Photobehavioral differentiation in natural populations of Drosophila: changes of photoresponse over time in Drosophila pseudoobscura and Drosophila persimilis.

The photobehavior of a sympatric assemblage of Drosophila pseudoobscura and D. persimilis from California was examined over a 13-month period. During that time, certain aspects of the behavior remained constant (e.g., the mean resting photoresponse), while other aspects changed (e.g., the level of genotypic variation of the resting photoresponse of D. persimilis). The data support the contention of Rockwell et al. [Rockwell, R. F., Cooke, F., and Harmsen, R. (1975). Behav. Genet. 5:189-202] that genotypic variation and phenotypic plasticity are central features of photobehavior in natural populations of these species. The evolutionary importance of such genotypic variation and phenotypic plasticity is discussed.