Linking Ecology and Epidemiology to Understand Predictors of Multi-Host Responses to an Emerging Pathogen, the Amphibian Chytrid Fungus

Abstract

Variation in host responses to pathogens can have cascading effects on populations and communities when some individuals or groups of individuals display disproportionate vulnerability to infection or differ in their competence to transmit infection. The fungal pathogen, Batrachochytrium dendrobatidis (Bd) has been detected in almost 700 different amphibian species and is implicated in numerous global amphibian population declines. Identifying key hosts in the amphibian-Bd system–those who are at greatest risk or who pose the greatest risk for others–is challenging due in part to many extrinsic environmental factors driving spatiotemporal Bd distribution and context-dependent host responses to Bd in the wild. One way to improve predictive risk models and generate testable mechanistic hypotheses about vulnerability is to complement what we know about the spatial epidemiology of Bd with data collected through comparative experimental studies. We used standardized pathogen challenges to quantify amphibian survival and infection trajectories across 20 post-metamorphic North American species raised from eggs. We then incorporated trait-based models to investigate the predictive power of phylogenetic history, habitat use, and ecological and life history traits in explaining responses to Bd. True frogs (Ranidae) displayed the lowest infection intensities, whereas toads (Bufonidae) generally displayed the greatest levels of mortality after Bd exposure. Affiliation with ephemeral aquatic habitat and breadth of habitat use were strong predictors of vulnerability to and intensity of infection and several other traits including body size, lifespan, age at sexual maturity, and geographic range also appeared in top models explaining host responses to Bd. Several of the species examined are highly understudied with respect to Bd such that this study represents the first experimental susceptibility data. Combining insights gained from experimental studies with observations of landscape-level disease prevalence may help explain current and predict future pathogen dynamics in the Bd system.

A pesticide paradox: fungicides indirectly increase fungal infections

“…, Gervasi et al. ) because the infection disrupts osmotic and electrolyte balance that is controlled by their skin, which can eventually lead to cardiac arrest (Voyles et al. ).…”

Emerging Chytrid Fungal Pathogen, Batrachochytrium Dendrobatidis, in Zoo Amphibians in Thailand

“…The prevalence of infection was quite low compared to the pattern of disease emergence seen in other parts of the world, although a higher prevalence was shown among non-native species of amphibians. The NJ phylogenetic analysis revealed the evolutional lineage of Bd ZFT-CU1 was not closely related with the global panzootic lineage (Bd-GPL), where it is not clear if the difference in clinical manifestation and virulence fi nding may be due to intraspecifi c diversity of Bd lineages [3,23], different amphibian resistance levels or the regional presence of antifungal symbionts [40]. According to Bataille et al (2013), Bd is endemic to Asia as a potentially benign pathogen, and if so then Asian amphibians have probably evolved mechanisms of resistance to or tolerance for at least the local endemic strains of Bd and hence chytridiomycosis.…”

“…An extensive variation in host responses within and among species or even within the same amphibian family has been experimentally documented [15]. Genotypic differences among pathogen isolates can directly affect virulence [22][23].…”

“…The panzootic lineage (Bd-GPL) is globally distributed and appears to be the primary cause of the Bd-driven declines of amphibian populations worldwide [3,[15][16][21][22][23], while the other lineages are less virulent [4,17,[24][25][26]. Several novel Bd genotypes that are deeply divergent from the potentially hypervirulent Bd-GPL are increasingly being described from geographic localities without any reported disease-associated amphibian declines [16,[22][23].…”

“…This may suggest that the complex evolutionary history of Bd contains more novel branches that have yet to be discovered [27]. Understanding what lineage is infecting an individual would enable the refi nement of quarantine and conservation measures [23].…”