Grafting the molecular phylogenetic tree with morphological branches to reconstruct the evolutionary history of the genus Zaprionus (Diptera: Drosophilidae)

Abstract

A molecular phylogeny for the drosophilid genus Zaprionus was inferred using a mitochondrial (CO-II) and a nuclear (Amyrel) gene using 22 available species. The combined molecular tree does not support the current classification, dubbed phylogenetic, based entirely upon a morphocline of forefemoral ornamentation. For species for which DNA was not available, phylogenetic positioning was only assigned using morphological characters. In order to avoid conflict between DNA and morphology in the combined analyses (supermatrix method), we developed a new method in which few morphological characters were sampled according to an a priori homoplasy assessment on the consensus molecular tree. At each internal node of the tree, a number of synapomorphies was determined, and species with no molecular sequences were grafted thereon. Analogously to tree vocabulary, we called our method 'morphological grafting'. New species groups and complexes were then defined in the light of our findings. Further, divergence times were estimated under a relaxed molecular clock, and historical biogeography was reconstructed under a maximum likelihood model. Zaprionus appears to be of recent origin in the Oriental region during the Late Miocene ( approximately 10 MYA), and colonization of Africa started shortly after ( approximately 7 MYA) via the maritime route of the Indian Ocean Islands. Most of the morphological and ecological diversification took place, later, in Western Africa during the Quaternary cyclic climatic changes. Furthermore, some species became recent invaders, with one, Zaprionus indianus, has successfully invaded South and North America during the last decade.