Review
Pulse Heat Stress and Parasitism in a Warming World

https://doi.org/10.1016/j.tree.2020.04.002Get rights and content

Highlights

  • Global change affects ecosystems not only by gradual warming, but also by pulse heat stress events that can occur over shorter timescales.

  • Recent increases in the frequency and magnitude of pulse warming events, coupled with apparent links between parasite transmission and temperature, make it urgent that we understand how pulse heat stress influences parasitism.

  • Pulse and gradual warming affect parasitism in fundamentally different ways, because pulse warming generally occurs on physiological timescales, while gradual warming occurs on evolutionary timescales.

  • We present a framework for understanding the effects of pulse heat stress on the interactions between hosts and parasites.

Infectious disease outbreaks emerged across the globe during the recent 2015–2016 El Niño event, re-igniting research interest in how climate events influence disease dynamics. While the relationship between long-term warming and the transmission of disease-causing parasites has received substantial attention, we do not yet know how pulse heat events – common phenomena in a warming world – will alter parasite transmission. The effects of pulse warming on ecological and evolutionary processes are complex and context dependent, motivating research to understand how climate oscillations drive host health and disease. Here, we develop a framework for evaluating and predicting the effects of pulse warming on parasitic infection. Specifically, we synthesize how pulse heat stress affects hosts, parasites, and the ecological interactions between them.

Section snippets

Rising Tide, Ebbing Tide, or Tsunami? Disease in a Warming World

In 2015 and 2016, an epidemic of Zika virus spread across 31 countries. That outbreak – and upticks in the prevalence of other deadly infectious diseases – was attributed to increased temperatures during the concurrent El Niño event, which decreased incubation time of the Zika virus and increased vector abundance by facilitating mosquito populations [1]. Elevated temperatures may increase or decrease disease transmission (see Glossary), and the amplitude of these changes can vary in response to

Parasitism and Pulse Heat Stress

Pulse warming can increase or decrease parasitism, depending on its effects on host and parasite populations and their interactions, and on dynamic environmental drivers. In 2002, Mouritsen and Poulin [28] thoroughly reviewed the relationship between pulse warming and parasitism as it was understood at the time. Twenty years later, there is now sufficient evidence to synthesize across case studies, draw general conclusions, and to build a framework to organize the mechanisms linking parasite

Impacts of Pulse Warming on Parasites

We begin by considering the parasite’s perspective – that is, by isolating the direct effects of pulse warming on parasite individuals and populations both inside and outside of the host (Figure 2A, ii and iv, Key Figure). The indirect effects are considered below; see Impacts of Pulse Warming on Hosts). Pulse warming can directly alter parasite vital rates, energy expenditures, and virulence. Because these parameters are, in turn, key determinants of parasite abundance and transmission, pulse

Impacts of Pulse Warming on Hosts

In contrast to parasites, hosts can be either endothermic or ectothermic. We expect that responses to pulse warming will vary between endothermic and ectothermic hosts, since ectotherms conform to the ambient temperature (or approximate the ambient temperature, in the case of behavioral thermoregulation), whereas endotherms maintain a relatively consistent internal temperature. Pulse warming can influence host resistance and survival as well as range and habitat use, and thus the direct impacts

Impacts of Pulse Warming on Ecological Interactions and Evolution

Pulse warming can influence ecological interactions by directly influencing parasitism and by altering community structure. Pulse warming can influence individuals and populations of hosts and parasites, but it can also influence the composition of entire communities, with implications for parasite transmission. Parasitism is a vitally important ecological interaction that influences all organisms and is intimately intertwined with ecosystem structure. For example, in tropical reef

Concluding Remarks and Future Perspectives

In light of all the avenues we explore above: should ecologists expect a rising tide, an ebbing tide, or a tsunami of wildlife disease in response to pulse warming events? Considering the current evidence, we conclude that simple predictions are not possible, and that researchers must weigh the effects of warming on their focal hosts, parasites, and corresponding communities to develop predictions for their system. The combination of pulse warming and disease can increase uncertainty in

Acknowledgments

D.C.C. was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award # NA18NWS4620043B. C.L.W. was supported by a grant from the US National Science Foundation (OCE-1829509), a Sloan Research Fellowship from the Alfred P. Sloan Foundation, a UW Innovation Award from the UW President’s Innovation Imperative, and a UW Royalty Research Fund Award.

Glossary

Amplification effect
hypothesis that increasing community species richness causes an increase in the rate of parasite transmission.
Behavioral fever
thermal choice for warmer environments to upregulate immune response.
Behavioral thermoregulation
regulation of body temperature by altering behavior.
Competent host
a host in which a parasite can transmit infection to another susceptible host or vector.
Complex life cycle
parasitic life cycle that involves the sequential use of two or more host species.

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    Twitter: @ClaarDanielle (D.C. Claar).

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