Session 53: Amphibian DiseaseRoom: Ballroom 111B2022-07-31 15:30 - 17:00 |
| Moderator: Alessandro Catenazzi |
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1. 15:30 Role of a disease-tolerant species in amplifying transmission of chytridiomycosis in tropical montane frog communities. Alessandro Catenazzi*, Florida International University; Alexander Shepack, University of Notre Dame; David Burkart, Montgomery College; Brandon LaBumbard, University of Massachusetts Boston; M. Isabel Diaz, Universidad Nacional San Antonio Abad de Cusco; Alex Ttito, Universidad Nacional San Antonio Abad de Cusco; Allison Byrne, University of California Berkeley; Sarah Kupferberg, University of California Berkeley; Elena Grasselli, Universita di Genova acatenazzi@gmail.com
Many infectious diseases fade away once the density of susceptible hosts becomes too low to sustain new outbreaks. The amphibian fungal disease chytridiomycosis is remarkable due to its lack of host specificity for infection, but high virulence for some taxa and groups with aquatic reproductive modes. We have worked in montane forests hosting diverse frog communities in the Andes to Amazon region, where chytridiomycosis is associated with the loss of 35% of species at mid to high elevations. Why has chytridiomycosis not disappeared following the extirpation of most of the aquatic breeding species? We studied gladiator treefrogs, Boana gladiator, which are among the few aquatic-breeding species still common in the montane creeks. Using a combination of genomic, analytical, and experimental approaches, we examined how gladiator frogs tolerate chytrid infection, and we hypothesized that disease tolerance may help gladiator frogs amplify transmission to sympatric, susceptible frog species. We found that gladiator frogs might prevent the onset of symptomatic chytridiomycosis and repair skin disturbance with the help of symbiotic skin bacteria and a newly characterized skin peptide. Highly infected gladiator frogs and tadpoles shed zoospores at higher rates than sympatric species, and share the same strain of the global panzootic lineage of chytridiomycosis. Because the range distribution of gladiator treefrogs overlaps with the distribution of many threatened and highly endemic frogs, these tolerant hosts could contribute to the persistence of chytridiomycosis and continuance of detrimental effects on anuran biodiversity. |
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2. 15:45 Assessing the threat of Batrachochytrium dendrobatidis to ranid frogs of the Western US. Anat Belasen*, University of Texas abelasen@utexas.edu
Despite decades of research on the frog-killing fungus Batrachochytrium dendrobatidis (Bd), predicting its impacts on amphibian populations contains to elude researchers and managers. Understanding the drivers of variation in Bd prevalence, infection intensity, and disease outcomes among individuals and populations within the same host species may be key to predicting whether and where disease-related declines will happen. I will present ongoing collaborative research on two western US ranids that exhibit variation in Bd susceptibility: Rana boyliiandR.yavapaiensis. For R. boylii, a large interdisciplinary collaborative effort allowed us to clarify patterns in Bd infections over the past 127 years, across the extant range of the speices (Southern California to Oregon), and in relation to key environmental factors. Our study opens the door for future research on the variation in disease susceptibility across populations of R. boylii, and provides a model for other wide-ranging threatened species. For R. yavapaiensis, a rich body of research suggests that both genetic and environmental factors drive intraspecific variation in susceptibility across the species' extant range (Arizona). Leveraging historical museum collections and molecular methods designed for Ancient DNA, we are evaluating whether historical disease outbreaks are associated with selection on candidate Bd response genes. The goal of these research projects is to improve prediction and mitigation of disease outbreaks in vulnerable wild amphibian populations. |
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3. 16:00 Incorporating Species Susceptibilities and Climate Change into Models of Batrachochytrium salamandivorans Risk in the United States. Matthew Grisnik*, Tennessee State University; Matthew Gray, University of Tennessee; Jonah Piovia-Scott, Washington State University; Davis Carter, University of Tennessee; William Sutton, Tennessee State University grisnikmatt@gmail.com
Worldwide, amphibian populations are threatened by several factors including climate change, habitat destruction, and emerging pathogens. Within emerging pathogens, the fungal pathogen Batrachochytrium salamandivorans (Bsal) has been associated with recent European salamander die-offs. This emerging pathogen has led to increased concern of spread to the United States, which is a world hotspot for salamander diversity. While Bsal has not been detected in the United States, the first step in disease-risk analyses is to predict areas of potential spread of the pathogen. Previous work has attempted to predict the risk of Bsal in the United States, however the effects of climate change on the Bsal niche, as well as the variability in susceptibility of salamander species were not incorporated. The objective of this work was to incorporate variation in salamander susceptibility and changing environmental conditions driven by climate change to create a predictive map of potential Bsal emergence in the United States. To generate this prediction, we used a combination of layers to represent introduction risks, variation in species susceptibility, and climate change driven climatic niche shifts. To model introduction risks we used a combination of distance to wildlife trade and park visitation rates. Species susceptibility and changes in risk due to climate change were modeled using MaxENT and randomforest algorithms to create climatic niche models for all United States salamander species as well as Bsal under current and predicted climatic conditions. These layers were then combined to form a map predicting risk associated with Bsal emergence in the United States. |
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4. 16:15 Disease susceptibility within a reintroduction program: mucosome effectiveness and Bd susceptibility in four species of harlequin toad (Bufonidae: Atelopus). Luke Linhoff*, Smithsonian Conservation Biology Institute & National Zoological Park; Brian Gratwicke, Smithsonian Conservation Biology Institute & National Zoological Park; Roberto Ibañez, Smithsonian Tropical Research Institute linhoffl@si.edu
The Panama Amphibian Rescue and Conservation Project has established captive populations of highly threatened amphibian species that experienced catastrophic declines from the amphibian chytrid fungus. Understanding how much variation in susceptibility to the fungal pathogen exists between species and individuals is useful to understand the potential for adaptation and for mechanistic studies of disease tolerance. Assessing variation of disease susceptibility has typically proved difficult without lethal disease exposure trials. Thus, understanding susceptibility in highly threatened species is problematic due to the rarity and conservation value the animals. Our study utilizes five species of surplus, captive-bred animals (N = 100), including four species of harlequin toad (Bufonidae: Atelopus). An experimental live-pathogen exposure trial was paired with a non-invasive assay of mucosome effectiveness to inhibit the chytrid fungus to correlate predicted to observed disease susceptibility within the animals. We then non-invasively profiled mucosome effectiveness of frogs within the captive breeding program that were not included in the live pathogen trial. We ranked 12 captive species by likely disease susceptibility and explore individual variation of mucosome effectiveness within some individuals. Finally, we are exploring whether observed differences in skin secretion effectiveness are transferred from parent to offspring by comparing effectiveness within known pedigrees of sibling groups. Our results may have broad conservation implications for managing captive amphibian populations. |
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5. 16:30 Hellbender mortality post captive-to-wild translocation involves Bd, but it’s complicated. Rebecca Hardman*, Florida Fish and Wildlife Conservation Commission; Sherri Reinsch, Nashville Zoo at Grassmere; Wesley Sheley, University of Tennessee; Marley Machara, Tennessee State University; Heather Schwartz, Nashville Zoo at Grassmere; Sandy Skeba, Nashville Zoo at Grassmere; Dale McGinnity, Nashville Zoo at Grassmere; Debra Miller, University of Tennessee; William Sutton, Tennessee State University lavalizard17@gmail.com
Hellbenders,Cryptobranchus alleganiensis, are large fully aquatic salamanders found in rivers and streams in the eastern United States. They are declining throughout their range and captive head-starting programs are becoming necessary to augment populations. We implemented the first captive to wild release in Tennessee of zoo-raised adult hellbenders during the summer of 2021. To prevent potential chytridiomycosis due to expected Batrachochytrium dendrobatidis (Bd) exposure in released animals, we placed terbinafine -impregnated slow-release implants subcutaneously in half of individuals. Other factors implemented to reduce stress of release into wild streams included introduction of river water weekly 3 month pre-release, and introduction of the common wild food item, crayfish, 1 month pre- release. All animals were also surgically implanted coloemically with radio transmitters and monitored weekly for movements and signs of disease. Within 6 weeks of release, we observed severe disease and mortality in a majority of individuals. In several individuals, we were able to collect antemortem and/or postmortem samples including skin swabs, blood work, skin peptide washes, and full necropsies with histopathology and pathogen testing. A notable finding was that although terbinafine implants did significantly reduce Bd load they had no effect on disease manifestation or survival. Clinicopathological findings of this syndrome and plans to reduce future disease risk in 2022 releases will be discussed. |