Sexual selection in sticklebacks in the field: correlates of reproductive, mating, and paternal success

Abstract

Male sticklebacks display multiple ornaments, and these ornaments have been shown to be preferred by females in laboratory experiments. However, few field data exist, and it is not known whether these preferences are simultaneously or sequentially operative in a single population. We report correlates of reproductive success in two stickleback populations that differ in their ecology, over several periods within their breeding season. In both populations larger males had higher reproductive success, but not in all periods of the breeding season. Reproductive success increased with redness of the throat only in the Wohlensee population, and only in one period that was characterized by low average success. In the Wohlensee population, the parasitic worm Pomphorhynchus laevis is abundant, and reproductive success decreased with the presence of the parasite. In the Roche population, males with nests concealed in a plant had higher mating success. These nests were less likely to fail, suggesting that females preferred to spawn in concealed nests because of higher offspring survivorship. The different sexual traits appear to reveal different aspects of male quality (multiple message hypothesis): females probably find large males attractive because of their higher paternal quality, but it seems more likely that red males are preferred for better genetic qualities. Females also discriminate on territory quality, and male traits may be important in competition for these territories. The correlates of reproductive success were not consistent during the season, probably due to changes in the availability of ripe females. Such fluctuating selection pressures will contribute to the maintenance of genetic variation in sexual traits. Key words: embryo survivorship, Gasterosteus aculeatus, mating success, multiple ornaments, nest concealment, optimum brood size, paternal effort, paternal success, Pomphorhynchus laevis, reproductive success, sexual selection, sticklebacks. [Behav Ecol 10:696‐706 (1999)]