AGE-RELATED DIFFERENCES IN REPRODUCTIVE TACTICS IN THE 3-SPINED STICKLEBACK, GASTEROSTEUS-ACULEATUS

Three-spined sticklebacks have two main reproductive tactics. The 'normal' tactic is to establish a territory, build a nest, and court females. When eggs are obtained the males aerate them and defend them against predators. Some males attempt to steal fertilizations from the territorial male during courtship, leaving him to care for eggs he did not fertilize. The use of the two tactics by two age-classes of males was investigated. Although both territorial and non-territorial males of both age-classes sometimes sneak fertilizations, younger non-territorial males did so the most frequently. Younger males were more likely to steal fertilizations, whereas older males were more likely to establish territories, build nests and care for young. Younger males also produced more sperm and more motile sperm than older males. This greater sperm production may be an alternative means of competing with older/bigger males for territories. Older non-territorial males were more likely to steal nests than younger males. There was no evidence that females discriminate among males on the basis of their size or age. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.