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.
Under laboratory conditions, female three-spined sticklebacks (Gasterosteus aculeatus L.) show a mating preference for intensely red-colored males. We verified this female choice in the field by observing a freshwater stickleback population in its natural habitat. During the egg collection phase, individual courting males were localized with the aid of a dummy of a ripe female, caught and photographed under standardized conditions, and released. After males had stopped collecting eggs, we counted the number of eggs in the nests. The more intense a male's red breeding coloration, the more eggs he received. Simultaneous female choice experiments in the laboratory suggested that ripe females of this population preferred redder males. Breeding activities of the males in the field were clustered and seem to be synchronized within clusters. At one of the breeding sites, more intense red males were in better physical condition, but this was not the case at another site. Although several synchronized breeding cycles were observed, the majority of males seem to complete only one breeding cycle.
Summary
1. The three‐spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition‐dependency of relative pectoral fin size in males and the relationship with male parasite load.
2. Reproductively active males possessed relatively larger pectoral fins than females in both wild‐caught and laboratory‐bred fish.
3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs.
4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.
In July 1999, 49 three-spined sticklebacks were sampled from Enos Lake, Canada. Here a benthic/limnetic species pair is known to exist. In the sample, six individuals (12%) were of intermediate phenotype. These represent 17% of the 35 males in the sample. This large number of intermediates contrasts with the 1% in previous samples reported in 1984 and 1992 and may signal the collapse of the species pair. 2001 The Fisheries Society of the British Isles
Individual male three-spined sticklebacks in the field, often collected eggs for longer (up to 10 days) than had been reported for sticklebacks in captivity (3-6 days). The probability that a male stopped collecting eggs increased with the number of eggs already present, and possibly with the age of the eggs. Males with nests hidden under a plant were more likely to continue collecting than males with exposed nests. These results are discussed in the light of theoretical considerations that predict when males should stop collecting further eggs. 1999 The Fisheries Society of the British Isles
Egg survival in manipulated nests of three-spined sticklebacks Gasterosteus aculeatus in the field was not significantly different from that in unmanipulated nests.
Fish that perform paternal care may increase their fitness by choosing nest sites that enhance survival and development of embryos. We studied nest-site choice with respect to dissolved oxygen concentration and water temperature in males of the three-spined stickleback (Gasterosteus aculeatus), a small fish species with exclusive male parental care that usually breeds in the littoral zone of freshwaters of the Northern hemisphere. Fathers oxygenate the embryos by fanning movements of their pectoral fins. We expected choice for conditions at potential nest sites that would benefit offspring development, i.e., higher temperature and higher dissolved oxygen concentration. In the laboratory, we offered males a choice between two potential nest sites that differed in dissolved oxygen concentration or water temperature. Males preferred to build a nest at sites with a higher dissolved oxygen level or higher temperature and thus chose sites that would promote embryo development.
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