Parasite-mediated selection against inbred Soay sheep in a free-living, island population
Parasite-mediated selection against inbred Soay sheep in a free-living, island population
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DOI：
10.1111/j.1558-5646.1999.tb04538.x
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发表时间：
1999-08-01
期刊：
影响因子：
3.3
通讯作者：
Pemberton, JM
中科院分区：
文献类型：
--
作者：
Coltman, DW;Pilkington, JG;Pemberton, JM
寄生虫被认为提供了一种选择性力量，能够促进自然种群的遗传变异。很少考虑到这种作用的途径是通过寄生虫介导的反对近亲繁殖的选择。如果寄生虫对寄主施加了适应性成本，并且近亲的后代由于近交导致的纯合子增加而对寄生虫更敏感，那么寄生虫介导的死亡可能会选择对近交个体不利。这一假设尚未在自然脊椎动物种群中得到验证。本研究表明，通过微卫星杂合性评估，相对近交系的Soay羊（Ovis aries）更容易受到胃肠道线虫的寄生，相互作用表明，高种群密度的成年羊的易感性最大。在苏格兰圣基尔达的Hirta岛上，在越冬死亡率高的时期，高度寄生的个体不太可能存活。更多近交系的个体也不太可能存活，这是由于它们对寄生虫的易感性增加，因为在实验中通过驱虫处理清除了胃肠道寄生虫负担的绵羊中，近交系的存活是随机的。这种选择的结果是，圣基尔丹苏伊羊的平均微卫星杂合性随着年龄的增长而增加。我们认为，寄生虫介导的选择通过去除杂合较少的个体来维持这个小岛屿种群的遗传变异。
Parasites are thought to provide a selective force capable of promoting genetic variation in natural populations. One rarely considered pathway for this action is via parasite-mediated selection against inbreeding. If parasites impose a fitness cost on their host and the offspring of close relatives have greater susceptibility to parasites due to the increased homozygosity that results from inbreeding, then parasite-mediated mortality may select against inbred individuals. This hypothesis has not yet been tested within a natural vertebrate population. Here we show that relatively inbred Soay sheep (Ovis aries), as assessed by microsatellite heterozygosity, are more susceptible to parasitism by gastrointestinal nematodes, with interactions indicating,greatest susceptibility among adult sheep at high population density. During periods of high overwinter mortality on the island of Hirta, St. Kilda, Scotland, highly parasitised individuals were less likely to survive. More inbred individuals were also less likely to survive, which is due to their increased susceptibility to parasitism, because survival was random with respect to inbreeding among sheep that were experimentally cleared of their gastrointestinal parasite burden by anthelminthic treatment. As a consequence of this selection, average microsatellite heterozygosity increases with age in St. Kildan Soay sheep. We suggest that parasite-mediated selection acts to maintain genetic variation in this small island population by removing less heterozygous individuals.