GENETIC PATTERNS OF INTERCHANGING DREISSENA POLYMORPHA POPULATIONS: OBSERVATIONS AND EXPECTATIONS.

J.C. Mueller and E.M. Griebeler. Institute of Zoology, University of Mainz, 55099 Mainz, Germany

The opening of a newly constructed canal is the starting signal of a comprehensive natural dispersal experiment. Populations are given the opportunity to expand into new areas or to mix with pre-existing populations on the other side. The analysis of the spatio-temporal dynamics of the genetic population structure enables the investigation of interchange processes even within single species. We analysed by allozyme and microsatellite markers the mutual interchange of Dreissena polymorpha populations across the newly constructed Main-Danube canal in Central Europe. We found that the initially different populations on both sides of the canal refer to different invasion routes from the Pontocaspian region. The initial allele frequency difference degraded rapidly in the canal neighbourhood over the investigated time period of about 8 years. An asymmetric pattern reflected the overall water management across the canal and thus lay particular emphasis on the passive larval movements as a significant factor for population structure in Dreissena polymorpha. In order to assess the effects of individual movements on the spatial genetic structure, we developed a simulation model of demographic and dispersal processes within an interchange zone. Model results about the rate of genetic homogenisation and disequilibrium patterns are compared with observations.