GENETIC, ACCLIMATIZATION, AND ONTOGENIC EFFECTS ON HABITAT SELECTION BEHAVIOR IN DAPHNIA-PULICARIA

Daphnia pulicaria from three different populations were observed to ex press within-population variation in habitat-choice behavior in field assays. Individuals from different habitats (i.e., lake depths) were i solated and cultured as clonal lines under standard conditions. Habita t choices by clonal descendants were then estimated in the held, using replicate experimental columns. There was significant heritable and o ntogenetic variation in habitat choice, but the heritable effect was s mall relative to the phenotypic variation of the original isolates. In a second set of experiments, D. pulicaria that were acclimatized to d ifferent habitats showed a strong tendency to choose the habitat to wh ich they had been acclimatized. These data suggest that a given genoty pe can use a wide range of habitats, given appropriate acclimatization . Although genetic variation is significant, we hypothesize that natur al selection on correlated ecological traits is more likely to maintai n patterns of genotypic segregation among habitats in Daphnia.