Induction of androgenetic development of the brook charr (Salvelinus fontinalis) × Arctic charr (Salvelinus alpinus) hybrids in eggs derived from the parental species

Failure of interspecific androgenesis between brook charr (Salvelinus fontinalis, Mitchill 1814) and Arctic charr (Salvelinus alpinus, L.) has been attributed to the conflict between the egg cytoplasm of one species and the sperm nucleus of the other species. To overcome this incompatibility, sperm derived from the brook charr × Arctic charr hybrid male was used to induce androgenetic development in eggs originating from the parental species as well as their hybrids. The eggs were subjected to 420 Gy of X-radiation to damage the maternal nuclear DNA and inseminated with untreated sperm. Haploid zygotes were exposed to high hydrostatic pressure shock (7000 psi for 4 min), which was applied 420 min after insemination to inhibit the first cell cleavage and recover the diploid state of the zygote. The androgenetic diploid offspring that hatched from the brook charr, the Arctic charr and the hybrids eggs had survival rates of 4.7 ± 0.6%, 1.2 ± 0.4% and 16.8 ± 0.5%, respectively. Drastic mortality among the hatched androgenetic individuals was observed within the first five months of rearing. Cytogenetic analysis of the androgenetic progenies exhibited residues of the irradiated maternal nuclear genome in the form of radiation-induced chromosome fragments in 47% of the specimens that were examined. Interactions between the egg cytoplasm and the sperm nucleus, the low quality of the gametes, the expression of homozygous paternal lethal alleles and the incomplete inactivation of the maternal chromosomes were identified as factors responsible for the large mortality among androgenetic embryos and hatchlings.