The effects of body size, aggression and nuptial coloration on competition for territories in male threespine sticklebacks, Gasterosteus aculeatus

Abstract

Reproductive male threespine sticklebacks differing in size were paired against each other in an aquarium large enough to accommodate a single territory. In these contests one male became dominant and nested while its opponent became subordinate and spent most of the time hiding on the bottom or hovering at the water surface. The larger male in each contest generally dominated and this tendency increased as size disparity between opponents increased. A weight difference of 15% was sufficient to provide a competitive advantage to the heavier male. The size distribution of males indicated that such disparity occurs commonly between opponents from this study population in nature. The study failed to confirm the association between nuptial coloration and dominance reported in a recent study of this species, but this is probably attributable to the similarity of coloration among males used in the present study. Opponents differed widely in the number of bites they directed to a live test male placed in their territory. There was no correlation, however, between this measure and the male's tendency to dominate in a contest.