Rana nigromaculata Hallowell, Proc. Acad. Nat. Sci. Philadelphia, [12]:500 (for 1860), 1861 (type locality, Simoda, Japan).
Specimens examined (47).—Central National Forest, near Pup´yong-ni, 6 (KU); 2 mi. S Ch´orwon, 5 (KU); 4 mi. W Ch´ungju, 2 (KU); 7 mi. W Ch´ungju, 1 (KU); 2 mi. E Hoengsong, 1 (KU); 8 mi. SW Kunsan, 1 (KU); 1 mi. NW Oho-ri, 5 (KU); 5 mi. ENE Pusan, 2 (KU); 5 mi. ESE Seoul, 9 (KU); 6 mi. E Seoul, 3 (KU), 10 (UMMZ); 6 mi. NNE Sogwi-ri, Cheju Do, 2 (KU).
Description.—Back brownish or grayish (greenish in life), having few, indistinct or well-defined, dark blotches, or extensive blackish areas (representing fusion of markings); pale, middorsal stripe (pale green, buff or yellowish in life) from snout to anus, sometimes as wide as interorbital width, but indistinct or lacking when pattern on back absent; blackish bar often present behind tympanum; posterior surface of thigh mottled; underparts pale yellow to whitish, sometimes having a few dusky marks on throat; longitudinal ridges between dorsolateral folds indistinct in some small frogs; largest female and male having respective snout-vent lengths of 100 and 70.
Remarks.—Rana nigromaculata is the most abundant ranid in central Korea and, in a general way, the ecological equivalent of Rana pipiens in temperate North America. The species is associated with most aquatic habitats, from rocky streams to rice fields and large impoundments. In the vicinity of Seoul the din of large breeding congresses was heard more or less continuously from mid-April to mid-May. Large numbers of juveniles (approximately one inch long) were noticed first on July 8 and were present
thereafter for about three weeks, being commonest in standing water after heavy rains or during prolonged showers. These data and the different sizes of individuals collected at the same time suggest either variable growth or, more probably, an extensive breeding season. Our earliest and latest dates of collection are April 16 and October 7. The Korean name for "frog," most often applied to R. nigromaculata, sounds something like "keg-oh-ree." The call is a prolonged, raspy, staccato croak, sometimes with a rising inflection at the end.
In addition to the localities listed above, the species was observed 5 mi. W Kwangju and 3 mi. S Osan.
Despite a high degree of individual variation, Rana nigromaculata seemingly varies geographically as well; some subspecies probably should be recognized, but the species as a whole has never been thoroughly studied systematically. The division of R. nigromaculata into three subspecies by Schmidt (1927:563-567) was considered untenable by Fang and Chang (1931:95-98), and it has been regarded by most recent authors as a variable, monotypic species.
The named subspecies R. n. chosenica (Okada, 1931:89, with type locality at Seoul, and geographically restricted to Korea) was considered a subspecies of Rana plancyi by Shannon (1956:36). The most trenchant characters of plancyi seem to be the wide dorsolateral folds, the uniform greenish dorsum, the presence of dermal pustules on the back between the dorsolateral folds, and the lack of a mottled pattern on the posterior surface of the thigh. Among our specimens of R. nigromaculata, the width of the dorsolateral folds is variable, a uniform greenish dorsum is found only in large males, dermal pustules are mixed with ridges in only one male (KU 38733), and all have a spotted or mottled pattern on the posterior surface of the thigh. All of our specimens having an indistinct pattern on the back, or lacking a pattern, are males and resemble the photographs of males published by Moriya (1954: pl. I, fig. 5) and Liu (1936: pl. IV, figs. 1-2); juveniles of both sexes and large females have contrasting patterns.
None of our frogs seems, therefore, clearly referable to the species plancyi, although some characters are suggestive of plancyi. Moriya (op. cit.:19), who studied variation of R. nigromaculata in Japan, noted that one of the most distinct populations there (R. n. brevipoda) resembled Rana plancyi. Ting (1939) discovered that nigromaculata and plancyi were cross-fertile and raised hybrid
larvae through metamorphosis. Pope and Boring (1940) suggested hybridization between the two species in eastern China, and the above mentioned facts suggest to us the possibility of hybridization in other regions.