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学同质化的物种中发现隐蔽支系的证据，其中多数支系最终被证实为演化上独立的物种。渡鸦（Common Raven，*Corvus corax*）存在两个深度分化的线粒体DNA（mitochondrial DNA，mtDNA）支系：一支仅局限分布于北美西部，另一支则呈泛北极分布。这两大演化支暗示美国西部可能存在隐蔽物种。我们针对该假说展开验证：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相关的适合度后果开展实验；同时检验性与线粒体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支系呈随机模式，选型交配与非选型交配配对的生殖成功率无显著差异；两类支系在存活率与资源利用方面亦无区别。除一支支系表现出更高移动性的趋势外，两类支系在形态或行为特征上均无显著差异。上述结果表明，两类线粒体DNA支系之间不存在基因流障碍，且该种群中的线粒体DNA支系已发生再度融合，这大概率源于两类支系个体间缺乏生态或信号分化。因此，在渡鸦种群中，线粒体DNA的系统地理结构更可能反映了过往的隔离事件，而非当前已分化为独立物种。