Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, PO Box 1066, Blindern, N-0316 Oslo, Norway.
Mol Ecol. 2011 Sep;20(18):3823-37. doi: 10.1111/j.1365-294X.2011.05182.x. Epub 2011 Jul 18.
Homoploid hybrid speciation in animals is poorly understood, mainly because of the scarcity of well-documented cases. Here, we present the results of a multilocus sequence analysis on the house sparrow (Passer domesticus), Spanish sparrow (P. hispaniolensis) and their proposed hybrid descendant, the Italian sparrow (P. italiae). The Italian sparrow is shown to be genetically intermediate between the house sparrow and Spanish sparrow, exhibiting genealogical discordance and a mosaic pattern of alleles derived from either of the putative parental species. The average variation on the Z chromosome was significantly reduced compared with autosomal variation in the putative parental species, the house sparrow and Spanish sparrow. Additionally, divergence between the two species was elevated on the Z chromosome relative to the autosomes. This pattern of variation and divergence is consistent with reduced introgression of Z-linked genes and/or a faster-Z effect (increased rate of adaptive divergence on the Z). F(ST) -outlier tests were consistent with the faster-Z hypothesis: two of five Z-linked loci (CHD1Z and PLAA) were identified as candidates for being subject to positive, divergent selection in the putative parental species. Interestingly, the two latter genes showed a mosaic pattern in the (hybrid) Italian sparrow; that is, the Italian sparrow was found to be fixed for Spanish sparrow alleles at CHD1Z and to mainly have house sparrow alleles at PLAA. Preliminary evidence presented in this study thus suggests that sex chromosomes may play a significant role in this case of homoploid hybrid speciation.
动物中的同倍杂种形成过程了解甚少，主要是因为缺乏充分记录的案例。在这里，我们对家麻雀（Passer domesticus）、西班牙麻雀（P. hispaniolensis）及其假定的杂交后代意大利麻雀（P. italiae）进行了多位点序列分析。结果表明，意大利麻雀在遗传上介于家麻雀和西班牙麻雀之间，表现出谱系上的不和谐和来自假定亲本物种的等位基因的镶嵌模式。与假定的亲本物种（家麻雀和西班牙麻雀）的常染色体变异相比，Z 染色体上的平均变异显著降低。此外，与常染色体相比，两个物种在 Z 染色体上的分歧度更高。这种变异和分歧模式与 Z 连锁基因的减少渗入或更快的 Z 效应（Z 上适应性分歧的速率增加）一致。F(ST) 异常值检验与更快的 Z 假说一致：五个 Z 连锁基因座中的两个（CHD1Z 和 PLAA）被鉴定为可能在假定的亲本物种中受到正向、分歧选择的候选基因。有趣的是，后两个基因在家雀（杂种）中表现出镶嵌模式；也就是说，意大利麻雀在 CHD1Z 处被鉴定为西班牙麻雀等位基因固定，而在 PLAA 处主要具有家麻雀等位基因。本研究初步证据表明，性染色体可能在这种同倍杂种形成过程中发挥重要作用。
