Lessons from Timor: Shells are poor taxonomic indicators in Asperitas land snails (Stylommatophora,Dyakiidae)

The limacoid land snail Asperitas Gude, 1911 encompasses several vividly coloured, yet poorly known species that are distributed throughout the Lesser Sunda Islands, Sulawesi, and the Moluccas. We examined the variation in shell morphology, including the use of geometric morphometrics, and reproductive anatomy of snails from Timor and several adjacent islands. These studies revealed that none of the taxa described from Timor and considered to be endemic to this island could be reliably distinguished from any of the others. In addition to the systematic ambiguity of morphological characteristics, we uncovered rather low amounts of genetic differentiation in the mitochondrial marker cytochrome c oxidase subunit I that was not consistent with the current taxonomy. Based on these observations, we conclude that there is just a single Asperitas species on Timor that exhibits notable variability in shell characters and body colour. This variability is ascribed to the combined effects of polymorphic colour patterns with locally varying selection in different habitats and along altitudinal gradients. Individuals from the adjacent islands of Flores, Sumbawa, Solor and Romang, which are deemed to represent distinct species-level taxa, exhibit similar amounts of variation in shell and body colour. They exhibit a consistent reproductive anatomy and overall negligible amounts of mitochondrial differentiation from the populations on Timor. Patterns in shell variation do not lend support to previously held ideas that different Sunda Islands harbour distinct radiations of polytypic Asperitas species. By contrast, we suggest that the taxonomic diversity of Asperitas has been overestimated for the over-reliance on shell features and that many presently accepted taxa are likely mere synonyms of fewer and more widespread species.