Range expansion to record-breaking elevations influences, but does not eliminate, Batrachochytrium dendrobatidis infections for Andean anurans

Climate change impacts emerging infectious disease events through multiple mechanisms, but the influence it exerts through driving host range shifts has been little explored. For instance, range shifts may affect pathogen transmission by altering the connectivity of host populations. Additionally, range expanding hosts and pathogens will have different physiological responses to the suites of novel, challenging conditions they are exposed to, influencing infection outcomes. We studied the fungal pathogen Batrachochytrium dendrobatidis (Bd) on three anuran amphibians in the Cordillera Vilcanota, Peru: Pleurodema marmoratum, Telmatobius marmoratus, and Rhinella spinulosa. There, these species have undergone a climate-driven range expansion into recently deglaciated habitat to become both the highest elevation amphibians and the highest elevation cases of Bd infection globally. We analyzed Bd genetics, infection metrics, and sublethal impacts along the colonization front (3,900—5,400 m asl) to explore how elevational range expansion affected host-pathogen dynamics. Amphibian range shifts have enabled new connectivity across the once continuously glaciated Cordillera Vilcanota, but genetic evidence suggests that Bd disperses so frequently and extensively that this novel connectivity has not contributed significantly to overall Bd dispersal. Although amphibians have not escaped Bd infection outright through upslope expansion in the Cordillera Vilcanota, Bd growth does appear to be constrained at the highest reaches of the Vilcanota. We present evidence that Bd infection has different sublethal costs for amphibians at the new elevations they have colonized, but whether the costs are mitigated or exacerbated by extreme elevation may be moderated by amphibian microhabitat use.