Data from: Genomic evidence that resource-based trade-offs limit host-range expansion in a seed beetle

Trade-offs have often been invoked to explain the evolution of ecological specialization. Phytophagous insects have been especially well studied, but there has been little evidence that resource-based trade-offs contribute to the evolution of host specialization in this group. Here, we combine experimental evolution and partial genome resequencing of replicate seed beetle selection lines to test the trade-off hypothesis and measure the repeatability of evolution. Bayesian estimates of selection coefficients suggest that rapid adaptation to a poor host (lentil) was mediated by standing genetic variation at multiple genetic loci and involved many of the same variants in replicate lines. Sublines that were then switched back to the ancestral host (mung bean) showed a more gradual and variable (less repeatable) loss of adaptation to lentil. We were able to obtain estimates of variance effective population sizes from genome-wide differences in allele frequencies within and between lines. These estimates were relatively large, which suggests that the contribution of genetic drift to the loss of adaptation following reversion was small. Instead, we find that some alleles that were favored on lentil were selected against during reversion on mung bean, consistent with the genetic trade-off hypothesis.

生态特化的演化过程常通过权衡机制加以解释。植食性昆虫(phytophagous insects)是该领域研究最为充分的类群，但目前鲜有证据表明，基于资源的权衡能够推动该类群寄主特化的演化。本研究结合实验演化与重复豆象选择系的部分基因组重测序技术，对遗传权衡假说进行验证，并量化演化的可重复性。基于贝叶斯方法估算的选择系数显示，对劣质寄主小扁豆(lentil)的快速适应性演化，由多个遗传位点上的现存遗传变异所介导，且各重复选择系中涉及的变异位点高度重合。后续被转回祖先寄主绿豆(mung bean)的亚系，其对小扁豆的适应性丧失过程更为缓慢且波动显著（可重复性更低）。我们可通过系内与系间等位基因频率的全基因组差异，获得方差有效种群大小(variance effective population size)的估算值。该估算值相对较大，表明遗传漂变在寄主转回后适应性丧失过程中的贡献较小。与之相反，我们发现部分在小扁豆上受正向选择的等位基因，在转回绿豆的选择压力下受到负向选择，这与遗传权衡假说的核心预测相符。