Abstracts (first author)
Speciation history of the Atlantic eelsPDF
Allopatric speciation has generally been considered the most prominent process for the evolution of new species. Although evidence for sympatric speciation has increased recently it is still controversial to what degree it occurs in nature. Hence, it is generally accepted that allopatric speciation should be the null hypothesis against which sympatric speciation is tested. Marine environments often have no obvious geographic barriers, which makes sympatric speciation a likely scenario. However, only few marine organisms have the characteristics that make them good candidates for testing mode of speciation. The European and American eel (Anguilla anguilla and A. rostrata) are panmictic species that spawn in the Sargasso Sea. Their spawning area and time overlap considerably. Hybrids are rarely observed, indicating reproductive barriers. In this study we conduct whole mitochondrial genome and RAD sequencing to investigate the speciation history of the two Atlantic species of eel. Using coalescence based analyses we estimate divergence time to test the hypothesis that speciation occurred long time ago in sympatry. As a result of continental drift the distance between the spawning grounds increased, causing selection on e.g. duration of the larval phase. The alternative hypothesis concerns speciation in allopatry during the Pleistocene. Glaciations significantly decreased the amount of available habitats in coastal regions and freshwater bodies. Hence, population size is likely to have undergone a severe decrease. The smaller population sizes of European and American populations would result in reduced overlap of spawning area leading to reproductive isolation. The impact of the last glaciation on effective population size is assessed by conducting Bayesian skyline plots based on the mtDNA. Finally, patterns of genome-wide selection between the two species are analyzed using RAD sequence data in order to detect genes and genomic regions involved in speciation.