Bailey R I, Tesaker M R, Trier C N, Saetre G-P
Department of Biosciences, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, Oslo, Norway.
J Evol Biol. 2015 Jun;28(6):1257-69. doi: 10.1111/jeb.12652. Epub 2015 Jun 1.
Homoploid hybrid speciation (HHS) requires reproductive barriers between hybrid and parent species, despite incomplete reproductive isolation (RI) between the parents. Novel secondary sexual trait values in hybrids may cause prezygotic isolation from both parents, whereas signals inherited by the hybrid from one parent species may cause prezygotic isolation with the other. Here we investigate whether differences in male plumage function as a premating barrier between the hybrid Italian sparrow and one of its parent species, the house sparrow, in a narrow Alpine hybrid zone. Italian sparrow male plumage is a composite mosaic of the parental traits, with its head plumage most similar to its other parent, the Spanish sparrow. We use geographical cline analysis to examine selection on three plumage traits, 75 nuclear single nucleotide polymorphisms (SNPs) and hybrid indices based on these SNPs. Several SNPs showed evidence of restricted introgression in the Alps, supporting earlier findings. Crown colour exhibited the narrowest plumage cline, representing a 37% (range 4-65%) drop in fitness. The cline was too narrow to be due to neutral introgression. Only crown colour was significantly bimodal in the hybrid zone. Bimodality may be due to RI or a major QTL, although fitness estimates suggest that selection contributes to the pattern. We discuss the implications with respect to HHS and the species status of the Italian sparrow.
同倍体杂交物种形成（HHS）需要杂种与亲本物种之间存在生殖隔离，尽管亲本之间存在不完全生殖隔离（RI）。杂种中出现的新的第二性征值可能导致与双亲的合子前隔离，而杂种从一个亲本物种继承的信号可能导致与另一个亲本的合子前隔离。在此，我们研究了在一个狭窄的阿尔卑斯杂交带中，意大利麻雀雄性羽毛的差异是否作为其与亲本物种之一家麻雀之间的交配前隔离屏障。意大利麻雀雄性羽毛是亲本性状的复合镶嵌，其头部羽毛与另一个亲本西班牙麻雀最为相似。我们使用地理渐变分析来研究对三种羽毛性状、75个核单核苷酸多态性（SNP）以及基于这些SNP的杂交指数的选择。几个SNP显示出在阿尔卑斯山存在基因渐渗受限的证据，支持了早期的研究结果。头顶颜色表现出最窄的羽毛渐变，代表适合度下降了37%（范围为4 - 65%）。这种渐变太窄，不可能是由于中性基因渐渗造成的。在杂交带中只有头顶颜色显著呈现双峰分布。双峰分布可能是由于生殖隔离或一个主要的数量性状位点（QTL），尽管适合度估计表明选择促成了这种模式。我们讨论了这对于同倍体杂交物种形成以及意大利麻雀物种地位的意义。
