The phylogeography of Indoplanorbis exustus (Gastropoda: Planorbidae) in Asia

Abstract

AbstractBackgroundThe freshwater snailIndoplanorbis exustusis found across India, Southeast Asia, central Asia (Afghanistan), Arabia and Africa.Indoplanorbisis of economic importance in that it is responsible for the transmission of several species of the genusSchistosomawhich infect cattle and cause reduced livestock productivity. The snail is also of medical importance as a source of cercarial dermatitis among rural workers, particularly in India. In spite of its long history and wide geographical range, it is thought thatIndoplanorbisincludes only a single species. The aims of the present study were to date the radiation ofIndoplanorbisacross Asia so that the factors involved in its dispersal in the region could be tested, to reveal potential historical biogeographical events shaping the phylogeny of the snail, and to look for signs thatI. exustusmight be polyphyletic.ResultsThe results indicated a radiation beginning in the late Miocene with a divergence of an ancestral bulinine lineage into Assam and peninsular India clades. A Southeast Asian clade diverged from the peninsular India clade late-Pliocene; this clade then radiated at a much more rapid pace to colonize all of the sampled range ofIndoplanorbisin the mid-Pleistocene.ConclusionsThe phylogenetic depth of divergences between the Indian clades and Southeast Asian clades, together with habitat and parasitological differences suggest thatI. exustusmay comprise more than one species. The timescale estimated for the radiation suggests that the dispersal to Arabia and to Southeast Asia was facilitated by palaeogeographical events and climate change, and did not require human involvement. Further samples from Afghanistan, Africa and western India are required to refine the phylogeographical hypothesis and to include the African Recent dispersal.