Population genetic consequences of a diapause: a species comparison of two calanoid copepods (Eudiaptomus spec.)
The widespread calanoid copepods Eudiaptomus graciloides and E. gracilis co-occur in a number of European lakes and are morphologically similar, but only E. graciloides is capable to produce diapausing eggs. Therefore, these two sister-species are ideal to investigate the genetic impact of a life-cycle with a diapause in a between-species comparison. Firstly, I established microsatellite libraries for both Eudiaptomus species, since no primer pairs were available to amplify microsatellite loci. I hypothesized that diapausing eggs, as a consequence of their high dispersal capacity, lead to higher gene flow and, hence, to less genetic differentiation between populations of E. graciloides compared to E. gracilis. To test this hypothesis I investigated 16 E. gracilis and 17 E. graciloides populations at three different spatial scales (investigation of isolation-by-distance in a range of 100, 1000, and >1000 km) using the length polymorphism of 10 microsatellite loci from the previously developed microsallite libraries. Further, I hypothesized that the occurrence of a diapausing egg bank in E. graciliodes results in higher effective population sizes (Ne) compared to E. gracilis, due to the maintenance of genetic diversity. Therefore, I estimated effective population sizes from four temporal samples taken from a lake in northern Germany. Additionally, I related effective populations sizes to the ecological population sizes for both Eudiaptomus species. In order to obtain information on the genetic role of diapause in Eudiaptomus species over longer time scales, the variation of mitochondrial DNA sequences from populations from three lakes in northern Germany was studied in a joint project with A. J. Bohonak, M. D. Holland, B. Santer, C. M. Kearns, and N. G. Hairston (Jr.).