Frogs of the Rana pipiens Complex in the Northern and Central Plains States

Abstract

The geographic distributions of three forms of the Rana pipiens complex were determined from samples of populations collected in South Dakota, Nebraska, Kansas, northwestern Missouri and western Iowa. A few samples from Minnesota and North Dakota were also examined. In most samples, the different forms can readily be identified morphologically. Calls were analyzed for the northern and western forms and were found to correlate with the expected morphotypes. The northern and western forms are sympatric along the Missouri, Elkhorn and Platte Rivers in southeastern South Dakota, eastern Nebraska and western Iowa. Probable hybrids, together with both parental types, were found at a number of localities in the zone of sympatry. The eastern form occurs in southeastern Kansas and is found in sympatry with the western form along a narrow zone of overlap. The results of this study are consistent with the interpretation that the three forms are specifically distinct. The northern, western and eastern forms correspond to Rana pipiens, R. blairi and R. sphenocephala of other authors. Until recently, leopard frogs of the Rana pipiens complex have usually been considered to be members of a single wide-ranging species with gene exchange occurring readily between adjacent populations. H-owever, considerable evidence has accumulated which indicates that the complex may actually consist of a number of largely allopatric populations which are maintaining separate genetic identities. McAlister (1962), utilizing a morphological analysis of adult characters, suggested that there are three distinguishable morphologic types in Texas. Post and Pettus (1966) reported two morphologically distinct forms of Rana pipiens in eastern Colorado. Mecham (1968) described two morphologically distinct forms sympatric in the White Mountains of eastern Arizona. Littlejohn and Oldham (1968), utilizing sound spectrographic analysis of mating calls of male frogs, reported four different call types from the south central United States. Three of these correspond to the three morphotypes described by McAlister (1962) and were designated as western, eastern and southern types. The western call type