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

Authors

  • CAROLYN S. McBRIDE,

    1. Center for Population Biology, University of California, Davis, CA 95616, USA
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      Present address: Laboratory of Neurogenetics and Behavior, The Rockefeller University, 1230 York Avenue, Box 63, New York, NY 10065, USA

  • ROBIN VAN VELZEN,

    1. National Herbarium of the Netherlands – Wageningen Branch, Biosystematics Group, Wageningen UR, Generaal Foulkesweg 37, 6703 BL Wageningen, The Netherlands
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  • TORBEN B. LARSEN

    1. Jacobys Alle 2, 1806 Frederiksberg, Denmark
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  • The authors met and began this collaboration through a mutual interest in Afrotropical butterflies. Carolyn McBride uses a combination of field, molecular genetic, and computational approaches to study host adaptation in insects, particularly as it relates to speciation. She recently finished her PhD at the University of California Davis and is now a postdoc at The Rockefeller University in New York. Robin van Velzen is a PhD student at the Wageningen University, supervised by Freek Bakker, working on ecology, evolution and systematics of species of Cymothoe and their Rinorea host plants. He is especially interested in host plant associations and underlying mechanisms, as well as their influence on patterns of diversification. Torben Larsen is the author of the standard works on butterflies of Arabia, Kenya and West Africa. He is currently working on a monograph of the African Hesperiidae as well as coordinating in-depth butterfly surveys of selected African forests for long-term monitoring.

Carolyn Sarah McBride, Fax: 212-327-7238; E-mail: lmcbride@rockefeller.edu

Abstract

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.

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