Anatomical and molecular studies reveal several cryptic species of the endemic genus Mandarina (Pulmonata: Helicoidea) in the Ogasawara Islands

Abstract

The endemic genus Mandarina from the Ogasawara Islands in the north-western Pacific has undergone a significant adaptive radiation, and so is of interest in understanding speciation in land snails. While the majority of Mandarina species are easily recognized because underlying morphological differences in genital characters are mirrored by differences in the shell and ecology, we show here that the genus also includes several cryptic species. On the basis of anatomical characters described here, and supported by previously published phylogenies using mitochondrial rRNA sequences, we conclude that five distinct species were previously included in two nominal species: Mandarina hayatoi n. sp., and M. kaguya n. sp., both previously M. hahajimana, are a morphologically variable, allopatric/parapatric species complex on the Hahajima archipelago; M. tomiyamai n. sp. is conchologically similar to M. hirasei on Chichijima, but with distinct genital morphology. Populations of these cryptic species may have similar shells because of convergent evolution, a result of adaptation to similar arboreal lifestyle, so divergence of sexual organs must have occurred independently of habitat preference. These findings therefore support the assertion that sexual selection is an additional factor in the radiation of Mandarina. © The Author 2008. Published by Oxford University Press on behalf of The Malacological Society of London, all rights reserved.