Amphibian species vary in their learned avoidance response to the deadly fungal pathogen Batrachochytrium dendrobatidis.
Abstract
Lethal and sublethal effects of pathogens should theoretically select for host avoidance of these pathogenic organisms. Some amphibians can learn to avoid the pathogenic fungus Batrachochytrium dendrobatidis (Bd) after one infection-clearance event. Here, we investigated whether four taxonomically distinct amphibians, Cuban tree frogs Osteopilus septentrionalis, southern toads Anaxyrus (Bufo) terrestris, greenhouse frogs Eleutherodactylus planirostris and pine woods tree frogs Hyla femoralis, exhibited any innate or learned avoidance of Bd on a moist substrate and, if so, what cues they used to identify the fungus. Cuban tree frogs, pine woods tree frogs and greenhouse frogs did not appear to exhibit detectable innate or learned avoidance of Bd. However, southern toads learned to avoid Bd after only one exposure. Southern toads avoided any treatment containing Bd metabolites but did not avoid treatments that lacked Bd metabolites even when dead zoospores were present. Bd metabolites appeared to be the cues that amphibians use to avoid Bd. These metabolites may have a distinct smell or may cause discomfort, which would be consistent with a classical or Pavlovian conditioning response. Synthesis and applications. Not all species of amphibians respond the same way to Bd exposure; some can learn to avoid Bd and the metabolites it produces, while others do not. These findings have important implications for both management practices and policy, and should be considered when developing disease models and conservation plans for amphibians.