Biological diversity or nomenclatural multiplicity: the Thai freshwater snail Neoradina prasongi Brandt, 1974 (Gastropoda: Thiaridae)

Abstract

A key aspect of evolutionary systematics research is the distinction between nomenclatural multiplicity and biological diversity. Unravelling the latter is only possible by identifying true biological entities, i.e., species and evolutionary lineages instead of an accumulation of nominal taxa. This is particularly difficult to achieve for species with high phenotypic plasticity, such as thiarid freshwater snails, a speciose family notorious for its taxonomic diversity. Exceptionally fraught with problems is a complex of nominal species in the genera Melanoides and Stenomelania. In addition to these genera, morphologically almost indistinguishable shells were the basis for the description of Neoradina prasongi and the establishment of Neoradina. To test whether these shells represent specimens from a distinct evolutionary lineage, we studied representative material of all three genera from Thailand, i.e., Neoradina prasongi and syntopically occurring and/or conchologically similar species, using molecular genetics, shell characters via geometric morphometrics, radula morphology, and reproductive biology. The molecular study of mitochondrial 16S rRNA and COI gene fragments unambiguously supports the distinction of the six species examined, most notably Neoradina prasongi as a distinct lineage. Geometric morphometrics of shell shapes allowed distinguishing species currently assigned to Stenomelania s. str. from the other studied species. Radula characters were uninformative. Our findings confirm the prevalence of different reproductive modes in these viviparous freshwater snails (i.e., the release of larval or juvenile stages). The combined results of our genetic analyses were ambiguous for implications on genus affiliations and did not support the classification of some species as part of Stenomelania, affecting the taxonomic stability of the current conception of these genera. Our results are a crucial first step towards a better understanding of the diversity found within these taxonomically problematic thiarids, emphasizing the need for evolutionary systematics approaches, in order to properly evaluate truly biological diversity in contrast to nomenclatural multiplicity.

Key words:

• evolutionary systematics
• Indo-Australian Archipelago
• Melanoides tuberculata
• Stenomelania aspirans
• Thailand

Acknowledgements

We thank Bernhard Hausdorf (ZMH), Thomas von Rintelen and Christine Zorn (ZMB), Ronald Janssen (SMF), Michael Schrödl (ZSM), Ted von Proschwitz (GNM), Gustav Paulay (FLMNH), and Paul Callomon (ANSP) for granting access to their collections and for making type material and additional samples available for study. We thank two anonymous reviewers for their constructive criticism on earlier versions of the manuscript, as well as Elliot Shubert and Barna Páll-Gergely for very helpful editorial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772000.2019.160686.

Associate Editor: Barna Páll-Gergely