Pruisscher Peter, Nylin Sören, Gotthard Karl, Wheat Christopher W
Department of Zoology, Stockholm University, Stockholm, Sweden.
Mol Ecol. 2018 Aug 13. doi: 10.1111/mec.14829.
Diapause is a life history strategy allowing individuals to arrest development until favourable conditions return, and it is commonly induced by shortened day length that is latitude specific for local populations. Although understanding the evolutionary dynamics of a threshold trait like diapause induction provides insights into the adaptive process and adaptive potential of populations, the genetic mechanism of variation in photoperiodic induction of diapause is not well understood. Here, we investigate genetic variation underlying latitudinal variation in diapause induction and the selection dynamics acting upon it. Using a genomewide scan for divergent regions between two populations of the butterfly Pararge aegeria that differ strongly in their induction thresholds, we identified and investigated the patterns of variation in those regions. We then tested the association of these regions with diapause induction using between-population crosses, finding significant SNP associations in four genes present in two chromosomal regions, one with the gene period, and the other with the genes kinesin, carnitine O-acetyltransferase and timeless. Patterns of allele frequencies in these two regions in population samples along a latitudinal cline suggest strong selection against heterozygotes at two genes within these loci (period, timeless). Evidence for additional loci modifying the diapause decision was found in patterns of allelic change in relation to induction thresholds over the cline, as well as in backcross analyses. Taken together, population-specific adaptations of diapause induction appear to be due to a combination of alleles of larger and smaller effect size, consistent with an exponential distribution of effect sizes involved in local adaption.
滞育是一种生活史策略，它使个体能够停止发育，直到有利条件恢复，通常由缩短的日照长度诱导，而日照长度因当地种群的纬度而异。虽然理解像滞育诱导这样的阈值性状的进化动态有助于深入了解种群的适应过程和适应潜力，但滞育光周期诱导变异的遗传机制尚不清楚。在这里，我们研究了滞育诱导纬度变异背后的遗传变异以及作用于它的选择动态。通过对蝴蝶Pararge aegeria两个种群之间的差异区域进行全基因组扫描，这两个种群在诱导阈值上有很大差异，我们识别并研究了这些区域的变异模式。然后，我们使用种群间杂交测试了这些区域与滞育诱导的关联，在两个染色体区域中的四个基因中发现了显著的单核苷酸多态性关联，一个区域与周期基因相关，另一个区域与驱动蛋白、肉碱O - 乙酰转移酶和无时间基因相关。沿着纬度梯度的种群样本中这两个区域的等位基因频率模式表明，在这些位点内的两个基因（周期基因、无时间基因）上对杂合子有强烈的选择。在与梯度上诱导阈值相关的等位基因变化模式以及回交分析中，发现了其他修饰滞育决定的位点的证据。综上所述，滞育诱导的种群特异性适应似乎是由于效应大小较大和较小的等位基因的组合，这与局部适应中涉及的效应大小的指数分布一致。
