Abstract
In order to obtain further information about the mechanisms which maintain the remarkable isozyme polymorphisms at the Est-β locus of D. virilis, several components of fitness were compared among electrophoretically different genotypes. Esterase activities are statistically the same among three genotypes (BB, BD and DD) with similar genetic backgrounds.
Under near optimal culture conditions, the following components were examined separately for three genotypes: fecundity, hatchability, egg-to-adult viability and developmental time. No significant differences were observed among genotypes for any of these components.
Under competitive conditions in which two or three genotypes coexist in a culture vial, relative egg-to-adult viability of each genotype was estimated at several genotype frequency levels. Except for one case in which a rare DD genotype was more viable than abundant ones, the relative viability did not differ among coexisting genotypes and no clear and consistent evidence of frequency-dependent selection was obtained.
The results of the present experiments suggested that esterase isozyme variants are of no great adaptive significance, so far as they are at the same level of enzyme activity.
