Recent species in old Islands: the origin of introduced populations of Litoria aurea (Anura: Hylidae) in New Caledonia and Wallis

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.

新喀里多尼亚，地处西南太平洋的巨型热带岛屿，尽管其生物多样性丰富，却仅栖息着一种两栖动物——金斑蟾蜍（Hylidae科）。本研究运用分子（CO1和ND4基因测序）和形态计量学数据，探究了该物种的地理起源及殖民时间。本研究旨在验证该物种是否在人类抵达岛屿之前通过跨洋扩散抵达，或是在近期通过人为引入。研究发现，该物种内部存在微弱的种群遗传结构，与澳大利亚相比，新西兰、新喀里多尼亚和瓦利斯地区的单倍型多样性较低。在新喀里多尼亚和瓦利斯地区，或这两个岛屿之间，没有发现显著的遗传分化。我们观察到澳大利亚种群与岛屿种群之间存在较高的形态计量学差异，而岛屿种群之间则存在较低的形态计量学差异。我们的结果支持了岛屿青蛙起源于澳大利亚的假说。鉴于遗传分化的低水平，从始新世到更新世期间，从澳大利亚到新喀里多尼亚和/或瓦利斯的跨海扩散的可能性无法得到支持。我们的结果与近期人类引入的假设相一致，最有可能发生在欧洲时期。我们的数据支持了古老岛屿新喀里多尼亚历史上缺乏两栖动物的记载，并符合新的生物地理学范式，即该岛屿在始新世出现后完全重新殖民。为了解释这种青蛙在广布且丰富的海洋岛屿上的成功，相对于正在衰退的澳大利亚，需要更多的研究。