Swept ashore: Transoceanic dispersals and the biogeographic origins of Australian gekkonid lizards

Wesley Read , Ian Brennan, Sarin Tiatragul , Paul M Oliver, Alex Pyron, Todd Jackman, Alan Lemmon, Emily Lemmon, Chris Austin, Craig Moritz , J. Scott Keogh, Stephen M Zozaya , Aaron Bauer

Oceanic dispersal is a rare mode of long-distance dispersal where taxa colonize disconnected islands or continents, sometimes resulting in new radiations. Australia has been isolated from other continental landmasses during the last 45 million years, and overwater colonisation has played a critical role in shaping its contemporary biota. Here, we investigate the biogeographic origins of Australian gekkonid lizards. Previous work has attributed the polyphyly of Australian gekkonids to multiple independent colonizations, some potentially via oceanic dispersal. To test this, we estimated phylogenetic relationships and divergence times using a genome-wide dataset for this globally distributed family and reconstructed ancestral biogeographic ranges. Our phylogeny reveals rapid diversification near the K-Pg boundary, coinciding with the crown origin of the family. Remarkably, ancestral range estimates indicate that gekkonids colonized Australia across eight independent events, the highest number by any non-volant vertebrate family. Most notably, the genus Christinus likely rafted at least 6,400 kilometres across the Indian Ocean—among the longest documented oceanic dispersals by a non-volant vertebrate. These findings emphasise the dominant role of oceanic dispersal in shaping the exceptionally diverse Australian squamate biota.