ADAPTIVE EVOLUTION VIA A MAJOR GENE EFFECT - PEDOMORPHOSIS IN THE MEXICAN AXOLOTL

Although adaptive evolution is thought to depend primarily on mutation s of small effect, major gene effects mag underlie many of the importa nt differences observed among species in nature. The Mexican axc.lotl (Ambystoma mexicanum) has a derived mode of development that is charac terized by metamorphic failure (paedomorphosis), an adaptation for an entirely aquatic life cycle. By using an interspecific crossing design and genetic linkage analysis, a major quantitative trait locus for ex pression of metamorphosis was identified in a local map of amplified f ragment length polymorphisms. These data are consistent with a major g ene hypothesis for the evolution of paedomorphosis in A. mexicanum.