Amphibians (Amphibia) is the class of poikilothermic (also known as cold-blooded) terrestrial vertebrates that usually retain the aquatic larval stage; hence, proximity to fresh water is typical for a majority of the species. Breeding takes place in water (or wet soil), and the aquatic larvae (which breathe through the gills) metamorphose and subsequently live on land.
The food of adults and some larvae (in salamanders) consists of small invertebrates; otherwise, adults eat invertebrates, whereas frog and toad larvae eat detritus and algae and small invertebrates.
The majority of amphibians live in wet tropical and subtropical areas, from where species richness decreases northward and southward. Few amphibian species cross the Arctic Circle: one salamander, one toad, and four frog species. However, they cannot be considered as true Arctic species because the main part of their distribution ranges covers the Subarctic and the temperate zone. Their penetration into the Arctic is usually with wood vegetation, particularly by intrazonal landscapes of river valleys. However, further dispersal in moist tundra landscapes also occurs in woodless areas. These species have evolved some mechanisms for survival in the severe climatic conditions of the north, such as seasonal changes in biochemistry and physiology, relatively fast accumulation of special cryoprotectant substances preventing the formation of ice crystals breaking cell walls, high ability of amylases to maintain high activity during a sharp fall in temperature, relatively high connection of adults with wetlands during the nonbreeding season, freeze tolerance of spawn, and relatively fast development of embryos and larvae (allowing them to complete transformation from the embryo to the terrestrial animal during a short activity period in high latitudes). These species form stable and sometimes dense populations in the Arctic.
The Siberian newt, Salamandrella keyserlingii (Caudata: Hynobiidae), is a small amphibian with a total length of 119-162 mm. It has 11-15 costal grooves on each body side; its tail is slightly shorter, equal, or slightly longer than the body including the head; coloration is brown, bronze-brown, olive or grayish with dark spots and a light, often golden or silver longitudinal dorsal band. This newt has the widest geographical range of any recent amphibian species, c.12 million km2, and is the most widespread amphibian species in the Arctic. It lives in Russia, the north of Kazakhstan, Mongolia, China, Korea, and Japan. Over a considerable part of the northern margin of its range, this species crosses the Arctic Circle. The northern margin of the range extends in the former Soviet Union from the Russian Plain (Arkhangelskaya Province: c.64°40' N 43° E) eastward to the Arctic part of the Urals (Tyumenskaya Province, south of Yamal Peninsula: c.67°56' N 67°51' E), through the south of Taymyr Peninsula, Krasnoyarsk Kray (the Avam River: c.71° N 93° E) to the north of the Sakha Republic (c.70-71° N: Kyusyur Settlement—Kazachie Village on the Yana River—the Chukochya River mouth), Magadanskaya Province and Chukotka Peninsula (the northernmost known localities are Apapelgino
Settlement: 69°47' N 170°36' E, Palyavaam River valley 60 km from Chaun Bay: 68°45' N, 171°43' E; Palyavaam River middle current 66 km upstream of Levtuttutveem River: 68°27' N 174°37' E; Amguema River left bank at the confluence of its tributary Ekitiki River: 67°40' N 181°17' E; Kanchalan River: 65°40' N 177°4' E; and Anadyr Settlement: 64°43' N 177°24' E). The newt usually inhabits various forests, but in the Arctic zone it lives in riparian groves (mainly composed of the larch, Larix sibirica) and in woodless tundra with moss and small lakes.
The Siberian newt is a unique amphibian in terms of its freeze tolerance. Adults are able to survive freezing to -35°C to -40°C and can move at +0.5°C to +1°C. Biochemical analysis has revealed seasonal changes in concentrations of the cryoprotectant, glyc-erol, which is reallocated from the liver into other organs before hibernation. As a result, the tissues and organs do not freeze even at -20°C, and crystals of water, which can break cell walls, are located in extracellular cavities and under the skin. The eggs can survive short-term freezing in the ice. Adults can survive in a frozen state for a very long time. Sometimes such frozen salamanders, found in the permafrost at a depth of 4-14 m, "revive" after melting. About ten such instances are known, mainly from northeastern Siberia. As a rule, such animals die soon after melting, but sometimes they survive for a long time. The age of one such specimen excavated from a depth of 11 m was determined as 90±15 years, much more than the life span in "common" individuals. In the northern part of the range, the newts enter hibernacula in August or early September. The newt hibernates in rotten trees, under logs, snags, in holes, etc., usually in groups of five to ten (up to 200) individuals, sometimes singly. Hibernacula may be located within up to 200-500 m distance from ponds. At the beginning of hibernation (August-September), the permafrost alleviates significant fluctuations of the air temperature, and the fluctuations of temperature in hibernacula do not exceed 0.5-1.5°C. When the mean daily temperature approaches zero, the conditions in hibernacula become almost thermostatic, which is maintained for 10-20 days. Hibernation grounds (moss, rotten trees, etc.) do not alleviate daily fluctuations of temperature, which depends mainly on the air temperature and peculiarities of the snow cover. Nevertheless, even at the ambient temperatures of -45°C to -50°C, the temperatures in hibernacula fall to -18°C to -23°C for only two to three days (depth 5-10 cm, thickness of snow 30-35 cm). Snow cover plays the main role in this stabilization of temperature. The temperature increases with depth due to "warming" by the permafrost, the temperature of which is higher than that on the ground surface. Thus, the biochemical freeze tolerance of the
Siberian newt in combination with the peculiarities of its hibernacula allow the species to survive near the Arctic Circle. The total duration of overwintering at the north is not less than c. 75% year. Only 4-10% of the annual activity falls within the aquatic phase, which tends to increase in duration northward. In the northern part of the species distribution, reproduction is extended (sometimes up to one month), which seems to depend mainly on the thawing of the soil. The clutch is a pair of egg sacs connected to one another by a very short mucous stalk, which serves to attach the clutch to the substrate. Each sac contains 14-166 eggs (usually 50-90 eggs). The duration of embryonic and larval development is shorter at the north due to a short activity period.
The common toad, Bufo bufo (Anura: Bufonidae), is the central and the northernmost member of the Bufo bufo species complex. This is a large toad, 50-130 mm in length, with prominent parotoids (a pair of wartlike glands at the back of the head); the tympanic membrane is not visible; and males have no external resonator to amplify their calls. The toad has second and third toes with paired tubercles on the underside; no tarsal fold; dorsal skin as a rule with rounded tubercles, sometimes with sharp top; and a white-grayish, gray, brown, or olive-brown dorsal surface with more or less developed dark spots. The common toad is widespread in Europe and West Siberia, penetrating into East Siberia. The northern margin of the range extends from Norway and northern Sweden through the north of Russia, from the northern shore of the White Sea in Murmanskaya Province (Kandalaksha Nature Reserve: 66°35' N 33°13' E) and covers the whole of Karelia. In Arkhangelskaya Province, the range runs from the environs of Arkhangel'sk City (64°36' N 40°32' E) to Pinezhsky Nature Reserve (64°35' N 43°03' E). Then the margin extends southerly to the Arctic Circle southeastwards to the Irkutskaya Province of Russia in East Siberia (c.58° N 96° E to 56° N 100° E). Thus, the common toad crosses the Arctic Circle only in the western part of its distribution: in Fennoscandia, while eastward the northern margin of the range is shifted gradually more and more southward, in negative relation to the increased severe climatic conditions in East Siberia. The common toad is associated mainly with the forest zone, where it prefers coniferous forests with marshes. Large open areas are avoided, but in forested landscapes the toad readily inhabits bushlands, meadows, fields, glades, etc. Hibernation occurs on land in rotten trees, burrows, etc. The toads hibernate singly or in groups from September to the beginning of November to March-June, depending on the altitude and latitude. Breeding occurs from March to June (usually late April-May) and lasts for three to seven (up to 14) days at a single site. Various types of wetlands are used for spawning. However, at the north, reproduction occurs in shallow areas of lakes and rivers. The clutch has the shape of very long (upto 1-2 m) strings with spawn. Metamorphosis occurs from the middle to late summer.
The common frog, Rana temporaria (Anura: Ranidae), is the central member of the group of brown frogs, which is widespread in Europe and Asia. The name R. temporaria has been used for almost all species of Eurasian brown frogs, including the species living in the Arctic. This is a medium-sized frog, from 33 to -100 mm; the body is corpulent and the snout is rounded; males have internal guttural resonators; dorsal coloration is olive, olive-brown, gray-brown, brown, gray, yellowish, or rufous; there is a V-shaped dark glandular spot on the neck and a large dark temporal spot behind the eyes; and the belly and hind legs are white from below, yellowish or grayish with a blotched-like pattern formed by brown, brownish-gray, or almost black spots. The frog inhabits Europe from the Pyrenees to the Urals and West Siberia. In Fennoscandia, the northern range margin corresponds approximately to the coast of the Norwegian and the Barents seas to the area between Kharlovka and Voyatka rivers (c.68°20' N 37°20' E). Then the margin runs beyond the Arctic Circle southward to the northern coast of Kandalaksha Bay. Southeastward, in Arkhangelskaya Province, the margin corresponds to the coast of the White Sea, including the Kanin Peninsula. From the latter, it runs southeastward and eastward through Komi Republic in Russia, approximately along the line: lower Shapkina River in Ust-Tsilma District (c.67° N 53° E)—Vorkuta City (67°29' N 64°00' E), then to the Polar Urals (Yamalo-Nenet Autonomous Okrug in Tyumen Province: Shchuchya River, ca. 67° N 69° E). Then the margin runs southward to Kurganskaya Province of Russia and northern Kazakhstan. The species lives on many marine and lake islands, but the indication for Kolguev Island in the east of the Barents Sea needs further verification. The common frog inhabits various forests, in which it penetrates tundra. In the northern part of its range, the species tends to occur near ponds, lakes, and rivers, spending more time in water. At the northern limit of its distribution, this species lives in the forest and true tundras, usually on the shores of permanent lakes. In particular, in the Kola region, the common frog inhabits depositions of ancient glaciers in valleys, slopes of hills and the sea coast, as well as areas of northern taiga. In the Arctic, the common frog breeds in depressions in rocks, flooded plains, swamps, ponds, and the littoral zones of lakes. This species is quite resistant to low temperatures: it does not stop activity at +2°C to +3°C. Hibernation starts after the first frosts, and finishes before the time when the mean night temperature exceeds zero. The latest appearance (early June) and earliest disappearance (late August) within the range are in the Polar Urals. The eggs are deposited usually after the night temperature rises above zero. The clutch, as in other brown frogs, has the shape of a large clump. The clutches, deposited by a group of frogs, form a dense aggregation. The aggregation allows alleviation of sharp fluctuations of temperature and penetration of small natural enemies. The embryonic and larval development ends in late summer to autumn.
The moor frog, Rana arvalis (Anura: Ranidae), is a small animal 36-80 mm in length, with the snout more or less terminating in a point. The male has internal guttural resonators. It has a smooth flank and thigh skin; gray, light-olive, yellowish, brown, or rufous dorsal coloration; a V-shaped dark glandular spot on the neck; a light mid-dorsal band frequently present (especially in northern populations); and a white or yellowish belly without pattern or with pallid brownish or grayish spots on the throat and chest. The frog inhabits a large area from southern Sweden and Finland to France, southeastern Europe and Siberia. The northern limit of the range runs from southern Sweden eastward through the Arctic Circle to the northern Sweden, Murmanskaya Province of Russia (Kandalakshsky Nature Reserve: 66°35' N 33°13' E) and northern Karelia, then through northern Arkhangelskaya Province (Pinezhsky Nature Reserve: 64°35' N 43°03' E—south of the Kanin Peninsula, Chesha River delta—Nenets Autonomous Okrug, Tobseda Settlement: c.68°30' N 52°30' E)—Komi Republic (Vorkuta City: 67°29' N 64°00' E)— Tyumenskaya Province (Yamalo-Nenets Autonomous Okrug, Kharvuta Settlement on the Khadyta-Yakha River: c.67°40' N 70° E)—Krasnoyarsk Region (Taymyr Autonomous Okrug, Khantaika River basin: c.68° N 87° E), then southeastward to Yakutia below the Arctic circle. Thus, in Fennoscandia R. arvalis penetrates less northward in the Arctic than another brown frog, R. temporaria. However, in contrast to the latter species, it occurs in the Siberian Arctic, while R. temporaria does not penetrate farther northeastward than the Polar Urals. The moor frog penetrates tundra in association with arboreal vegetation, primarily along river valleys. At the northern limit of its distribution, in tundra, it lives near water bodies: rivers and lakes. In the shrubby tundra, it lives in sedge bogs and in lichen-sedge-moss tundras. In forest-tundra open woodlands, the moor frog is abundant in the riparian forests and associated bogs. In Europe, R. arvalis is probably a more thermophilous species, with lower requirements to humidity of the environment, than the sympatric R. temporaria. When these two frogs coexist in the same habitat, the first species more often lives in more open and well-illuminated habitats; it enters hibernation a little earlier and leaves it a little later; and the reproduction takes place a little later. The latest appearance (June) and earliest disappearance (September) within the moor frog range is in the Polar Urals. Spawning and early development occur in stagnant waters, including lakes, swamps, etc. The spawn is deposited as a clump, sometimes two to three clumps. The clutches do not form uniform masses and are positioned in a pond singly. The absolute duration of life (measured in years) is more at the north (tundra zone) than southerly. However, the duration of life measured by the periods of activity should be similar on various latitudes.
The Siberian wood frog, Rana amurensis (Anura: Ranidae), is a brown frog of 38-84 mm length; the snout is moderately sharp; male resonators are reduced; dorsal coloration is grayish or gray-brown with dark spots; temporal spot is large; a light mid-dorsal band is present; flank and thigh skin are granular, the granules are often red; and the belly is white or white-yellowish with large, irregular, partially fused blood-red spots. This frog inhabits Western and East Siberia, the Russian Far East, Korea, northern and central Mongolia, and northeastern China. The Arctic regions are reached in Russia, where the northern margin of the species' range extends eastwards from Sverdlovskaya and Tyumenskaya provinces to Krasnoyarsk Region to Irkutskaya Province, then northeastward in Yakutia, where the species exceeds the Arctic Circle approximately along the line: upper flow of the Vilyui River—upper flow of the Markha River (c.66° N 114° E)—Zhigansk Town on the Lena River (c.67° N 124° E)—upward by the Lena River to Siktyakh and Buuru settlements (c.70°30' N 125° E)—Khaiyr Lake in the lower Omoloi River area (c.71° N 133° E). Then the margin runs southeastward approximately along the line: Verkhoyansky District, Tylgys Settlement (30 km northward from the Arctic Circle)—Verkhnekolymsky District, Usun-Kyuyol Settlement (c.67°40' N 155° E)—Magadanskaya Province (Srednekansky District, Balygychan and Seimchan Settlements, c.63° N 152° E). Then the margin runs southward to the shore of the Sea of Okhotsk. Information on the presence of the Siberian frog in several localities in northern Yakutia between 70 and 72° N needs further verification. The Siberian frog lives in coniferous, mixed and deciduous forests, within which it penetrates the tundra zone. The connection with water bodies (overgrown river valleys with flood-plain ponds and lakes) is typical in the northernmost areas. Although its freeze tolerance has not been studied, this frog, together with the Siberian newt, may be the most cold-tolerant amphibian in the world. The ecology above the Arctic Circle was unstudied, but it seems to be basically similar to that in R. temporaria and R. arvalis in the polar regions.
The wood frog, Rana sylvatica (Anura: Ranidae), is a brown frog of 34-83 mm length. Dorsal coloration is from pink to dark brown, with a prominent dark mask ending abruptly behind the eardrum; a light mid-dorsal band is sometimes present; and the belly is white, sometimes with dark mottling. This species is widespread in the northern part of North America, where it lives from the east of USA (North Carolina, Tennessee, and Arkansas) northward and northeastward to Minnesota and Wisconsin, then to Canada (Saskatchewan, Alberta, British Columbia, and Mackenzie) and Alaska. This frog lives north of the Arctic Circle in areas westward from the Mackenzie District of Canada (the northernmost record is the Mackenzie River delta, Yellowknife) to Alaska (Bettles) in USA. The Alaskan part of this species distribution is closest to the range of the Old World brown frogs. The systematic and phylogenetic relationships of R. sylvatica with Eurasian brown frogs remain unexplored. The wood frog lives mainly in woods, but in the northernmost areas it lives in tundra. Hibernation is finished there in late April—May; the breeding season in the Mackenzie region is May-July. As in other studied northern amphibian species, the liver is the primary site of cryoprotectant production in the wood frog. The induction of cryoprotectant synthesis seems to be triggered solely by the initiation of freezing at the body extremities. This species is able to survive extracellular freezing at subzero temperatures from -2°C to -4°C for periods up to two weeks.
There are two old records of the great crested newt, Triturus cristatus (Caudata: Salamandridae), from Lapland, Sweden, made above the Arctic Circle. This may indicate possible penetration of this species into the Arctic.
Sergius L. Kuzmin
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