Effect of light on egg-laying rate and mating speed in phototactic strains of Drosophila

Abstract

IN Drosophila, phototactic behaviour can be quantitatively described using Hirsch–Hadler classification mazes¹. Flies entering the maze make a series of 15 consecutive light–dark choices and receive phototactic scores ranging from 1.0 (highly photonegative) to 16.0 (highly photopositive). A photoneutral population has an expected mean photoscore of 8.5. The phototaxis maze has provided a useful tool for the characterisation of phototactic behaviour in natural populations of Drosophila and for the creation of photopositive and photonegative strains of flies by artificial selection. Natural populations of D. melanogaster and D. pseudoobscura are photoneutral in general, but respond rapidly to selection for positive or negative phototactic behaviour^2,4,7,8. Genetic analysis of phototaxis in Drosophila suggests that this behaviour is a polygenic trait with low heritability^3,4,6. Suspension of artificial selection results in rapid reversion to photoneutrality which illustrates the principle of genetic homeostasis and suggests that changes in fitness accompany selection for photopositive and photonegative behaviour⁸.