FrogLog 103 PDF here - Amphibian Specialist Group

Diseases and Toxicology
Pathophysiology in Mountain
yellow-legged frogs
(Rana muscosa) during a
chytridiomycosis outbreak
By Jamie Voyles, Vance T. Vredenburg, Tate
S. Tunstall, John M. Parker, Cheryl J. Briggs &
Erica Bree Rosenblum
The disease chytridiomycosis is
one of the causes of catastrophic
declines of amphibians around the world.
Chytridiomycosis is caused by the pathogen
Batrachochytrium dendrobatidis (Bd),
which infects amphibian skin. Although we
have a basic understanding of pathogenesis
from laboratory experiments, many of
the details have not been determined.
Furthermore, it is unknown if disease
development is similar in wild amphibian
populations.
To gain a better understanding of the
pathophysiology in wild amphibian
populations, we collected blood
biochemistry measurements during an
outbreak in Mountain yellow-legged frogs
(Rana muscosa) in the Sierra Nevada
Mountains of California. Chytridiomycosis
has been studied intensively in this system;
Bd was initially detected in a small number
of individuals and then spread within and
Appearance and behavior of Mountain yellow-legged
frogs (Rana muscosa) and during a chytridiomycosis
outbreak in Sixty Lakes Basin, Sierra Nevada
Mountains, California. A) A frog showing clinical signs
of severe chytridiomycosis including abnormal posture.
B) Dead frogs following a chytridiomycosis outbreak in
Milestone Basin. Photo: Vance T. Vredenburg.
46 | FrogLog 20 (4) | Issue number 103 (July 2012)
between populations in a wave-like pattern,
causing mass die-offs in R. muscosa
populations. We collected morphological
and blood biochemistry measurements
during the outbreak in order to 1) better
understand the pathophysiology of
chytridiomycosis; and 2) determine if the
physiological effects observed in laboratory
inoculation experiments are analogous to
disease development in wild amphibians.
We found that pathogen load was
significantly associated with disruptions in
indicators of fluid and electrolyte balance,
such as body mass, protein, hematocrit and
electrolyte concentrations. Yet Bd load was
not associated with indicators of acid-base
balance such as blood pH, carbon dioxide
and bicarbonate. Some of the indicators
of osmotic balance, especially hematocrit,
provided evidence of dehydration in
diseased frogs, which is a new finding in the
study of chytridiomycosis pathophysiology.
Even moderate dehydration in association
with reductions in blood plasma solute
concentrations suggests that frogs with
chytridiomycosis have a more pronounced
loss of electrolytes than previously
estimated.
These findings indicate that disease
development is consistent across multiple
species and in both laboratory and natural
conditions. We recommend integrating
an understanding of chytridiomycosis
pathophysiology with mitigation practices
to improve amphibian conservation.
For example, we suggest that electrolyte
supplementation could be used in
conjunction with antifungal treatments
to reduce the risk of mortality when frogs
are showing clinical signs of disease. The
optimal combination for a particular
species may require additional background
work (e.g. to determine the best treatments
accounting for host life-stage, behavioral
and/or ecological characteristics), but the
application of well-informed treatment
practices is an attainable goal for amphibian
conservation biologists.
J. Voyles et al., PloS ONE 7, e35374
(2012), doi:10.1371/journal.pone.0035374.
Ecophysiology meets conservation:
understanding the role of disease
in amphibian population declines
By Andrew R. Blaustein, Stephanie S. Gervasi,
Pieter T.J. Johnson, Jason T. Hoverman, Lisa K.
Belden, Paul W. Bradley & Gisselle, Y. Xie
Infectious diseases are intimately
associated with the dynamics of
biodiversity. However, the role that
infectious disease plays within ecological
communities is complex. The complex
effects of infectious disease at the scale of
communities and ecosystems are driven by
the interaction between host and pathogen.
Whether or not a given host–pathogen
interaction results in progression from
infection to disease is largely dependent
on the physiological characteristics of the
host within the context of the external
environment. Here, we highlight the
importance of understanding the outcome
of infection and disease in the context of
host ecophysiology using amphibians as
a model system. Amphibians are ideal for
such a discussion because many of their
populations are experiencing declines and
extinctions, with disease as an important
factor implicated in many declines and
extinctions. Exposure to pathogens and
the host’s responses to infection can
be influenced by many factors related
to physiology such as host life history,
immunology, endocrinology, resource
acquisition, behaviour and changing
climates. In our review, we discuss
the relationship between disease and
biodiversity. We highlight the dynamics of
three amphibian host–pathogen systems
that induce different effects on hosts and
life stages and illustrate the complexity of
amphibian – host–parasite systems. We
then review links between environmental
stress, endocrine–immune interactions,
disease and climate change.
A. R. Blaustein et al., Phil. Trans. R. Soc.
Biol. 367, 1688 (2012).
Growth, development and
incidence of deformities in
amphibian larvae exposed as
embryos to naphthenic acid
concentrations detected in the
Canadian oil sands region
By Steven D. Melvin and Vance L. Trudeau
Naphthenic acids (NAs) have been
identified as harmful environmental
contaminants that influence survival,
growth and development of wildlife.
Amphibian larvae are particularly
susceptible to waterborne contaminants,
but little information exists regarding
exposure of amphibian embryos or
tadpoles to NAs. Our results demonstrate
that embryos of Lithobates pipiens and
Silurana tropicalis exposed to 2-4 mg/l of
a commercial NA blend suffer significant
reductions (32% and 25%, respectively) in
growth and development upon hatching.
Increased incidences of deformities were
observed in exposed individuals of both
species, but were only significant in L.
pipiens. Embryos suffered 100% mortality
following exposure to 6 mg/l NAs, and
narcosis at lower concentrations. LC50