Assessment of mutagenic damage following ethyl methanesulfonate mutagenesis in the axolotl (Ambystoma mexicanum)

When male axolots (Ambystoma mexicanus) were treated with 100 mg/liter of ethyl methanesulfonate (EMS), a dominant lethal effect was obtained. Embryonic survival of F1 progeny was most severely reduced between about 50 and 150 days after treatment. Dominant lethal lesions probably consist of chromosome breaks that lead to loss of parts of chromosomes or entire chromosomes. The appearance of embryos with a single nucleolus was used to assess this type of damage. The peak incidence of such embryos coincided with the peak of dominant lethality. At 25 mg/liter EMS, there was no significant dominant lethal effect, but as many as one-fourth of the embryos appeared morphologically abnormal during the period between 50 and 120 days after treatment. A small but significant number of embryos with a single nucleolus were also obtained. To assess possible recessive lethal damage, androgenetic haploids were produced from some of the mutagenized males. A broad trough of reduced haploid survival was obtained at 100 mg/liter, suggesting that damage is produced in most or all spermatogenic stages. At 10 mg/liter, where there was no dominant lethal effect or significant incidence of embryos with a single nucleolus, a broad period of reduced haploid survival was also obtained. Though we cannot exclude the possibility that chromosome abnormalities contribute to the reduced haploid survival, even at this low dose, the type of damage being assessed is almost certainly less severe than that leading to dominant lethality.