Evaluating the effects of temperature, salinity, starvation and autotomy on molting success, molting interval and expression of ecdysone receptor in early juvenile mud crabs, Scylla paramamosain

Abstract Newly molted first stage juvenile mud crabs (C1), Scylla paramamosain , were subjected to different temperatures (14, 20, 26, 32 and 39 °C), salinity (5, 10, 20, 30 and 40), starvation conditions and autotomy (for the autotomy experiment, the second stage crabs (C2) were used) to assess their effects on molting success, molting interval and corresponding expressions of the crab's ecdysone receptor (EcR). The results showed that at a low temperature of 14 °C no molt occurred with a subdued EcR mRNA level detected. In contrast, a higher temperature of 32 °C induced a significant increase in the expression of EcR gene and dramatically reduced the C1 molting interval as compared to other treatments. As the temperature further increased to 39 °C and after a period of 6 or more hours the expression of EcR gene dropped abruptly and all C1 crabs died without molt. On the other hand, a low salinity of 5 increased EcR mRNA levels at 72 h and shortened the molting interval significantly whilst high salinity of 40 resulted in the opposite. No significant difference in percentage molting success was detected among salinity from 10 to 40. When C1 crabs were subjected to starvation for longer than 48 h, the expression of EcR was found to be significantly repressed as compared to the feeding control, in which none of the starved crabs successfully molted. Meanwhile, although the molting success of C2 crabs was not significantly affected by autotomy, the molting interval significantly increased from 5.8 days for intact crabs to 6.2 days for the autotomized crabs. Interestingly, when compared to intact crabs, the expression level of EcR gene in autotomized crabs was at first repressed (i.e. during the first 120 h) but increased sharply to a level significantly higher than the control at 134 h (i.e. during premolt stage of the autotomized crabs). Our results showed that temperature, salinity, starvation and autotomy all affected molting of early juvenile mud crabs and changes in their EcR mRNA levels appeared to play an important role in regulating the molting process. The current experiment also showed that S. paramamosain early juveniles could withstand a broad range of temperatures and salinity, therefore highlighting their adaptability to the seasonal variation in salinity and temperature of natural habitat.