Dybowski's Frog

Vomerine teeth present. Posterior part of the tongue free and forked. Toes webbed. Omosternum and sternum ossified. Pupil of the eye horizontal. Snout moderately sharp. Male with internal vocal sacs. Shin shorter than body by 1.75-2.25 times. When the shins are positioned perpendicularly to the body axis, the heels overlap. When the hind leg is stretched along the body, the tibio-tarsal articulation reaches the eye, sometimes the tip of the snout and, in a few cases, exceeds the latter. Inner metatarsal tubercle not very large, shorter than the first toe by 1.7-3.5 times. Flank and thigh skin smooth. Dorsal coloration brown, brown-olive, olive or greyish, with dark spots (spots are sometimes absent). Temporal spot large. Lower surface of the hind legs with pallid orange-pink tints. In the male, the throat and belly are white-yellowish, sometimes with blue tints, with no spots. In contrast to the male, the female belly (often throat as well) has reddish, brownish or pink-yellowish spots alternating with blue spots; sometimes female red-brownish. Besides the ventral coloration, male differs from female by having paired vocal sacs and nuptial pads on the first finger. During the breeding season, both male and female coloration becomes brighter.Rana dybowskii belongs to the brown frog group of species. In the past (and sometimes at present), these frogs have been considered as the species R. temporaria Linne, 1758. Later, brown frogs from the Russian Far East and adjacent areas were considered as several species, and this form is now designated often as Rana chensinensis David, 1875. However, recent studies revealed R. chensinensis to be a species complex, studies of which are in progress. These studies revealed significant genetic and morphological distinctions between populations from the type territory of Rana chensinensis David, 1875 sensu stricto (Shaanxi Province of China) and the populations of the Rana chensinensis complex from Beijing (China) and Japan living northeastwards (i.e. closer to the populations from the Russian Far East). The populations of the R. chensinensis complex from Shaanxi and from the Russian Far East are separated geographically by a considerable distance inhabited by other, also different, populations belonging to this complex. The overall extent of their differences appears to be comparable with that between other brown frog species from the Far East. So the specific name Rana chensinensis David, 1875 should not be used for the frogs from the Primorye and adjacent territories. Therefore, according to priority, their name should be Rana dybowskii Gunther, 1876. It should be emphasized that the systematics of brown frogs from the Far East needs further study. However, the name Rana dybowskii Gunther, 1876, by priority, will be preserved for at least the populations from its type territory and adjacent areas. The brown frogs from Korea, designated here by the same name, may belong to a separate species.

The distribution of R. dybowskii is not known definitely because of the unstudied taxonomic status of some populations of the brown frogs of the Far East (see Comments). As frogs from large regions of the Russian Far East and adjacent territories are considered to be the species R. dybowskii, we can conclude that this form inhabits the Russian Far East, the southeast of East Siberia, Korea, and Eastern China (provinces Heilongjiang, Liaoning and Jilin). In Russia, the range margin starts from the Chinese border near the confluence of the Zeya River into the Amur River (Blagoveshchensk City: 50º15'N, 127º34'E) and a little westwards, then runs northwestwards and northwards by the valley of Zeya River and its tributaries to the system of the Aldan River in Yakutia, then northwards to Ust-Aldan District and then turns eastwards to Tompon District (Khandyga Settlement: ca. 62º38'N, 136ºE) and Okhotsk District in Khabarovsk Region. Southern margin of the range runs by China and Korea. The species lives mainly in wooded regions; it rarely occurs in unwooded areas. The frog lives mainly in broad-leafed and mixed pine-broad-leafed forests, coniferous forests, valley groves etc. At the western limit of its range, in the Zeya River valley, this species inhabits riparian forests consisting of poplar, alder, willow etc. At the northern border of its range, in Yakutia, the frog occurs in wet lowland meadows, osiers, edges of mixed forests and willow-birch groves. Spawning occurs in stagnant and semi-flowing water in puddles, swamps, ponds, lakes, ditches and river pools.

This frog is a common and abundant amphibian, and in some places of the Russian Primorye Region its density reaches more than one hundred individuals per hectare. At the northern limit of the distribution, in Yakutia, the abundance is about ten times lower. Hibernation occurs from the second half of September - early November to late March - early May, depending on latitude, weather and habitat. The frogs hibernate in water, mainly in swift-flowing rivers and streams with stony bottoms. Hibernation in groups, sometimes of more than a thousand individuals, is typical. Mass mortality caused by hypoxia is typical in the frog hibernacula. Reproduction occurs from late March - second half of June (usually in April - May). Breeding choruses are typical. Amplexus is pectoral. The clutch contains about 350-4000 eggs. The embryos develop more rapidly within egg masses than within single clutches. Many breeding ponds dry before the end of embryogenesis. In such cases large aggregations of spawn have a better chance to survive during periods with no rain than do individual clutches. Metamorphosis occurs in the second half of June - late September, but usually in late June - July. Sexual maturity is attained probably in the 2nd-3rd year of life; the maximum age is 5-6 years. Algae, higher plants, and detritus compose the main food of the tadpoles. In contrast with many other syntopic amphibians, the larvae of this frog often attack the eggs of their own species and those of the Siberian Newt (Salamandrella keyserlingii), sometimes totally destroying them. Newly metamorphosed froglets prey primarily on Acarina, Collembola, Thysanoptera, Hymenoptera, and Cicadodea. Adult individuals primarily eat Mollusca, Aranei and Insecta. They prey upon not only terrestrial but sometimes aquatic invertebrates. Feeding does not stop during the reproductive season, at least in some individuals.

Most probably, the populations of R. dybowskii are not declining, except for some of them suffering due to mass collecting for purposes of Chinese traditional medicine.

Industrial pollution and urbanization negatively influence frog populations. Construction of large dams on the Zeya River has flooded large areas of R. dybowskii habitats which has caused the extinction of the species from mountain valleys and expansion in the gap between the parts of the species range in southern Yakutia and the upper part of the Amur River basin. This frog is an important component in traditional Chinese medicine. Before the October Socialist Revolution 1917 in Russia, the valley of the Razdolnaya River in the Primorye Region was one of the main areas of its mass collecting by Chinese people. When this collecting was stopped, frogs from Heilongjiang Province in China were collected. Special frog farms were constructed in China for breeding and management of commercial stocks of the wood frogs. Nevertheless, in the 1990s, many Chinese people have immigrated to the Russian Far East and the mass collecting of R. dybowskii, mainly in Primorye Region, has resumed. Although local inspectors and customs prevent some cases of the frog overcollecting and illegal export, the problem remains real. Rana dybowskii is well adapted for life in an anthropogenically altered environment. From the point of view of synanthropization, it resembles the European Common Frog (Rana temporaria): it is common in secondary forests, in hayfields, gardens, parks etc. It also occurs in some large cities.

Dybowski's frog (Rana dybowskii) is a species of true frog found in Northeast Asia. It is found in the Russian Far East, the Korean Peninsula, and the Japanese island of Tsushima. It may also exist in northeastern China, but this has not been confirmed.

The Dybowski's frog is fairly tolerant of human disturbance; however, it has been threatened across portions of its range due to heavy collection for use in traditional Chinese medicine. It breeds in slow-moving and stagnant water, and when not breeding, is most commonly found in woodlands. The species covers a wide range of altitudes, from sea level to 900 m, and possibly higher.

Adult Dybowski's frogs have a body length of 4.5–7.5 cm (1.8–3.0 in). The head and body are relatively broad; the skin is generally smooth, but with some small protuberances along the back. The male has a pair of vocal sacs which are used during the mating season. The back is largely tan to dark brown, and the belly is white.