Geographic distribution and light-dependent behavior in Drosophila.

Drosophila species fall into three classes with respect to the effect of light on their reproductive behavior: Class I, species that mate equally well in light or darkness; Class II, those merely inhibited by darkness; Class III, species whose mating is blocked by darkness. Species in the three classes also differ in the extent of their geographic distribution, with Class I including widely distributed and cosmopolitan species and Class III those that are endemic. Class II species have an intermediate distribution pattern. The behavioral differences among species reflects the degree to which courtship information is locked-in on unique visual stimuli, as well as indicating differences in the underlying genetic architecture of flexible versus specialized forms. It may be anticipated that most species of Drosophila will be found light dependent. Similar organizational differences in other forms relying on visual courtship stimuli may be reflected in correlation between distribution and behavioral reliance on a single sensory input. Dependence on a single sensory input offers a unique variety of methods for biological control of species that requires a particular sensory system for information transfer.