Jack Taylor Orford, Hung Tan, Jake M Martin, Bob B M Wong, Lesley Ann Alton

Amphibians are the most threatened vertebrate class globally, with many species at risk of extinction. Multiple factors have been implicated in the global decline of amphibian populations, and it has been hypothesised that interactions between these stressors may be responsible for such rapid declines. Increased ultraviolet (UV) radiation as a result of ozone depletion has been identified as one such stressor. Exposure to UV radiation has been shown to have detrimental effects on amphibian survival, development, and behaviour. UV radiation has also been shown to exacerbate the effects of other stressors, such as chemical pollutants. Chemical pollution has been recognised as another major factor contributing to amphibian declines, particularly, endocrine-disrupting chemicals. 17β-trenbolone is a potent anabolic steroid used in the agricultural industry to increase muscle mass in cattle, and has been repeatedly detected in the environment where amphibians live and breed. At high concentrations, 17β-trenbolone exposure has been shown to impact amphibian survival and gonadal development. In the present study, we investigated the effects of one-month exposure to environmentally realistic levels of UV radiation and 17β-trenbolone, both in isolation and in combination, on the morphology and behaviour of spotted marsh frog tadpoles (Limnodynastes tasmaniensis). We found that neither stressor in isolation affected the morphology or behaviour of tadpoles, nor did we find any interactive effects. The results from our 17β-trenbolone treatment are consistent with recent research suggesting that, at environmentally realistic concentrations, tadpoles may be less vulnerable to this pollutant compared to other vertebrate classes (e.g. fish). The absence of UV radiation-induced effects found in this study could be due to species-specific variation in susceptibility to UV radiation, as well as the UV dosage utilised in the present study. We suggest future research incorporates long-term studies using multiple stressors at environmentally realistic levels to accurately identify the threats, and subsequent consequences, that amphibians face in natural conditions.