Factors influencing the competitive ability of certain wild stocks of Drosophila.

Abstract

The fitness and viability of wild stocks of D. melanogaster of various origins have been studied by submitting experimental populations to competition. Laboratory stocks raised as small populations were weak competitors, whereas those raised as large ones were strong competitors. For comparison, analogous experiments were carried out with stocks collected in natural populations. These wild stocks were superior to the standard stock in their fitness characteristics. To explain these observations, more or less homozygous strains were derived experimentally from a wild stock that was highly heterozygous initially; these derivative strains were tested in a similar way. The decrease in viability that was observed in small populations resulted from inbreeding, which fairly rapidly reduced fertility and other fitness characteristics. Therefore, when the maintenance of viability is desirable, flies collected from nature should be raised as large laboratory populations.