Threatened Neotropical mollusks: analysis of shape differences in three endemic snails from High Paraná River by geometric morphometrics

Abstract

Abstract. Variation in shape among one living and two extinct aquatic snails of genus Aylacostoma, using geometric morphometrics methods of thin plate splines and multivariate analysis of partial warp scores was investigated. Analysis was performed to evaluate the diagnostic capability of this method and to explore shell shape differences, due to the lack of another data, in an attempt to answer why only one of the species persisted in the wild. Sixteen landmarks in a bi-dimensional space for 32 shells of type, paratype and reference specimens deposited in museums of Argentina were defined. Shape variation was decomposed into uniform and non-uniform components. Statistically significant differences in spire and aperture were found for the first 9 non-uniform components explaining more than 95% of local variation observed. Differences could be related to a differential use of habitat and/or to the degree of exposure to water current. Larger aperture found in the extinct species could be associated to habitats and substrata with the highest water currents, whereas the smaller aperture in the third species could be related to the preference for more protected habitats, like those where actually inhabit.