Recent species in old Islands: the origin of introduced populations of Litoria aurea (Anura: Hylidae) in New Caledonia and Wallis
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New Caledonia is a megadiverse tropical island in the southwest Pacific, however, inhabited by only one species of amphibian, Litoria aurea (Hylidae). We used both molecular (CO1 and ND4 gene sequencing) and morphometric data to explore its geographical origin and timing of colonisation. We tested whether this species arrived through transoceanic dispersal before human arrival in the island, or recently through anthropogenic introduction. We found a weak phylogeographical structure within this species, and lower haplotype diversity in New Zealand, New Caledonia and Wallis compared to Australia. No significant genetic differentiation was found between pairs of populations in New Caledonia and Wallis, or between pairs of population from these two islands. We observed a high level of morphometric differentiation between Australian and island populations, and a low level of morphometric differentiation between island populations. Our results support an Australian origin for insular frogs. The possibility of a trans-marine dispersal from Australia to New Caledonia and/or Wallis in-between the Eocene and the Pleistocene cannot be favoured, given the low level of genetic differentiation. Our results are consistent with a recent human introduction, most likely during European times. Our data support the historical absence of amphibians in the old island New Caledonia, and is consistent with the new biogeographical paradigm that this island was totally re-colonized after emergence in Eocene. More studies are necessary to explain the success of this frog in oceanic islands, where it is widespread and abundant, compared to Australia, where it is declining.