Abstract
The phototactic behavior of a population, derived from 11 iso-female lines of D. melanogaster collected in Okinawa, Japan, was studied by using a maze apparatus. Directional selections for positive and negative phototaxis were performed for 35 generations. The realized heritability for the first 20 generations was estimated to be 2.3% and 2.7% for the positive and negative phototactic behaviors, respectively.
The response to selection for photopositive and photonegative directions advanced symmetrically for the early generations, but it was biased for the later generations.
The response of the photopositive population to the reverse selection was about two times stronger than that of the photonegative population.
The mean photoscores of hybrid populations maintained by disruptive selection and of hybrid populations between photopositive and photonegative flies at generations 27, 31 and 35 inclined gradually to photonegative side. In such populations, the polygenes manifesting the photonegative behavior was epistatic or partially dominant over the polygenes manifesting the photopositive behavior.
