Data from: Random interbreeding between cryptic lineages of the Common Raven: evidence for speciation in reverse

DNA sequence studies frequently reveal evidence of cryptic lineages in morphologically uniform species, many of which turn out to be evolutionarily distinct species. The Common Raven (Corvus corax) includes two deeply divergent mtDNA lineages: one lineage seems restricted to western North America and the other is Holarctic in distribution. These deep clades hint of the possibility of cryptic species in the western United States. We tested this hypothesis in a population consisting of an equal proportion of both mtDNA clades, by quantifying mating patterns and associated fitness consequences with respect to mtDNA. We also tested for morphological, behavioural and ecological correlates of sex and mtDNA clade membership. Mate pairings were random with respect to mtDNA clades, and there were no differences in reproductive success between assortatively and nonassortatively mated pairs. We found no differences in survival or resource use between clades. There were no differences in morphological or behavioural characters between mtDNA clades, except one clade trended towards greater mobility. These results suggest there are no barriers to gene flow between mtDNA clades and argue that the mtDNA clades have remerged in this population, likely due to a lack of ecological or signal differentiation between individuals in each lineage. Hence, in Common Ravens, phylogeographic structure in mtDNA is a reflection of likely past isolation rather than currently differentiated species.

DNA序列研究常可在形态均一的物种类群中发现隐存支系的相关证据，其中多数支系最终被证实为演化上独立的物种。普通渡鸦（Common Raven，学名Corvus corax）存在两个高度分化的线粒体DNA（mtDNA）支系：一支仅分布于北美西部，另一支的分布范围覆盖全北界（Holarctic）。这两个深度分化的演化支暗示，美国西部存在隐存物种的可能性。我们以两类线粒体DNA支系占比均等的种群为研究对象，通过量化交配模式及其与线粒体DNA相关的适合度效应，对该假说展开验证；同时还检测了性别与线粒体DNA支系归属在形态、行为及生态特征上的相关性。研究结果显示，交配配对与线粒体DNA支系呈现随机模式，选型交配与非选型交配配对的繁殖成功率并无显著差异；不同支系个体在存活率或资源利用模式上均无显著区别；两类支系在形态与行为特征上也未发现显著差异，仅其中一支表现出移动性更强的趋势。上述结果表明，两类线粒体DNA支系间不存在基因流障碍，且该种群内的线粒体DNA支系已发生重新融合，这一现象大概率源于两类支系个体在生态特征或信号层面缺乏分化。因此，在普通渡鸦中，线粒体DNA的系统地理结构（phylogeographic structure）反映的是其过往的隔离历史，而非当前已分化为独立的物种。