Molecular rates and evolutionary pathways during speciation: Identification and relative importance of biotic and abiotic factors

The East African Great Lakes are famous for their species flocks counting hundreds of endemic cichlid fishes. Today they represent prime model systems for the study of those mechanisms and processes giving rise to species flocks. Recent advances in the field of molecular biology have allowed novel insights into the evolutionary process which would not have been possible with traditional methods alone. The research grant "Molecular and ecological aspects of speciation" (P12339) aimed to elucidate those evolutionary mechanisms which drive or influence the origin of species. We chose to study the cichlid flock of Lake Tanganyika and two groups of marine fishes. The Lake Tanganyika species flock and our marine model groups in the Mediterranean Sea have the advantage to represent an evolutionarily old and thus "mature" stage of adaptive radiation, old enough to be thoroughly analyzed by means of molecular phylogenetic methods which is often problematic in younger species flocks. We used mitochondrial DNA sequences and nuclear markers to perform phylogenetic and population genetic analyses. Our research was highly successful and so far resulted in five publications in high-ranked international scientific journals (Molecular Biology and Evolution, Journal of Molecular Evolution, Molecular Ecology, Journal of Fish Biology and Systematic Biology). Five additional publications are in press, six are presently in review and six more being written. Thirteen masters theses and three PhD theses were completed in the framework of this grant. We are especially happy about the establishment of a scientific cooperation with the University of Zambia at Lusaka and the Fisheries Department of the Republic of Zambia at Mpulungu, because we feel that any successful research in Africa needs the active involvement of local scientists. A first masters thesis in cooperation with the Institute of Limnology of the Austrian Academy of Sciences and the University of Delft was the result of this agreement of understanding. Our first major goal was to construct a robust phylogeny of the entire Lake Tanganyika cichlid flock, as a basis for further detailed studies on particular evolutionary lineages. Our results showed that the Lake Tanganyika flock is much more complex as currently recognized. It goes back to eight seeding lineages that gave rise to the present diversity. It also became clear that one of the widely accepted notions, that adaptive radiation proceeds in isolation to neighboring biota and that the evolving species radiate into particular habitats of a lake, does not hold. Instead, it appears that the Tanganyika cichlid radiation also affected neighboring rivers and lakes where it catalyzed another faunal revolution. Our results on the two groups of marine fishes further showed stunning similarity to the findings of African cichlid fishes: the high frequency of parallel (convergent) evolution of particular trophic types. We could further demonstrate a specific mode of speciation which was so far questioned for animal kingdom: the origin of a new species via hybridization of two mother species. This was demonstrated for a narrowly distributed rock cichlid, Neolamprologus marunguensis. The second major goal of our grant was to elucidate the dynamics of ongoing speciation processes. Therefore we analyzed gene flow in three model species along five adjacent localities. This design allows to isolate species- specific influences on the amount of gene flow over geographic distances from abiotic influences due to the characteristics of the habitat itself. We used mitochondrial DNA sequences in parallel to nuclear markers and also determined a series of ecological key parameters of the species in question. We also developed a method to determine the age structure of tropical freshwater fishes. Thereby we showed that small differences in the ecology have a great impact on the dispersal ability of a species, and thus also on the geographic distribution of genetic variation within a species. Certain species thus have a higher capacity to undergo further speciation than others, depending on their biological characteristics.