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Internally generated predator-prey dynamics modify genotype selection.
Nelson, William1, MCCAULEY, EDWARD1, WRONA, FREDERICK2, 1 2
ABSTRACT- Most freshwater zooplankton populations show seasonal shifts in genotype frequencies over a season but the strength and timing is often not correlated with environmental factors. An alternative is that dynamic changes in food supply alter genotype selection. Zooplankton graze on phytoplankton, forming a tightly coupled predator-prey system. It has been shown previously that zooplankton genotypes significantly influence life history and population growth characteristics. We investigated how the temporal stability of the zooplankton-phytoplankton interaction alters genotype selection in microcosm experiments using different genotypes of Daphnia pulex interacting with a diverse edible algal community. We manipulated temperature (15°C and 25°C), zooplankton genetic diversity, and nutrient levels. Population abundance was estimated over many generations and genotype proportions were determined using protein electrophoresis. We found a wide range of predator-prey dynamics, from stability at 15°C to cycles in enriched tanks at 25°C. Corresponding with these different population dynamics, we found different genotype selection. Weak changes in genotype frequency were strongly associated with cyclic population dynamics, whereas strong genotype selection occurred with stable dynamics. Using inverse methods, we found that genotype selection occurred when the population was experiencing food-dependent mortality near equilibrium. Selection was never pronounced when the population had high birth rates or mortality following a strong burst of reproduction. This establishes a tight link between features of the population dynamics and genetic selection.
KEY WORDS: population dynamics, predator-prey interaction, genotype selection