ROA: Evolutionary Dynamics of Speciation by Polploidy in Treefrogs

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Polyploidy in higher animals is generally rare, but more than fifteen species of five different families of frogs and toads have been discovered. The subjects of this research are two widely ranging North American gray treefrogs - the polyploid species Hyla versicolor, a tetraploid (2 times normal chromosome number) and its diploid counterpart, h. chrysoscelis. The main goal is to learn if H. versicolor arose more than once from H. chrysoscelis or as a hybrid between ancestral h. chrysoscelis and another diploid, h. avivoca. The multiple-origin hypotheses will be tested by comparing the nucleotide sequences of mitochondrial DNA from frogs of all three species from widespread areas through their distribution. The hypothesis of multiple- origin will be supported if in an evolutionary tree based on sequence data, different populations of H. versicolor occupy different branches. In other words, the two species in the same area of the range would be more similar to each other than individuals of the same species from different parts of the range. A second goal is to compare differences in the acoustic properties of the mating calls of H. versicolor and H. chrysoscelis in areas where they occur together (sympatry) with differences between areas where only one species occurs (allopatry). Because the frogs use mating calls alone to identify correct mates, and because mismatings lead to sterile, triploid hybrids, the working hypothesis is that differences within sympatry will be greater than differences between allopatric populations.