Coors Anja, Vanoverbeke Joost, De Bie Tom, De Meester Luc
Laboratory of Aquatic Ecology and Evolutionary Biology, Katholieke Universiteit Leuven, Ch. De Bériotstraat 32, 3000 Leuven, Belgium.
Aquat Toxicol. 2009 Oct 19;95(1):71-9. doi: 10.1016/j.aquatox.2009.08.004. Epub 2009 Aug 14.
Provided that gene flow is not too high, selection by local environmental conditions in heterogeneous landscapes can lead to genetic adaptation of natural populations to their local habitat. Pollution with anthropogenic toxicants may create pronounced environmental gradients that impose strong local selection pressures. Toxic contaminants may also directly impact genetic structure in natural populations by exhibiting genotoxicity or by causing population declines resulting in genetic bottlenecks. Using populations of Daphnia magna established from the dormant egg banks of ponds located in a landscape dominated by anthropogenic impact, we aimed at detecting evidence for local adaptation to environmental contamination. We explored the relationship between land use around the 10 investigated ponds, population genetic diversity as measured by neutral genetic markers (polymorphic allozymes) and the tolerance of the populations originating from these ponds to acute lethal effects of two model toxicants, the pesticide carbaryl and the metal potassium dichromate. Genetic diversity of the populations as observed by neutral markers tended to be negatively impacted by agricultural land use intensity (Spearman rank correlation, R=-0.614, P=0.059), indicating that genetic bottlenecks may have resulted from anthropogenic impact. We experimentally observed differences in susceptibility to both carbaryl and potassium dichromate among the studied pond populations of D. magna (analysis of deviance, P<0.001). Because the experimental design excluded the possibility of physiological adaptation of the test animals to the toxicants, we conclude that the differences in susceptibility must have a genetic basis. Moreover, carbaryl tolerance levels of the populations tended to increase with increasing agricultural land use intensity as described by ranked percentage of land coverage with cereal and corn crop in the proximity of the ponds (Spearman rank correlation, R=0.602, P=0.066). Together, these two findings provide evidence for local adaptation of D. magna populations to pesticide contamination. Overall, the results demonstrate the potential selection pressure imposed by anthropogenic pollution and provide evidence that genetic erosion in natural Daphnia populations is related to anthropogenic impact.
只要基因流动不是过高，在异质景观中由当地环境条件进行的选择可导致自然种群对其当地栖息地的遗传适应。人为有毒物质的污染可能会形成明显的环境梯度，从而施加强烈的局部选择压力。有毒污染物还可能通过表现出遗传毒性或导致种群数量下降从而造成遗传瓶颈，直接影响自然种群的遗传结构。我们利用从受人为影响主导的景观中池塘的休眠卵库建立的大型溞种群，旨在检测对环境污染进行局部适应的证据。我们探究了10个被调查池塘周边的土地利用情况、通过中性遗传标记（多态性等位酶）测量的种群遗传多样性，以及源自这些池塘的种群对两种模型有毒物质（农药西维因和金属重铬酸钾）急性致死效应的耐受性之间的关系。通过中性标记观察到的种群遗传多样性往往受到农业土地利用强度的负面影响（斯皮尔曼等级相关，R = -0.614，P = 0.059），这表明遗传瓶颈可能是由人为影响导致的。我们通过实验观察到，在研究的大型溞池塘种群中，对西维因和重铬酸钾的易感性存在差异（偏差分析，P < 0.001）。由于实验设计排除了试验动物对有毒物质进行生理适应的可能性，我们得出结论，易感性差异必定有遗传基础。此外，正如池塘附近谷物和玉米作物覆盖土地的排名百分比所描述的那样，种群对西维因的耐受水平往往随着农业土地利用强度的增加而升高（斯皮尔曼等级相关，R = 0.602，P = 0.066）。这两个发现共同为大型溞种群对农药污染的局部适应提供了证据。总体而言，结果证明了人为污染施加的潜在选择压力，并提供了证据表明自然大型溞种群中的遗传侵蚀与人为影响有关。
