LEVELS OF GENETIC COMPATIBILITY OF <i>RANA AREOLATA</i> WITH SOUTHWESTERN MEMBERS OF THE <i>RANA PIPIENS</i> COMPLEX (ANURA: RANIDAE)

Abstract

Rana pipiens, the common leopard frog, has the widest distribution of any native anuran of the United States, ranging from Canada to Costa Rica. It has been variously considered as consisting of several species (Kauffeld, 1933) or subspecies (Wright and Wright, 1949). Most workers consider the complex to be composed of a single species. Normally most members of a species exhibit the same level of genetic compatibility when intercrossed. However, hybridization experiments between northern and southern members of Rana pipiens show a high level of incompatibility. This difference has been attributed to a no,rth-south adaptation to temperature (Moore, 1946a). These and other experiments by Moore (1946, 1947, 1949, 1950, 1964), Ruibal (1955, 1957), and Volpe (1954, 1957) have led to the general belief that the Rana pipiens complex is one species composed of a series of interbreeding populations, but showing progressively greater genetic differences (embryonic defects) as the latitudinal or altitudinal distance increases between the parent populations. According to this interpretation, the pipiens complex constitutes a single gene pool despite the fact that its range extends from the tropics to the subarctic region (Moore, 1964). A new interpretation (Moore, 1967) is that the complex is composed of a number of differentiated allopatric populations, each adapted to the