Parental care tactics of three-spined sticklebacks living in a harsh environment

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Abstract
The three-spined stickleback (Gasterosteus aculeatus) is characterized by paternal care of fertilized eggs. We carried out field experiments to evaluate the response of males to simulated risks to their broods and themselves in relation to brood size and age, time of breeding season, age of parent, nest-site characteristics (depth, distance from shore, distance to nearest nest, degree of nest cover), and water temperature. For males with eggs in their nests, we chased the male away from the nest to simulate the arrival of a bird predator and measured the time until return, a measure of risk taking. There was no relationship between return time and the number or the age of eggs. There was a small but significant relationship between the distance of the nest from the shore and return time. Males with nests farther from the shore tended to return sooner. No other environmental variable explained a significant proportion of the variation in return time. Return time was unrelated to either time of breeding season or male age. In another experiment, a model of a rival male conspecific was placed near the guardian's nest, simulating a potential threat to the eggs. Again, we found no relationship between aggression to the model and egg number or egg age. Males with nests in deeper water were less aggressive than those with nests in shallower water, but no other environmental variable explained a significant proportion of the variation in aggression. Male age was unrelated to the amount of aggression, but males became more aggressive as the season progressed. Our results contrast with previous studies of parental behavior in this species. Possible reasons for these differences are discussed.

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