EAWAG, Department of Aquatic Ecology and ETH-Zurich, Institute of Integrative Biology (IBZ), Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland E-mail:
Evolution. 2012 Mar;66(3):867-881. doi: 10.1111/j.1558-5646.2011.01472.x. Epub 2011 Nov 23.
Microevolutionary responses to spatial variation in the environment seem ubiquitous, but the relative role of selection and neutral processes in driving phenotypic diversification remain often unknown. The moor frog (Rana arvalis) shows strong phenotypic divergence along an acidification gradient in Sweden. We here used correlations among population pairwise estimates of quantitative trait (P(ST) or Q(ST) from common garden estimates of embryonic acid tolerance and larval life-history traits) and neutral genetic divergence (F(ST) from neutral microsatellite markers), as well as environmental differences (pond pH, predator density, and latitude), to test whether this phenotypic divergence is more likely due to divergent selection or neutral processes. We found that trait divergence was more strongly correlated with environmental differences than the neutral marker divergence, suggesting that divergent natural selection has driven phenotypic divergence along the acidification gradient. Moreover, pairwise P(ST) s of embryonic acid tolerance and Q(ST) s of metamorphic size were strongly correlated with breeding pond pH, whereas pairwise Q(ST) s of larval period and growth rate were more strongly correlated with geographic distance/latitude and predator density, respectively. We suggest that incorporating measurements of environmental variation into Q(ST) -F(ST) studies can improve our inferential power about the agents of natural selection in natural populations.
微进化对环境空间变化的响应似乎无处不在，但选择和中性过程在驱动表型多样化方面的相对作用仍然常常未知。沼泽蛙（Rana arvalis）在瑞典的酸化梯度上表现出强烈的表型分化。在这里，我们使用种群间定量性状（来自共同培养的胚胎耐酸能力和幼体生活史性状的 P(ST) 或 Q(ST)）和中性遗传分化（来自中性微卫星标记的 F(ST)）的估计值之间的相关性，以及环境差异（池塘 pH 值、捕食者密度和纬度），来检验这种表型分化是否更可能是由于分歧选择还是中性过程造成的。我们发现，性状分化与环境差异的相关性强于中性标记的分化，这表明分歧的自然选择沿酸化梯度驱动了表型的分化。此外，胚胎耐酸能力的成对 P(ST) 和变态大小的 Q(ST) 与繁殖池塘 pH 值强烈相关，而幼虫期和生长率的成对 Q(ST) 与地理距离/纬度和捕食者密度的相关性分别更强。我们认为，将环境变化的测量纳入 Q(ST) -F(ST) 研究可以提高我们对自然种群中自然选择因子的推断能力。
