Parallel Electromorph Variation in the Diploid-Tetraploid Gray Treefrog Complex

Abstract

The tetraploid treefrog Hyla versicolor and its diploid progenitor, H. chrysoscelis, are extremely similar morphologically and ecologically, and they share virtually all of the same major protein polymorphisms. Sympatric populations of H. versicolor and H. chrysoscelis were sampled from widely separated localities in Texas, Oklahoma, Missouri, Illinois, and the Indiana-Ohio area. The data were analyzed by means of a statistic that measured the degree to which the two species parallel one another in terms of electromorph frequency. Of 11 polymorphic loci, 5 were significantly correlated (P < 0.05), and 3 more bordered on significance. Several explanations for these results are possible: parallel selection for shared electromorphs in similar environments, extensive gene flow between ploidy levels in areas of contact, multiple origins of the tetraploid in different areas of the diploid range, and some combination of these possibilities. Available data suggest that natural selection is the major factor responsible for parallel patterns of electromorph frequencies.