Effect of sub-lethal concentrations of urea on the development of endemic arboreal tree frog, Polypedatus cruciger (Amphibia: Racophoridae)

Amphibian decline has become a worldwide problem today. Climate change, UV radiation, diseases, contaminants, and fertilizers could be considered as the main reasons. The present study was carried out to investigate the effect of urea on the survival, growth, behaviour and morphology of the endemic arboreal tree frog Polypedatus cruciger (Anura: Ranidae). First, the Lethal Concentration 50 (LC50) of urea on 10 days old post-hatched tadpoles was determined. After the estimation of LC50, the tadpoles were exposed to three sub-lethal concentrations of urea, namely, 7.0 g/L, 7.5 g/L and 8.2 g/L. The effects were investigated from the age of 10 days until they became adults. The impact of sub-lethal concentrations of urea for the survivals, snout-vent length and weight showed significant differences (p<0.05), and a strong negative correlation existed when compared to the control. The tadpoles were very sensitive to urea as they showed several behavioural changes such as reduction in feeding, growth retardation and inability to grow up to the adult stage. The observed external morphological changes under the laboratory conditions included edema, abdominal lesions, colour change, tail deformations and rupturing of tadpoles. The impact of urea on the amphibians in the field may be severe due to the synergistic effects of different pollutants. This may adversely affect amphibians, as their life stages are associated with the agroecosystems and may cause a severe decline in amphibian fauna in Sri Lanka.