Hedrick Philip W, Parker Karen M
Department of Biology, Arizona State University, Tempe, Arizona, 85287-1501.
Evolution. 1998 Feb;52(1):194-199. doi: 10.1111/j.1558-5646.1998.tb05152.x.
Sequence variation at a major histocompatibility complex (MHC) gene, assumed to be involved in parasite and pathogen resistance, was examined in the endangered Gila topminnow (Poeciliopis o. occidentalis), from the four watersheds where they remain in the United States. This is the first estimate of variation in MHC genes in natural populations of an endangered species. The population that has experienced the most bottlenecks historically was monomorphic for MHC variation. Another population, which earlier had been found to be the only population polymorphic for allozymes, had five MHC alleles, four different from those found in the other populations. Overall, nine different alleles were found. The four populations were highly divergent at MHC with four of the six population pairs not sharing any alleles. However, the magnitude of differentiation between populations on the amino-acid level varied fivefold for the populations that shared no alleles. Using single-stranded conformational polymorphism (SSCP), these alleles segregated consistently with Mendelian expectations in families. Because of the high genetic differentiation between these populations for a potentially adaptive gene, we recommend that the four watersheds be examined further for separate conservation and management.
在濒危的吉拉鳉鱼（Poeciliopis o. occidentalis）中，研究了假定与寄生虫和病原体抗性有关的主要组织相容性复合体（MHC）基因的序列变异，该研究涵盖了它们在美国境内仍有分布的四个流域。这是对濒危物种自然种群中MHC基因变异的首次估计。历史上经历瓶颈效应最多的种群在MHC变异方面是单态的。另一个种群，之前被发现是唯一在等位酶方面具有多态性的种群，有五个MHC等位基因，其中四个与其他种群中发现的不同。总体而言，共发现了九个不同的等位基因。这四个种群在MHC上高度分化，六个种群对中有四个没有共享任何等位基因。然而，对于没有共享等位基因的种群，在氨基酸水平上种群间的分化程度相差五倍。使用单链构象多态性（SSCP）方法，这些等位基因在家族中与孟德尔遗传预期一致地分离。由于这些种群在一个潜在适应性基因上存在高度的遗传分化，我们建议对这四个流域进行进一步研究，以便进行单独的保护和管理。
