Early exposure to nonlethal predation risk by size-selective predators increases somatic growth and decreases size at adulthood in three-spined sticklebacks.

Predation has an important influence on life history traits in many organisms, especially when they are young. When cues of trout were present, juvenile sticklebacks grew faster. The increase in body size as a result of exposure to cues of predators was adaptive because larger individuals were more likely to survive predation. However, sticklebacks that had been exposed to cues of predators were smaller at adulthood. This result is consistent with some life history theory. However, these results prompt an alternative hypothesis, which is that the decreased size at adulthood reflects a deferred cost of early rapid growth. Compared to males, females were more likely to survive predation, but female size at adulthood was more affected by cues of predators than male size at adulthood, suggesting that size at adulthood might be more important to male fitness than to female fitness.