Preparing for invasion: Assessing risk of infection by chytrid fungi in southeastern plethodontid salamanders

Abstract

Understanding the responses of naïve communities to the invasion of multihost pathogens requires accurate estimates of susceptibility across taxa. In the Americas, the likely emergence of a second amphibian pathogenic fungus (Batrachochytrium salamandrivorans, Bsal) calls for new ways of prioritizing disease mitigation among species due to the high diversity of naïve hosts with priorB. dendrobatidis(Bd) infections. Here, we applied the concept of pathogenic potential to quantify the virulence of chytrid fungi on naïve amphibians and evaluate species for conservation efforts in the event of an outbreak. The benefit of this measure is that it combines and summarizes the variation in disease effects into a single numerical index, allowing for comparisons across species, populations or groups of individuals that may inherently exhibit differences in susceptibility. As a proof of concept, we obtained standardized responses of disease severity by performing experimental infections withBsalon five plethodontid salamanders from southeastern United States. Four out of five species carried natural infections ofBdat the start of the experiments. We showed thatBsalexhibited its highest value of pathogenic potential in a species that is already declining (Desmognathus auriculatus). We find that this index provides additional information beyond the standard measures of disease prevalence, intensity, and mortality, because it leveraged these disease parameters within each categorical group. Scientists and practitioners could use this measure to justify research, funding, trade, or conservation measures.

Panzootic chytrid fungus exploits diverse amphibian host environments through plastic infection strategies

“…Infected amphibian skin and in culture transcriptome data. We selected RNA-Seq data from Bd in culture studies (21,22,31,33) and amphibian infection trials (21,22,(28)(29)(30)32,(34)(35)(36)(37) and generated new infection transcriptome data for two amphibian species (see Table S1 for NCBI Short Read Archive accession codes and further information about transcriptome files). Data selection was made based on sequencing strategy (Illumina sequencing technology), experiment day, sequencing coverage, and number of biological replicates.…”

“…Data selection was made based on sequencing strategy (Illumina sequencing technology), experiment day, sequencing coverage, and number of biological replicates. Likewise, new transcriptomes from eleven skin samples of experimentally infected Eleutherodactylus coqui (36) and Desmognathus auriculatus (37) individuals were sequenced on an Illumina NovaSeq 6000 S4 2x150 flow cell after RNA extraction and cDNA library preparation using, respectively, QIAGEN RNeasy® Plus Mini Kit and NEBNext® Ultra™ II Directional RNA Library Prep Kit following manufacturers' protocols. We measured the quantity and quality of the RNA and cDNA libraries using Qubit and Bioanalyzer.…”

Introduction to the special issue: Ecoimmunology in ectotherms

“…In the SI, Friday et al (2020) showed B. salamandrivorans infection in five salamanders species. The authors demonstrated an interspecific variation in the salamanders' survival when exposed to the fungus, from complete survival for Desmognatus apalachicolae, D. conanti , and Eurycea guttolineata , to almost 100% mortality for D. auriculatus and E. cirrigera .…”

“…The authors demonstrated an interspecific variation in the salamanders' survival when exposed to the fungus, from complete survival for Desmognatus apalachicolae, D. conanti , and Eurycea guttolineata , to almost 100% mortality for D. auriculatus and E. cirrigera . Higher mortality was also associated with higher B. salamandrivorans infection intensities in the susceptible species (Friday et al, 2020). Moreover, a co‐infection of Batrachochytrium salamandrivorans and B. dendrobatidis in D. auriculatus was associated with higher mortality, demonstrating that for some salamander species, either or both of these pathogens could drive the species to extinction (Friday et al, 2020).…”

“…Higher mortality was also associated with higher B. salamandrivorans infection intensities in the susceptible species (Friday et al, 2020). Moreover, a co‐infection of Batrachochytrium salamandrivorans and B. dendrobatidis in D. auriculatus was associated with higher mortality, demonstrating that for some salamander species, either or both of these pathogens could drive the species to extinction (Friday et al, 2020). The authors also applied the pathogenic potential to quantify the virulence of chytrid fungi on naive amphibians; this measure's benefit is that it combines and summarizes the variation in disease effects into a single numerical index, allowing for comparisons across species, populations, or groups of individuals that may inherently exhibit differences in susceptibility (Friday et al, 2020).…”