The idea that new species can arise as a by-product of natural selection acting on ecological and morphological traits is gaining increasing support from studies of recently diverged species. In this seminar, I present evidence for rapid ecological and morphological divergence in cichlid fishes living in small, isolated crater lakes in Tanzania. I begin by describing phylogenomic evidence for a striking case of body size–related speciation among predatory, open-water cichlids in crater Lake Kingiri (approximately 600 m in diameter). I then turn to a second example from crater Lake Masoko (approximately 700 m in diameter), where speciation appears to be linked to habitat differences. Here, I focus first on the role of visual adaptations in driving divergence, before presenting quantitative evidence showing how natural selection acts on ecological and morphological traits. Together, these case studies help to clarify how natural selection can drive ecological speciation, a process that likely underlies the remarkable and much more extensive cichlid mega-radiations of the East African Great Lakes.

Martin Genner is an ecologist and evolutionary biologist, with interests in the origins of diversity (speciation and adaptive radiation), how it is maintained (species coexistence) and how it is influenced by changing environments (climate and invasive species). His research focusses on fishes, and he has worked most extensively on species from East African freshwaters, European seas and the Southern Ocean. His research uses a wide range of approaches, including field surveys of biodiversity, analyses of long-term fisheries data, experimental field studies, quantitative observations of behaviour, and analyses of morphology.  He also uses analyses of environmental DNA, stable isotope ratios, and genome/transcriptome/methylome data for the study of biodiversity, genetic structure and evolutionary adaptation.