dependence of the pulse frequency the two species are easily distinguished where they occur together. At a given temperature, the pulse frequency for the gray treefrog is approximately one-half that of Cope's gray treefrog.

The gray treefrog has 48 chromosomes (4n), and is sometimes referred to as the tetraploid gray treefrog in scientific literature. Cope's gray treefrog, or the diploid gray treefrog, retained its 2n (24) original chromosome count. Hybridization between these species results in early mortality of many larvae.