Ex situ thermal acclimation alters temperature selection with limited post-release effects in an endangered frog ( Rana muscosa )

Abstract Amphibian declines driven by the fungal pathogen Batrachochytrium dendrobatidis (Bd) pose major challenges for conservation, particularly for cold-adapted species occupying habitats where temperatures may be less limiting to Bd growth. Host thermal behaviour can influence infection dynamics, and thermal environments during developmental stages may shape disease susceptibility and performance. We tested whether exposing endangered mountain yellow-legged frogs (Rana muscosa) to different developmental ex situ thermal treatments prior to a reintroduction event altered selected temperature and post-release habitat use, Bd outcomes and apparent survival. Temperature-selection trials revealed that selected temperature was moderately repeatable among individuals. Contrary to predictions, frogs reared in a high temperature treatment subsequently selected cooler temperatures than frogs reared under standard conditions. After release at a Bd-positive site, high temperature treatment frogs exhibited marginally higher short-term apparent survival. However, survival declined rapidly regardless of treatment and we found no treatment-based differences in microhabitat use or Bd patterns, possibly due to low detection rates in the field. These results demonstrate that R. muscosa shifts selected temperature in response to thermal acclimation during rearing, but that such shifts may not translate to improved establishment in Bd-positive environments. Optimizing reintroduction outcomes for Bd-susceptible amphibians will likely require combining husbandry-based thermal conditioning with complementary Bd mitigation strategies.