Individual behavioural variation and growth in female sheepshead swordtails, Xiphophorus birchmanni

Animals constantly face the challenge of balancing the trade-off between risk and reward when foraging. Individuals exhibit personality-related trait differences, often associated with foraging strategies that influence resource acquisition and can carry fitness consequences. These differences are often expressed in a social context, where group dynamics influence individual resource acquisition. If predation risk is low, social interactions are a primary predictor of individual variation in fitness. Here, we tested whether individual boldness, sociability, and social foraging behaviour predicted variation in growth in wild-caught females of a tropical freshwater fish (Xiphophorus birchmanni). We assessed boldness, sociability, and foraging behaviour of individuals within social groups over three consecutive days, then measured individual growth in body size and mass after 44 days. Boldness and sociability were positively correlated, but independent of social foraging. Individuals that foraged earlier and spent more time feeding showed greater growth over the subsequent 44-day period. Neither boldness nor sociability had any effect on growth. Since female fecundity scales with body size, behaviour in a social context may be a more robust predictor of fitness than individual boldness when predation risk is high.