Analysis of a Hybrid Zone between Chorus Frogs of the Pseudacris nigrita Complex in the Southern United States

Morphological and electrophoretic data provide evidence for the occurrence of a narrow zone of hybridization between two taxa of the Pseudacris nigrita complex in the southern border area of Louisiana and Mississippi. Although more than half the individuals in the hybrid zone could be classified as hybrids, and there is evidence of backcrossing, the taxa remain genetically distinct in areas adjacent to the hybrid zone. Hence they may be regarded as biological species. These taxa show a different type of interaction in the east, where they are sympatric, and appear to hybridize only infrequently, if at all. Comparative studies of the different interactions between these taxa in different areas of their ranges may provide a significant clue to the evolution of sympatry.