The effect of sex, age, and boldness on inhibitory control

Inhibitory control requires an individual to suppress impulsive actions in favour of more appropriate behaviours to gain a delayed reward. It plays an important role in activities such as foraging and initiating mating, but high within-species variation suggests that some individuals have greater inhibitory control than others. A standard index of inhibitory control used in many taxa is measuring how long an animal persists in trying to move itself or an appendage (e.g. its hand) through a transparent barrier to reach a reward. Although recent nonhuman studies have investigated how different factors are associated with variation in inhibitory control, these studies have rarely considered how these factors interact. Here we investigated how sex, age, personality (boldness) and the type of reward stimulus interact to predict the degree of motor inhibitory control in eastern mosquitofish, Gambusia holbrooki. We measured inhibitory control using a standard detour assay, ‘boldness’ (time to emergence in a novel environment), and the rate of learning. There were three different reward stimuli: a shoal of females, a shoal of males or a mixed-sex shoal. Individuals were tested in four consecutive trials, always with the same reward type, to quantify short-term learning. These measures were repeated at 7, 14 and 21 weeks after maturation to examine the effect of age. Females had significantly greater inhibitory control than males. Regardless of sex, older fish had significantly greater inhibitory control than younger fish, and boldness predicted learning ability. The type of reward stimuli had no sex-specific effect on inhibitory control. We discuss the biological significance of these sources of variation in inhibitory control, and the importance of accounting for them in studies examining individual differences in cognitive abilities.