Gynogen induction and diploid restoration in the Pacific oyster Crassostrea gigas

• Main Author: Kent, GN
• Format: Thesis
• Language: English
• Published: 2010
• Subjects: Pacific oyster; Oyster culture; Pacific; Crassostrea gigas
• Online Access: https://eprints.utas.edu.au/20761/; https://eprints.utas.edu.au/20761/1/whole_KentGregNeil2010_thesis.pdf

A large proportion of stock improvement in agriculture and more recently aquaculture has come through breeding strategies that work to isolate and fix favourable characters and eliminate undesirable genetic qualities in the target species. The development of homozygous breeding lines, which allow fixing of desirable traits need to be progressed to enhance the effectiveness of breeding strategies. Such lines would also be a valuable research tool for examining genetic versus environmental influence on reproductive biology and stock performance. One potentially rapid and effective method that may produce 100% homozygous individuals is to create what are known as "double-haploids", by suppressing the 1st cell cleavage in haploid zygotes. This project investigated the efficacy of haploid production in the Pacific oyster, Crassostrea gigas, by examining UV irradiation of the paternal DNA, and restoration to the diploid state using the chemicals 6-dimethylaminopurine (6-DMAP) or Cytochalasin B (CB) to suppress either polar body I, polar body II or 1st Cleavage of activated eggs. Additionally, the use of a recessive colour phenotype was examined as a marker to identify parentage of putative gynogen offspring. Sperm Viability via a membrane integrity test ranged between 78-80% viable for controls (no UV exposure) and was significantly greater than all treatment exposures except 60 second low energy exposure (601±22μWcm⁻²s⁻¹), with 300 second high energy exposure (1063±15μWcm⁻²s⁻¹) causing the greatest reduction in sperm viability, ranging between 32-52%. There was no significant difference in egg activation between controls and treatments. In contrast, there was a significant reduction in development of embryos to D larvae with controls averaging approximately 40% development to D stage and the lowest energy treatment (60 seconds @ 601±22μWcm⁻²s⁻¹) averaging a little over 1%. UV radiation of sperm had a significant effect on embryo ploidy levels, with all treatments 180 seconds or longer resulting in less than 20% of ...