Population Fitness of Geographic Strains of Drosophila serrata as Measured by Interspecific Competition

Abstract

Biological evolution results from natural selection promoting or conserving the adaptedness of populations of organisms to their changing environments. The fitness, or adaptedness, of a population to its environment is a property of prime importance in evolutionary studies. Population adaptedness must be quantified in order to measure the effect of natural selection on a population, or in order to compare meaningfully different populations.Average population size after achievement of an equilibrium, and numbers of individuals produced per unit time, were used as measures of the relative adaptedness of three geographic strains of D. serrata (Ayala, 1965). The adaptedness of the populations was estimated at two temperatures, 19C and 2SC. The experiments reported now represent an attempt to measure the fitness of these three geographic strains of D. serrata by their performance in interspecific competition. Three experiments were carried out. In the first experiment each strain of D. serrata competed with a standard strain of D. pseudoobscura; in the second experiment they competed with a strain of D. melanogaster; and in the third experiment each strain of D. serrata competed with a strain of D. nebulosa. The first two experiments were performed at 25C, and the third at 19C. One objective of these experiments was to find out whether there was any consistency among the estimates of relative fitness in the various interspecific competitions, and of these estimates with those obtained in the previous experiment where fitness was measured by population size and productivity of single-species populations. MATERIALS AND METHODS

Intraspecific Competition and Population Structure in Rotifers

“…Pimentel et al (1965) showed that it takes about 7 generations for houseflies to eliminate blow flies in laboratory culture at 28°C. Similarly, it takes Drosophila serrata about 6 generations to eliminate D. pseudoobscura in population cages (Ayala 1970). Finally, Frank (1957) reported Daphnia pulicaria eliminated D. magna in approximately 4 generations under his experimental conditions.…”

“…Park et al (1964) report Tribolium castaneum (strain C-IV) eliminated T. confusum (strain B-ll) after 30 generations, however, other strains coexisted much longer. Similarly, it takes Drosophila serrata about 6 generations to eliminate D. pseudoobscura in population cages (Ayala 1970). Similarly, it takes Drosophila serrata about 6 generations to eliminate D. pseudoobscura in population cages (Ayala 1970).…”

Population biology of avena. VI. The role of genetic polymorphisms in the outcome of interspecific competition

“…), resulted from using random mixtures of genotypes within each species. Ayala (1969Ayala ( , 1970 reported on several experiments in Drosophila designed to test the role of genetic variation in interspecies competition. Several theoretical hints are found in the papers by Levin (1971), Macarthur & Levins (1966), and Larkin (1963).…”

Competition studies inDrosophila: Relative fitness and adaptedness of six closely related species

“…However, in competition experiments, D. funebris was rapidly eliminated. Barker and Podger (1970) found that D. melanogaster raised in mixed cultures were less fecund than those of pure cultures, while D. simulans showed reverse effect, in contrast to the reports of Ayala (1968Ayala ( , 1969bAyala ( , 1970and Nirmala (1973). They have demonstrated the existence of correspondence between adaptedness obtained from single species populations and those based on interspecies phenomena.…”