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RESEARCH PRODUCT

Diel vertical migration by Daphnia longispina in a Spanish lake: Genetic sources of distributional variation

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Individuals of many zooplankton species undergo diel vertical migration in which they move toward the surface after sunset and return to deeper waters at dawn. However, even when vertical migration can be clearly demonstrated by mapping the distributions of individuals at noon and midnight, at any given time the population is usually scattered over ‘a broad range of depths. This paper focuses on a major potential source of the variance associated with depth distributions. We have used electrophoretic analysis of isozymes to identify “clones” of Daphnia longispina in a Spanish lake. In September 199 1, two clones constituted 5 5% of the individuals collected at noon and midnight on each oftwo successive days. While both displayed significant diel vertical migration, one clone was consistently located deeper in the water column than the other clone. Our results constitute the first demonstration from a field study of Daphnia that a single population is genetically subdivided into groups having different patterns of diel vertical migration. Intrapopulational genetic variation for vertical migration patterns may explain a significant portion of the variability in the depth distributions of zooplankton populations.