EVOLUTION OF BROAD AND SPECIFIC COMPETITIVE ABILITY IN NOVEL VERSUS FAMILIAR ENVIRONMENTS IN DROSOPHILA SPECIES

We used nine pairs of competing Drosophila melanogaster and Drosophila simulans populations to test three hypotheses. (1) Weaker competitors undergo greater evolutionary increases in competitive ability, compar ed with stronger ones. (2) Increased competitive ability against a spe cific competitor population causes a correlated increase in competitiv e ability against other competitor populations. (3) In a novel environ ment, adaptation to the abiotic environment contributes more to compet itive ability than adaptation to the competitor population. After 11 g enerations of competition, initially weaker competitor populations sho wed relatively greater increases in competitive ability. Broad and spe cific competitive abilities, the latter being specific to a particular competitor population, were positively correlated in both familiar an d novel environments. Adaptation to the abiotic environment seemed to be a more important component of competitive ability in the novel envi ronments. We conclude that in geographically structured species, bioti c and abiotic factors affecting the evolution of competitive ability m ay interact to help create a mosaic of outcomes that can affect the ev olutionary dynamics of the interaction over the range of the competing species.