Data from: Ecological adaptation and reproductive isolation in sympatry: genetic and phenotypic evidence for native host races of Rhagoletis pomonella

Ecological speciation-with-gene-flow may be an important mode of diversification for phytophagous insects. The recent shift of Rhagoletis pomonella from its native host downy hawthorn (Crataegus mollis) to introduced apple (Malus domestica) in the northeastern United States is a classic example of sympatric host race formation. Here, we test whether R. pomonella has similarly formed host races on four native Crataegus species in the southern United States: western mayhaw (C. opaca), blueberry hawthorn (C. brachyacantha), southern red hawthorn (C. mollis var. texana), and green hawthorn (C. viridis). These four southern hosts differ from each other in their fruiting phenology and in the volatile compounds emitted from the surface of their fruits. These two traits form the basis of ecological reproductive isolation between downy hawthorn and apple flies in the North. We report evidence from microsatellite population surveys and eclosion studies supporting the existence of genetically differentiated and partially reproductively isolated host races of southern hawthorn flies. The results provide an example of host shifting and ecological divergence involving native plants and imply that speciation-with-gene-flow may be commonly initiated in Rhagoletis when ecological opportunity presents itself.

存在基因流的生态物种形成（ecological speciation-with-gene-flow）或许是植食性昆虫物种多样化的重要模式。美国东北部的苹果实蝇（Rhagoletis pomonella）从其原生寄主柔毛山楂（Crataegus mollis）转移至引入种苹果（Malus domestica）的事件，是同域宿主种群分化（sympatric host race formation）的经典案例。本研究旨在检验，美国南部的苹果实蝇是否同样在四种原生山楂属（Crataegus）植物上形成了宿主种群：西部五月山楂（C. opaca）、蓝莓山楂（C. brachyacantha）、南方红山楂（C. mollis var. texana）以及绿色山楂（C. viridis）。这四种南部寄主的结果物候期与果实表面释放的挥发性化合物均存在差异，而这两类性状正是北美北部柔毛山楂与苹果实蝇之间生态生殖隔离的核心基础。本研究通过微卫星种群遗传学调查与羽化实验，获得了支持南部山楂实蝇存在遗传分化且具有部分生殖隔离的宿主种群的证据。研究结果为基于原生植物的宿主转移与生态分化提供了实例，并暗示当生态机遇出现时，实蝇属（Rhagoletis）类群或许普遍会通过存在基因流的生态物种形成路径启动物种分化。