Endemic Lineages of Batrachochytrium dendrobatidis Are Associated With Reduced Chytridiomycosis-Induced Mortality in Amphibians: Evidence From a Meta-Analysis of Experimental Infection Studies.

Anat M Belasen,Kelly R Zamudio,Molly C Bletz,Imani D Russell

doi:10.3389/fvets.2022.756686

Abstract

Emerging infectious wildlife diseases have caused devastating declines, particularly when pathogens have been introduced in naïve host populations. The outcome of disease emergence in any host population will be dictated by a series of factors including pathogen virulence, host susceptibility, and prior opportunity for coevolution between hosts and pathogens. Historical coevolution can lead to increased resistance in hosts and/or reduced virulence in endemic pathogens that allows stable persistence of host and pathogen populations. Adaptive coevolution may also occur on relatively short time scales following introduction of a novel pathogen. Here, we performed a meta-analysis of multi-strain Batrachochytrium dendrobatidis (Bd) infection experiments to test whether: (1) amphibian hosts exhibit lower mortality rates when infected with strains belonging to endemic Bd lineages relative to the Global Panzootic Lineage (Bd-GPL), hypothetically owing to long co-evolutionary histories between endemic Bd lineages and their amphibian hosts; and (2) amphibians exhibit lower mortality rates when infected with local Bd-GPL strains compared with non-local Bd-GPL strains, hypothetically owing to recent selection for tolerance or resistance to local Bd-GPL strains. We found that in a majority of cases, amphibians in endemic Bd treatments experienced reduced mortality relative to those in Bd-GPL treatments. Hosts presumed to have historically coexisted with endemic Bd did not show reduced mortality to Bd-GPL compared with hosts that have not historically coexisted with endemic Bd. Finally, we detected no overall difference in amphibian mortality between local and non-local Bd-GPL treatments. Taken together, our results suggest that long-term historical coexistence is associated with less disease-induced mortality potentially due to hypovirulence in endemic Bd lineages, and that more recent coexistence between amphibians and Bd-GPL has not yet resulted in reduced host susceptibility or pathogen virulence. This corroborates previous findings that Bd-GPL introduced via the global amphibian trade has a high capacity for causing disease-induced mortality.

Highlights

Emerging wildlife diseases pose significant threats to global biodiversity, but the mechanisms by which some hosts are able to survive recently emerged diseases are not yet fully understood [1]
In the Historical Adaptation (HA) analysis, Batrachochytrium dendrobatidis (Bd) genotype was associated with a significantly positive log Risk Ratio according to the interceptonly model, indicating that Bd-GPL infections resulted in higher mortality relative to endemic lineages of Bd (RR = 1.79, Z = 3.99, p < 0.0001; Figure 2)
We found strong support for potential historical adaptation: we detected a significant effect of Bd genotype on Risk Ratio such that endemic Bd lineages on average resulted in reduced mortality relative to Bd-GPL, regardless of whether hosts have historically coexisted with endemic Bd lineages

Summary

Introduction

Emerging wildlife diseases pose significant threats to global biodiversity, but the mechanisms by which some hosts are able to survive recently emerged diseases are not yet fully understood [1]. While contemporary conditions (i.e., local abiotic and biotic environments) may significantly influence host susceptibility [e.g., [5]] and/or pathogen virulence [reviewed in Turner et al [6]], prior interactions between host and pathogen populations may contribute to significant variability in disease outcomes. When the co-evolutionary trajectory between host and pathogen takes the form of a classical oscillating arms race between host resistance and pathogen virulence, different host and pathogen populations may exhibit different levels of resistance and virulence at the same point in time [9]. In these cases, current infection outcomes can vary according to host-pathogen co-evolutionary history, leading to a “geographic mosaic” of disease threat [10]

Methods

Results

Conclusion