Shaun Walton, Rhodes University, South Africa (Dr. M. Villet)
Project title: Phylogenetic relationships and evolutionary history of the tribe Dirini (Lepidoptera: Satyrinae)
The Dirini (Verity 1953) are a largely grassland-affiliated tribe of butterflies within the Satyrinae that are endemic to South Africa. The tribe contains 28 species (38 taxa) in the seven genera Dira, Dingana, Serradinga, Torynesis, Tarsocera, Aeropetes and Paralethe; and is sister to the Melanitini.
Apart from a number of individual genus-level revisions that have looked at the species relationships within Tarsocera, Dingana, Dira and Paralethe; no study since that of the extensive but now outdated work on the higher classification of the satyridae (Miller, 1968) has focused on the in-group relationships of the genera within the context of the tribe. Van Son (1955) described the life history, morphology and habits of each of the genera in much detail but because no higher taxonomic structure had been put in place at the time, he did not compare the relationship of the genera to one another in detail.
For my honours research project this year 1784 base pairs from the COI (841bp), EF1-a (553 bp) and wingless (390 bp) gene regions were sequenced for 21 of the 28 species in the tribe. This data set in combination with van Sons morphological work was used to infer the relationships of the in-group genera. Out-groups from the closely related tribes Melanitini and Haeterini were used to test the monophyly of the tribe. Estimates of divergence times were calculated using a relaxed molecular clock. The monophyly of the tribe and the in-group genera was strongly supported. Key findings are the highly likely basal in-group position of Paralethe, the sister-taxon relationship of Aeropetes and Tarsocera and the lack of support for the monophyly of any of the five currently recognised species within Torynesis. Estimates of divergence times indicate that the tribe is approximatley 27 my old and has undergone two major radiations since its advent. The first in the mid-ate Oligocene shortly after the radiation of the grasses (Poaceae) and the second in the early-middle Pliocene that coincides with the aridification of southern Africa and a second expansion and more localized diversification of the grasses. The high species diversity within the tribe appears to be a partial taxonomic artefact that has resulted from the misinterpretation of presumed microclimate determined phenotypic variation within species. Further sampling of the in-group taxa is needed to confirm the monophyly of each of the seven genera, further resolve in-group relationships and establish a stronger basis for future biogeographical and evolutionary studies within southern Africa. I intend to continue this work for my MSc theses starting in 2009.
The exceptionally high level of endemism and widespread geographic distribution of this tribe make it highly suitable for investigating the historical biogeography of southern Africa. The tribe also has great potential for investigating topics such as evolutionary host plant relationships, speciation and phenotypic plasticity. Finally as many of the species within the tribe have very reduced and isolated distributions the tribe can be used as a keystone group for promoting habitat and insect conservation within southern Africa’s afromontane and grassland biomes.