Abstract
Rates of growth and reproduction of the pathogens that cause emerging infectious diseases can be affected by local environmental conditions; these conditions can thus influence the strength and nature of disease outbreaks. An understanding of these relationships is important for understanding disease ecology and developing mitigation strategies. Widespread emergence of the fungal disease chytridiomycosis has had devastating effects on amphibian populations. The causative pathogen, Batrachochytriumdendrobatidis (Bd), is sensitive to temperature, but its thermal tolerances are not well studied. We examined the thermal responses of three Bd isolates collected across a latitudinal gradient in eastern Australia. Temperature affected all aspects of Bd growth and reproduction that we measured, in ways that often differed among Bd isolates. Aspects of growth, reproduction, and their relationships to temperature that differed among isolates included upper thermal maxima for growth (26, 27, or 28°C, depending on the isolate), relationships between zoospore production and temperature, and zoospore activity and temperature. Two isolates decreased zoospore production as temperature increased, whereas the third isolate was less fecund overall, but did not show a strong response to temperature until reaching the upper limit of its thermal tolerance. Our results show differentiation in life-history traits among isolates within Australia, suggesting that the pathogen may exhibit local adaptation. An understanding of how environmental temperatures can limit pathogens by constraining fitness will enhance our ability to assess pathogen dynamics in the field, model pathogen spread, and conduct realistic experiments on host susceptibility and disease transmission.
Highlights
Emerging infectious diseases can have devastating effects on wildlife populations [1,2], and in some cases a single disease can drive a species to extinction before the cause is identified or understood [3]
We studied how constant temperatures influence the growth and reproduction in vitro of three different Batrachochytrium dendrobatidis (Bd) isolates collected across a latitudinal gradient to: (a) examine how a range of temperatures influences the growth and reproduction of Bd in vitro, and whether these patterns are consistent across isolates; (b) examine the exact nature of the upper thermal limit to Bd growth, which ceases abruptly between 25°C and 28°C
Most treatments reached the stationary phase by Day 9; cool-temperature treatments (13, 15, 17 and 19°C) developed more slowly, and when the experiment was terminated on Day 14 growth was still occurring at 13°C for New South Wales (NSW) and TAS, and at both 13°C and 15°C for QLD
Summary
Emerging infectious diseases can have devastating effects on wildlife populations [1,2], and in some cases a single disease can drive a species to extinction before the cause is identified or understood [3]. Disease emergence can be caused by human encroachment into wildlife populations, habitat degradation, the global translocation of plants and animals, and ‘spillover’ of pathogens from human and domestic animal populations to local wildlife [2,4]. There is growing concern that climate warming and increasingly variable weather could increase pathogen development, transmission, and host susceptibility [1,4]. Understanding how pathogens respond to their environment and hosts will aid in the development of strategies to mitigate disease in wildlife populations. We do not yet understand the role of climate in disease spread, or even how temperature influences pathogen functional performance [1]
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