Abstract
BackgroundEmerging infectious diseases (EIDs) are contributing to species die-offs worldwide. We can better understand EIDs by using ecological approaches to study pathogen biology. For example, pathogens are exposed to variable temperatures across daily, seasonal, and annual scales. Exposure to temperature fluctuations may reduce pathogen growth and reproduction, which could affect pathogen virulence, transmission, and environmental persistence with implications for disease. We examined the effect of a variable thermal environment on reproductive life history traits of the fungal pathogen Batrachochytrium dendrobatidis (Bd). Bd causes chytridiomycosis, an emerging infectious disease of amphibians. As a pathogen of ectothermic hosts, Bd can be exposed to large temperature fluctuations in nature. To determine the effect of fluctuating temperatures on Bd growth and reproduction, we collected temperature data from breeding pools of the Yosemite toad (Anaxyrus canorus), a federally threatened species that is susceptible to chytridiomycosis. We cultured Bd under a daily fluctuating temperature regime that simulated Yosemite toad breeding pool temperatures and measured Bd growth, reproduction, fecundity, and viability.ResultsWe observed decreased Bd growth and reproduction in a diurnally fluctuating thermal environment as compared to cultures grown at constant temperatures within the optimal Bd thermal range. We also found that Bd exhibits temperature-induced trade-offs under constant low and constant high temperature conditions.ConclusionsOur results provide novel insights on variable responses of Bd to dynamic thermal conditions and highlight the importance of incorporating realistic temperature fluctuations into investigations of pathogen ecology and EIDs.
Highlights
Emerging infectious diseases (EIDs) are contributing to species die-offs worldwide
Optical density growth measurements We quantified total culture growth over time by measuring culture optical density (OD490; [51, 59, 60]), and we compared the effects of temperature treatments on Batrachochytrium dendrobatidis (Bd) growth by fitting three-parameter logistic growth curves to OD490 measurements using a nonlinear mixed effects modeling approach [49]
Bd cultures grown at 7.5 °C, 17.5 °C, 27.5 °C, or a daily fluctuating temperature profile differed in time to and productivity at peak zoospore release (Fig. 2b; analysis of variance (ANOVA), df = 3, F = 42.2, P < 0.001)
Summary
Emerging infectious diseases (EIDs) are contributing to species die-offs worldwide. We can better understand EIDs by using ecological approaches to study pathogen biology. We examined the effect of a variable thermal environment on reproductive life history traits of the fungal pathogen Batrachochytrium dendrobatidis (Bd). To understand the drivers of EIDs, the rapidly developing field of disease ecology integrates traditional approaches of parasite biology into ecological and Lindauer et al BMC Ecol (2020) 20:18 virulence [38], understanding the responses of these life history traits to thermal heterogeneity may reveal important patterns in infectious disease. Zoosporangia produce the generation of zoospores and release them into the environment or back onto the amphibian host [6, 35] This life cycle requires temperatures between approximately 2–27 °C in vitro, with an optimal temperature range between 15 and 25 °C and a drop in reproduction and viability above 27 °C [51, 66, 73, 78]. Because increases in Bd loads correlate with the severity of chytridiomycosis [72, 74], exposure to temperatures above the Bd thermal maximum that negatively affect Bd growth and reproduction may decrease infection intensities and slow disease progression [23, 26, 62]
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