WHAT INSIGHTS INTO THE DEVELOPMENTAL TRAITS OF URODELES DOES THE STUDY OF INTERSPECIFIC HYBRIDS PROVIDE

Natural and artificial hybrids represent an important source of materi al for developmental and evolutionary studies of urodeles. We review t he available literature on hybrid salamanders, emphasizing the unique developmental insights that these organisms provide. Of particular int erest is the application of new molecular tools to identify DNA marker s for traditional characters in developmental research, and we discuss our own results using Bulk Segregant Analysis to identify RAPD marker s for the white phenotype in the axolotl. We pay particular attention to the inferences that can be drawn from the many disparate crosses be tween ambystomatid salamanders that vary in their metamorphic response . These crossing experiments suggest that 1) metamorphosis is dominant to paedomorphosis, 2) that different ambystomatids use different gene tic mechanisms to block metamorphosis and become sexually mature, larv al paedomorphs, and 3) metamorphosis may be controlled by a few geneti c loci. As increasingly sophisticated molecular approaches are applied to these and other hybrid crossing schemes, it should be possible to understand the mechanistic basis of a wide variety of developmental ch aracters that differentiate urodele species.