title: A further cost for the sicker sex? Evidence for male-biased parasite-induced vulnerability to predation.
abstract: Males are typically the sicker sex. Data from multiple taxa indicate that they are more likely to be infected with parasites, and are less "tolerant," or less able to mitigate the fitness costs of a given infection, than females. One cost of infection for many animals is an increased probability of being captured by a predator. A clear, hitherto untested, prediction is therefore that this parasite-induced vulnerability to predation is more pronounced among males than females. We tested this prediction in the sexually size dimorphic guppy, Poecilia reticulata, in which females are typically larger than males. We either sham or experimentally infected guppies with Gyrodactylus turnbulli, elicited their escape response using an established protocol and measured the distance they covered during 60 ms. To discriminate between the effects of body size and those of other inherent sex differences, we size-matched fish across treatment groups. Infection with G. turnbulli reduced the distance covered during the escape response of small adults by 20.1%, whereas that of large fish was unaffected. This result implies that parasite-induced vulnerability to predation is male-biased in the wild: although there was no difference in escape response between our experimentally size-matched groups of males and females, males are significantly smaller across natural guppy populations. These results are consistent with Bateman's principle for immunity: Natural selection for larger body sizes and longevity in females seems to have resulted in the evolution of increased infection tolerance. We discuss the potential implications of sex- and size-biased parasite-induced vulnerability to predation for the evolutionary ecology of this host-parasite interaction in natural communities.
authors.affiliation: School of Biosciences Cardiff University Cardiff UK; Center for Adaptation to a Changing Environment (ACE) ETH Zürich Swiss Federal Institute of Technology Zürich Switzerland; Department of Aquatic Ecology EAWAG Swiss Federal Institute of Aquatic Science and Technology Dübendorf Switzerland.
authors.forename: Jessica F
authors.identifier: 0000-0001-8939-5149
authors.initials: JF
authors.lastname: Stephenson
authors.affiliation: School of Biosciences Cardiff University Cardiff UK; Present address: Evolutionary Biology Centre Uppsala University Uppsala Sweden.
authors.forename: Cormac
authors.identifier: 0000-0001-9865-4608
authors.initials: C
authors.lastname: Kinsella
authors.affiliation: School of Biosciences Cardiff University Cardiff UK.
authors.forename: Joanne
authors.initials: J
authors.lastname: Cable
authors.affiliation: School of Environmental Sciences University of East Anglia Norwich Research Park Norwich UK.
authors.forename: Cock
authors.initials: C
authors.lastname: van Oosterhout
keywords: Bateman's principle for immunity; Gyrodactylus; Poecilia reticulata; infection tolerance; parasite‐induced vulnerability to predation; sex‐biased parasitism