Reproductive character displacement by inversion of coiling in clausiliid snails (Gastropoda, Pulmonata)

In land snails, a change in the direction of coiling, being associated with a shift in the position of the genital apparatus, may act as a barrier against hybridization between sympatric species. Putative reproductive character displacement by an inversion in chirality has been reported in only a few land snails, based on observations in the field and interbreeding experiments. In this study, we present a new case of possible reproductive character displacement in the direction of coiling, in the clausiliid snail Isabellaria dextrorsa. This species is dextral, in contrast with its nearest relatives, including I. torifera and I. lophauchena, which share plesiomorphic sinistral coiling. Whereas I. dextrorsa occurs in sympatry and even syntopically with I. lophauchena throughout most of its range, the sinistral species have a mosaic distribution. Phylogenetic analyses of mitochondrial cytochrome c oxidase subunit I (COI) sequences demonstrated that I. dextrorsa constitutes a clade with I. torifera. In this clade, a shift in coiling direction occurred at least twice, maybe triggered by the presence of a sympatric congeneric sinistral species. The analyses separated the sequences of all I. dextrorsa samples from those of sympatric and syntopic I. lophauchena samples. The failure to demonstrate gene flow between these species is consistent with the hypothesis of genetic isolation by reproductive character displacement.