Evolution of Aquatic Biota: Tigerfishes and others

Nearly 300 Tigerfishes genotyped from 17 African countries...

In 2000, I initiated field collecting and the planning of a detailed study of Africa's tigerfishes, the predatory, freshwater characiformes of the genus Hydrocynus. This has developed into a collaborative Pan-African study, not least thanks to the fine work by Sarah Goodier for her MSc under the auspices of the Africa Earth Observatory Network (then at UCT until closed down in 2011). Nearly 300 fishes have been sampled from a total of 23 principal rivers within 15 geographically isolated drainage basins in West, East and Central Africa. These represent a total of 17 African countries: from Mali and The Gambia to Kenya and Ethiopia and south to South Africa and Mozambique.

Initial genotyping was carried out in Colleen O'Ryan's Population Genetics Laboratory, Dept of Molecular and Cell Biology, at UCT. An expanded survey and detailed analyses continue under auspices of AEON's Geoecodynamics Research Hub, Stellenbosch University

This tigerfish research is part of integrated research on wetlands biodiversity. The biological insights continuing to be obtained dovetail with efforts to decipher the geological intricacies of an evolutionary narrative. Integral to Geoecodynamics Research, the evolution of Hydrocynus aims to reconstruct details of drainage evolution across tropical Africa, with a focus on deciphering recent events in the Kalahari Epeirogeny. These phylogeographic studies of fishes build on the synthesis published by Skelton (1994). My close association with the Southern African Institute for Aquatic Biodiversity (SAIAB) is a key component with this research on tigerfishes and other fishes in the Zambezi and Congo basins. Additional biotic indicators of landscape evolution are being studied, including lechwe antelopes. The latter focus has entailed a detailed review of lechwe taxonomy (including the description of the Upemba lechwe, Kobus anselli as new to science).

The inaugural publication on tigerfish evolution is published in PLoS One. An overview of the project (Cotterill and Goodier 2009) summarizes the described diversity of Hydrocynus,and also places the phylogeographic aspects of the research into the context of drainage evolution.

Aspects of fieldwork along the Bas Congo river were filmed for a National Geographic documentary, which highlights the Goliath Tigerfish, Hydrocynus goliath. This documentary also highlights the unique hydrology and remarkable fish fauna of the Bas Congo. See recent studies by Markert et al. BMC Evolutionary Biology 2010, 10:149, and results of velocity mapping that reveal the unique bathymetry and hydrodynamics of the 150m deep channel of the Bulu reach of the Bas Congo (Jackson et al. 2009).

The recent study of rheophilic [rapid-loving] Cichlid Fishes by Schwarzer et al (2011) employed a Geoecodynamics methodology - gene trees and molecular clocks - to estimate that the Bas Congo began to incise the western rim of Africa in the late Miocene. Geoecodynamics undergirded the reconstruction of where and when ancestral lineages of Steatocranus and Nanochromis underwent adaptive radiations in the spectacular rapids of the Bas Congo, and so testifies to when the river incised deep gorges across the Crystal Mountains. This geobiological estimate of the age of Earth's deepest river agrees with available geological reconstructions. The study exploited the high fidelity of these little fishes to fast-flowing rapids - their "torrential aquatic habitats", which they have tracked through space and time.