Phylogenetic relationships within the lizard clade Xantusiidae: using trees and divergence times to address evolutionary questions at multiple levels.

Xantusiidae (night lizards) is a clade of small-bodied, cryptic lizards endemic to the New World. The clade is characterized by several features that would benefit from interpretation in a phylogenetic context, including: (1) monophyletic status of extant taxa Cricosaura, Lepidophyma, and Xantusia; (2) a species endemic to Cuba (Cricosaura typica) of disputed age; (3) origins of the parthenogenetic species of Lepidophyma; (4) pronounced micro-habitat differences accompanied by distinct morphologies in both Xantusia and Lepidophyma; and (5) placement of Xantusia riversiana, the only vertebrate species endemic to the California Channel Islands, which is highly divergent from its mainland relatives. This study incorporates extensive new character data from multiple gene regions to investigate the phylogeny of Xantusiidae using the most comprehensive taxonomic sampling available to date. Parsimony and partitioned Bayesian analyses of more than 7 kb of mitochondrial and nuclear sequence data from 11 loci all confirm that Xantusiidae is monophyletic, and comprises three well-supported clades: Cricosaura, Xantusia, and Lepidophyma. The Cuban endemic Cricosaura typica is well supported as the sister to all other xantusiids. Estimates of divergence time indicate that Cricosaura diverged from the (Lepidophyma+Xantusia) clade ≈ 81 million years ago (Ma), a time frame consistent with the separation of the Antilles from North America. Our results also confirm and extend an earlier study suggesting that parthenogenesis has arisen at least twice within Lepidophyma without hybridization, that rock-crevice ecomorphs evolved numerous times (>9) within Xantusia and Lepidophyma, and that the large-bodied Channel Island endemic X. riversiana is a distinct, early lineage that may form the sister group to the small-bodied congeners of the mainland.