Northern origin and diversification in the central lowlands? – Complex phylogeography and taxonomy of widespread day geckos (Phelsuma) from Madagascar

Day geckos of the Phelsuma lineata group are widespread in Madagascar and have been historically split into numerous species and subspecies based almost exclusively on differences in coloration and body size. We apply phylogenetic and phylogeographic methods to examine the biogeography and taxonomy of these lizards, including explicit tests of various biogeographic predictions and based on a molecular data set covering much of the distribution ranges of all species and subspecies of P. lineata, P. dorsivittata, P. comorensis, P. hoeschi, P. kely, and P. pusilla in Madagascar (and the Comoros archipelago for P. comorensis). Sequences of the mitochondrial 16S rRNA and the nuclear RAG-1 gene fragment were determined from 376 samples, and a multigene mtDNA phylogeny of the species group was constructed for the main phylogroups identified in the 16S haplotype network. We used the 16S sequences to estimate the geographic location of the ancestor of each major mtDNA clade and to infer their demographic history using a variety of statistical tools. Our phylogeny separates the taxa analyzed into two well-supported major subclades mainly occurring in the north respectively east of the island. Mismatch distribution of samples together with rejection of neutrality, the results of Bayesian Skyline Plots analysis, and a star-like network suggests a recent demographic expansion for the P. l. lineata lineage into the eastern lowlands, while the highland (P. l. elanthana) and northern clades (P. dorsivittata and P. l. punctulata) show signatures of rather stable populations. A major genetic discontinuity observed coincided with a northern lowland stretch that separates mid-altitude rainforests in the north from those in the center and south. Our analysis points to numerous unsolved taxonomic problems in this group of geckos, especially in the small-sized taxa (P. hoeschi, P. kely, P. pusilla), and provides a basis for a future comprehensive taxonomic revision, which will require integrative analysis of molecular, morphological and chromatic data as well as careful examination of type specimens.