Long-term changes in metapopulation genetic structure: a quarter-century retrospective study on low-Arctic rock pool Daphnia.

Population genetic surveys approximately 25 years apart examined the distribution and abundance of asexual clones of the freshwater zooplankter Daphnia pulex complex in rock pools near Churchill, Manitoba, Canada. In 1984-1985, melanic members of this species complex were present in 131 rock pools at this site, but were only detected in 90 of these pools in 2007-2008. Allozymic surveys conducted during these two time periods revealed that 59 per cent of these populations showed unchanged clonal composition. Total clonal replacement occurred in 8 per cent of the populations, while the others (33%) included a mixture of 'resident' clones and new 'colonists'. We discuss these changes in light of shifts in biotic and abiotic factors. We also discuss the use of rock pool habitats as 'sentinel' systems for examining long-term environmental changes in the ecological genetics of aquatic organisms in the Arctic.