Lygosomine phylogeny and the origins of Australian scincid lizards

Abstract

Aim: Australian scincid lizards represent three distinct groups within the cosmopolitan clade Lygosominae, the Egernia, Eugongylus and Sphenomorphus groups. This paper presents a time-calibrated phylogeny for Lygosominae that provides the necessary temporal framework for assessing the contributions of immigration from Asia and of Gondwanan inheritance in the derivation of the Australian scincid fauna. Location: Australasia, Asia, Africa. Methods: Phylogenetic relationships and divergence times were inferred from novel BDNF, c-mos and PTPN12 sequences (2408 aligned sites). Results: Lygosomine monophyly is well supported, and there is strong support for monophyly of the Egernia, Eugongylus and Sphenomorphus groups. A sistergroup relationship of Tribolonotus (distributed in Melanesia and the Papuan Region) and the Egernia group is strongly supported in both Bayesian and maximum likelihood analyses. Australian representatives of the Sphenomorphus group compose a significantly supported clade estimated to have originated c. 25 Ma. An age of c. 18 Ma is inferred for a strongly supported clade comprising Australian representatives of the Egernia group; this clade diverged from Corucia zebrata (confined to the Solomon Islands) c. 25 Ma and from Tribolonotus c. 54 Ma. A well-supported clade including all Australian Eugongylus group taxa sampled is estimated to have arisen c. 20 Ma. Main conclusions: The Australian Sphenomorphus group is nested within the more inclusive Sphenomorphus group (distributed primarily in Asia and Australasia), suggesting comparatively recent descent from a colonizing Asian ancestor; the divergence times inferred here indicate that colonization occurred during the mid Cenozoic, subsequent to the rifting of Australia from Antarctica. An Oligocene origin of the extant Eugongylus group fauna of Australasia (the basal members of which are distributed in the Southwest Pacific) indicates that Eugongylus group lygosomines also dispersed to Australia relatively recently. The Egernia group diverged from Tribolonotus in the Early Eocene; however, extant Egernia group lygosomines originated only during the Late Oligocene, implying extensive pruning of stem taxa (i.e. extinction). As a result, inferences of the timing of dispersal into Australia are associated with substantial uncertainty, although independent palaeontological evidence suggests that the Egernia group entered Australia prior to the Oligocene, immediately after (or perhaps before) the separation of Australia and Antarctica.