Abstract
Hybridization by introduced taxa is a major threat to native species. Characterizing human introductions is thus one of the missions of conservation geneticists. Here we survey a declining population of the regionally endangered European tree frog (Hyla arborea) in the Grangettes natural reserve (Rhone valley, Western Switzerland), where previous evidence indicated human introduction of the Italian taxon Hyla intermedia. We combined fast-evolving mitochondrial and nuclear markers and an extended sampling to conduct population genetic analyses of the Grangettes and putative source areas. We show that the Grangettes population is a hybrid swarm, with all individuals featuring recent nuclear admixture and mitochondrial DNA of introduced H. intermedia, most likely of proximate south Alpine origin. In contrast, H. arborea and H. intermedia hardly introgress in their natural parapatric ranges, consistent with an advanced reproductive isolation. From our results, even distantly-related species can endanger the genetic integrity of local taxa in the context of introductions. Potential hybrid incompatibilities may thus account for the strong decline of this population, despite important conservation efforts. Although their hybrid nature makes them a priori unworthy of any protection, we propose specific measures to recover local H. arborea gene pool and preserve tree frogs in the Grangettes, the last population remaining from this heavily impacted part of the Alps.
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Acknowledgments
We thank JM Fivat (Grangettes Nature Reserve), A Horn and R Sermier for assistance during fieldwork. CD thanks M Pajković for discussion and inspiration, and SD is grateful to N Grandjean for office support. Funding was provided by the Swiss National Science Foundation (grant 31003A_129894 to NP) and by the University of Lausanne (PhD fellowship from the Faculty of Biology and Medicine to CD).
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The authors declare no conflict of interest. Our study was approved by the Service de la Consommation et des Affaires Vétérinaires du Canton de Vaud (Epalinges, Switzerland; authorization No.°1798) and our research was carried out in compliance with the Convention on Biological Diversity (CBD) and Convention on the Trade in Endangered Species of Wild Fauna and Flora (CITES); DNA of adult frogs was sampled using non-invasive techniques and tadpole collection was done without impact on populations.
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Christophe Dufresnes and Sylvain Dubey have equally contributed to this work.
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Dufresnes, C., Dubey, S., Ghali, K. et al. Introgressive hybridization of threatened European tree frogs (Hyla arborea) by introduced H. intermedia in Western Switzerland. Conserv Genet 16, 1507–1513 (2015). https://doi.org/10.1007/s10592-015-0745-x
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DOI: https://doi.org/10.1007/s10592-015-0745-x