Increased predation risk on mothers affects survival of parasites feeding on the offspring

Organisms are often simultaneously prey for predators and hosts for parasites. The two challenges require different defence mechanisms, which may be traded off if based on the same resources. We investigated how predation risk perceived by mothers affects, via a maternal effect, the survival of parasites feeding on offspring. In an experiment on great tits, Parus major, we manipulated the perceived predator density for females before and during ovulation by simulating the presence of either birds of prey (sparrowhawks) or controls (song thrushes) in their breeding habitat. To test exclusively for the maternal effect as a consequence of the higher perceived predation risk, the offspring were raised by foster parents without treatment. We then let groups of hen-fleas, the main ectoparasite of the great tit, feed on nestlings from both treatment groups for a fixed period of time, and thereafter measured flea survival under standardized laboratory conditions. Fleas feeding on offspring of mothers experiencing increased predation risk before egg laying survived significantly longer than those feeding on control nestlings. Higher survival may be associated with maternal stressors transferred via the egg to the host offspring or may result from the resolution of an investment trade-off, whereby maternal resources can be used to prepare the offspring to deal with either increased predation risk or parasites. This finding emphasizes the need for understanding multitrophic interactions arising from the interplay between parasite- and predator-induced maternal effects and their consequences for parasite population dynamics, the composition of ecological communities and host–parasite coevolution.