuss how attributes of genome architecture and sex-biased demography may contribute to these results.
Recent theory on the genetic basis of local adaptation predicts that X-linked genes should nearly always make a larger contribution to local adaptation than autosomal genes. To test this prediction, we expanded upon a widely-used reciprocal cross method for estimating the influence of the X-chromosome on phenotypic divergence between populations (captured by the X-linked divergence metric, IX, from Reinhold 1998). In the present study, we developed indices for estimating the contributions of the X-chromosome (IX), the autosomes (IA), and cytoplasmic and Y-linked genes (ICY) to phenotypic divergence between populations. We used reciprocal crosses from two geographically distinct populations of Drosophila melanogaster collected from along a latitudinal gradient to generate F1 and F2 males that were then phenotyped for a series of four ecologically important and clinally variable traits: heat resistance, desiccation and starvation resistance, and wing size (a proxy for body size). In contrast to the theoretical predictions, we find that divergence is dominated by autosomal genes, and genes with uniparental inheritance (e.g., mitochondria, Y). We discuss how attributes of genome architecture and sex-biased demography may contribute to these results.
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