Molecular genetic analysis of Daphnia in the English Lake District: species identity, hybridisation and resting egg banks

1. Taxonomic issues in many Daphnia species complexes are often confused by a high degree of phenotypic plasticity and by interspecific hybridisation. Here, we employ molecular genetic tools to confirm the species composition and incidence of hybridisation in extant and resting egg populations of Da phnia from Windermere and Esthwaite Water in the English Lake District. 2. A combination of species-diagnostic allozymes and mtDNA, confirms that c ontemporary populations are dominated by a single species, D. galeata. 3. We present the first account of genetic characterisation of dated 'resti ng' eggs using microsatellites and mtDNA, employing PCR-based DNA recovery, thus providing a temporal dimension to taxonomic patterns. Thirty years ag o, two species were present in Esthwaite, D. galeata and D, hyalina, but Wi ndermere populations were dominated by D. galeata only. 4. The use of PCR-based mtDNA RFLP analysis as a species-diagnostic tool, a nd microsatellites to monitor clonal diversity, provide a valuable approach for long-term studies, especially in populations free from the complicatin g effect of frequent hybridisation. The detailed limnological records avail able for many large lakes, and associated changes in land-use, pollutants a nd climate, combined with long-term ephippial molecular genetic data, provi de opportunities for exploring natural and anthropogenic impacts on genetic and community structure.