Phylogeny-based species delimitation in Philippine slender skinks (Reptilia: Squamata: Scincidae) III: taxonomic revision of Brachymeles gracilis and description of three new species

Species diversity in skinks in the genus Brachymeles recently has undergone a state of flux, with numerous taxonomic discoveries over the past few years. Newly available, robust data sets from morphological data and molecular sequences have revealed that taxonomic diversity within this unique groupof lizards is substantially underestimated. In this third recent monographic revision of a major Brachymeles clade, we review the medium-sized, pentadactyl species of the Brachymeles gracilis Complex (now known to include B. pathfinderi) and describe three new species in this unique clade of endemic Philippine lizards. For more than three decades B. gracilis has been recognized as a single polytypic, ‘‘widespread’’ species. The species’ wide geographic range has persisted as a result of weak sampling, morphologically similar body sizes, scale pigmentation, and patterns of scalation among populations. However, previous authors have noted morphological variation between populations on different islands, as well as in geographically different subregions across the large southern island of Mindanao in the Philippines. Our new data build on theseobservations and extend them to inference of species boundaries. We evaluate both morphological and genetic data to define species limits in B. gracilis and its close relatives, and our data indicate that the ‘‘widespread’’ species B. gracilis is actually a complex of at least six distinct lineages. In order to clarify the status of B. suluensis (a species collected only once, in 1918) we redescribe this enigmatic taxon. Phylogenetic analyses of available B. gracilis sampling reveal that some of these lineages are not each others’ closest relatives, but are all genetically distinct. All but two of the taxa we define possess allopatric geographic ranges and differ from their congeners by numerous diagnostic characters of external morphology, and therefore should be recognized as full species in accordance with any lineage-based species concept. Over the past 3 yr, the species diversity of the genus Brachymeles has increased by 125%.