Validity of the subspecies paradigm - a case study of the nymphalid butterfly Polygonia faunus

• Subspecies are commonly used taxonomic units to formally describe intraspecific geographic variation in morphological traits. However, the concept of subspecies is not clearly defined, and there is little agreement about what they represent in terms of evolutionary units, and whether they can be used as reliably useful units in conservation, evolutionary theory and taxonomy. Although the validity of subspecies has been tested using a multi-marker genetic approach in vertebrates, such studies have been rare in invertebrates. We here test the validity of well-characterized subspecies in the butterfly Polygonia faunus using a combination of mitochondrial sequences and eight microsatellites. We have also investigated the phylogeographic Structure of P. faunus and test whether similarities in host-plant use among populations is related to genetic similarity. Neither the nuclear nor the mitochondrial dataset corroborated subspecies groupings. We found three welldefined genetic clusters corresponding to California, Arizona and (New Mexico + Colorado). There was little structuring among the remaining populations, probably due to gene flow across populations. We found no support for the hypothesis that similarities in host use are related to genetic proximity. The results indicate that the species underwent a recent rapid expansion, probably from two glacial refugia in western North America. The mitochondrial haplotype network indicates at least two independent expansion phases into eastern North America. Ourresults clearly demonstrate that subspecies in P. faunus do not conform to the structuring of genetic variation. More studies on insects and other invertebrates are needed to understand how widespread this phenomenon is. Results in this study will be crucial in designing further experiments to understand the evolution of host plant utilization in this species.

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NATURVETENSKAP  -- Biologi -- Zoologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Zoology (hsv//eng)

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