Biosystematics of Biomphalaria spp. with an emphasis on Biomphalaria glabrata

Abstract

We review the characters and approaches that have been used to build the systematics of the genus Biomphalaria with special emphasis on Biomphalaria glabrata. Shell characters can be used to distinguish groups of species, but are of limited use for separating closely allied species because of wide ecophenotypic variation. The anatomy of reproductive tracts (e.g., shape and size of penial complex), reviewed here for most extant species, is more informative, but still not fully diagnostic. Recent molecular phylogenies clarified the relationships among most extant species. African species were shown to be of recent origin, and closely allied to B. glabrata and several taxa were synonymized (e.g., several African species) and/or grouped into species complexes (e.g., the Biomphalaria straminea group). Reproductive isolation has unfortunately been little used for clarifying species boundaries, as well as to detect potential areas of hybridization, in Biomphalaria. That some species of Biomphalaria mainly reproduce through self-fertilization certainly sets a practical limit to such investigation. Molecular studies have also indicated that B. glabrata is structured into several, rather deeply separated, main clades. As these clades are partially reproductively isolated from one another, B. glabrata might well be a species complex. Biomphalaria is the main intermediate host of the agent of intestinal schistosomiasis Schistosoma mansoni. Contrary to previous claims, snail susceptibility to this parasite cannot be used as a tool for building Biomphalaria systematics. We conclude that about 26 species of Biomphalaria can be recognized today, four of which are found in Africa only. We also plead for further work based on an integrated approach including morphology, molecular markers and experimental analysis of reproductive isolation, as well as ecology and biogeography. © Springer Science+Business Media, LLC 2011. All rights reserved.