Immune function is a costly line of defense against parasitism. When infected with a parasite, hosts frequently lose mass due to these costs. However, some infected hosts (e.g. highly resistant individuals) can clear infections with seemingly little fitness losses, but few studies have tested how resistant hosts mitigate these costly immune defenses. We explored this topic using eastern red-backed salamanders Plethodon cinereus and the fungal pathogen Batrachochytrium dendrobatidis (Bd). Bd is generally lethal for amphibians, and stereotypical symptoms of infection include loss in mass and deficits in feeding. However, individuals of P. cinereus can clear their Bd infections with seemingly few fitness costs. We conducted an experiment in which we repeatedly observed the feeding activity of Bd-infected and non-infected salamanders. We found that Bd-infected salamanders generally increased their feeding activity compared to non-infected salamanders. The fact that we did not observe any differences in mass change between the treatments suggests that increased feeding might help Bd-infected salamanders minimize the costs of an effective immune response.

Global temperatures and infectious disease outbreaks are simultaneously increasing, but linking climate change and infectious disease to modern extinctions remains difficult. Thethermal mismatch hypothesispredicts that hosts should be vulnerable to disease at temperatures where the performance gap between themselves and parasites is greatest. This framework could be used to identify species at risk from a combination of climate change and disease because it suggests that extinctions should occur when climatic conditions shift from historical baselines. We conducted laboratory experiments and analyses of recent extinctions in the amphibian genusAtelopusto show that species from the coldest environments experienced the greatest disease susceptibility and extinction risk when temperatures rapidly warmed, confirming predictions of thethermal mismatch hypothesis. Our work provides evidence that a modern mass extinction was likely driven by an interaction between climate change and infectious disease.