# Amphibian Chytrid Fungus Infection Influences Calling Investment in Male Brown Toadlets

## TL;DR

This study shows that male brown toadlets infected with a fungus produce more pulses in their calls, possibly to increase mating chances.

## Contribution

The study provides new evidence supporting the terminal investment hypothesis in amphibians infected with chytrid fungus.

## Key findings

- Infected male brown toadlets produced advertisement calls with more pulses than uninfected males.
- The findings support the terminal investment hypothesis in the context of chytrid fungus infection.
- The results suggest that infection may influence host attractiveness, fitness, and disease transmission.

## Abstract

The sublethal effects of infection and disease on male advertisement behaviour remain 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, while also accounting for interrelationships with intrinsic and extrinsic factors known to influence calling behaviour. We found that infected males produced calls with more pulses 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.

The sublethal effects of infection and disease on male advertisement behaviour remain poorly understood. Here we show that male brown toadlets infected with the amphibian chytrid fungus produce calls with more pulses 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.