Systematics and diversity of the Streptaxidae (Gastropoda: Stylommatophora) : with particular reference to the East African region

This thesis addresses the understudied systematics, evolution, biogeography and diversity of the Streptaxidae, a speciose, near pan-tropical family of carnivorous land-snails. A phylogeny of the Streptaxoidea is inferred from nuclear and mitochondrial DNA (114 taxa from Africa, the Indian Ocean, Asia, South America and Europe). Streptaxidae are monophyletic while all subfamilies and several genera are polyphyletic. Subfamily-level clades originate in a basal polytomy, unresolved by morphology, dating to the early Cenozoic, perhaps corresponding to a rapid radiation and the key innovation of penial hooks. Several Cenozoic trans-oceanic dispersals are evident. Each major shell morphology, a penial sheath and a dart like genital stimulator show homoplasy. Peak diversity in East Africa results from speciation among numerous relict lineages. The "streptaxomorph" growth mode unique to certain streptaxids is investigated using Raupian morphometries. In ontogeny, a single deviation of the coiling axis occurs, relating to the angles of inclination of the aperture and between the columellar margin and the axis. This may be an adaptation to environmental regimes. Across taxa streptaxomorphs have relatively narrower shells and larger buccal masses, which may be adaptations to carnivory. A phylogeographic study of Ptychotrema geminatum from forest sites across Uganda is conducted to test competing hypotheses on the location of Pleistocene forest refugia. These were shown to be in low-lying areas of the far west, not montane areas of the south-west, and not on the shores of Lake Victoria. Expansion was episodic and may have involved chance dispersal. Population structure, which is so marked as to suggest cryptic species are present, is not accompanied by morphological change beyond that induced by current environmental conditions. Anatomical data on Streptaxoidea is compiled and considerably added to, to produce a new annotated family- and genus-group classification. Two new subfamilies and at least four new genera are required for known taxa. The megadiverse genus Gulella is redefined and considered to be a species flock within which relationships are unresolved.EThOS - Electronic Theses Online ServiceGBUnited Kingdo