Effects of Temperature on Batrachochytrium dendrobatidis Infection of Amphibians

Alyssa Carroll Department of BiologyArcadia UniversityGlenside, PA 19038

Library InvestigationDr. Christopher Binckley

Abstract

Introduction

Results

AcknowledgementsReferences

Results

Results

One third of all amphibian species are listed as endangered, & Batrachochytrium dendrobatidis (Bd), is a chytrid fungus causing mass mortality of amphibians. Perhaps started by the global amphibian trade, it is linked to mass die offs of amphibians on every continent. Temperature is the primary factor regulating its spread, allowing prediction of Bd movement & which specific amphibian populations are at risk. Temperature is correlated to infection prevalence, & is the most consistent factor in the persistence of Bd. Some amphibian species are resistant to infection, possibly helping spread Bd by acting as reservoirs. As explained by the naïve prey hypothesis, populations of amphibians previously unexposed to Bd are dying quickly, as they have little immunity to this novel pathogen. Studies done by Sapsford et al, 2013, Piovia-Scott et al, 2011, & Savage et al, 2011 all indicated an optimal temperature range for Bd growth of between 17 & 23 C°. Treatment & conservation tactics should consist of mapping possible areas of outbreaks & prophylactically treating populations with antifungals, or collecting species for preservation in captivity. .

Piovia-Scott J, et al. 2011. Biological Conservation, 144, 2913-2921.

Sapsford SJ, et al. 2013. Plos ONE 8.12: 1.

Savage AE, MJ. Sredl, & KR Zamudio. 2011. Biological Conservation 144, 1910-1915.

I would like to thank my thesis advisor, Dr. Binckley, for his guidance while writing this thesis, & my peer editor, Joseph O’connor. I would also like to thank Emily Evans, Cecily Mullin, & my parents for all their support.

Figure 1. Relationship between Bd prevalence & air temperature. As air temperature increases, the proportion of infected adults declines. Temperatures higher than 23 °C kills Bd. Sapsford et al, 2013.

• There are over 6,000 amphibian species & one third are listed as endangered or threatened.

• Batrachochytrium dendrobatidis is a fungal pathogen linked to amphibian population declines, perhaps spread globally by the international wildlife trade

• Bd spores live on keratinized areas of the body, causing a thickening of the skin that disrupts cutaneous respiration, the ability to expel excess solutes & eventually lead to death

• The fungus has two life stages: an immobile reproductive stage, & a motile zoospore stage which spread between individuals- the greater the number of zoospores the more severe the infection

• Bd kills many amphibians in a short amount of time, & has been linked to over 200 extinctions including the Panamanian Gold Frog, the Wyoming Frog & the Australian Gastric Brooding frog

• Some species of frogs show an innate immunity to the fungus. Reservoir hosts may to keep the fungus in the environment

• Some infected captive populations have responded well to antifungal or hot water treatment

Figure 2. Australian Gastric Brooding Frog, now extinct. Reproduced from Dailytech.com

Figure 3. Dead Yellow-Legged Mountain Frogs found in the Sierra Nevada Mountains. Photo Credit V. Vredenburg

Figure 5. Prevalence of Bd in each of the four commonly found amphibian species at study sites. L= larvae, M= metamorph, S= sub adult, A=adult. In Rana cascadae, sub adults & adults were affected the most. Sub adults were affected the most across all four species. Piovia-Scott et al, 2011.

Figure 4. (A) Prevalence of Bd infection & moralities at each study site. (B) Mean infection prevalence & mortalities across all sites. (C) Average infection intensity measured in zoospores across all studies sites over winters. Savage et al, 2011.

• Batrachochytrium dendrobatidis has an optimal temperature for growth & viability that averages between 17 & 23 °C with temperatures out of this range substantially slowing the growth or killing the fungus

• Bd has a higher infection intensity on sub adults & adults, most likely due to having more keratinized areas than larvae

• Previously exposed populations can live with low amounts of zoospores without producing lethal affects

• Identification of at-risk species should be made using temperature as the guiding factor so individuals can be collected for safe keeping until populations are able to be reestablished in the wild

• A safe, effective treatment of antifungals should be found & used in wild populations to prevent any further loss

Conclusions & Future Directions