The ambystomatid salamanders exhibit a striking diversity of life-history patterns, including species with obligate metamorphosis, species with obligate paedomorphosis, and still other species that can pursue either pathway facultatively. To re-examine two hypotheses, regarding paedomorphosis. The progeny from interspecific crosses will be analyzed using a combined genetical and ecological approach. Hybrid larvae created by mating Ambystoma mexicanum (an obligate paedomorph) with A. tigrinum (from an obligately metamorphosing population) will be scored for life-history pathway under various food and temperature treatments. The co-segregation of morphological traits, growth rates, isozymes, and RFLP markers in the second- generation offspring will be examined in an attempt to identify major loci contributing to these developmental characteristics. By combining an ecological perspective and modern molecular tools in a genetical analysis of life history variation, this study will make fundamental contributions to our knowledge of the evolutionary mechanisms underlying the present-day diversity of developmental pathways in an important group of vertebrates.
