Data from: Allopatric origin of cryptic butterfly species that were discovered feeding on distinct host plants in sympatry

Surveys of tropical insects are increasingly uncovering cryptic species - morphologically similar yet reproductively isolated taxa once thought to comprise a single interbreeding entity. The vast majority of such species are described from a single location. This leaves us with little information on geographic range and intraspecific variation and limits our ability to infer the forces responsible for generating such diversity. For example, in herbivorous and parasitic insects, multiple specialists are often discovered within what were thought to be single more generalized species. Host shifts are likely to have contributed to speciation in these cases. But when and where did those shifts occur, and were they facilitated by geographic isolation? We attempted to answer these questions for two cryptic species within the butterfly Cymothoe egesta that were recently discovered on different host plants in central Cameroon. We first used mtDNA markers to separate individuals collected on the two hosts within Cameroon and then extended our analysis to incorporate individuals collected across the entire pan-Afrotropical range of the original taxon. To our surprise, we found that the species are almost entirely allopatric, dividing the original range and overlapping only in the narrow zone of West-Central Africa where they were first discovered in sympatry. This finding, combined with analyses of genetic variation within each butterfly species, strongly suggests that speciation occurred in allopatry, probably during the Pleistocene. We discuss the implications of our results for understanding speciation among other cryptic species recently discovered in the tropics and argue that more work is needed on geographic patterns and host usage in such taxa.热带昆虫调查正日益揭示隐存物种（cryptic species）——一类形态相似却生殖隔离的类群，此前曾被认定为单一可杂交的种群。目前绝大多数此类物种仅基于单一地点的标本被描述，这使得我们对其地理分布范围与种内变异的认知极为有限，也制约了我们推断驱动这类多样性产生的演化动力的能力。例如，在植食性与寄生性昆虫中，研究人员常在原本被认为是单一广食性物种的类群内，发现多个专食性支系。这类案例中，寄主转换大概率推动了物种形成过程。但这类寄主转换究竟发生于何时何地，是否由地理隔离所促成？我们针对喀麦隆中部不同寄主植物上新近发现的蝴蝶Cymothoe egesta内的两个隐存物种，尝试解答上述疑问。我们首先利用线粒体DNA标记（mtDNA markers）对喀麦隆境内两种寄主上采集的个体进行区分，随后将分析范围拓展至覆盖该原类群整个泛非洲热带分布区的采集样本。令我们意外的是，这两个物种几乎完全呈异域分布（allopatric），分割了原类群的分布范围，仅在西非-中非的狭窄区域存在重叠——该区域正是二者首次被发现同域分布（sympatry）的地点。这一发现结合对两种蝴蝶各自的遗传变异分析，有力表明物种形成过程发生于异域环境中，时间大概率处于更新世时期。我们探讨了本研究结果对理解热带地区新近发现的其他隐存物种种化过程的启示，并提出：针对此类类群的地理分布模式与寄主利用模式，仍需开展更多研究工作。