Validation and description of two new north-western Australian Rainbow skinks with multispecies coalescent methods and morphology

Abstract

While methods for genetic species delimitation have noticeably improved in the last decade, this remains a work in progress. Ideally, model based approaches should be applied and considered jointly with other lines of evidence, primarily morphology and geography, in an integrative taxonomy framework. Deep phylogeographic divergences have been reported for several species ofCarliaskinks, but only for some eastern taxa have species boundaries been formally tested. The present study does this and revises the taxonomy for two species from northern Australia,Carlia johnstoneiandC. triacantha. We introduce an approach that is based on the recently published method StarBEAST2, which uses multilocus data to explore the support for alternative species delimitation hypotheses using Bayes Factors (BFD). We apply this method, jointly with two other multispecies coalescent methods, using an extensive (from 2,163 exons) data set along with measures of 11 morphological characters. We use this integrated approach to evaluate two new candidate species previously revealed in phylogeographic analyses of rainbow skinks (genusCarlia) in Western Australia. The results based on BFD StarBEAST2, BFD* SNAPP and BPP genetic delimitation, together with morphology, support each of the four recently identifiedCarlialineages as separate species. The BFD StarBEAST2 approach yielded results highly congruent with those from BFD* SNAPP and BPP. This supports use of the robust multilocus multispecies coalescent StarBEAST2 method for species delimitation, which does not requirea prioriresolved species or gene trees. Compared to the situation inC. triacantha, morphological divergence was greater between the two lineages within Kimberley endemicC. johnstonei, which also had deeper divergent histories. This congruence supports recognition of two species withinC. johnstonei. Nevertheless, the combined evidence also supports recognition of two taxa within the more widespreadC. triacantha. With this work, we describe two new species,Carlia insularissp. nov andCarlia isostriacanthasp. nov. in the northwest of Australia. This contributes to increasing recognition that this region of tropical Australia has a rich and unique fauna.