THE GENETIC STRUCTURE AND DISPERSAL OF THE MAYFLY BAETIS RHODANI INTO STREAMS RECOVERING FROM ACIDIFICATION.

H.C. Williams, S.J. Ormerod, and M.W. Bruford. Department of Biosciences, University of Wales Cardiff, Cardiff, South Wales, U.K. CF10 3TL

Around half of the 25,000 km of rivers in Wales are affected by acidification. Recent re-surveys and experiments have shown that invertebrate recovery does not accompany increased pH. Two alternative hypotheses currently under investigation to explain this mis-match are that potential colonists: i) are reaching the recovering streams but not persisting and ii) are not reaching the streams. This paper focuses on the second hypothesis using a widespread, abundant, and acid-sensitive species, Baetis rhodani. The genetic structure of B. rhodani was examined using mitochondrial DNA. British and European populations have unique DNA sequences (haplotypes) that differ by only a few base substitutions. A phylogenetic analysis revealed 3 distinct haplo-groups, independent of geographic location. An enzyme assay was developed to identify the main haplo-group from the 2 smaller groups, thus ensuring only 1 distinct species was used to investigate dispersal. Microsatellite DNA markers were developed to investigate the possibility that B. rhodani could disperse into streams recovering from acidification. There was no genetic differentiation among streams within or between catchments up to distances of 120 km, indicating frequent inter-catchment dispersal. This suggests that dispersal is unlikely to limit the recolonisation of previously acidified streams.