Robinson Jacqueline A, Ortega-Del Vecchyo Diego, Fan Zhenxin, Kim Bernard Y, vonHoldt Bridgett M, Marsden Clare D, Lohmueller Kirk E, Wayne Robert K
Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Interdepartmental Program in Bioinformatics, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Curr Biol. 2016 May 9;26(9):1183-9. doi: 10.1016/j.cub.2016.02.062. Epub 2016 Apr 21.
Genetic studies of rare and endangered species often focus on defining and preserving genetically distinct populations, especially those having unique adaptations [1, 2]. Much less attention is directed at understanding the landscape of deleterious variation, an insidious consequence of geographic isolation and the inefficiency of natural selection to eliminate harmful variants in small populations [3-5]. With population sizes of many vertebrates decreasing and isolation increasing through habitat fragmentation and loss, understanding the extent and nature of deleterious variation in small populations is essential for predicting and enhancing population persistence. The Channel Island fox (Urocyon littoralis) is a dwarfed species that inhabits six of California's Channel Islands and is derived from the mainland gray fox (U. cinereoargenteus). These isolated island populations have persisted for thousands of years at extremely small population sizes [6, 7] and, consequently, are a model for testing ideas about the accumulation of deleterious variation in small populations under natural conditions. Analysis of complete genome sequence data from island foxes shows a dramatic decrease in genome-wide variation and a sharp increase in the homozygosity of deleterious variants. The San Nicolas Island population has a near absence of variation, demonstrating a unique genetic flatlining that is punctuated by heterozygosity hotspots, enriched for olfactory receptor genes and other genes with high levels of ancestral variation. These findings question the generality of the small-population paradigm that maintains substantial genetic variation is necessary for short- and long-term persistence.
对珍稀濒危物种的遗传学研究通常聚焦于定义和保护基因独特的种群，尤其是那些具有独特适应性的种群[1, 2]。而对于理解有害变异的情况则关注较少，有害变异是地理隔离以及自然选择在小种群中清除有害变异效率低下的一种潜在后果[3 - 5]。随着许多脊椎动物的种群规模因栖息地破碎化和丧失而减小且隔离程度增加，了解小种群中有害变异的程度和性质对于预测和增强种群的持续性至关重要。海峡群岛狐（Urocyon littoralis）是一种侏儒化物种，栖息于加利福尼亚州的六个海峡群岛，由大陆灰狐（U. cinereoargenteus）演化而来。这些孤立的岛屿种群在极小的种群规模下已经存续了数千年[6, 7]，因此，它们是在自然条件下测试有关小种群中有害变异积累观点的一个模型。对海峡群岛狐全基因组序列数据的分析表明，全基因组变异显著减少，有害变异的纯合性急剧增加。圣尼古拉斯岛种群几乎没有变异，呈现出一种独特的基因停滞状态，其间穿插着杂合性热点，这些热点富含嗅觉受体基因和其他具有高水平祖先变异的基因。这些发现对小种群范式的普遍性提出了质疑，该范式认为保持大量遗传变异对于短期和长期的种群存续是必要的。
