Speciation and adaptive radiation

Lake Chala by Jacco van Rijssel

We investigate the mechanisms of speciation and adaptive radiation with a focus on processes that take place within lakes, in parapatry or sympatry. We wish to understand the intrinsic evolutionary constraints to speciation as well as the environmental triggers of speciation. We think it is most often the interaction between intrinsic lineage traits and extrinsic factors that determine the extent of diversification and adaptive radiation that a lineage may achieve.
Whenever possible we study the entire speciation continuum from the incipient stage of speciation with very incomplete extrinsic postzygotic and premating isolation to completely isolated sister species and fully fledged adaptive radiations all within the same evolutionary lineage. African cichlids are excellent for this, as are stickleback, char and whitefish in high latitudes. We combine investigations into the ecology, behavior, morphology and natural history of populations and species with population genomic analyses of adaptation and isolation and with phylogenetic analyses of evolutionary relationships. We investigate the roles of different agents of ecological and sexual selection, the role of ecological opportunity, evolutionary innovation and interspecific hybridization in speciation and adaptive radiation.

We have been studying the radiations of haplochromine cichlid fish in African lakes for more than 25 years. Currently we work mostly in Lake Victoria, Lake Mweru and some other smaller lakes. These radiations are the largest and fastest known animal species radiations on Earth. We have shown that speciation is driven by strong interactions between natural and sexual selection, and that unusually large standing genetic variation and ancient hybridization events facilitate this. We have also shown indications of a latitudinal gradient in adaptive radiation with more radiations at lower latitudes.
We are studying several other young lacustrine radiations of fish in temperate and cold  climates. Our focus are whitefish and char in the deep subalpine lakes on the feet of the European Alps. Many species are endemic to single lake chains and have evolved in the past 15’000 years. We study the entire fish assemblages of these lakes in order to learn about the interactions among lineages, and the roles of immigration and speciation in community assembly. 
We are studying Threespine stickleback, a major model system in evolutionary and ecological genomics. We capitalize on the circumstance that the large lakes and associated streams of Switzerland have only been colonized by stickleback in the past 150 years. We have shown that colonization involved several distinct lineages from distant parts of Europe that have admixed their genes to various extents in different parts of Switzerland. We have also shown that genetically and phenotypically distinct ecotypes have evolved despite gene flow in several lake systems of Switzerland, suggesting incipient speciation. We seek to understand the ecological and behavioral mechanisms that drive this very early stage of speciation and the sources of the genetic variation that facilitate it.