title: Fighting while parasitized: can nematode infections affect the outcome of staged combat in beetles?
abstract: The effects of non-lethal parasites may be felt most strongly when hosts engage in intense, energy-demanding behaviors. One such behavior is fighting with conspecifics, which is common among territorial animals, including many beetle species. We examined the effects of parasites on the fighting ability of a saproxylic beetle, the horned passalus (Odontotaenius disjunctus, Family: Passalidae), which is host to a non-lethal nematode, Chondronema passali. We pitted pairs of randomly-chosen (but equally-weighted) beetles against each other in a small arena and determined the winner and aggression level of fights. Then we examined beetles for the presence, and severity of nematode infections. There was a non-significant tendency (p = 0.065) for the frequency of wins, losses and draws to differ between beetles with and without C. passali; non-parasitized individuals (n = 104) won 47% of their fights while those with the parasite (n = 88) won 34%, a 13% difference in wins. The number of nematodes in a beetle affected the outcome of fights between infected and uninfected individuals in an unexpected fashion: fighting ability was lowest in beetles with the lowest (p = 0.033), not highest (p = 0.266), nematode burdens. Within-fight aggression was highest when both beetles were uninfected and lowest when both were infected (p = 0.034). Collectively, these results suggest the nematode parasite, C. passali, is associated with a modest reduction in fighting ability in horned passalus beetles, consistent with the idea that parasitized beetles have lower energy available for fighting. This study adds to a small but growing body of evidence showing how parasites negatively influence fighting behavior in animals.
authors.affiliation: Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Vasquez
authors.affiliation: Department of Evolutionary Anthropology, Duke University, Durham, North Carolina, 27708, United States of America.
authors.forename: Anna
authors.initials: A
authors.lastname: Willoughby
authors.affiliation: Odum School of Ecology, University of Georgia, Athens, Georgia, 30602, United States of America.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Davis
mesh_terms: D000374:Aggression; D000818:Animals; D001517:Coleoptera / Q000469:parasitology / Q000502:physiology*; D005260:Female; D006790:Host-Parasite Interactions; D008297:Male; D009348:Nematoda / Q000502:physiology*
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