Climatic oscillations during the Mio/Pliocene epochs induced cladogenesis in the terrestrial snail genus Gittenedouardia (Mollusca: Gastropoda: Cerastidae) from South Africa

Abstract

In South Africa, the terrestrial snail genus Gittenedouardia is the most species-rich member of the Cerastidae, where it is primarily distributed in the highly fragmented Afrotemperate and Indian Ocean coastal belt (IOCB) forest biomes. Phylogenetic relationships and cladogenetic events within the genus remain unstudied. In this respect, we reconstructed a dated phylogeny for eight Gittenedouardia species, and two populations identified to genus level using a combined mitochondrial (16S rRNA and COI) DNA sequencing dataset analysed using Bayesian inference and Maximum Likelihood framework. Furthermore, we investigated the population genetic substructure of the three widely distributed species (Gittenedouardia spadicea, G. natalensis and G. arenicola) for the COI locus, while also subsampling these species using the nuclear DNA ITS-2 locus. Phylogenetic results based on the combined mtDNA dataset supported the monophyly of Gittenedouardia and revealed three major clades and deep genetic structure among the three widely distributed species. Divergence-time estimates suggest that diversification within Gittenedouardia occurred during the middle Miocene/late Pliocene, a period characterised by a decrease in precipitation and the contraction of the Afrotemperate and IOCB forest biomes. We used two species delimitation methods, (PTP and STACEY) to infer putative species in G. spadicea, G. natalensis and G. arenicola. The two methods recovered a large number of evolutionary distinct units, with minimal consensus in the exact number of lineages. Our findings suggest the presence of undescribed diversity, necessitating the need for taxonomic revisionary work on Gittenedouardia. We discuss the climatic factors which may have contributed to the observed cladogenesis and compare our results with other studies of forest dwelling faunal taxa.