Aguilar Andres, Roemer Gary, Debenham Sally, Binns Matthew, Garcelon David, Wayne Robert K
Department of Organismic Biology, Ecology, and Evolution, University of California, Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 2004 Mar 9;101(10):3490-4. doi: 10.1073/pnas.0306582101. Epub 2004 Feb 27.
The San Nicolas Island fox (Urocyon littoralis dickeyi) is genetically the most monomorphic sexually reproducing animal population yet reported and has no variation in hypervariable genetic markers. Such low levels of variation imply lower resistance to pathogens, reduced fitness, and problems in distinguishing kin from non-kin. In vertebrates, the MHC contains genes that influence disease resistance and kin recognition and may be under intense balancing selection in some populations. Hence, genetic variation at the MHC might persist despite the extreme monomorphism shown by neutral markers. We examine variation of five loci within the MHC of San Nicolas Island foxes and find remarkably high levels of variation. Further, we show by simulation that genetic monomorphism at neutral loci and high MHC variation could arise only through an extreme population bottleneck of <10 individuals, approximately 10-20 generations ago, accompanied by unprecedented selection coefficients of >0.5 on MHC loci. These results support the importance of balancing selection as a mechanism to maintain variation in natural populations and expose the difficulty of using neutral markers as surrogates for variation in fitness-related loci.
圣尼古拉斯岛狐（Urocyon littoralis dickeyi）在基因上是迄今报道的最单一的有性繁殖动物种群，在高变遗传标记上没有变异。如此低水平的变异意味着对病原体的抵抗力较低、适应性降低以及难以区分亲属和非亲属。在脊椎动物中，主要组织相容性复合体（MHC）包含影响抗病性和亲属识别的基因，并且在一些种群中可能受到强烈的平衡选择。因此，尽管中性标记显示出极端的单一性，但MHC的遗传变异可能仍然存在。我们研究了圣尼古拉斯岛狐MHC内五个位点的变异，发现变异水平非常高。此外，我们通过模拟表明，中性位点的遗传单一性和高MHC变异只能通过大约10 - 20代以前小于10个个体的极端种群瓶颈产生，同时伴随着MHC位点上大于0.5的前所未有的选择系数。这些结果支持了平衡选择作为维持自然种群变异的一种机制的重要性，并揭示了使用中性标记作为与适应性相关位点变异的替代指标的困难。
