Molecular and Acoustical Verification of Hybrids of Cope's Gray Treefrogs (Dryophytes chrysoscelis) and Pine Woods Treefrogs (Dryophytes femoralis) in Virginia and North Carolina

In recent years, hybridization has come into focus as a potent force with a myriad of evolutionary outcomes. Natural hybridization has been documented across the hylid treefrog genus Dryophytes, but few studies have demonstrated the origins of putative natural hybrids. Here, we use molecular and acoustical data to test the parentage of 2 putative D. chrysoscelis x D. femoralis hybrids found in the wild in Virginia and North Carolina. Using 1 mitochondrial and 4 nuclear loci, we demonstrate that these 2 individuals are genetically intermediate between D. chrysoscelis (Cope's Gray Treefrog) and D. femoralis (Pine Woods Treefrog), with differing maternal species. The mating calls of hybrids are consistent with those of previous studies and feature a breakdown in structure that may result from an intermediate phenotype between the unpulsed and pulsed notes of the respective parent species. While hybridization between the 2 species is apparently rare, our results combined with previous laboratory studies demonstrate the potential for introgressive hybridization, necessitating further work to identify the extent of hybridization in the system.