Epizootic to enzootic transition of a fungal disease in tropical Andean frogs: Are surviving species still susceptible?

<div><p>The fungal pathogen <i>Batrachochytrium dendrobatidis</i> (Bd), which causes the disease chytridiomycosis, has been linked to catastrophic amphibian declines throughout the world. Amphibians differ in their vulnerability to chytridiomycosis; some species experience epizootics followed by collapse while others exhibit stable host/pathogen dynamics where most amphibian hosts survive in the presence of Bd (e.g., in the enzootic state). Little is known about the factors that drive the transition between the two disease states within a community, or whether populations of species that survived the initial epizootic are stable, yet this information is essential for conservation and theory. Our study focuses on a diverse Peruvian amphibian community that experienced a Bd-caused collapse. We explore host/Bd dynamics of eight surviving species a decade after the mass extinction by using population level disease metrics and Bd-susceptibility trials. We found that three of the eight species continue to be susceptible to Bd, and that their populations are declining. Only one species is growing in numbers and it was non-susceptible in our trials. Our study suggests that some species remain vulnerable to Bd and exhibit ongoing population declines in enzootic systems where Bd-host dynamics are assumed to be stable.</p></div

Variation in Bd infection prevalence for eight species of frogs in the montane forests of Manu National Park, Peru.

<p>Frogs were sampled during the dry season of 2012, approximately a decade after the Bd epizootic caused a collapse of montane amphibian communities.</p

Differences in survival and Bd infection intensity in two species of marsupial frogs <i>Gastrotheca</i> (Hemiphractidae).

<p>(A, B) Percentage survival, and (C, D) variation in log-transformed zoospore equivalents (Bd infection intensity) of Bd-exposed individuals of <i>Gastrotheca excubitor</i> (left panels) and <i>G</i>. <i>nebulanastes</i> (right panel). The shaded band represents the period of daily immersion in itraconazole solution to clear infection, while the shaded box represents the period of experimental exposure to Bd. Red lines represent individuals that died during the trial.</p

Variation in prevalence and intensity of infection (log-transformed zoospore equivalents, ZE) in eight species of tropical montane frogs in the Peruvian Andes during May–October 2012.

<p>Variation in prevalence and intensity of infection (log-transformed zoospore equivalents, ZE) in eight species of tropical montane frogs in the Peruvian Andes during May–October 2012.</p

Differences in survival and Bd infection intensity in two non-susceptible species of terrestrial-breeding frogs, <i>Pristimantis danae</i> and <i>Pristimantis pharangobates</i> (Craugastoridae).

<p>(A, B) Percentage survival, and (C, D) variation in log-transformed zoospore equivalents (Bd infection intensity) of Bd-exposed individuals of <i>Pristimantis danae</i> (left panels) and <i>P</i>. <i>pharangobates</i> (right panel). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186478#pone.0186478.g002" target="_blank">Fig 2</a> for caption details.</p

Differences in survival and Bd infection intensity in two susceptible species of terrestrial-breeding frogs, <i>Pristimantis platydactylus</i> and <i>Pristimantis toftae</i> (Craugastoridae).

<p>(A, B) Percentage survival, and (C, D) variation in log-transformed zoospore equivalents (Bd infection intensity) of Bd-exposed individuals of <i>Pristimantis platydactylus</i> (left panels) and <i>P</i>. <i>toftae</i> (right panel). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0186478#pone.0186478.g002" target="_blank">Fig 2</a> for caption details.</p

Survival analysis for Bd susceptibility trials of eight species of tropical montane forest frogs subjected to control or experimental treatment.

<p>Population ratios are calculated from relative abundances of populations before and after the epizootic using leaf litter plots (plot) and visual encounter surveys (VES) in 1998–1999 and 2008–2009. Treatments with no mortality are indicated with NA’s for <i>P</i>-value and days to death. Population ratios provided are based on visual encounter surveys except for cryptic species that were assessed using leaf litter plot surveys indicated by ^L.</p

CarolFest 2013 December 4, 2013

Concert ProgramCarolFest 2013 December 4, 201