Does local adaptation to resources explain genetic differentiation among Daphnia populations?

Substantial genetic differentiation is frequently observed among populations of cyclically parthenogenetic zooplankton despite their high dispersal capabilities and potential for gene flow. Local adaptation has been invoked to explain population genetic differentiation despite high dispersal, but several neutral models that account for basic life history features also predict high genetic differentiation. Here, we study genetic differentiation among four populations of Daphnia pulex in east central Illinois. As with other studies of Daphnia, we demonstrate substantial population genetic differentiation despite close geographic proximity (< 50 km; mean θ = 0.22). However, we explicitly tested, and failed to find evidence for, the hypothesis that local adaptation to food resources in these populations. Recognizing that local adaptation can occur in traits unrelated to resources, we estimated contemporary migration rates (m) and tested for admixture to evaluate the hypothesis that obser...