Age-dependent effects of developmental experience on morphology, performance, dispersal and survival in a translocated, endangered species.
While ex situ breeding programs are critical tools for species recovery, translocations using animals reared under human care can face low success rates, often related to increased dispersal and reduced survival. These issues may be related to a mismatch between ex situ environments and natural habitats. Natal habitat preference induction, wherein individuals seek out habitat similar to that they experienced during development, may provide one explanation for this phenomenon. While exposure to naturalistic environments and pre-release training can mitigate these issues, there may be developmental windows within which these sorts of experiences are most transformative. We characterized the impacts of environmental experience at different developmental stages on morphology, performance and post-translocation dispersal and survival in the endangered mountain yellow-legged frog Rana muscosa. We exposed frogs of different ages (N = 146 one-year-olds, hereafter juveniles; N = 110 two-year-olds, hereafter subadults) to different water flow regimes to mimic stream conditions of reintroduction sites. We measured morphology and swimming performance before and after treatment. Frogs were translocated into the wild and monitored to collect data on movement and survival. Stream experience resulted in significantly longer proportional limb lengths and improved swimming performance for juvenile but not subadult frogs. After translocation, stream experienced subadults exhibited significantly lower post-release movement than control subadults. There was no effect of treatment on juvenile movement, which was significantly higher than in subadults. Stream experience significantly boosted apparent survival for juveniles but not subadults, but subadults exhibited higher survival overall. Synthesis and applications. Our results suggest that early-life experience with naturalistic conditions in ex situ facilities can significantly impact morphology, performance and post-translocation movement and survival, and that the effects are age dependent. Pre-release training is a vital component of conservation translocations, including for herpetofauna, which are increasingly involved in translocations and are sometimes considered more 'hard-wired'. We recommend that practitioners consider a broader array of survival skills and tailor pre-release treatments to specific developmental windows. Providing critical experiences during development and releasing younger animals better prepared for life in the wild may be cost-effective recovery strategies.