Amphibian chytrid fungus infection influences calling investment in male brown toadlets

The sublethal effects of infection and disease on male advertisement behaviour remains poorly understood. The ‘terminal investment hypothesis’ proposes that infected organisms will increase reproductive investment when their future reproductive prospects decline. Evidence to support this hypothesis has come from reports that some anuran amphibians respond to infection with the amphibian chytrid fungus pathogen by elevating calling activity. However, the generality of this response remains unclear, justifying studies in more anuran species. The aim of the present study was to provide a preliminary examination of the terminal investment hypothesis by investigating the relationship between chytrid fungus infection status and male calling behaviour in wild Australian brown toadlets (Pseudophryne bibronii). Across four populations, we examined correlations between infection status and spectral and temporal properties of the biphasic advertisement call, whilst also accounting for interrelationships with intrinsic and extrinsic factors known to influence calling behaviour. We found that infected males produced calls with more pulses and high pulse repetition rate compared to uninfected males. The association we report supports the terminal investment hypothesis, and has the potential to impact host attractiveness, host fitness, and disease transmission. Our findings join a small yet growing body of evidence that chytrid fungus impacts frog calling behaviour, and more broadly, that pathogens modify host reproductive behaviour.