The impact of predation risk and of parasitic infection on parental care in brooding crustaceans

Parental care is common in vertebrates, but less common in invertebrates, tending to occur in species that have relatively few young that can be protected from the physical or biotic environment. Individuals will be selected to trade off current and future reproductive success, leading to adaptive changes in brood care behaviour in response to predation risk. Investment in brood care may also be reduced as a result of costs of parasitic infection. Here we investigated the impact of predator cues and of parasite infection on brood care behaviour in amphipod crustaceans. We found no evidence for any reduction in brooding behaviour or reproductive success in response to infection by vertically transmitted microsporidian parasites. This may reflect the mechanism of parasite transmission, as vertically transmitted parasites rely on host reproduction to pass to the next generation. However, we found evidence for changes in brood care behaviour in response to increased risk of predation. Larger Crangonyx pseudogracilis females, with higher oxygen demands for their broods, showed a reduction in active brood care when exposed to predator cues. Additionally, Gammarus duebeni were found to reduce brooding duration in response to predator cues; we suggest that this earlier release of juveniles is likely to enhance survival of the brood, by spreading the risk of predation on juveniles.