Evolutionary dynamics of species diversity in fish – an interdisciplinary research program in ecology, evolution and conservation
Friday seminar by Ole Seehausen
A fundamental challenge to our understanding of biodiversity is to explain why some species undergo adaptive radiations, diversifying extensively into many and varied species, while others do not. Both extrinsic environmental factors and intrinsic lineage-specific traits influence diversification, but few studies have addressed how such factors interact. Radiations of cichlid fishes in the African Great Lakes provide some of the most dramatic cases of species diversification. However, most cichlid lineages in African lakes have not undergone adaptive radiations. To investigate why adaptive radiation does and does not occur, we compiled data on cichlid colonization and diversification in many African lakes, along with lake environmental features and information about the traits of colonizing cichlid lineages. We find that extrinsic environmental factors related to ecological opportunity and intrinsic lineage-specific traits related to sexual selection both strongly influence whether cichlids radiate. Thus, for cichlids, adaptive radiation is predictable – but only when both species’ traits and environmental factors are jointly considered.
After species diversity has evolved, it remains vulnerable for millenia to rapid evolutionary collapse through introgressive hybridization, a mechanism referred to as the reversal of speciation. If adaptive radiation is predictable, so should be its collapse when environments change.
We analysed historical and contemporary data of fish radiations from 17 pre-alpine European lakes and reconstructed changes in genetic species differentiation through time using historical samples. We provide evidence that here like in the cichlids, species diversity evolved in response to ecological opportunity, and that anthropogenic eutrophication, by diminishing this opportunity, has recently caused the sudden loss of species diversity through speciation reversal and demographic decline. Across these radiations, the magnitude of eutrophication explains the pattern of species loss and levels of genetic and functional distinctiveness among remaining species. Extinction by speciation reversal may be more widespread than is currently appreciated. Preventing such loss of species diversity will require that conservation efforts identify and protect the eco-evolutionary processes that generate and maintain species.
Prof. Dr. Ole Seehausen
Eawag: Swiss Federal Institute of Aquatic Science and Technology
Fish Ecology and Evolution