Comparative Study On Stress Resistance And Methylation Among The Inbred And Hybrid Offsprings For Chinese And Korea Sea Cucumber(apostichopus Japonicus)

Part one: A comparative study on salinity and high- temperature resistance among the inbred and hybrid offsprings for Chinese sea cucumber and Korea sea cucumberThe Apostichopus japonicus(sea cucumber) is one of the most important aquaculture species in China.In recent years, some problems, such as natural resource depletion,genetic degradation, and frequent diseases outbreak, have hindered the sustainable development of sea cucumber culture in China. Hybridization between different populations is an effective means of breed improvement in aquatic animals.The objective of this research is to determine the temperature and salinity tolerance of inbred and hybrid offsprings of China and Korea Apostichopus japonicus populations.Four hybridized combinations were made using complete dual cross, including C(♀)×C(♂)、K(♀)×K(♂)、K(♀)×C(♂)and C(♀)×K(♂).Four groups of Apostichopus japonicuswere acclimated at 16℃ and 30 psu for one week. In salinity tolerance trials, the salinity of ?-1 to determine the USS(upper critical salinity)and UCS(upper critical salinity)The sea cucumbers were also transferred directly into a series of higher salinity(36, 38, 40, 42, 44psu) and lower salinity(21, 19, 17, 15, 13, 11psu) to measure the USTL(upper salinity tolerance limit), and LSTL(lower salinity tolerance limit).In temperature tolerance trials, temperature tolerances of four groups were estimated by abrupt transferred to seawater with critically high temperature(27, 28, 29, 30, 31℃)or to seawater whose temperature rised 1℃ per hour. The results indicated that LT50(lethal temperature 50)of both the hybrid group were higher than that of Korea sea cucumber, but lower than that of Chinese sea cucumber, 50%UST(lethal temperature of 50% when the water temperature rose gradually)of C(♀)×K(♂)was higher than other three groups.In terms of ULS50, the hybrids were also higher than Korea self-fertilized group.One-way analysis of variance indicated that 50%USS of C(♀)×K(♂)was significantly higher than that of K(♀)×K(♂), however,LLS50(Lower lethal salinity 50)and 50%LSS of K(♀)×C(♂)were the lowest,which were significantly different with those of K(♀)×K(♂).The results suggest that the intraspecies hybrids have moderate heterosis in heat and salinity tolerance,which means that the stress resistance of A. japonicus could be improved effectively by crossbreeding.Part two:A comparative study on nonspecific immunity among the inbred and hybrid offsprings for Chinese sea cucumber and Korea sea cucumber under stressThe main objective of this experimental research was to estimate the immune response of a hybrid of two populations of sea cucumber to stress during transportation. In this research there are four experimental groups, include China sea cucumber♀×China sea cucumber♂(C(♀)×C(♂)),Korea sea cucumber♀×Korea sea cucumber♂(K(♀)×K(♂)),China sea cucumber♀×Korea sea cucumber♂(C(♀)×K(♂)) and Korea sea cucumber♀×China sea cucumber♂(K(♀)×C(♂)). Results show that there were no diference between the initial phagocytic activity of all four group of sea cucumber, although CK>KC>CC>KK. After the stress, it show a significantly down on the phagocytic activity at 1h. similarly, catalase activity and superoxide dismutase activity increased significantly, which of the hybrid were notably higher than the inbreed. The catalase activity of the CK were 27.49% and 24.29% higher than the average value of their parents, while the superoxide dismutase activity 7.78% and 10.56% higher respectively. However after the stress,the lysozyme activity were decreased and the variation trend were the same. Hence, it is an effective way to improve immunity of sea cucumber by crossbreeding.Part three: A comparative study on methylation content among the inbred and hybrid offsprings for Chinese Korea Apostichopus JaponicusChinese sea cucumber(C) and Korea sea cucumber(K) are two kind of geographic population. Four hybridized combinations were made using complete dual cross, including C(♀)×C(♂)?K(♀)×K(♂)?K(♀)×C(♂) and C(♀)×K(♂). To check the methylation levels of four kind of Apostichopus japonicus by methylation sensitive amplification polymorphism(MSAP) used 10 pairs of selective primers?The results show that the methylation levels of C(♀)×C(♂)?K(♀)×K(♂)?K(♀)×C(♂)and C(♀)×K(♂)were 33.4%, 27.6%, 27.1%, 31.6%, and the methylation levels of the hybrids were siglificantly lower than their parents.