1. Effects of Temperature on Batrachochytrium dendrobatidis Infection of
Amphibians
Alyssa Carroll
Department of Biology
Arcadia University
Glenside, PA 19038
Library Investigation
Dr. Christopher Binckley
Abstract
Introduction
Results
Acknowledgements
References
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