Effects of latitudinal, seasonal, and daily temperature variations on chytrid fungal infections in a North American frog

As human activities alter environmental conditions, the emergence and spread of disease represents an increasing threat to wildlife. Studies that examine how host–pathogen relationships play out across seasons and latitudes can serve as proxies for understanding how natural and anthropogenic changes in climate may influence infection and disease dynamics. Amphibians are ideal host organisms for studying the impacts of climate on disease because they are ectothermic and threatened by chytridiomycosis, a recently emerged and globally important disease caused by fungal pathogens in the genus Batrachochytrium. Previous studies suggest that temperature affects the interaction between amphibians and Batrachochytrium pathogens. However, a clearer understanding of this host–pathogen–environment interaction is needed to predict how the risk of chytridiomycosis will vary in space and time. Here, we investigate how daily, seasonal, and latitudinal variations in temperature affect the incidence and impact of Batrachochytrium dendrobatidis (Bd) infection in a broadly distributed host, the northern cricket frog (Acris crepitans), using a combination of field and laboratory studies. In a four‐year field study conducted at three latitudes, we found that daily maximum air temperature over a 15‐d period prior to sampling best predicted patterns of Bd infection and that the lightest infection loads followed periods when these temperatures exceeded 25°C. In a laboratory exposure experiment, we found pathogen load and mortality to be greater at temperatures that mimic winter temperatures at the southern extent of this host's range than for scenarios that mimic temperature conditions experienced in other areas and seasons. Taken together, our findings suggest that changes in temperature across timescales and latitudes interact to influence the dynamics of infection and disease in temperate amphibians. Many pathogens have life cycles and transmission mechanisms that are temperature‐dependent (Altizer et al. 2013), and the abilities of host organisms to defend themselves against pathogens can be affected by temperature (Butler et al. 2013). As such, global climate change is likely to impact patterns of disease emergence and spread (Rohr and Raffel 2010). The Earth's annual mean surface temperature is projected to increase by 0.3°–4.8°C between 2005 and the year 2100, with concurrent shifts in seasonal and finer‐temporal climate patterns also expected (Stocker et al. 2013). For example, nighttime minimum temperatures are predicted to increase more than daytime maximum