长牡蛎(Crassostrea gigas)与熊本牡蛎(C. sikamea)杂交的受精细胞学观察及子一代的生长比较

CYTOLOGICAL OBSERVATIONS OF NUCLEAR BEHAVIOR AND COMPARATIVE GROWTH OF THE HYBRIDS BETWEEN CRASSOSTREA GIGAS AND C. SIKAMEA

以长牡蛎和熊本牡蛎为材料,进行了4个组合的杂交和自交实验。利用DAPI染色观察了长牡蛎和熊本牡蛎正反杂交的受精卵在受精,减数分裂和早期卵裂过程中的核相变化。结果表明,在长牡蛎♀×熊本牡蛎♂正交组,熊本牡蛎精子进入长牡蛎卵子后,激活卵子完成2次减数分裂,同时,精核出现了两次明显的体积膨大扩散过程。但是,大部分受精卵不再继续进行胚胎发育。在熊本牡蛎♀×长牡蛎♂反交组中,受精卵内核行为的变化与正交组相同。正反交组的胚胎发育过程都具有明显的不同步现象。对各实验组子一代的生长和存活的研究结果表明,幼虫阶段,杂交后代的壳高、壳长均明显小于自交组;长牡蛎♀×长牡蛎♂自交组(GG)和熊本牡蛎♀×长牡蛎♂杂交组(SG)的存活率高于长牡蛎♀×熊本牡蛎♂杂交组(GS)和熊本牡蛎♀×熊本牡蛎♂自交组(SS)。稚贝和成贝阶段,杂交组子一代在壳高、壳长和存活率3个生长指标上均小于自交组。

We investigated interspecific hybridization between two cupped oysters Crassostrea gigas and C. sikamea, and observed nuclear behavior during meiosis and early development under a fluorescence microscope with DAPI stain. We found that, following the incorporation of C. sikamea sperms, the eggs of C. gigas initiated the resumption of meiotic maturation. During the meiotic process of the maternal chromosomes, sperm nuclei enlarged at two distinct phases. Sperm nuclei underwent a rapid, initial enlargement during metaphase I, but condensed slightly during polar body formation, and re-enlarged during female pronuclear development. Similar phenomena were also seen in the hybrid cross between female C. sikamea and male C. gigas. Asynchronism of egg development was remarkable in the two reciprocal hybrid crosses. In the hybrid cross between female C. gigas and male C. sikamea, after the incorporation of sperm into the egg cytoplasm, most eggs did not resume the meiotic maturation. Growth and survival rates at larval, juvenile and adult stages were compared between two reciprocal hybrid crosses （G ♀×S ♂, GS and S ♀×G♂, SG） and two parental groups （G ♀×G ♂, GG and S ♀×S♂, SS）, respectively. Larval growths of hybrid crosses were inferior to those of the parental groups. The larval survival rates of GG and SG crosses were superior to those of GS and SS crosses. The growth and survival at juvenile and adult stages of hybrid cross were inferior to those of the parental groups, showing no heterosis in the characteristics of shell height, shell length and survival for the hybrid crosses between C. gigas and C. sikamea.