Spatial and temporal genetic heterogeneity in a natural Daphnia population

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Abstract
Temporal and spatial genetic changes in a Daphnia pulex population inhabiting a permanent pond were examined for 2½ years. Spatial autocorrelation analysis indicated that electrophoretically identified genotypes were frequently distributed non-randomly in the pond, both vertically and horizontally. Water quality variation in the pond was associated with life history differences of three clones in laboratory experiments. Data from additional life table experiments indicated that temperature and food concentration affected genotype fitness components; no single genotype was most fit under all conditions indicating genotype-environment interactions. Manipulations of dissolved oxygen levels revealed further that one clone displaced another clone at high, but not at low oxygen levels. These results imply that spatial and temporal environmental heterogeneity may be significant in the maintenance of genetic variation (clonal diversity) in planktonic cladoceran populations.