Evolution of tangle-veined flies: systematics, biogeography and functional traits in southern African Nemestrininae (Nemestrinidae)

Abstract

The evolution of traits and biogeography of the three southern African endemic genera of the Nemestrinidae: Moegistorhynchus, Prosoeca and Stenobasipteron. These genera are of particular interest due to the exaggerated mouth parts of some species and their role as important pollinators of numerous plants, including rare and endangered species. Most taxonomic studies on southern African nemestrinids date back 50 or more years ago, and the group lacks a phylogenetic framework, thus hindering comprehensive study of their systematics, trait evolution and biogeography. In this thesis, I evaluate the boundaries of a species complex in Prosoeca and reconstruct a phylogenetic framework for the southern African Nemestrininae. Furthermore, I use the phylogenetic framework to reconstruct the evolution of proboscis length and biogeographic patterns. To delimit species in the Prosoeca peringueyi complex, I quantified morphological variation and established whether this was associated with genetic variation within and between gene regions. Phylogenetic analysis of the complex using the mitochondrial COI gene revealed two well-supported clades, that are supported by morphological traits, one of which is described as a new species. Four gene regions were also used to reconstruct a phylogenetic tree of the three southern African Nemestrininae genera, including 58 morphospecies. The topology suggests that a monophyletic Moegistorhynchus is sister to a paraphyletic Prosoeca, with Stenobasipteron nested within Prosoeca. Half of the morphospecies in this phylogeny did not correspond to described species, thus highlighting a substantial taxonomic impediment in this group. The phylogenetic tree was used to reconstruct the evolution of proboscis length in the southern African Nemestrininae. Stochastic character mapping showed transitions between all states (short, long and very long), but shifts occurred more frequently from shorter to longer lengths. The ancestral proboscis state was estimated to be longer than the median proboscis length of the clade. Lastly, I reconstructed the biogeographical patterns of the southern African Nemestrininae. A Fynbos origin during the Miocene was estimated for this clade, with multiple shifts between biomes along the tree. Together, these results illustrate the need for further systematic and taxonomic work in this clade, as well as in the Nemestrinidae more broadly to gain a firmer understanding of their phylogenetic relationships and diversity. The evolution of proboscis length and biome occupancy appear to be labile within this clade. This work provides a phylogenetic framework for the southern African clade of Nemestrininae and contributes to our understanding of the patterns of evolution, diversification and migration of these ecologically important pollinators.