Lovers and fighters: male stickleback, Gasterosteus aculeatus, differ in their responses to conflicting stimuli

Many behaviours cannot be performed simultaneously, which forces animals to decide which behaviour to perform. In a behavioural trade-off, individuals should act as if they have weighed these alternatives before acting. Because the costs and benefits of performing specific behaviours are likely to differ between individuals as a result of different environmental and/or genetic backgrounds, individuals should vary in the decisions they make. Male threespine stickleback establish territories and nest close to one another; thus, they may be faced with a decision: fight a potential rival male or court a female. To assess how males respond to the presence of conflicting stimuli, males were presented with a dummy female alone, a dummy male alone, a dummy male and a dummy female simultaneously, and two dummy females simultaneously. Repeatability scores indicated that individuals were consistent in their responses to a given stimulus within a treatment yet differed from one another in their responses. For example, some males were more vigorous courters than others. In the female–male treatment, some males focused on only one of the stimuli while others divided their time between the two. This finding suggests that males may use different strategies when conflicting stimuli are present. Few studies have empirically examined the choices that territorial males make when these competing options are presented simultaneously, even though this situation is probably common in the wild. This study provides insight into male decision making when stimuli that elicit mutually incompatible behaviours are present and suggests that there may be a genetic basis to these differences.