Condition-dependent reproductive effort in frogs infected by a widespread pathogen

Area of Science:

• Ecology
• Evolutionary Biology
• Amphibian Disease

Background:

• Host responses to infection can involve adaptive changes in reproduction to minimize fitness costs.
• The pathogenic fungus Batrachochytrium dendrobatidis (Bd) poses a significant threat to amphibian populations worldwide.

Purpose of the Study:

• To investigate the impact of Batrachochytrium dendrobatidis infection on the reproductive behavior (calling probability) of the stream-breeding rainforest frog Litoria rheocola.
• To understand how host body condition and season interact with infection status to influence reproductive effort.

Main Methods:

• Field observations of Litoria rheocola populations in a rainforest environment.
• Statistical analysis of calling probability in relation to infection status, body condition, and season.
• Comparison of calling behavior between infected and uninfected individuals.

Main Results:

• Calling probability in uninfected frogs was consistent across seasons and body conditions.
• Infected frogs exhibited seasonal variation in calling probability, with lower rates in winter and higher rates in summer.
• Infected frogs' calling probability was strongly and positively correlated with body condition; poor-conditioned infected frogs called less, while good-conditioned infected frogs called more than uninfected ones.

Conclusions:

• Litoria rheocola employs a plastic life-history strategy, adjusting reproductive effort in response to Batrachochytrium dendrobatidis infection.
• Adaptive responses may lead to minimal selection on disease susceptibility if infected males in good condition maintain reproductive rates.
• Positive relationships between reproductive effort and body condition in infected males suggest selection for mechanisms mitigating infection impacts.