Alkylation Treatment of the Mexican Axolotl: An Approach to the Isolation of New Mutations

SYNOPSIS. Most of the known mutants of the axolotl were uncoveredby R. R. Humphrey through inbreeding laboratory stock or wildanimals imported from Mexico. All are spontaneous in origin.We believe that chemical mutagenesis may be useful for increasingboth the frequency and variety of new mutations. For our experiments,we have chosen the alkylating agent ethyl methanesulfonate (EMS),because its mode of action is reasonably well understood. Thoughwe were unable to establish a lethal dose of EMS by intraperitonealinjection, we were successful when we administered the compounddirectly in the water. In the weeks immediately after treatment,females administered sublethal doses did not ovulate, exceptin response to large injections of follicle stimulating hormone.Recovery took several months. Treated males showed more normalperformance, in terms of courtship and the number of spermatophoresproduced. At low doses, and short intervals after treatment,embryos from spawnings with treated males survived nearly aswell as controls. Survival reached a minimum about a month afterthe male had been treated, then improved again. This depressionand recovery may be correlated with the stage of sperm maturationat the time of treatment. Treatment of mature sperm from spermatophoresaffected only their ability to fertilize eggs in an artificialinsemination; fertile eggs developed normally. The most promisingprocedure would, therefore, seem to be treatment of the male.Following mutagenesis, we propose that gynogenesis be used toaid in the rapid identification of new recessive mutations.