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.

The influence of species frequency, temperature regime and previous development condition on relative competitive ability between Drosophila melanogaster and Drosophila simulans

“…A similar phenomenon has been reported by Barker and Podger (1970b) on studying the fecundity of these same species raised either in pure or mixed cultures. Because, in nature, D. melanogaster and D. simulans can develop together on the same food, and usually do, the preceding result appears to be of interest with the aim of finding more natural laboratory culture conditions for D. simulans.…”

“…In this respect, the productivity of D. melanogaster is lower when their adults have been developed together with D. simulans than in pure cultures. This is unexplained and parallel to the results of Barker and Podger (1970b), who found that D. melanogaster decreases its 105 fecundity, with respect to control cultures, when raised with D. simulans. Compared with D. melanogaster, the response of D. simulans to the experimental treatments is very different.…”

“…It is also usual in the laboratory to use adults developed in pure-species cultures, although it appears to be quite general that when D. melanogaster and D. simulans compete in nature they develop on the same food. Some laboratory reports showed that adults of D. melanogaster and D. simulans exhabited some differences in sexual behavior (Eoff, 1973) or fitness components (Barker & Podger, 1970b), depending on whether they developed together in the same culture vial or in two separate vials. For this reason, we have also estimated the effect of the previous adult development condition of both species, together or alone, on their competitive ability.…”

COMPETITIVE HIERARCHIES IN LABORATORY DROSOPHILA

“…That the various laboratory Drosophila species actually have a potential to compete in various ways is reflected in the fact that at high densities the effects of interspecific competition on population growth rate generally are distinguishable from the effects of intraspecific competition (Barker and Podger, 1970;Levin, 1969;Wallace, 1974). Yet, in the limit of one species displacing the other in a series of vials, it appeared from our analysis that the strains are all doing qualitatively much the same thing in their competitive interaction.…”

Interspecific competition between Drosophila melanogaster and Drosophila simulans: Effects of adult density on adult viability

“…Biological systems are intrinsically complex, and in that and the present study, unmeasurable changes in any one of many 'constant' factors could easily have resulted in the random, but significant, small differences between replicates. Adult viability (survival) differences between species have been recorded by Barker & Podger (1970b) and Tantawy & El-Wakil (1970) for Drosophila, and by Lloyd & Park (1962), Mertz, Park & Youden (1965), and Park, Mertz & Petrusewicz (1961) for Tribolium. Differences within species were reported by Heidenthal, Nelson & Clark (1972) for Habrobracon; by Crovello & Hacker (1972) for Aedes aegypti; by Mertz, Park & Youden (1965) and Park, Mertz & Petrusewicz (1961) for Tribolium; and by Birch, Dobzhansky, Elliot & Lewontin (1963), Buzzati-Traverso (1955), Clark & Gould (1970), Maynard Smith (1958a) and Tantawy (1961) for Drosophila.…”