The genetics of phototaxis in Daphnia magna: Existence of three phenotypes for vertical migration among parthenogenetic females

Using a cloning technique, we revealed the existence of three phototactically distinct types in Daphnia magna, viz. negatives, positives, and gipsies. The latter migrate continuously between a low and a high light intensity. The expression of this behaviour is genetically determined, although positives and negatives can reversibly switch into gipsies.It is proposed that two opposite genotypes exist, with the gipsy behaviour epigenetically induced. All juveniles behave more or less uniformly, irrespective of their origin. The phototactic responses develop rather late during ontogenesis.