Abstract

The detrimental effects of parasite infection include modulation of behaviors important to host fitness. The Mink Frog, Lithobates septentrionalis, is the final host of the digenean flatworm, Halipegus eccentricus, which inhabits the eustachian tube. Extreme infection results in complete occlusion of the eustachian tubes and could adversely affect a frog's hearing. The tympanic membranes are coupled internally through the buccal cavity via open eustachian tubes, making them vulnerable to pressure changes induced by obstruction from the presence of H. eccentricus, accumulated necrotic tissue, and mucus resulting from the infection. We tested phonotactic response in male L. septentrionalis to determine whether acoustic response is affected by infection of H. eccentricus. We placed frogs, in turn, in a floating choice arena, gave them 10 min to acclimate and 10 min to respond to a conspecific advertisement call broadcast from a speaker. We tracked the frogs and recorded positive phonotaxis when the frog approached the broadcast speaker. We measured individual frogs, checked them noninvasively for infection, and released them at the capture site. Infection rates were moderate: 43% of males had at least one H. eccentricus in one or both sides. Parasite infection significantly affected phonotaxis response; parasite-free males exhibited significantly more, and parasitized males significantly fewer, positive responses than expected. Although response measures, including time to response, did not differ significantly between the two groups of males, this behavioral assay provides good evidence that infection by H. eccentricus affects a frog's ability to localize and respond to a conspecific call.