Insular biogeographic origins and high phylogenetic distinctiveness for a recently depleted lizard fauna from Christmas Island, Australia.

Paul M Oliver,Harold G Cogger,Robert N Fisher,Mozes P K Blom,John C Z Woinarski,Jonathan Q Richmond

doi:10.1098/rsbl.2017.0696

Paul M Oliver, Harold G Cogger + Show 4 more

Open Access

https://doi.org/10.1098/rsbl.2017.0696

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Abstract

Striking faunal turnover across Asia and Australasia, most famously along the eastern edge of the Sunda Shelf or ‘Wallace's Line’, has been a focus of biogeographic research for over 150 years. Here, we investigate the origins of a highly threatened endemic lizard fauna (four species) on Christmas Island. Despite occurring less 350 km south of the Sunda Shelf, this fauna mostly comprises species from clades centred on the more distant regions of Wallacea, the Pacific and Australia (more than 1000 km east). The three most divergent lineages show Miocene (approx. 23–5 Ma) divergences from sampled relatives; and have recently become extinct or extinct in the wild, likely owing to the recent introduction of a southeast Asian snake (Lycodon capucinus). Insular distributions, deep phylogenetic divergence and recent decline suggest that rather than dispersal ability or recent origins, environmental and biotic barriers have impeded these lineages from diversifying on the continental Sunda Shelf, and thereby, reinforced faunal differentiation across Wallace's Line. Our new phylogenetically informed perspective further highlights the rapid loss of ancient lineages that has occurred on Christmas Island, and underlines how the evolutionary divergence and vulnerability of many island-associated lineages may continue to be underestimated.

Highlights

For over 150 years, biogeographers have noted marked biotic turnover between the Asian and Australian regions. This is most striking at the transition between the eastern edge of the Sunda Shelf and the islands of Wallacea [1], widely referred to as Wallace’s Line
We show that four endemic Christmas Island reptile species are nested within radiations centred on Wallacea, Australia or the Pacific
Genetic divergences at the ND2 locus between these lineages (0.043–0.063% pairwise uncorrected) are low for gecko species [16]. These lineages sit within a broader late Miocene radiation centred on Wallacea, from which several dispersals westwards onto islands and other coastal or savannah habitats around the edge of the Sunda Shelf are inferred [17]

Summary

Introduction

For over 150 years, biogeographers have noted marked biotic turnover between the Asian and Australian regions This is most striking at the transition between the eastern edge of the Sunda Shelf and the islands of Wallacea (the Lesser Sundas and Sulawesi) [1], widely referred to as Wallace’s Line. This turnover has been linked to the former isolation and disjunct history of the Asian and Australian continental plates [2]. Coupled with recent Lycodon driven extinctions, this suggests that biotic interactions or other environmental barriers, rather than dispersal ability, may underpin the contemporary rarity of these taxa on large landmasses west of Wallace’s Line

Methods

Results and discussion

20. Linkem CW et al 2013 Stochastic faunal exchanges