Do Parasite Infections Effect Fighting Ability in Beetles

David Vasquez, a student from Virginia Tech, worked with Andy Davis in the Odum School of Ecology to examine the effect that parasite infections have on the fighting ability of beetles.

David Vasquez1, Andy Davis2

1Virginia Polytechnic Institute and State University,

2Odum School of Ecology, University of Georgia

Parasites, by definition, subsist off their host’s resources, which can drain energy. This can have negative consequences for the host, especially during energy-intensive activities. Fighting is common in most animals that are territorial, or that are protective of young. Few studies have examined the effect of parasites on fighting capacity in animals. The bess beetle (Odontotaenius disjunctus) is a saprolytic insect common in forests within the eastern United States, and it is susceptible to a naturally-occurring nematode parasite (Chondronema passali). We examined the effect of infections on the outcome of staged fights in this beetle. Beetles were selected based on weight (so that each pair contained similarly-sized individuals), then placed in a small wooded arena to observe fighting behavior. A video camera recorded 3 minutes of fighting. Afterwards, beetles were killed and dissected to determine gender and parasite status. From the videos, an external observer recorded the number of bouts, wins and losses for each pair, and the overall winner. A total of 78 beetles were used in the experiment; 40% were infected with C. passali. 31 infected beetles were the overall winner in 52% of their matches, while uninfected beetles won 48% of fights (this was not significantly different X2 test). However, when fights were grouped by infection severity, we found that beetles with the highest infection score (thousands of nematodes) won 71% of their battles, while the least-infected beetles only won 25% of the time. This is counter-intuitive to the idea that infection has a negative energetic effect on host fitness.

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