Program in Ecology, Evolution and Conservation Biology, University of Illinois, 515 Morrill Hall, 505 S Goodwin Avenue, Urbana, IL 61801, USA.
Mol Ecol. 2010 Aug;19(15):3076-87. doi: 10.1111/j.1365-294X.2010.04728.x.
Substantial genetic differentiation is frequently observed among populations of cyclically parthenogenetic zooplankton despite their high dispersal capabilities and potential for gene flow. Local adaptation has been invoked to explain population genetic differentiation despite high dispersal, but several neutral models that account for basic life history features also predict high genetic differentiation. Here, we study genetic differentiation among four populations of Daphnia pulex in east central Illinois. As with other studies of Daphnia, we demonstrate substantial population genetic differentiation despite close geographic proximity (<50 km; mean theta = 0.22). However, we explicitly tested and failed to find evidence for, the hypothesis that local adaptation to food resources occurs in these populations. Recognizing that local adaptation can occur in traits unrelated to resources, we estimated contemporary migration rates (m) and tested for admixture to evaluate the hypothesis that observed genetic differentiation is consistent with local adaptation to other untested ecological factors. Using Bayesian assignment methods, we detected migrants in three of the four study populations including substantial evidence for successful reproduction by immigrants in one pond, allowing us to reject the hypothesis that local adaptation limits gene flow for at least this population. Thus, we suggest that local adaptation does not explain genetic differentiation among these Daphnia populations and that other factors related to extinction/colonization dynamics, a long approach to equilibrium F(ST) or substantial genetic drift due to a low number of individuals hatching from the egg bank each season may explain genetic differentiation.
尽管周期性孤雌生殖浮游动物具有较高的扩散能力和基因流动潜力，但在其种群中经常观察到明显的遗传分化。尽管具有较高的扩散能力，但局部适应被认为可以解释种群遗传分化，但也有一些中性模型可以解释基本的生活史特征，这些模型也预测会有较高的遗传分化。在这里，我们研究了伊利诺伊州中东部的四个 Daphnia pulex 种群之间的遗传分化。与其他 Daphnia 研究一样，尽管地理上非常接近（<50 公里；平均 theta = 0.22），但我们证明了种群遗传分化非常明显。然而，我们明确测试并未能找到证据支持这样一种假设，即这些种群存在对食物资源的局部适应。认识到局部适应可能发生在与资源无关的特征上，我们估计了当代的迁移率（m）并进行了混合检验，以评估以下假设，即观察到的遗传分化与对其他未经测试的生态因素的局部适应一致。使用贝叶斯分配方法，我们在四个研究种群中的三个中检测到了移民，其中一个池塘中移民成功繁殖的证据非常充分，这使我们能够拒绝局部适应限制基因流的假设，至少对于这个种群是如此。因此，我们认为局部适应不能解释这些 Daphnia 种群之间的遗传分化，而与灭绝/殖民动态、达到平衡 F(ST)的漫长途径或由于每个季节从卵库中孵化的个体数量较少而导致的大量遗传漂变等其他因素可能解释了遗传分化。
