Amphibia-Reptilia 36 (2015): 65-81 Recent species in old Islands: the origin of introduced populations of Litoria aurea (Anura: Hylidae) in New Caledonia and Wallis Violaine Nicolas 1 , Philippe Grandcolas 1 , Frédéric Braux 1 , Hervé Jourdan 2 , Atoloto Malau 3 , Arnaud Couloux 4 , Annemarie Ohler 1,∗ Abstract. 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. Keywords: Amphibia, invasive species, mitochondrial DNA, morphometry, phylogeography. Introduction Species diversity is unevenly distributed across the globe, with terrestrial diversity concentrated in a few restricted biodiversity hotspots (Gaston, 2000). Understanding the origin of species rich- ness in Earth’s biodiversity hotspots constitutes one of the most significant intellectual chal- lenges to ecologists and biogeographers, and is vital to develop effective conservation strate- gies. New Caledonia is a large and megadiverse tropical island in the southwest Pacific (fig. 1), 1 - Institut de Systématique, Évolution, Biodiversité, ISYEB – UMR 7205 – CNRS, MNHN, UPMC, EPHE, Muséum national d’Histoire naturelle, Sorbonne Uni- versités, 57 rue Cuvier, F-75005, Paris, France 2 - IMBE, Aix-Marseille Université/CNRS/IRD/UAPV, UMR 237 IRD, BPA5, 98848 Nouméa, New Caledonia 3 - Service de l’Environnement Wallis et Futuna, BP 294 Mata’ Utu, 98600 Uvéa – Wallis-et-Futuna, France 4 - Genoscope, Centre national de Séquençage, 2 rue Gaston Crémieux, Case postale 5706, 91057 Evry Cedex, France ∗ Corresponding author; e-mail: annemarie.ohler@mnhn.fr situated 1220 km from Australia and 1700 km from New Zealand. The origin of this hotspot of biodiversity has traditionally been traced back to the fragmentation of Gondwana, specif- ically the separation of Australia around 80 Ma (Raven and Axelrod, 1972; Morat et al., 1986; Jaffré, 1992; Chazeau, 1993; de Laubenfels, 1996; Lowry, 1998). This assumption of an old origin of the local biota was based on both the antiquity of New Caledonia’s geological base- ment and the presence of many so-called relict groups (Raven and Axelrod, 1972; Raven, 1979; Morat et al., 1986; Grandcolas et al., 2014). This widely accepted Gondwanan paradigm and continental characterization of New Caledonia was recently questioned in the light of geo- logical and phylogenetic evidence (Murienne et al., 2005, 2008; Grandcolas et al., 2008). These studies showed clear geological evidence for Palaeocene marine transgression, suggest- ing that the biota was much more recent, and emphasized the absence (or presence of few lo- cal representatives) of certain widely distributed © Koninklijke Brill NV, Leiden, 2015. DOI:10.1163/15685381-00002978