The pathogenic fungus
- NSF-PAR ID:
- 10294044
- Date Published:
- Journal Name:
- Biology Letters
- Volume:
- 17
- Issue:
- 8
- ISSN:
- 1744-957X
- Page Range / eLocation ID:
- 20210207
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Batrachochytrium dendrobatidis (Bd) is associated with drastic global amphibian declines. Prophylactic exposure to killed zoospores and the soluble chemicals they produce (Bd metabolites) can induce acquired resistance toBd in adult Cuban treefrogsOsteopilus septentrionalis . Here, we exposed metamorphic frogs of a second species, the Pacific chorus frogPseudacris regilla , to one of 2 prophylactic treatments prior to liveBd exposures: killedBd zoospores with metabolites, killed zoospores alone, or a water control. Prior exposure to killedBd zoospores with metabolites reducedBd infection intensity in metamorphic Pacific chorus frogs by 60.4% compared to control frogs. Interestingly,Bd intensity in metamorphs previously exposed to killed zoospores alone did not differ in magnitude relative to the control metamorphs, nor to those treated with killed zoospores plus metabolites. Previous work indicated thatBd metabolites alone can induce acquired resistance in tadpoles, and so these findings together indicate that it is possible that the solubleBd metabolites may contain immunomodulatory components that drive this resistance phenotype. Our results expand the generality of this prophylaxis work by identifying a second amphibian species (Pacific chorus frog) and an additional amphibian life stage (metamorphic frog) that can acquire resistance toBd after metabolite exposure. This work increases hopes that aBd -metabolite prophylaxis might be widely effective across amphibian species and life stages. -
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 toadsAnaxyrus (Bufo )terrestris , greenhouse frogsEleutherodactylus planirostris and pine woods tree frogsHyla 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. -
Abstract To combat the loss of species due to emerging infectious diseases, scientists must incorporate ecological parameters, such as temperature and humidity, to understand how the environment affects host–pathogen interactions. The fungal disease chytridiomycosis is a compelling case study to investigate the role of both temperature and humidity on infectious disease, as both the fungal pathogen (
Batrachochytrium dendrobatidis, Bd ) and the host (amphibians) are heavily influenced by these abiotic factors. We performed two experiments to investigate the importance of relative humidity and temperature on frog immunity (production of antimicrobial skin secretions) and disease development in captive golden frogs (Atelopus zeteki ) of Panama. We found that the quantity of skin secretions significantly decreased over time in frogs moved from low to medium and high relative humidity treatments. FollowingBd exposure, frogs in high temperature (26–27 °C) and high relative humidity (80–90%) had lower pathogen loads and survived significantly longer than frogs kept in all other treatment conditions, including high temperature and low relative humidity. These results suggest that high relative humidity may be an important, although less understood, mediator ofBd infection and the survival of golden frogs. Because the environment can drastically alter disease dynamics, understanding how temperature and humidity influence chytridiomycosis outcomes in golden frogs may be essential for the success of the reintroduction of captive frogs. -
Abstract Batrachochytrium dendrobatidis (Bd) has been associated with massive amphibian population declines worldwide. Wildlife vaccination campaigns have proven effective for mitigating damage from other pathogens, and there is evidence that adult frogs can acquire resistance to Bd when exposed to killed Bd zoospores and the metabolites they produced.Here, we investigated whether Cuban treefrogs tadpoles
Osteopilus septentrionalis can gain protection from Bd through exposure to a prophylaxis treatment composed of killed zoospores or soluble Bd metabolites. We used a 2 × 2 factorial design, crossing the presence or absence of killed zoospores with the presence or absence of Bd metabolites. All hosts were subsequently exposed to live Bd to evaluate susceptibility.Exposure to killed zoospores did not induce a protective response. However, tadpoles exposed to Bd metabolites had significantly lower Bd intensity and prevalence than tadpoles that were not exposed to metabolites.
The metabolites Bd produce pose no risk of Bd infection and therefore make an epidemiologically safe prophylaxis treatment, protecting tadpoles against Bd. This work provides a promising potential for protecting amphibians in the wild as a disease management strategy for controlling Bd‐associated declines.
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Abstract Batrachochytrium dendrobatidis (Bd) is a pathogenic fungus that has devastated amphibian populations globally by causing the disease chytridiomycosis.Batrachochytrium dendrobatidis is capable of infecting non‐amphibian hosts, such as crayfish, and has been detected on reptile and bird species. Given the taxonomic heterogeneity in the known hosts and vectors of Bd, it is likely that there is a diversity of undiscovered non‐amphibian hosts of the fungus.Here, we investigated whether Bd could survive on freshwater snails (
Physella acuta ) andCladophora algae. We exposed small and large snails (n = 15 snails/size category),Cladophora algae (n = 5), and artificial spring water controls (ASW;n = 5) to live Bd. We also maintained Bd‐free control snails (n = 5 snails/size category) in ASW. All treatments were maintained for 7 weeks at 18°C. Mortality was checked three times a week, snails were weighed every 2 weeks, and 7 weeks after exposure, the snails, algae, and water were tested for Bd using quantitative polymerase chain reaction.We found that Bd did not grow on live snails, algae, or ASW long term. Additionally, live snails (
n = 20) collected from Bd‐positive ponds in California were all negative for Bd, as well. Given that we found no Bd on the experimentally exposed or field swabbed snails, snails are probably not a reservoir host of Bd.While negative results are often not published, Bd is one of the deadliest pathogens on earth; it is essential to know what is and is not capable of maintaining Bd for well‐designed disease models.