MATING CALL AND STAGE OF SPECIATION IN THE <i>MICROHYLA OLIVACEA—M. CAROLINENSIS</i> COMPLEX

Abstract

This report deals with variations in mating call in a species group of narrowmouthed frogs (genus Microhyla) 2 and with the possible evolutionary significance of these variations. Anurans were studied because differences in mating call serve as important isolation mechanisms in these animals. The particular species complex was selected because it has populations which appear to be in intermediate stages of speciation. A western, xeric-adapted population that has been called Microhyla olivacea is distributed from the Gulf of California northeastward to eastern Texas and Oklahoma and northwestern Missouri. An eastern, mesic-adapted population that has been called M. carolinensis is distributed through the southern half of the eastern United States and reaches westward to eastern Texas and Oklahoma. The ranges of the two populations overlap in a strip running from the Gulf of Mexico into northeastern Oklahoma (fig. 1). Hecht and Matalas (1946) reported nmorphological intermediates between the unmottled olivacea and the dorsally and ventrally mottled ccarolinensis from a station in the overlap zone in southern Texas and fron another in eastern Oklahoma. They hypothesized that the two are either approaching complete isolation or that previously existing isolating mechanisms have