Deconstructing a controversial local range expansion: conservation biogeography of the painted reed frog (Hyperolius marmoratus) in South Africa
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Local range expansions might either be the response of populations to climate or landscape change, or be caused directly by human intervention. In the latter case the expansion would be considered the first in the steps leading to a biological invasion. In species typically not the subject of human commerce, distinguishing the causes of local range expansions is problematic. Range dynamic theory provides a basis for doing so, and, when used to assess phylogeographical information, can be a powerful conservation biogeographical approach. Here we adopt this approach to resolve the controversial case of the recent range expansion of the painted reed frog ( Hyperolius marmoratus) in southern South Africa. Within the last decade, H. marmoratus has spread westward approximately 500 km from its historical range. This local range expansion could either represent human-mediated jump dispersal, or a response to landscape or climate change. To date, the latter has been assumed, although not universally. Using a phylogeographic approach to investigate these competing hypotheses, a portion of the mitochondrial COI gene was sequenced for individuals from within the historical range (n= 178), and four putatively introduced populations in dams (n= 121). There was substantial geographical population structure within the historical range, and these populations were significantly different from the dam populations (ΦST= 0.817,P< 0.001). The presence of one or a few dissimilar haplotypes in the dams suggests that introductions are from a number of different sources. This, in conjunction with new survey data, supports the hypothesis that recent establishment of these populations is the result of human-mediated jump dispersal. The impact of this range expansion on ecosystem functioning is unknown, but given the rapid spread of this species and its potential influence on ecosystems, safeguards should be put in place to control further introductions and to restrict the currently invasive populations.