Food or fear: hunger modifies responses to injured conspecifics in tadpoles

Animals must balance the conflicting needs to forage and avoid predation. The optimal balance of risk and reward should depend on the individual’s state, particularly hunger status. Satiated individuals are hypothesized to react more strongly to risk than hungry individuals, for which the necessity for food overrides perceived danger. We tested this in wood frog (Lithobates sylvaticus) tadpoles by comparing the response of fasted and fed tadpoles to injured conspecifics (alarm cue) and uninjured conspecifics (control). Food restriction significantly affected the activity levels of tadpoles and the impact of injured conspecific cues on activity. Fed tadpoles responded little to these cues, tending to decrease activity. Hungry tadpoles were more active overall and responded to injured conspecific cues by increasing activity. We propose that hungry tadpoles increase their activity in response to an injured conspecific because, in addition to indicating danger, this cue represents a nutrient source for this opportunistically cannibalistic species, and hungry tadpoles should thus adopt risky behavior to acquire this valuable resource. Differences in hunger may therefore explain variation among studies of tadpole responses to injured conspecifics. Future studies in aquatic organisms should consider the role of hunger status when assessing antipredator behavior.