2020 ESA Annual Meeting (August 3 - 6)

COS 151 Abstract - American Bullfrogs (Lithobates catesbeianus) as disease reservoirs in Vermont and Brazilian amphibian communities

Lauren Ash1, Karla M. Campião2, Cauê P. Teixeira2 and Nicholas J. Gotelli1, (1)Biology, University of Vermont, Burlington, VT, (2)Zoology, Univerisade Federal do Paraná, Curitiba, Brazil
Background/Question/Methods

Ranavirus has the capability of causing sudden, mass amphibian mortality events; yet, its factors are not entirely understood, especially in areas where diversity and endemism are highest. The Atlantic Forest of Brazil is one such area; however, neither amphibian diversity nor amphibian pathogens are well-characterized. Ranaviruses have been documented in low prevalences across Vermont; however, American Bullfrog (Lithobates catesbeianus) populations have exhibited increased ranavirus prevalence, with individuals retaining high amounts of virus. Although native to the eastern United States, L. catesbeianus are invasive in Brazil and have been suggested as reservoirs for the chytrid fungus, due to their ability to withstand the onset of disease once infected. Ranaviruses have been detected in Bullfrogs farmed in captive facilities in Brazil, but the goal of this study was to determine whether ranavirus had spread beyond these farms. We further investigated whether these Bullfrogs retained large amounts of virus and whether there was an association between ranavirus and endoparasites. We collected 58 L. catesbeianus individuals in seven sites near the Atlantic Forest. Helminth parasites were extracted from each organ and identified to family level. Liver samples were tested for ranavirus using quantitative PCR to amplify a conserved region in its major capsid protein.

Results/Conclusions

In Vermont, Bullfrog populations had ranavirus prevalences of up to 80%, with tissue samples containing from 60,000 to 2 million viral copies. In Brazil, 3 of 7 L. catesbeianus populations were infected with ranavirus, with prevalences ranging from 10% to 100%. Contrary to Vermont populations, the positive individuals harbored low amounts of virus, with fewer than 200 viral copies. Additionally, although there was no statistical relationship between virus amount and parasite abundance, sites without ranavirus had higher average parasite abundance (p=0.0168). This suggests a potential interaction between ranavirus and helminths, and further studies should be conducted to further explore the relationship and its consequences. We may be observing differences between native and invasive populations if the Brazilian ranavirus is a different strain and not as co-adapted to its invasive host. Additionally, we sampled mostly juvenile Bullfrogs in Vermont, while adults were captured in Brazil. Individuals could harbor high amounts of virus as they metamorphose and are able to survive and retain lower amounts as adults. If virus is being shed into the environment, these low-level infections could amplify disease transmission in native Brazilian anurans, and the Bullfrog invasion poses an even greater threat to Atlantic Forest biodiversity than previously supposed.