Evolution of tangle-veined flies: systematics, biogeography and functional traits in southern African Nemestrininae (Nemestrinidae)
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Date
2021
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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.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.