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.