1. Climate Change Expected to Increase Pathogen Invasibility in Asia
Laurence Henson, Raul Figueroa, Vance T. Vredenburg
Department of Biology, San Francisco State University, San Francisco, CA, USA, 94132
Results
Introduction
Changing environmental conditions (e.g. temperature, precipitation, etc.) caused by climate change may affect species in subtle ways. For instance, amphibians, threatened worldwide (Matthews, 2003) may become immunocompromised when exposed to temperature ranges beyond their native habitat, or some species may benefit by changes in temperature by expanding the future possible range of suitable habitat. Introduced worldwide, the American Bullfrog (Rana (Lithobates) catesbeiana) is a potential carrier of the deadly pathogenic fungus (Daszak, et al. 2004), Batrachochytrium dendrobatidis (Bd), which causes amphibian chytridiomycosis, a disease linked to hundreds of amphibian extinctions globally (Olson, et al. 2013). We propose that future climate change scenarios (i.e. temperature increases) may help both increase the future distribution of the invasive American bullfrog and pose a serious threat to native amphibian hosts, which may already by stressed by climate change. We chose to focus on Asia due to its unique Bd dynamics, specifically the lack of Bd epizootics compared to other continents (Swei et al. 2011).
Discussion
If American bullfrogs are efficient spreaders of Bd, these results indicate an increasing threat of Bd exposure to native species in South Korea as well as other areas in Asia. We believe that habitat suitability models can help to better predict the future distribution of invasive species like the American bullfrog and may also help predict areas most vulnerable to Bd invasions. This approach may help focus conservation efforts to the most vulnerable geographic areas. However, there is still a need to survey these regions and collect specimen data.
***Some studies have shown that R. catesbeiana could contain low infection levels might not be picked up by PCR analysis, but could still spread Bd to susceptible amphibian species. (Greenspan)
****Using GIS to predict the effects of frog trade on the distribution of R. catesbeiana and the Bd infection levels could provide less accurate results. (Hanselmann)
Future Directions
Collect data from field samples to determine current Bd prevalence in regions of high R. catesbeiana suitability.
Check historical records for any signs of Bd prevalence in South Korea and Japan.
Identify all Bd susceptible species in South Korea and Japan that were predicted to have an increase in overlap with R. catesbeiana in 2050.
Collect swab samples from live specimen in South Korea and Japan and determine Bd infection intensity in the various susceptible amphibian species in this region.
Compare Bd infection intensity collected from live specimen to the predicted species occurrence of R. catesbeiana.
Fig. 1 R. catesbeiana Asia Habitat Suitability Model (2000)
Predicted distribution of R. catesbeiana in the year 2000 based on climate models from DIVA-GIS and museum samples from the HerpNet database.
Fig. 2 R. catesbeiana Asia Habitat Suitability Model (2050)
Predicted distribution of R. catesbeiana in the year 2050 based on climate models from DIVA-GIS and museum samples from the HerpNet database.
Methods
Study Design:
We used DIVA-GIS to build habitat suitability models (HSM) for the American bullfrog and Bd susceptible native amphibians based on present (2000's) and future (2050) climate conditions.
We then used QGIS to calculate the percent change in overlap between possible range of American bullfrogs and native amphibians based on the possible changes in distribution predicted by our HSMs. 
Using current climate change models from DIVA-GIS, global museum samples were taken from Berkeley Maps and extrapolated to Asia to map the current and potential distribution of Rana (Lithobates) catesbeiana by 2050.
Collected latitude, longitude, and elevation data from 1783 global museum specimens recorded in Berkeley Mapper and used presence data to create species occurrence maps of R. catesbeiana in DIVA-GIS based on climate change models in the year 2000 and (2.5 kilometers per unit scale)
Independent Variables:
Additional variables introduced in distribution map
Annual mean temperature
Temperature seasonality
Mean monthly temperature range
Min/ Max temperature of coldest/ warmest month
Annual precipitation
Precipitation variation per season
Humidity range
Elevation
GIS:
Used QGIS to create difference map between species occurrence of all amphibians present in Asia and R. catesbeiana and calculated the percentage of overlap between the species occurrence maps per square kilometer.
Fig. 3 Bd Susceptible Hosts Habitat Suitability Model (2000)
Predicted distribution of Bd susceptible amphibians in the year 2000 based on climate models from DIVA-GIS and museum samples from the HerpNet database.
Fig. 4 Bd Sucetible Hosts Asia Habitat Suitability Model (2050)
Predicted distribution of Bd susceptible amphibians in the year 2000 based on climate models from DIVA-GIS and museum samples from the HerpNet database.
Literature Cited
AmphibiaWeb: Information on amphibian biology and conservation. [web application] Berkeley, California: AmphibiaWeb. Available: 
Daszak, et al. (2004). Experimental Evidence that the Bullfrog (Rana catesbeiana) is a Potential Carrier of Chytridiomycosis, An Emerging Fungal Disease of Amphibians. Journal of Herpetology. Vol. 14:
Forero-Medina, German., Joppa, Lucas., Pimm, Stuart L. (2010). Constraints to Species’ Elevational Change as Climate Changes. Conservation Biology. Vol 25 (1):
Greenspan, et al. (2012). Transmission of Batrachochytrium Dendrobatidis to Wood Frogs (Lithobates Sylvaticus) via a Bullfrog (L. catesbeianus) Vector. Journal of Wildlife Diseases: July 2012, Vol. 48, No. 3, pp
Goka, et al (2009). Amphibian chytridiomycosis in Japan: distribution, haplotypes and possible route of entry into Japan. Molecular Ecology. Vol 18 (23):
Hanselmann, et al. (2004). Presence of an emerging pathogen of amphibians in introduced bullfrogs Rana catesbeiana in Venezuela. Journal of Biological Conservation. Vol. 120:
Hijmans R, Guarino L., Cruz M, and Rojas E: Computer tools for spatial analysis of climate change geospatial data: 1. DIVA-GIS.
Matthews, Kathleen. (2003). Response of Mountain Yellow-Legged Frogs, Rana muscosa, to Short Distance Translocation. Journal of Herpetology. Vol. 37 (3):
Olson, Deanna H., Aanensen, David M., Ronnenberg, Kathryn L., et al. (2013). Mapping the Global Emergence of Batrachochytridium Dendrobatidis, the Amphibian Chytrid Fungus. Public Library of Science. Vol 8 (2): e56802.
QGIS Development Team, QGIS Geographic Information System. Open Source Geospatial Foundation Project. 
Rodder, D., Schulte, U., Toledo, L. F. (2013). High environmental niche overlap between the fungus Batrachochytridium dendrobatidis and invasive bull frogs (Lothobates catesbeianus) enhance the potential of disease transmission in the Americas. North-Western Journal of Zoology. Vol 9 (1):
Rowley, et al. (2010). Impending conservation crisis for Southeast Asian amphibians. Biology Letters. Vol. 6 (3):
Schloegel, et al. (2009). Magnitude of US trade in amphibians and presence of Batrachochytrium dendrobatidis and ranavirus infection in imported North American bullfrogs (Rana catesbeiana). Journal of Biological Conservation. Vol. 142:
Swei, Andrea., Rowley, J. L., Rodder, Dennis., et al. (2011). Is Chytridiomycosis an Emerging Infectious Disease in Asia? Public Library of Science. Vol 6 (8): e23179.
Data were obtained from records held in the following institutions and accessed through the HerpNET data portal ( on 15 October 2013: California Academy of Sciences, San Francisco; Museum of Vertebrate Zoology, University of California, Berkeley.
Region 3
Region 2
Region 1
Fig. 6 Percent Change in R. catesbeiana overlap by 2050
Fig. 5 Difference Model for the Change in Distribution Overlap in 2050
Predicted result of climate change on the distribution patterns of amphibians in Asia. Difference model shows the overall change in overlap between the distribution of invasive Bd carrier R. catesbeiana and Bd susceptible amphibians (such as Rana muscosa) by the year 2050.
Areas in Red denote a net gain in overlap between predicted distribution patterns, Blue areas denote a net loss in overlap, and Green areas denote a lack of presence data.
Results:
For the American bullfrog, we found an increase in predicted habitat suitability in higher elevation areas in general with the biggest changes predicted in Japan, Korea, China, and India (Fig. 1-2). We also found that the ranges of native species would be affected (Fig 3-4). The difference between the present and future (2050) distributional overlap of the American bullfrog and native amphibians is predicted to increase by 61.4% (per Km2) in South Korea, 9.4% in Japan, and to decrease by 1% in China.
Acknowledgements
The National Science Foundation (VTV # ), the Center for Mathematics and Science Education at San Francisco State University, and the Climate Change Scholars Program (NSF # ).
Dr. Tendai Chitwere, Dr. Jamie Chan, and Danny Chau for their continued support and feedback of our work throughout this semester.