The power of hybridization between species to generate variation and fuel adaptation is poorly understood despite long-standing interest. There is, however, increasing evidence that hybridization often generates biodiversity, including via hybrid speciation. We tested the hypothesis of hybrid speciation in butterflies occupying extreme, high-altitude habitats in several mountain ranges in western North America with genome-wide DNA sequence data and probabilistic models. Using this approach, in concert with ecological experiments and observations and morphological data, we document multiple lineages of hybrid origin. These lineages have different genome compositions, and, in some cases, specific trait combinations that suggest unique and independent evolutionary histories. More generally, we show that hybridization is common and widespread in this group of butterflies, and that it occurs despite partial barriers to gene flow. Interestingly, this frequent hybridization is combined with limited dispersal among spatially isolated populations, such that it is not uncommon for genetic differences to be greater between distant conspecific populations than nearby heterospecific populations. Thus, we show that patterns of genetic variation in this group are multifaceted, and we argue that this complexity challenges simplistic notions concerning the organization of biological diversity into discrete, easily delineated and hierarchically structured entities.
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Host: Professor L. Lacey Knowles