Description Vomerine teeth present. Posterior part of the tongue free and forked. Toes webbed. Omosternum and sternum ossified. Pupil of the eye horizontal. Body chunky (or corpulent). Snout moderately sharp. When the shins are positioned perpendicularly to the body axis, the heels do not contact. Inner metatarsal tubercle large. Dorsal coloration usually green, yellowish-green, olive-green or greyish-green with dark spots which vary in number, size and arrangement. Light middorsal line and lines on dorso-lateral folds regularly present. No temporal spot. Belly white or yellowish-white, usually without spots. Male and female flanks become more yellowish at the breeding time. Males differ from females by having paired white vocal sacs behind the mouth angles and nuptial pads on the 1st finger.
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Austria, Belarus, Belgium, Bosnia and Herzegovina, Croatia, Czech Republic, Denmark, Estonia, France, Germany, Hungary, Italy, Kazakhstan, Latvia, Liechtenstein, Lithuania, Luxembourg, Moldova, Republic of, Montenegro, Netherlands, Norway, Poland, Romania, Russian Federation, Serbia, Slovakia, Slovenia, Sweden, Switzerland, Ukraine. Introduced: Spain, United Kingdom.
The species lives in Europe. The westernmost localities are in France (Garonne, Grenoble etc.) and Southern Italy. The southern margin of the range runs by Yugoslavia, Czech Republic, and Romania to the northwestern shore of the Black Sea, then from southern Ukraine northeastwards approximately along the line: Nikolaev Province - eastern part of Dnepropetrovsk Province and western part of Zaporozhie Province - southern part of Kharkov Province. Then it extends in Russia from Byelgorod Province to Voronezh Province, then northwards to Tambov Province then northeastwards to Penza Province and to the south of Ulyanovsk Province and to Samara Province. The northernmost localities are known from the Southern Norway and the Southern Sweden. From the southern coast of the Baltic Sea, the margin runs from Estonia to northwestern Russia, then eastwards and southeastwards approximately along the line: Leningrad Province - southern districts of Vologda Province - Kirov Province - Tataria and Bashkiria. From Tataria, the margin turns southwards to the northeast of Ulyanovsk Province and to Samara Province.
Rana lessonae inhabits deciduous and mixed forests. The frog penetrates steppe within forests and bushlands (e.g. riparian alder groves). It occurs primarily in stagnant water bodies such as lakes, ponds, swamps, large puddles and ditches, generally covered with dense herbaceous vegetation. The pools may be located within the forests, in glades and forest edges, in fields and flooded meadows. The frog occasionally stays in shallow pools along small rivers and streams. The presence of permanent water is necessary for the existence of R. lessonae populations. In the forest zone, when the air humidity is high, the frog frequently occurs on land far away from water bodies. Using chains of small ponds, the frog can migrate distances of up to 8 km.
Life History, Abundance, Activity, and Special Behaviors At most sites, this is a common amphibian. The population density of adults reaches one individual per few square meters of pond shore.
Hibernation occurs from September - late November to March - May. Frogs hibernate in water, rarely on land (but then in holes and burrows). Reproduction extends from late March - May to late June. Males form breeding choruses. Amplexus is pectoral (axillary). The clutch contains 440 - 4400 eggs. Metamorphosis occurs from June to October, usually in July - August. The tadpoles sometimes overwinter reaching an especially large size. Sexual maturity is attained probably in the 2nd-3rd year of life. The maximum life span is 6-12 years in different populations.
Tadpoles consume primarily algae: Cyanophyta, Chlorophyta etc. Juveniles eat large amounts of flies and fly larvae. They sometimes climb plant leaves (at a height up to 0.5 m) to forage. The food of adults consists mainly of terrestrial invertebrates (mainly insects). Aquatic organisms (Gerridae, Dytiscidae etc.) comprise usually less than a half of prey items. Feeding does not cease during the breeding season. The Pool Frog is not as voracious as the taxonomically and ecologically similar Marsh Frog (R. ridibunda), evidently due to its smaller body size. However, different amphibians and even juvenile grass snakes are consumed time by time.
Trends and Threats The species does not display overall decline, but local declines are known. They are caused usually by the same anthropogenic factors, as in R. ridibunda.
R. lessonae went extinct in england in the mid 1990's. Reintroduction attempts using populations from Norway and Sweden (started in 2005) appear to have been successful (John W. Wilkinson & John Buckley, FrogLog 2012).
Relation to Humans Some populations of R. lessonae survive even in large cities. Frogs readily colonize fisheries, the settling reservoirs of wood-treatment enterprises, drains etc. The building of new ponds and channels by people promotes local dispersal and population increase in this frog. However, extensive and numerous dispersals as seen in the related species R. ridibunda are not known.
Possible reasons for amphibian decline
General habitat alteration and loss Urbanization Loss of genetic diversity from small population phenomena