Genotypic interactions among competing strains and species of Drosophila.

VIDENCE is accumulating to support the observation that the fitness of a E particular genotype in a given environment may be improved or impaired by the presence in that same environment of conspecific carriers of other genotypes. This has been shown in Drosophila pseudoobscura by LEVENE, PAVLOVSKY and DOBZ,HANSKY (1954), and BEARDMORE (1963) ; in D. melanogaster by LEWONTIN (1955) ; in D. busckii by LEWONTIN and MATSUO (1963) ; in Tribolium by PARK ( 1936) , NEYMAN, PARK and SCOTT ( 1958), SOKAL and KARTEN ( 1963) and KARTEN (1965); in rice by ROY (1960); and in barley by GUSTAFFSON (1957). For additional references, see ALLEE, EMERSON, PARK, PARK, and SCHMIDT (1949) and SLOBODKIN (1958). POLIVANOV (1964) and DAWOOD and STRICKBERGER (1964) found that in D. melanogaster the frequency o f the mutant gene ebony is decreased more rapidly in competition with a heterozygous than with an inbred wild-type strain. Furthermore, the latter authors (unpublished) have shown that under conditions of crowding, ( 160 larvae per 5 ml of medium), the survival rate of ebony larvae is lower when grown on media containing either the larvae or biotic residue of a Samarkand strain (A6) than with an inbred strain (A2). The following experiment was undertaken in an attempt to clarify the effect of media conditioned by one genotype upon the fitness of competing genotypes.