Systematics of the phasianelloidea in Southern Africa : (Mollusca: Gastropoda: Vetigastropoda)
Nangammbi, Tshifhiwa Constance.
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The taxonomy and biogeography of the southern African pheasant shell fauna are poorly known. Thirty–one nominal taxa referable to Phasianelloidea have been described or recorded in this region, but no systematic revision of these has ever been undertaken. Morphological evidence suggests that 16 taxa represent valid species, 13 are synonyms and two represent incorrect identifications. DNA sequence data from mitochondrial COI and 16S markers are used to assess the validity of the described nominal southern African Tricolia species. Phylogenetic analyses recovered seven distinct clades. Tricolia adusta, T. elongata, T. formosa, T. kochii, T. saxatilis and T. neritina were recovered as distinct species. Tricolia africana and T. capensis are genetically indistinguishable. However, morphological characters of the shell are clearly diagnosable. This could be due to incomplete sorting (ancestral polymorphism) reflecting recent speciation with rapid morphological and ecological divergence co–incident with geographical separation. Similarly, there is little genetic differentiation between T. bicarinata, T. insignis and T. kraussi. In this case the similarity is also supported by morphological data as the three species are conchologically close with intergrading shell characters, and might even be one species exhibiting ecogeographic variation in shell form. Monophyly of the southern African Tricolia species is not supported as well as the relationship between these and the European Tricolia pullus. In the last chapter a molecular phylogeny based on sequence data from mtDNA (COI and 16S), nuclear (18S and 28S) and the combined data (COI, 16S, 18S and 28S) is presented for the Phasianelloidea. Bayesian inference analyses performed on the combined data support the monophyly of Tricolia sensu stricto, Eulithidium and Phasianella. Tricolia sensu lato is not monophyletic, as its southern Australian and Indo–West Pacific species do not cluster with its southern African and Eastern Atlantic representatives. The position of Hiloa and Gabrielona within the Phasianelloidea is unresolved. Phylogenetic reconstructions using bayesian inference support monophyly of the Phasianelloidea.