The last of us: social information enhances trappability in fruit flies

Abstract When facing novel conditions, animals must make decisions crucial to survival with little precedence. Such decisions are not made in isolation: animals collect information by observing conspecifics, suggesting that social information may modify the population-level impact of shifting environmental conditions. We tested the competing hypotheses that social information could help or hinder animals to avoid an evolutionary trap, a phenomenon often created by anthropogenic modification. By manipulating the magnitude of a social cue, we examined how the number of already-drowned conspecifics influenced fruit flies' (Drosophila melanogaster) responses to vinegar traps. We found that flies were faster to drown in traps with more conspecifics, supporting the hypothesis that social information can facilitate maladaptive decisions. Moreover, sex and prior mating experience drove variation in this response: mated females had higher survival probabilities compared to unmated females and males. This work highlights how anthropogenic change can shift the fitness benefits of social information reliance, potentially making evolutionary traps even deadlier.