American Society of Naturalists

Laura Ferguson and Brent Sinclair (Apr 2020)

Crickets show that predicting disease under climate change may be less complicated than we feared

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It’s hard enough to predict the effects of climate change on one species, but nature is full of complicated interactions between organisms and their pathogens. Even worse, although most experiments are done under constant temperatures, we know that temperatures fluctuate in the real world. Put these together, and the future of disease in a changing world appears impossibly complicated. To explore this complexity, Dr. Laura Ferguson, then a PhD student at Western University in Canada, and her supervisor, Dr. Brent Sinclair, infected spring field crickets with a pathogenic fungus under various thermal regimes. They found that both the crickets and the fungus were sensitive to temperature, and the thermal history of each player could impact their relative success during infection. Crickets used to fluctuating temperatures were better at fighting fungi than their warm counterparts, but fungi from the cold were generally better at killing crickets. Further, when the temperature fluctuated between day and night during infection, the outcome was markedly different from infections under more artificial, constant temperature regimes. But did a simple change to a more ecologically realistic temperature pattern make it impossible to predict the outcome of an infection? Remarkably, Ferguson and Sinclair found that they could easily predict the outcome of infections under the fluctuating temperatures by averaging the number of cricket deaths under constant warm or cold temperatures. Thus, although fluctuating temperatures must be accounted for when we predict future infection dynamics, it may be possible to make these predictions using simple experiments at constant temperatures. Although we have yet to determine how generalizable this predictability might be, these results suggest that understanding how temperature affects infection dynamics and disease under climate change is within our grasp.

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Abstract

Variable, changing, climates may affect each participant in a biotic interaction differently. We explored the effects of temperature and plasticity on the outcome of a host-pathogen interaction to try to predict the outcomes of infection under fluctuating temperatures. We infected Gryllus veletis crickets with the entomopathogenic fungus Metarhizium brunneum under constant (6°C, 12°C, 18°C or 25°C) or fluctuating temperatures (6°C to 18°C or 6°C to 25°C). We also acclimated crickets and fungi to constant or fluctuating conditions. Crickets acclimated to fluctuating conditions survived best under constant conditions if paired with warm-acclimated fungus. Overall, matches and mismatches in thermal performance, driven by acclimation, determined host survival. Mismatched performance also determined differences in survival under different fluctuating thermal regimes: crickets survived best when fluctuating temperatures favored their performance (6°C to 25°C), compared to fluctuations that favored fungus performance (6°C to 18°C). Thus, we could predict the outcome of infection under fluctuating temperatures by averaging relative host-pathogen performance under constant temperatures, suggesting that it may be possible to predict responses to fluctuating temperatures for at least some biotic interactions.