Genetical composition, temperature, density and selection in an enzyme polymorphism.

Selection in egg-to-adult viability was investigated at the Esterase-6 locus of Drosophila melanogaster. A factorial experiment was carried out with three variables, temperature, density and genetical composition; there were four temperatures (15 degrees, 20 degrees, 25 degrees and 30 degrees), three densities (115 ml, 10 ml and 2-5 ml of food). Strong frequency dependent selection was observed in many environments. The strength of the selection was very much modified by an interaction between temperature and density. The results are discussed in relation to evidence for a chemical mechanism which mediates frequency dependent selection, by conditioning, in the larval environment.