A taxonomic revision of Tritogenia Kinberg, 1867 and Michalakus Plisko, 1996 (Oligochaeta, Tritogeniidae) occurring in KwaZulu-Natal Midlands, South Africa, based on morphological and DNA sequence data.

Abstract

The conservation and monitoring of biodiversity depends on the knowledge of species identity and distribution. Southern Africa has a rich and characteristic megadrile fauna. Most of the fauna show high levels of endemism with closely related species often separated by subtle morphological characters. Grasslands and forests of South Africa have a diverse terrestrial earthworm fauna, but up to date systematic studies of most taxa are incomplete. Such studies are an opportunity to contribute to understanding evolutionary processes and to provide information for conservation. The genera Tritogenia and Michalakus occur in grasslands and forests in north-eastern part of South Africa in the KwaZulu-Natal province. This study investigated the taxonomic validity of the Tritogenia and Michalakus species in the KwaZulu-Natal Midlands. Ten species of Tritogenia and one of Michalakus are known from this region, with species descriptions based on morphological characters. In this study integrative taxonomy is employed, with both morphological and molecular data used to assess the reliability of traditional morphology-based techniques and the relationships among these species. Detailed comparative morphological observations from fresh Tritogenia material revealed a synonym (Tritogenia soleata Plisko, 1997 = Tritogenia shawi Plisko & Zicsi 1991). To gain further evidence for species level taxonomy and distribution patterns, a molecular phylogeny was constructed based on mitochondrial genes cytochrome c oxidase subunit I (COI) and 16S rRNA. A total of 146 individuals were sequenced for COI from 22 localities and 43 were sub-sampled for 16S rDNA. In most cases, the morphological and molecular data are congruent. The molecular data revealed that the genus Tritogenia is not monophyletic as previously thought. Michalakus initus Plisko 1996 nests within Tritogenia and this finding is observed in both morphological and molecular data. Tritogenia shawi is a cluster with the outgroup species not with other Midlands Tritogenia species. These findings demonstrate the value of using integrative taxonomy in highlighting/revealing the complexities of earthworm fauna in South Africa. The combined morphological and molecular data, though not well supported, ancestral character state reconstructions are generally in agreement with the morphological data in terms of which characters were useful in phylogeny construction.