A revision of the taxonomy and phylogenetic background of the South African genus Kazimierzus Plisko, 2006 (Oligochaeta: Kazimierzidae)

Abstract

Species identity and distribution information is important in conservation and monitoring of biodiversity. Megadrile fauna is very diverse in Southern Africa with most of the fauna demonstrating high levels of endemism, closely related species often separated by subtle morphological characters. Natural and various fertile biotopes of South Africa have a diverse terrestrial megadrile fauna, but to date, taxonomic and systematic studies of most taxa are incomplete. Such studies are vital as they contribute to the understanding of evolutionary processes and also provide information for conservation. To date, South African indigenous megadrile accredited to three strict indigenous families, Microchaetidae (s.str.), Tritogeniidae and Kazimierzidae, differ morphologically and differ also in their geographical distribution. The representatives of Kazimierzus, the only genus in Kazimierzidae, are known from the Western and South-Western Atlantic coast of South Africa, the area known for endemism in other invertebrate fauna and often associated with diverse flora. Considering these factors Kazimierzus was selected for the present study. The selected 25 Kazimierzus species occur in specific biotopes, their distribution is highly restricted to selected places, and most of them do not overlap. The study aimed to employ integrative taxonomy (morphology and molecular) to carry out a taxonomic revision of this genus and the objectives were1. to evaluate the validity of described species and provide an identification key to all species of Kazimierzus; 2. to determine the distribution of the genus Kazimierzus, in order to provide reliable data on species diversity, geographical distribution in Southern Africa and factors contributing to their distribution limits; this information is vital for conservation planning because earthworms can be used as bio-indicators of soil ecosystem health and 3. to investigate phylogenetic relationships within the genus. Kazimierzus was originally accredited to the family Microchaetidae (s. lato). Family Kazimierzidae was erected to accommodate Kazimierzus species because their morphology and anatomy were found to be different from the Microchaetidae (s. str) and also their geographic distribution confirmed separation from the other families. Four new species were described and a key to all species of Kazimierzus was constructed. DNA was extracted from twelve species and mitochondrial gene fragments (COI) were amplified and sequenced. Bayesian and maximum likelihood were used to determine phylogenetic relationships among species. The results validated the twelve species known currently. Cryptic diversity was observed in K. occidualis with genetic divergence greater than 12 % among populations. Kazimierzus franciscus and K. ljungstroemi have a low genetic variability suggesting close relatedness or probably conspecificity. A group of specimens from Clanwilliam are morphologically identical to K. sophieae but are genetically distinct and may belong to an undescribed taxon. These observations highlighted the importance of integrative taxonomy in earthworms in order to present reliable taxonomic and biogeographic data. A species distribution model was used to predict the distribution patterns of K. hamerae. Potentially new habitats were predicted along the Atlantic Ocean, in the southern part, as well as, in the north-western part of Namibia. The occurrence in Namibia was tested in the south, unfortunately no Kazimierzus specimens were found in the region where sampling was done. In addition, the model demonstrated that precipitation in the driest month is the most relevant predictor in spatial distribution patterns of K. hamerae. Because of the increasing awareness of the importance of earthworms in South Africa, indigenous earthworm species are given English common names. As such, all the species of Kazimierzus were given English common names. It is hoped that using common names may facilitate and increase the use of earthworms in conservation planning and environmental impact assessments. More farmers are showing interest in soil biology and it is hoped that, by giving earthworms English names, their importance and use will increase in the agricultural sector.