Invasion history and genetic population structure of riverine macroinvertebrates 1 1 Presented at the 94th Annual Meeting of the Deutsche Zoologische Gesellschaft in Osnabrück, June 4–8, 2001

Macroinvertebrate communities of large rivers have experienced dramatic species turnovers in the last decades, which still go on. The analysis of genetic population structure plays a central role in understanding and predicting these biological invasions. Two points of view are considered: the influence of the invasion history on the genetic structuring and the potential implications of genetic structure for future invasibility. Expectations about selectively neutral genetic variation in simple invasion models are compared to case studies of amphipods and Dreissena. The genetic patterns of one amphipod species of the Gammarus fossarum complex yield strong evidence for a stepwise regional colonisation. Other invasive amphipods show similar, but less clear genetic characteristics. Long-distance colonisation is probably common in Dreissena polymorpha, but subsequent downstream swamping of larvae obscures the expected genetic pattern by homogenising neighbouring populations. First, a brief review of general characteristics of riverine invasions is followed by a discussion of the utility of genetic tools for inferring taxon and source population identity.