Evolutionary genetics of metamorphic failure using wild-caught vs. laboratory axolotls (Ambystoma mexicanum)

In many organisms metamorphosis allows for an ecologically important habita t-shift from water to land. However, in some salamanders an adaptive life c ycle mode has evolved that is characterized by metamorphic failure (paedomo rphosis); these species remain in the aquatic habitat throughout the life c ycle. Perhaps the most famous example of metamorphic failure is the Mexican axolotl (Ambystoma mexicanum), which has become a focal species for develo pmental biology since it was introduced into laboratory culture in the 1800 s. Our previous genetic linkage mapping analysis, using an interspecific cr ossing design, demonstrated that a major gene effect underlies the expressi on of metamorphic failure in laboratory stocks of the Mexican axolotl. Here , we repeated this experiment using A. mexicanum that were sampled directly from their natural habitat at Lake Xochimilco, Mexico. We found no signifi cant association between the major gene and metamorphic failure when wild-c aught axolotls were used in the experimental design, although there is evid ence of a smaller genetic effect. Thus, there appears to be genetic variati on among Mexican axolotls (and possibly A. tigrinum tigrinum) at loci that contribute to metamorphic failure. This result suggests a role for more tha n one mutation and possibly artificial selection in the evolution of the ma jor gene effect in the laboratory Mexican axolotl.