Cryptic speciation and gene flow in a migratory songbird species complex: insights from the red-eyed vireo (Vireo olivaceus)

Migratory species that alternate between sympatry and allopatry over the course of an annual cycle are promising subjects for studies seeking to understand the process of speciation in the absence of strict geographic isolation. Here we sought to identify cryptic species and assess rates of gene flow in a clade of neotropical migrant songbirds in which geography and taxonomy are currently out of sync: the Red-Eyed Vireo (V. olivaceus) Species Complex. Phylogenetic, clustering, and statistical species delimitation analyses found that V. olivaceus includes two non-sister lineages migrating in opposite directions across the equator. Analyses of gene flow identified low levels of introgression between two species pairs, but none between northern and southern olivaceus. We also identified substantial well-supported conflicts between nuclear and mitochondrial topologies. Although the geographic distribution of mito-nuclear discordance is suggestive of hybridization and mitochondrial capture, ...在年度生命周期中交替呈现同域分布（sympatry）与异域分布（allopatry）的迁徙物种，是探究无严格地理隔离条件下物种形成过程的极具潜力的研究对象。本研究旨在鉴定分类学与地理分布目前尚不匹配的新热带迁徙鸣禽演化支中的隐存物种（cryptic species），并评估其基因流水平——该类群即为红眼绿鹃（Vireo olivaceus）物种复合体。系统发育、聚类及统计物种界定分析结果显示，V. olivaceus包含两个以相反方向跨赤道迁徙的非姊妹谱系。基因流分析发现，两组物种类群对间仅存在低水平的基因渐渗，而北部与南部的olivaceus类群间未检测到基因渐渗。本研究同时发现核基因与线粒体基因拓扑结构间存在大量得到显著支持的冲突。尽管核质冲突（mito-nuclear discordance）的地理分布暗示存在杂交与线粒体捕获现象，……