Effects of urea on behavior and functional traits of Asiatic toad (Bufo gargarizans) tadpoles
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.
KeywordsFertilizers Mosquito fish cues Activity levels Anti-predator behavior Functional traits Intraspecific trait variability
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.
- Anholt B, Negovetic S, Rauter C, Som C (2005) Predator complement determines the relative success of tadpoles of the Rana esculenta complex. Evol Ecol Res 7:733–741Google Scholar
- Burgett A, Wright C, Smith G, Fortune D (2007) Impact of ammonium nitrate on Wood Frog (Rana sylvatic) tadpoles: effects on survivorship and behavior. Herpetol Conserv Biol 2:29–34Google Scholar
- Davidson AM, Jennions M, Nicotra AB (2011) Do invasive species show higher phenotypic plasticity than native species and if so, is it adaptive? A meta-analysis: invasive species have higher phenotypic plasticity. Ecol Lett 14:419–431. https://doi.org/10.1111/j.1461-0248.2011.01596.x CrossRefPubMedGoogle Scholar
- Gallie JA, Mumme RL, Wissinger SA (2001) Experience has no effect on the development of chemosensory recognition of predators by tadpoles of the American toad, Bufo americanus. Herpetologica 57:376–383Google Scholar
- Gosner KL (1960) A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183–190Google Scholar
- Hamer A, Lane S, Mahony M (2002) The role of introduced mosquitofish (Gambusia holbrooki) in excluding the native green and golden bell frog (Litoria aurea) from original habitats in south-eastern Australia. Oecologia 132:445–452. https://doi.org/10.1007/s00442-002-0968-7 CrossRefPubMedGoogle Scholar
- IUCN (2016) IUCN red list of threatened species. http://www.iucnredlist.org/initiatives/amphibians
- Ji X, Zheng S, Lu Y, Liao Y (2006) Dynamics of floodwater nitrogen and its runoff loss, urea and controlled release nitrogen fertilizer application regulation in rice. Sci Agric Sin 39:2521–2530 (in Chinese with English abstract) Google Scholar
- R development Core Team (2011) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org/
- Relyea RA (2001) Morphological and behavioral plasticity of larval anurans in response to different predators. Ecology 82:523–540. https://doi.org/10.1890/0012-9658(2001)082%5b0523:MABPOL%5d2.0.CO;2 CrossRefGoogle Scholar
- Trenkel ME (2010) Slow-and controlled-release and stabilized fertilizers: an option for enhancing nutrient use efficiency in agriculture. IFA, International Fertilizer Industry Association, ParisGoogle Scholar
- Wang Q, Yang J, Chen J et al (2004) Dynamics of three kinds of nitrogen in surface water of rice field with an independent irrigation system. Chin J Appl Ecol 15:1182–1186 (in Chinese with English abstract) Google Scholar