Tetraploid induction in tropical oysters, Crassostrea belcheri (Sowerby) and Crassostrea iredalei (Faustino)

Abstract

Tetraploid induction has been conducted on temperate oysters but not on tropical oysters. In this study, different heat shocks (32, 35 and 38°C) and cold shocks (1, 4 and 7°C) were used to induce tetraploidy in two tropical oyster species, Crassostrea belcheri and Crassostrea iredalei, through meiosis I inhibition. Temperature shocks were applied on the newly fertilized eggs at 8-10 min post fertilization and terminated when second polar bodies began to form in the control eggs. The ploidy of the larvae and spat was determined via direct chromosome count. The percentage of larval survival until Day 20 was low (between 0.4% and 42.9%) for both temperature shocks and oyster species. No surviving larva was recorded for induction at 1, 4 and 38°C. Tetraploid spat was only recorded in C. iredalei but the percentage is low through heat shock induction of 32 and 35°C. This study shows that the tetraploid induction success rate was slightly higher in C. iredalei compared to C. belcheri. No surviving tetraploid spat were recorded for both oyster species through the cold shock method. This study shows that heat shock can be used to inhibit meiosis for the production of tetraploids but more experiments need to be conducted to determine the optimum temperature when dealing with tropical oysters.

Comparative study on tetraploid induction of the Fujian oyster Crassostrea angulata utilizing three typical methods

“…Furthermore, the oysters were carefully selected -the eggs were su ciently round, dark and abundant, and the sperm viability was the best of the best. Combined with the two details mentioned above, this study yielded viable tetraploids using all three methods, which was not achieved by others (Peachey and Allen 2016; Aileen Tan et al 2017).…”

“…The "cell-number defciency" hypothesis illustrated the failure to obtain viable tetraploids through inhibiting diploid fertilized eggs (Guo, 1991;Guo and Allen 1994b), which is predicated on the fact that a tetraploid cell is characterized with twice the nuclear material of a diploid cell. The abnormal nucleus/cytoplasm ratio presented in diploid cells would lead to abnormal mitosis and reduced cell numbers (Piferrer et al 2009; Peachey and Allen 2016; Aileen Tan et al 2017). However, viable and fertile autotetraploid C. gigas were successfully cultivated by the above means Ledu 2007, 2015), and they posited the oocyte size was not a limiting factor for the success of the induction to autotetraploidy.…”

Meiotic Spindle Formation Following Inhibition of First Polar Body Formation in the Zhikong Scallop (Chlamys farreri Jones et Preston)

“…Chromosome manipulation of marine bivalves has received considerable research interest. Following inhibition of polar body 1 (PB1) formation, tetraploids have been reported in Manila clam Ruditapes philippenarum (Li et al, 2017), Pacific abalone Haliotis discus hannai (Arai et al, 1986), American oyster Crassostrea virginica (Stanly et al, 1981), Pacific oyster Crassostrea gigas (Stephens and Dowing, 1988;McCombie et al, 2005), Hong Kong oyster Crassostrea hongkongensis (Qin et al, 2018), pearl oyster Pinctada martensii (He et al, 2000), and other mollusk species (Yamamoto and Sugawara, 1988;Guo and Allen, 1994;Yang et al, 2000a;Tan et al, 2017). When PB1 formation was blocked in C. gigas zygotes, observations of chromosome segregation revealed possible mechanisms of different ploidy formation (Guo et al, 1992).…”