Selection and body size in Drosophila pseudoobscura at different temperatures.

M U C H of our present knowledge about selection comes from experiments carried out in environments as constant and optimal as possible. (For general reviews, see ROBERTSON 1956; LERNER 1958; FALCONER 1960a.) Since an individual or a population must be able to cope with a range of environments, data about the extent to which selection gains for an adaptive character under one set of environmental conditions are retained when the population is transferred to other environments can add to our understanding of the genetic mechanisms of selection and adaptation. Such experiments are described below and deal with selection for wing length (a convenient index of body size) in Drosophila pseudoobscura at different temperatures. Body size is probably closely related to fitness of the flies in their natural habitats, and temperature affects size considerably in Drosophila.