Premating Isolating Mechanisms among Three Species of the Rana pipiens Complex in Texas and Southern Oklahoma

Prior tests of interfertility among 3 partly sympatric species of the Rana pipiens complex (R. berlandieri, R. blairi, and R. sphenocephala) have indicated poor development of postmating reproductive isolation. However, hybrids are uncommon in sympatric populations, so premating isolation must exist. Among the species studied, temporal isolation predominates. In areas of tri-sympatry, the breeding seasons of all three species are staggered, whereas in allopatric areas the breeding seasons are expanded. Habitat isolation and ethological isolation also appear to be important, at least among some sympatric combinations of leopard frogs in Texas. Hybrids are presumably more poorly adapted to either parental habitat than are nonhybrids; thus postmating selection for conspecific mating through hybrid inferiority is at least partly responsible for the reinforcement of breeding season displacement in sympatry.