title: Eaten alive: cannibalism is enhanced by parasites.
abstract: Cannibalism is ubiquitous in nature and especially pervasive in consumers with stage-specific resource utilization in resource-limited environments. Cannibalism is thus influential in the structure and functioning of biological communities. Parasites are also pervasive in nature and, we hypothesize, might affect cannibalism since infection can alter host foraging behaviour. We investigated the effects of a common parasite, the microsporidian Pleistophora mulleri, on the cannibalism rate of its host, the freshwater amphipod Gammarus duebeni celticus. Parasitic infection increased the rate of cannibalism by adults towards uninfected juvenile conspecifics, as measured by adult functional responses, that is, the rate of resource uptake as a function of resource density. This may reflect the increased metabolic requirements of the host as driven by the parasite. Furthermore, when presented with a choice, uninfected adults preferred to cannibalize uninfected rather than infected juvenile conspecifics, probably reflecting selection pressure to avoid the risk of parasite acquisition. By contrast, infected adults were indiscriminate with respect to infection status of their victims, probably owing to metabolic costs of infection and the lack of risk as the cannibals were already infected. Thus parasitism, by enhancing cannibalism rates, may have previously unrecognized effects on stage structure and population dynamics for cannibalistic species and may also act as a selective pressure leading to changes in resource use.
authors.affiliation: School of Biology , University of Leeds , Leeds LS2 9JT, UK.
authors.forename: Mandy
authors.initials: M
authors.lastname: Bunke
authors.affiliation: Centre for Invasion Biology, Department of Botany and Zoology , Stellenbosch University , Matieland 7602, South Africa.
authors.forename: Mhairi E
authors.initials: ME
authors.lastname: Alexander
authors.affiliation: Institute for Global Food Security, School of Biological Sciences , Queen's University Belfast BT9 7BL , , UK.
authors.forename: Jaimie T A
authors.initials: JT
authors.lastname: Dick
authors.affiliation: School of Biology , University of Leeds , Leeds LS2 9JT, UK.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Hatcher
authors.affiliation: Institute for Global Food Security, School of Biological Sciences , Queen's University Belfast BT9 7BL , , UK.
authors.forename: Rachel
authors.initials: R
authors.lastname: Paterson
authors.affiliation: School of Biology , University of Leeds , Leeds LS2 9JT, UK.
authors.forename: Alison M
authors.initials: AM
authors.lastname: Dunn
keywords: amphipod; behaviour; cannibalism; parasitism