Abstract: To investigate the responses of morphological and physiological characteristics in tadpoles of Pelophylax nigromaculatus to various water levels, a total of 480 tadpoles with similar sizes were treated with rapid, moderate and slow desiccation. Both the metamorphosis duration and average metamorphosis survival rate of specific developmental stages were counted. Their body and internal organ sizes, as well as the responsiveness to phytohemagglutinin (PHA-P) of froglets were measured after complete metamorphosis. The results showed that the metamorphosis duration of tadpoles in the control group was the longest. The average metamorphosis survival rate of different treatment groups ranged from 72.5% to 90.8%, which was the highest in the control group and the lowest in the rapid desiccation group. Body weight (BW) and body length (BL) of froglets in control and slow desiccation groups were significantly higher than those of moderate or rapid desiccation groups. Body width, ratio of BW to BL, carcass wet weight and the wet weight index of lung and fat body were the lowest in rapid desiccation group. There was no significant difference in the wet weight index of heart, spleen, kidneys and digestive organs, as well as the length index of different segments of whole digestive tract between groups. The maximal response value of froglets to PHA-P appeared at 3 h after injection in different treatments, which was significantly higher in moderate and slow desiccation groups than the control group. There was no significant difference between rapid desiccation group and any other groups. The tadpoles of P. nigromaculatus might accelerate the metamorphosis developmental process to cope with desiccation stress, accompanying with decreased atrophic body size and weakened cell-mediated immunity, which would harm tadpoles to successfully land.

Key words: Pelophylax nigromaculatus, drought stress, metamorphosis survival rate, morphological phenotype, internal organ size, phytohemagglutinin