African Great Rift Valley

Lake Malawi has more species of fish than any other lake in the world, but most are more closely related to other species living in the lake than to other species. So it appears that speciation is happening within the lake but how does this work? Most theories of speciation require populations to be isolated and then through local adaptations or genetic drift, the isolated populations begin to differ so that by the time they re-join the other isolated populations they can no longer interbreed. However, in a lake this cannot be happening because the habitats are contiguous and total isolation of a population should in theory be impossible. This project is working with a team of Nature publishing scientists trying to uncover the mechanisms of isolation. A series of crater lakes in southern Tanzania and which are just north of Lake Malawi provide an ideal series of laboratories because the cichlids in these lakes are also speciating, but they are much simpler systems than the extremely complex Lake Malawi.

One theory is that depth fidelity is isolating populations sufficiently that speciation can occur. The teams are using a series of techniques such as an underwater Remotely Operated Vehicle (ROV) and trapping to determine the relative abundance of the various species at different depths including any diurnal changes in distribution.

In addition, the lake structure, water quality and macroinvertebrate communities of these crater lakes are being determined, as well as an initial assessment of the bird communities around the lakes to help establish the biological importance of the region.

Over the border in Malawi the project is paired with a Malawian lake research centre, The Maru, which conducts underwater population and biodiversity surveys of the Lake’s cichlid fish populations, a water quality monitoring programme and a fisheries monitoring programme. The goals of each of these programmes is to gather more detailed baseline data sets of cichlid population dynamics in the Lake, its water quality and its fisheries and to assess the extent  to which correlations between the three data sets might help explain changes within them.