Systematics of Trogidae (Coleoptera) : new South African species, and a molecular phylogeny of the family

Abstract

At its inception, taxonomy simply provided guidelines for nomenclature. It has since developed into a science applied to problems relating to economics, conservation and even law. Taxonomy is arguably one of the most important pillars of the biological sciences, providing the framework from which all other studies are conducted. We expand this essential foundation by describing four new species of Trox in Chapter 2 of this dissertation - the first to be recorded in South Africa since Scholtz’s comprehensive revision of the family in 1980. All four new species are flightless and are restricted to densely vegetated areas. Based on their morphological characteristics, we conclude that the new species probably belong to the endemic South African “horridus”-group of Trox. At present, morphological studies suggest that Trogidae consists of only three genera – Polynoncus, Omorgus and Trox. The current consensus on the zoogeography of trogids, based on their current distribution patterns, is that they evolved in Central Pangaea, prior to the split that formed Laurasia and Gondwanaland. The Trox lineage is thought to have speciated in temperate Laurasia, invading Africa via a temperate faunal exchange route only after Gondwanaland had separated into the southern landmasses. However, in Chapter 3, our work, based on a molecular dataset, challenges these ideas. We investigated the phylogenetic relationships within the family by analysing the 16S ribosomal subunit gene on the mitochondrial genome, which has proved useful in investigating sub-familial relationships due to its fairly conserved nature. We performed both phenetic (Neighbor-Joining and Minimum Evolution) and likelihood (Parsimony, Maximum Likelihood and Bayesian Inference) analyses on the resulting molecular dataset. We found only partial support for the theories suggested by the morphological dataset. In all analyses, we find four major groups - Polynoncus, Omorgus, Holarctic Trox (Trox s. str.) and African Trox (Phoberus) - not three as suggested by previous morphological studies. We strongly support the promotion of Phoberus to full generic status as it is represented by a monophyletic group in all analyses. Given the evolutionary divergence suggested by our molecular phylogeny, we still propose a Pangaean origin for Trox sensu lato, but suggest that this lineage might have had its origin in what would become North Africa. It is likely to have inhabited the globe-spanning metamorphic geological features known as the Pan-African Belts, which would have offered the ancestral temperate biome preferred by this genus. We theorize that the formation of the Tethys Sea would have separated Trox s. str. from the Phoberus lineage. Copyright