Infection increases vulnerability to climate change via effects on host thermal tolerance

Abstract

Unprecedented global climate change and increasing rates of infectious disease emergence are occurring simultaneously. Infection with emerging pathogens may alter the thermal thresholds of hosts. However, the effects of fungal infection on host thermal limits have not been examined. Moreover, the influence of infections on the heat tolerance of hosts has rarely been investigated within the context of realistic thermal acclimation regimes and potential anthropogenic climate change. We tested for effects of fungal infection on host thermal tolerance in a model system: frogs infected with the chytrid Batrachochytrium dendrobatidis. Infection reduced the critical thermal maxima (CTmax) of hosts by up to ~4 °C. Acclimation to realistic daily heat pulses enhanced thermal tolerance among infected individuals, but the magnitude of the parasitism effect usually exceeded the magnitude of the acclimation effect. In ectotherms, behaviors that elevate body temperature may decrease parasite performance or increase immune function, thereby reducing infection risk or the intensity of existing infections. However, increased heat sensitivity from infections may discourage these protective behaviors, even at temperatures below critical maxima, tipping the balance in favor of the parasite. We conclude that infectious disease could lead to increased uncertainty in estimates of species’ vulnerability to climate change.

Pathogen exposure disrupts an organism's ability to cope with thermal stress

“…In adapting the framework that has previously been used to explore thermal limits across many taxa (Chown et al, ; Sgrò et al, ; Terblanche et al, ), we have highlighted the importance of considering different forms of thermal stress in the context of disease. Previous studies looking at the effect of disease on host thermal limits have focused on static temperature treatments (Gehman et al, ) or a single ramping rate (Greenspan et al, ). Our results show that more acute thermal stress resulted in the largest differences between healthy and infected individuals (both static and fast ramps, Figures and ).…”

“…Missing from the connection between infectious disease and global change is the capacity of pathogen exposure to disrupt a host's ability to cope with extreme environments (Greenspan et al, 2017). Assessing thermal limits has been a mainstay of global change biology (Bennett et al, 2018;Hoffmann, Chown, & Clusella-Trullas, 2012;Klockmann, Günter, & Fischer, 2017;Sunday, Bates, & Dulvy, 2011), but rarely applied to the study of host-pathogen interactions.…”

A review of the role of parasites in the ecology of reptiles and amphibians

“…Green Tree frogs ( Litoria caerulea ) experimentally acclimated to low temperatures had lower infection intensities when exposed to the amphibian chytrid fungus ( B. dendrobatidis) than those acclimated to higher temperatures (Greenspan et al . 2017b). The individuals exposed to sub‐optimal temperature were better able to fight the pathogen because their immune parameters were already adjusted to cope with the challenging environmental conditions.…”

Human-Pathogenic Isolations in Stagnant Water During Peruvian El Niño-Costero Phenomenon

“…Several countries are extremely susceptible to climate change, a phenomenon that not only has been causing irretrievable changes in our biodiversity but is changing the patterns of diseases affecting human health [1]. The greatest consequences for infectious diseases caused by climate change are the rapid modi cations in their transmission nowadays [2].…”