Department of Environmental Toxicology, University of California, Davis, Davis, CA.
Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, Davis, CA.
Mol Biol Evol. 2021 Apr 13;38(4):1306-1316. doi: 10.1093/molbev/msaa289.
As species struggle to keep pace with the rapidly warming climate, adaptive introgression of beneficial alleles from closely related species or populations provides a possible avenue for rapid adaptation. We investigate the potential for adaptive introgression in the copepod, Tigriopus californicus, by hybridizing two populations with divergent heat tolerance limits. We subjected hybrids to strong heat selection for 15 generations followed by whole-genome resequencing. Utilizing a hybridize evolve and resequence (HER) technique, we can identify loci responding to heat selection via a change in allele frequency. We successfully increased the heat tolerance (measured as LT50) in selected lines, which was coupled with higher frequencies of alleles from the southern (heat tolerant) population. These repeatable changes in allele frequencies occurred on all 12 chromosomes across all independent selected lines, providing evidence that heat tolerance is polygenic. These loci contained genes with lower protein-coding sequence divergence than the genome-wide average, indicating that these loci are highly conserved between the two populations. In addition, these loci were enriched in genes that changed expression patterns between selected and control lines in response to a nonlethal heat shock. Therefore, we hypothesize that the mechanism of heat tolerance divergence is explained by differential gene expression of highly conserved genes. The HER approach offers a unique solution to identifying genetic variants contributing to polygenic traits, especially variants that might be missed through other population genomic approaches.
随着物种努力跟上快速变暖的气候，从密切相关的物种或种群中有益等位基因的适应性基因渗入为快速适应提供了一种可能的途径。我们通过杂交两种耐热极限不同的种群来研究桡足类动物加利福尼亚 T. californicus 中适应性基因渗入的潜力。我们对杂种进行了 15 代的强烈耐热选择，然后进行了全基因组重测序。利用杂交进化和重测序 (HER) 技术，我们可以通过等位基因频率的变化来识别对热选择有反应的基因座。我们成功地提高了所选系的耐热性（以 LT50 衡量），同时来自南部（耐热）种群的等位基因频率更高。这些等位基因频率的可重复变化发生在所有 12 条独立选择的染色体上，这表明耐热性是多基因的。这些基因座包含的蛋白质编码序列差异小于全基因组平均水平的基因，表明这些基因座在两个种群之间高度保守。此外，这些基因座富含在非致死性热休克下，所选和对照系之间表达模式发生变化的基因。因此，我们假设耐热性分歧的机制是由高度保守基因的差异表达解释的。HER 方法为鉴定导致多基因性状的遗传变异提供了一种独特的解决方案，特别是通过其他群体基因组方法可能会错过的变异。
