Reduced MHC and neutral variation in the Galápagos hawk, an island endemic.
Reduced MHC and neutral variation in the Galápagos hawk, an island endemic.
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DOI：
10.1186/1471-2148-11-143
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发表时间：
2011-05-25
影响因子：
3.4
通讯作者：
Parker PG
中科院分区：
文献类型：
--
作者：
Bollmer JL;Hull JM;Ernest HB;Sarasola JH;Parker PG
主要组织相容性复合体(MHC)上的基因以通过平衡选择保持高度多态而闻名。然而，在小种群或瓶颈种群中，遗传漂移可能足够强大，足以压倒平衡选择的效果，导致MHC变异性降低。在这项研究中，我们研究了两个最近分化的鸟类物种的MHC进化：地方性加拉帕戈斯鹰(Buteo Galapagoensis)，它出现在小而孤立的岛屿种群中，以及它广泛分布的大陆近亲斯文森鹰(B.swainsoni)。我们在每个物种中至少扩增了两个MHC II B类基因拷贝。我们只从32只加拉帕戈斯鹰身上恢复了三个不同的序列，而我们从20只斯文森鹰身上扩增了20个独特的序列。大多数序列在系统发育网络中聚为两组，其中一组可能代表假基因或非经典基因座。与斯文森鹰相比，加拉帕戈斯鹰在17个微卫星座位上的中性遗传多样性也减少了。中性多样性的相应丧失表明，与斯文森鹰相比，加拉帕戈斯鹰MHC II B类基因的变异性降低主要是由于创始人事件以及随后在小种群中持续的遗传漂移。然而，净化选择也可以解释MHC等位基因数量较低的原因。如果新的疾病到达该群岛，参与适应性免疫反应的基因的这种缺乏变异可能会引起关注。
Genes at the major histocompatibility complex (MHC) are known for high levels of polymorphism maintained by balancing selection. In small or bottlenecked populations, however, genetic drift may be strong enough to overwhelm the effect of balancing selection, resulting in reduced MHC variability. In this study we investigated MHC evolution in two recently diverged bird species: the endemic Galápagos hawk (Buteo galapagoensis), which occurs in small, isolated island populations, and its widespread mainland relative, the Swainson's hawk (B. swainsoni). We amplified at least two MHC class II B gene copies in each species. We recovered only three different sequences from 32 Galápagos hawks, while we amplified 20 unique sequences in 20 Swainson's hawks. Most of the sequences clustered into two groups in a phylogenetic network, with one group likely representing pseudogenes or nonclassical loci. Neutral genetic diversity at 17 microsatellite loci was also reduced in the Galápagos hawk compared to the Swainson's hawk. The corresponding loss in neutral diversity suggests that the reduced variability present at Galápagos hawk MHC class II B genes compared to the Swainson's hawk is primarily due to a founder event followed by ongoing genetic drift in small populations. However, purifying selection could also explain the low number of MHC alleles present. This lack of variation at genes involved in the adaptive immune response could be cause for concern should novel diseases reach the archipelago.