Oral parasites alter male advertisement signals and female mate choice in the Green Treefrog ( <i>Dryophytes cinereus</i> )

Abstract Parasite infection can impact sexual signals such as advertisement calls through multiple mechanisms and is usually expected to negatively correlate with signal quality. However, many parasites infect their hosts by exploiting predator–prey relationships, thus some aspects of mate quality (i.e., body size, foraging ability) positively covary with infection risk. Here, we employ a system of oral frog tongueworm parasites (Halipegus occidualis) and Green Treefrog hosts (Dryophytes cinereus) to test the hypothesis that trophically transmitted parasites influence acoustic signals and mate choice in a natural population. Calling male frogs were recorded, parasites in the mouth were counted, and data on call characteristics were extracted using Audacity software and the R package warbleR. Males with high infection abundances produced calls that were shorter and had lower frequencies and different pulse structures than calls produced by uninfected or mildly infected males. Two-choice playback experiments revealed that females selected uninfected male calls only when highly infected male calls were the alternative; however, calls from males infected with a moderate number of worms were selected over those from uninfected males, indicating that the relationship between male signal quality and trophically transmitted parasite infection abundance is nonlinear and complex. Parasite infection generally altered expected relationships between some male traits (call frequency in kHz, call rate, body size) and mate choice, indicating parasite avoidance by females may alter how sexual selection acts on particular call traits and lead to complex patterns in mate choice.