Homoploid hybrid speciation in an extreme habitat. Science 314:1923–1925

According to theory, homoploid hybrid speciation, which is hybrid speciation without a change in chromosome number, is facilitated by adaptation to a novel or extreme habitat. Using molecular and ecological data, we found that the alpine-adapted butterflies in the genus Lycaeides are the product of hybrid speciation. The alpine populations possess a mosaic genome derived from both L. melissa and L. idas and are differentiated from and younger than their putative parental species. As predicted, adaptive traits may allow for persistence in the environmentally extreme alpine habitat and reproductively isolate these populations from their parental species. Homoploid hybrid speciation is character-ized by hybridization between parentalspecies that results in a derivative hybrid species without a change in chromosome number (1–6). A growing list of possible examples, such as African cichlids (7), cyprinid fishes (8), Rhagoletis fruit flies (9), Heliconius butterflies (10), and swallowtail butterflies (11), suggest that homoploid hybrid speciation in animals may be more common than previously thought. Model