Sierra Nevada Aquatic Research Laboratory

09 Jun, 05 PM - 14 Sep, 05 PM

Disease models suggest that, for generalist diseases, different hosts will have varying efficacy in transmitting diseases due to differences in their susceptibilities to infection and how long and intensely that infection is maintained. Thus, differences in host assemblages in a system should affect the overall prevalence of disease. I will test this theory by quantifying anuran communities in ponds in the Sierra Nevadas and correlating this with patterns of infection of Batrachochytridium dendrobatidis, the amphibian chytrid pathogen, in three species of anurans. I hope to shed light on why Bd causes significant mortality in some populations, but not others. In my research I will test the hypotheses that prevalence of Bd in a community is correlated to the density and reservoir potential of hosts in the pond and high Bd zoospore load in rapidly declining species is correlated with a lower mass/length ratio. Using data from extensive surveys by the California department of fish and game, I will pick four ponds with each of the following compositions: only pacific treefrogs, only western toads, only mountain yellow-legged frogs, pacific treefrogs and western toads, pacific tree frogs and mountain yellow-legged frogs, mountain yellow-legged frogs and western toads and pacific treefrogs, western toads and mountain yellow-legged frogs (for a total of 28 ponds). Ponds will be picked so that abiotic factors (permanence, size, depth and productivity) are as similar as possible. At each site, I will visually count the number of adults of each species present within 2 m of the edge of the pond. This is possible in these sites due to high water clarity and lack of vegetation around the pond edges at these sites. I will then collect thirty adults along a transect and thirty tadpoles of each species and record their mass, snout-vent length (to indicate size) and sex (of adults). To determine the health of individuals I divide the mass and snout-vent length (svl). The ratio of these two measurements is a rough indication of whether an individual is feeding to its potential. Individuals with high zoospore loads and relatively high mass:svl (as compared to the mass:svl of an uninfected individual) will be suspected reservoir hosts, as they shed lots of zoospores, but are not succumbing to an infection. Thus, B. boreas and H. regilla are suspected to have a weaker correlation between zoospore load and mass:svl in comparison to R. muscosa. Infection status will be measured by placing species in water for 30 minutes to induce them to shed zoospores (Hyatt et al. 2007). The water will be filtered and filters will be stored at 4?C and sent to the Storfer lab (Washington State University) for detection of Bd using Taqman realtime PCR (Boyle et al. 2004). This method will allow me to assess both the presence of Bd and the intensity of an infection. All animals will be released alive within two hours of collection. Tadpole density will be measured at each site using the pipe sampling technique (Werner et al. 2007) In addition, ponds will be surveyed for the following abiotic variables, which are known to effect growth of Bd and/or amphibian assemblages: temperature, pH, dissolved oxygen. Since Bd infections tend to increase throughout the summer (Briggs et al. 2005), there is the potential for ponds surveyed at later dates to show stronger infection rates than ponds surveyed earlier. To control for this undesired variable, I will survey ponds at increasingly higher elevations throughout the summer. Since higher elevation ponds thaw later and have breeding later in the season, I can capture the dynamics occurring in ponds during the same phenological period, even though there will be time differences. Ponds will be surveyed twice throughout the summer, in order to capture temporal dynamics. Data will be analyzed to how species composition (presence and abundance) at a site affects zoospore load and the proportion of individuals infected of each species. Abiotic measurements will be tested for any correlation with Bd infection patterns. To test if reservoir hosts have fewer costs of infection, I will analyze the effect of zoospore load on the svl:mass ratio for each species. Precautionary methods Bd is an emerging infectious disease with an unknown distribution and unknown epidemiology in northwestern PA. It is important exhibit caution when moving between sites so as not to increase movement of this or other pathogens between ponds. In order to limit transport of Bd equipment (including waders) will be rinsed in a 10% bleach solution before leaving any site. In addition, equipment will be dried overnight. Three hours in dry conditions will effectively kill zoospores (Johnson, 2003). References Boyle, DG, Boyle, DB, Olsen, V, Morgan, JAT and AD Hyatt. 2004. Rapid quantitative detection of chytridiomycosis Batrachochytrium dendrobatidis) in amphibian samples using real-time Taqman PCR assay. Diseases of Aquatic Organisms 60:141-148. Johnson, Megan. 2003 Working with Batrachochytrium dendrobatidis the amphibian chytrid fungus. Available online at: http://www.jcu.edu.au/school/phtm/PHTM/frogs/protocol/bd-protocols.pdf. Werner, EE, Skelly, DK, Relyea, RA an KL Yurewicz. 2007. Amphibian species richness across environmental gradient. Oikos: 1697-1712.

Visit #14550 @Sierra Nevada Aquatic Research Laboratory

Approved

Under Project # 9567 | Research

Effects of anuran assemblages on Batrachochytridium dendrobatidis dynamics among ponds

graduate_student - University of Pittsburgh

Reservation Members(s)

Maya Groner Jun 9 - Sep 14, 2008 (98 days)
Maya Groner Jun 9 - Sep 14, 2008 (98 days)

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