As one of the important contributors of biodiversity, amphibian populations are declining worldwide. Numerous factors are involved in these declines, one of them being the use of fertilizers in agriculture. This is especially true for tadpoles which can live in the fertilizer-polluted farmland water bodies until metamorphosis. The present study aimed to assess the effects of urea (CH4N2O), as one of the most economical and effective fertilizers, on the anti-predator behavior and intraspecific functional trait variability of Asiatic toad (Bufo gargarizans) tadpoles. Based on published literatures and the field observation of urea concentrations in China, glass beakers with a gradient of urea concentrations (0, 200, 400, 600, and 1200 mg/L) were prepared, with 10 tadpoles placed in each glass beaker. Each treatment was replicated three times. Mosquito fish (Gambusia affinis) cues were used as the predator disturbance, and three main functional traits (body mass, trunk bending shape, and eye position) were selected. Our results revealed that tadpoles activity levels decreased when exposed to urea as well as to mosquito fish cues. However, urea exposure did not alter the anti-predator behaviors of tadpoles. Additionally, we found that increasing urea concentrations might modify some functional traits of tadpoles. Importantly, urea disturbance decreased tadpoles intraspecific functional trait variability. (Functional similarity increased between developmental stages.) Given that functional similarity between developmental stages could potentially increase intraspecific competition, urea could indirectly reduce tadpoles survival by decreasing intraspecific traits variability.
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We thank Dengwei Yang for his help during the experiments. We also thank Jianwei Guo for editing the English. We are grateful to the two anonymous reviewers for their constructive comments that improve the manuscript. This work is supported by the National Key Programme of Research and Development, Ministry of Science and Technology (2016YFC0503200), the National Natural Science Foundation of China (31700353), the State Key Laboratory of Integrated Management of Pest Insects and Rodents (Y752781603), the West Light Foundation of Chinese Academy of Sciences (2016XBZG_XBQNXZ_B_007), the Important Research Project of Chinese Academy of Sciences (KJZG-EW-L13), a CSC (China Scholarship Council) scholarship to ZT and an Innovative Practice Training Program for College Students of Chinese Academy of Sciences to WXy.
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1.CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization and Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of BiologyChinese Academy of SciencesChengduChina
2.State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of ZoologyChinese Academy of SciencesBeijingChina
3.F. S Li Marine Science LaboratoryThe Chinese University of Hong KongShatinHong Kong