熊本牡蛎中国群体与美国群体杂交效应及杂交三倍体优势分析

Heterosis and triploid advantage between Chinese and American populations of Kumamoto oysters(Crassostrea sikamea)

为了评估熊本牡蛎(Crassostreasikamea)中国群体与美国群体的杂交效应与杂交三倍体优势,构建了杂交群体和自交群体,并使用细胞松弛素B诱导了杂交三倍体,比较分析了幼虫、稚贝与成贝的生长与存活优势。自交群体和杂交群体的幼虫、稚贝与成贝的培养条件均相同,室内培育幼虫,培育密度为4～5个/mL,自然海区养殖稚贝与成贝,养殖密度为40～45个/吊。结果表明,与自交组相比,杂交二倍体具有较高的卵裂率(13.61%)与D幼率(5.67%)(P<0.05),但杂交二倍体幼虫的壳高生长表现杂种劣势(–0.43%),而稚贝、成贝的壳长与壳高的生长表现杂种优势,平均优势率分别为3.96%与6.65%。杂交三倍体诱导组幼虫的壳高生长优势率为3.69%,稚贝及成贝的壳长与壳高平均生长优势率分别为12.69%与13.64%,并且日龄越大生长优势越显著。总体上,杂交三倍体诱导组在3～180日龄具有存活劣势,并且15日龄存活劣势率最大(–48.72%),而在360日龄存活优势率为6.70%。杂交二倍体幼虫与成贝均具有存活优势,平均优势率分别为10.44%与4.59%。本研究表明熊本牡蛎中美地理群体杂交二倍体的生长和存活优于自交二倍体,而杂交三倍体诱导组的生长优势较显著,并且在成贝期具有显著的成活率优势,表明杂交三倍体诱导组的优势来源于三倍体优势和部分杂种优势。

The Kumamoto oyster Crassostrea sikamea (Amemiya, 1928) is mainly distributed in Eastern Asia, from the southern coast of China to Korea and the Ariake Sea of Japan. Compared to other oysters, C. sikamea is known for its flavored meat and firm texture, and it is therefore preferred in commercial markets over other com- mercial oyster species. It has been one of the most important commercial species in the shellfish industry on the west coast of America since the 1950s. In China, the wild population of C. sikamea is abundant and is considered an important wild fishery resource. In our laboratory, two strains of C. sikamea have been developed for artificial hatchery breeding in recent years. Hybridization breeding is one of the important methods for developing a new strain of C. sikamea. Moreover, triploid marine bivalves generally have growth and survival advantages over common diploids. Therefore, hybridization for marine bivalves has gained increasing interest for scientists. In the present study, the hybrid diploids and triploids from two strains of the Chinese population and American popula- tion of C. sikamea were induced to evaluate the hybridization effect and triploid advantage. The conditions for larvae and adult rearing were the same throughout the entire period. The larvae were reared in indoor tanks, with a density of 4 5 individuals per milliliter water. The juveniles were farmed on the sea, with 40 45 individuals per sting of attachment. The results showed that the hybrid diploids had heterosis for cleavage rate (13.61%) and D larvae rate (5.67%) compared to that of the controls, while the larvae of hybrid diploids had negative heterosis for their shell height growth ( 0.43%). However, the juveniles and adults had heterosis of 3.96% and 6.65% for their shell height and shell length, respectively. On the other hand, the hybrid triploids had a growth advantage during the entire period, with high levels of advantage in the late growth stage. The larvae had a growth advantage of 3.69% on average, and the juveniles and adults had an advantage of 12.69% and 13.64% for their shell height and shell length, respectively. The hybrid triploids had negative survival rate from 3 days to 180 days, with a highest value of 48.72% at 15 days. However, a positive survival rate of 6.70% was detected at 360 days. In contrast, the hybrid diploids had a higher survival rate compared to that of the hybrid triploids, with mean survival advantages of 10.44% and 4.59% for the larvae and adults, respectively. The hybrid triploids had a significant growth advan- tage in the entire period and had a positive advantage of survival rate in the adults, suggesting that the advantages of hybrid triploids resulted from triploidy advantage and partial heterosis.