Data from: Geographic clines in wing morphology relate to colonization history in New World but not Old World populations of yellow dung flies

Geographic clines offer insights about putative targets and agents of natural selection as well as tempo and mode of adaptation. However, demographic processes can lead to clines that are indistinguishable from adaptive divergence. Using the widespread yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae), we examine quantitative genetic differentiation (QST) of wing shape across North America, Europe and Japan, and compare this differentiation with that of ten microsatellites (FST). Morphometric analyses of 28 populations reared at three temperatures revealed significant thermal plasticity, sexual dimorphism and geographic differentiation in wing shape. In North America morphological differentiation followed the decline in microsatellite variability along the presumed route of recent colonization from the southeast to the northwest. Across Europe, where S. stercoraria presumably existed for much longer time and where no molecular pattern of isolation by distance was evident, clinal variation was less pronounced despite significant morphological differentiation (QST>FST). Shape vector comparisons further indicate that thermal plasticity (hot-to-cold) does not mirror patterns of latitudinal divergence (south-to-north), as might have been expected under a scenario with temperature as the major agent of selection. Our findings illustrate the importance of detailed phylogeographic information when interpreting geographic clines of dispersal traits in an adaptive evolutionary framework.

地理渐变群（geographic clines）可为自然选择的假定靶标与作用因子，以及适应的速率与模式提供研究视角。然而，种群历史动态过程可形成与适应性分化难以区分的渐变群。本研究以广布性黄粪蝇*Scathophaga stercoraria*（双翅目：粪蝇科，Diptera: Scathophagidae）为研究对象，对北美、欧洲及日本的翅形开展数量遗传分化（quantitative genetic differentiation, QST）分析，并将该分化水平与基于10个微卫星标记的群体分化固定指数（FST）进行对比。对在3种温度下饲养的28个种群的形态测量分析显示，翅形存在显著的温度可塑性、雌雄二态性以及地理分化。在北美地区，形态分化与沿近期从东南向西北的殖民扩散路径出现的微卫星变异下降趋势相一致。在欧洲地区，黄粪蝇的存在时间显然更长，且未呈现显著的距离隔离（isolation by distance）分子模式，尽管存在显著的形态分化（QST>FST），但渐变变异却相对较弱。翅形向量比对分析进一步表明，温度可塑性（热-冷表型变化）并未呈现出与纬度梯度分化（南-北方向）一致的模式，这与以温度为主要选择因子的理论预期相悖。本研究结果表明，在适应性进化框架下解读扩散相关性状的地理渐变群时，详细的系统地理信息至关重要。