Interspecific Competition Between Drosophila Melanogaster and Drosophila Simulans. Effects of Larval Density and Short‐Term Adult Starvation on Fecundity, Egg Hatchability and Adult Viability

Abstract

The effects of variation in larval density and variation in proportions of the two species during development on the fitness components of fecundity, hatchability and adult viability were studied using the Oregon—R—C wild type strain of D. melanogaster and a vermilion mutant strain of D. simulans. In addition, the effects on these fitness components of a restricted period of starvation immediately following eclosion were studied. Thirty—two treatment combinations of species, species frequency, larval density and adult feeding were set up on each of two occasions, 14 days apart. Hatchability data were obtained only for the second time. This variable of time had significant effect on fecundity, which would contribute to the heterogeneity between generations in interspecific competition populations. Significant effects of larval density of fecundity were probably mediated through effects on adult body weight. D. melanogaster females raised in mixed species cultures were less fecund than those from pure cultures, while D. simulans showed the reverse effect. Therefore results in competition cultures cannot be predicted from those in pure species cultures. There were significant differences between the species for hatchability and viability, but these components of fitness showed relative few effects of the imposed treatments. The short—term adult starvation treatment was not as severe as that which occurs in at least some generations in interspecific competition populations. The effects of this and other environmental differences between this experiment and competition populations are discussed.