Disease refuge or ecological trap: location-specific performance of amphibian hotspot shelters

Many terrestrial ectotherms (amphibians, reptiles) select warm retreat sites which may provide opportunities to escape the impacts of pathogens that cannot tolerate high temperatures. Recent research has exploited this mismatch in host-pathogen thermal tolerance by providing sun-heated artificial hotspot shelters to protect endangered frogs from the amphibian chytrid fungus (Batrachochytrium dendrobatridis), which causes the disease chytridiomycosis. Artificial shelters comprised of masonry bricks and small greenhouses allow endangered frogs to stay warm in winter, reducing and clearing chytrid infections and developing resistance to future infection even under cold temperatures. Such shelters can be a valuable tool for conservation in sunny cool weather, but cloudy weather reduces the thermal benefit; and in too-cool conditions the warming creates a thermal regime where chytrid could grow faster. We monitored temperatures inside hotspot shelters constructed at two sites in Australia over winter: one in a cool semi-arid climate (Werribee, Victoria, Australia), and one in a humid subtropical climate (Sydney, NSW, Australia), to evaluate the thermal performance of shelters in different chytrid-impacted climates. Our monitoring of temperatures inside hotspot shelters found minor-to-negative outcomes at the cooler site, with shelters in Werribee exceeding 25°C for at least 1 h on only 13.1% of days, compared to 82.5% of days at the Sydney site. Hotspot shelters have great potential for frog conservation, but they are not a panacea because diversity in habitat conditions and target species responses will influence their success.