When to feed: decision making in sticklebacks, Gasterosteus aculeatus

Synopsis

The functional analysis of feeding, territory defense and nest-directed activities by reproductively mature male three-spined sticklebacks, Gasterosteus aculeatus, was carried out under controlled laboratory conditions. Territorial males were placed in motivational conflict between feeding and nest-directed activities by making performance of the two necessary activities spatially incompatible. During a limited time each day they had to choose between staying close to their nests to carry out nest-directed activities, and moving into a separate compartment of the observation tank to feed. Males were trapped for varying lengths of time within a central, neutral compartment as they moved between the nest compartment at one end of the tank and the feeding compartment at the other. Their choice of either compartment following such trapping was recorded as indicative of their dominant motivation state. Males tended to be nest dominant in these observations, but motivational dominance could be altered. Males deprived of food for longer periods of time, or presented with an empty food cup during the observation were more likely to be food dominant. If they had not been previously deprived of food, or if a sexually mature conspecific had just been presented in the territory, males were more likely to be nest dominant. The length of time males were trapped in a neutral compartment while in transit between the nest and food also significantly influenced their subsequent behavior. Longer interruptions were more likely to result in a change in the direction in which the male was moving, but only when he was moving towards the subdominant activity. This effect supports the hypothesis of time sharing as the mechanism regulating motivation in these fish.