Tympanic membrane absent. Skin smooth. Sternum ossified. Pupil of the eye is vertical. Webs between the toes well-developed. Inner metatarsal tubercle of hind foot quite large and spade-shaped. No male resonators. Body robust, hind legs short, head large. Inner metatarsal tubercle very large, yellow-brownish in color. Dorsal coloration yellow-grayish, brown-grayish or brown with large dark-brown or dark-olive spots and small reddish points. Belly white-grayish, without pattern or with rare gray points. The frontal surface between the eyes is more or less conspicuous. In contrast to the female, the male possesses a prominent oval gland on the upper surface of the upper arm, and has a smaller body. During the reproductive period the male possesses small tubercles on the palms and forearms.
The Italian subspecies, Pelobates fuscus insubricus, is morphologically quite similar. The only apparent differences are in general a brighter colouration, sometimes with a considerable number of small red or reddish points (especially in females). The head appears slightly larger and prominent.
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Austria, Belarus, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Italy, Kazakhstan, Latvia, Lithuania, Netherlands, Poland, Romania, Russian Federation, Serbia, Slovakia, Sweden, Switzerland, Turkey, Ukraine
The species includes two subspecies: P. fuscus insubricus(living in northern Italy, apparently extinct in southern Switzerland) and P. fuscus fuscus (inhabiting the main part of the range).
Pelobates fuscus fuscus is distributed in the plains and hills of Central, Eastern and Southeastern Europe, as well as Western Asia, towards the Southern Transuralia and Northern Kazakhstan. The northern margin of the range is limited by the shore of the Baltic Sea, where the distribution is unclear in its eastern part. The margin of the range extends approximately by the line: Pskov and Leningrad provinces (Luga District: ca. 58ºN) - south of Vologda Province - Southwestern Kostroma Province - north of Nizhegorodsk Province - Kirov Province (Nolinsk District) - Udmurtia - Perm Province (environs of Perm City: 58º00'N, 56º13'E) - Sverdlovsk and Tyumen provinces in the Western Siberia, where the easternmost records are Yalutorovsk and Uporovo districts (ca. 57ºN, 66º30'E). The common spadefoot is absent in the Ural Mountains. The southern margin of the range runs from Germany (Baden-Wurtemberg and Bayern) through Austria, Northeastern Yugoslavia, and Northern Bulgaria to the Black Sea. Eastwards from the Black Sea coast of Precaucasia (Krasnodar Region Novorossisk District, Abrau Peninsula: ca. 44º43'N, 37º30'E), the margin runs to Goryachii Klyuch Town, then to the Sravropol Region - Chechnya and foothill Daghestan (the area between the Kuma and Terek rivers, ca. 46ºE). Then the margin runs northwards and northeastwards approximately along the line Chernye Zemli in Kalmykia (ca. 48ºN, 44ºE) - north of Volgograd Province and the Volga River delta. Then the margin turns eastwards and to the south-south-east in northern Kazakhstan: along the valley of the Malyi Uzen River to Guriev City (47º09'N, 51º56'E). Eastwards, the range margin corresponds to the valleys of the rivers Bolshoi Uzen, Malyi Uzen, Kushum, Ural, Ilek, Emba, Irgiz, Turgai and their tributaries. Then the margin runs northeastwards across the Turgai Plain to Kustanai Province of Kazakhstan (Naurzum Nature Reserve: 51º03'N, 64º02'E) and northwards to Russia, through the Kurgan Province in Tyumen Province.
Pelobates fuscus insubricus is a dubious variety (genetical studies are currently in act), that has also a little know distribution in northern Italy. At the end of the 19th century it was known for about 50 localities, but at the beginning of the seventies (20th century) it was known for only a few localities. For this reason it was considered as a very threatened variety. Active researches carried out by a group of Italian and Swiss herpetologists led to the discoveries of many more localities, and now at the beginning of 21th century P. f. insubricus has been found in many new localities in Piedmont, Lombardy, Emilia Romagna, Friuli and Venetia. It was also known with historical findings in souther Switzerland (Canton Ticino), but it was not confirmed anymore.
Pelobates fuscus inhabits a wide spectrum of habitats, including different coniferous, deciduous and mixed forests and their edges, groves, steppes, meadows, fields, parks and gardens. However, in forests the common spadefoot prefers open sites. In arid areas, these frogs occur on sands, in wormwood steppes etc. In these places frogs usually live in close proximity to water bodies. In particular, in Northern Kazakhstan P. fuscus is concentrated near pools and on riverbanks consisting of sand with clay and covered with reeds. Individuals occur even on the shores of lakes with salt water. Its fossorial habits have resulted in a strict preference for soft friable soils and an avoidance of rocky and compact soils. Spawning and early development usually occur in permanent, stagnant, more or less deep (to 20-130 cm) water bodies covered with dense grass vegetation: ponds, lakes, flooded quarries, ditches etc. Pleobates fuscus insubricus s mainly known from sandy habitats in northern Italy, although it has been sometimes found in coniferous woods and hilly areas (e.g. Pineta di Classe, Ravenna; Ivrea surroundings, Torino).
Life History, Abundance, Activity, and Special Behaviors
The nominate subspecies is relatively rare at its western limit of distribution (in some areas in France, Belgium and The Netherlands). Throughout Central and continental Eastern Europe it is a common species, except for some marginal areas. In the center of the European part of the former Soviet Union, the abundance of adult toads reaches 45-50 individuals per 100 m2 of pond during the breeding period. Besides its own burrows, the common spadefoot hides in burrows of other animals or even under stones. In suitable habitats, the population density reaches 3-15 specimens per 100 m2, sometimes up to 23 specimens per 150 m2 or even 4-5 specimens per 1 m2. Maximum densities are reported in sandy and ploughed soils.
Little is known about Pelobates fuscus inubricus. Anyhow, the few populational studies confirmed its tendency to behave as an explosive breeder, with reproductive period confined to the early springtime rains (end of March – beginning of April). Only in this period it is virtually observable in epigean activity. Capture-recapture recent studies in a newly discovered breeding pond next to Torino revealed an unexpected abundance (captured about 300 specimens at a site where the species was not known before). It is therefore likely that the presumed rarity is also due to an objective difficulty to come in contact with the spadefoot.
Hibernation occurs from September to the beginning of October (November in the south) to March - April. Common spadefoots hibernate in deep, to 2 m, burrows in soil. These are burrows of other animals, or made by the toads. Burrows are made by digging movements of the hind legs using the large inner metatarsal tubercle. While digging, the animal uses its hind legs one after another in turn, and moves down into the soil posterior body end first. Once in the ground, the spadefoot starts to move loosened soil with its forelegs to bury the entrance.
Reproduction starts soon after the end of hibernation and extends sometimes to June. Males vocalize under water and do not form breeding choruses. Amplexus is pelvic (inguinal). The clutch contains 480-3000 eggs and resembles paired, thick, sausage-like cord up to 1 m in length. Embryogenesis takes 5-11 days, larval development from 56-110 days. Young tadpoles stay usually on bottom. They grow very fast and after 1-2 months attain a size of 35-50 mm and more. At this time, the tadpoles tend to stay on plants within the water column and often appear near the water surface. Metamorphosis occurs in July - September. Newly metamorphosed juveniles bury themselves near the shore and may overwinter there. Otherwise, tadpoles hibernate in unfrozen water and complete metamorphosis the following spring or summer; such tadpoles reach an especially large size. Their metamorphosis occurs usually in the next spring or summer. Recently metamorphosed juveniles in such cases are larger than those which completed their transformation within one season. The long larval period makes the species sensitive to pond quality. Sometimes larval mortality may be high due to the drying of wetlands. Otherwise, larvae may die in frozen water.
Concerning Pelobates fuscus insubricus it is worth stressing that, differently from the nomibnal race, the larval period is considerably shortened. In fact the metamorphosis of tadpoles born in April occurs not later than July. This is and evident ecological adaptation to the harsh conditions and warmer climate (in respect of central Europe) of northern Italy. This is also confirmed by the smaller size reached by tadpoles: 120 mm in insubricus vs. 180 in fuscus. Larval overwintering is not known for Italian populations.
Tadpoles consume detritus and plants, mainly algae, as well as animal matter: Protozoa, Rotatoria, Ostracoda, Copepoda, Cladocera, Mollusca, and sometimes injured tadpoles of their own and other species. Adults eat mainly crawling invertebrates and fast-flying insects are consumed less frequently.
Many invertebrate and vertebrate predators, as well as many parasitic worms attack the Common Spadefoot. Trematodes infest the Common Spadefoot in much higher numbers than in many other terrestrial amphibians. This may be related to the long larval period in as much as tadpoles overwinter in stagnant water bodies.
Trends and Threats
Evidently, P. fuscus was once distributed more widely in the past. For example, subfossil remains have been found in Crimea beyond its recent range, while in Estonia it was recorded much further northwards near Tallin City, at the end of the 19th century. The rarity of this species in these two areas in light of this record indicates that it has probably has undergone a considerable long-term decline there. The causes of this decline are not known but may be related to its very long larval development and high requirements for soil and water quality.
As said before the distribution of P. f. insubricus suggests not only an objective rarity (mainly due to pollution and anthropic disturbance), but also a more secretive life and difficulty of observation.
Relation to Humans
Pelobates fuscus seems to be very sensitive to water quality and the structure of the soil. Pollution of wetlands by industry, pesticides, mineral fertilizers, cattle, domestic wastes etc. are harmful to the larvae of this species. Other kinds of human economic activity (destruction of meadows, especially by cattle, urbanization, recreational driving, open wells in sites of the toads' concentration etc.) also have a negative influence. However, some kinds of anthropogenic activity lead to the local distribution of the Common Spadefoot Toad: construction of forest rides, irrigation channels etc. This species lives in settlements and even in large cities if suitable habitats are present, but usually does not attain high abundances in these places.
As concerning Pelobates fuscus insubricus there are histories and/or legends about the fact that before the Second World War the large tadpoles were systematically (?) fished to become part of human nutrition, cooked fried as fishes. It is also sometimes said that these tadpoels were sold at local markets. Personally (F. Andreone) we think that although not excluded that sometimes they could have been eaten, their regular fishing was almost ulikely.
Pelobates fuscus insubricus suffers for a series of problems and constraints. In the Po Plain the human settlements and heavy urban centers (such as Turin and Milan), added to intensive agriculture, make the life of plain organisms very difficult. This is the reason of local extinction and distribution shrinkage of many plaitional species and populations, among which Rana latastei, Emys orbicularis, Zootoca vivipara (plain populations), Vipera berus (plain populations), Rana temporaria (plain populations). Pelobates fuscus insubricus is likely the most heavily affected amphibian. In fact it suffers from (1) habitat distruction (original wetlands wre dried up and ponds are often eliminated), (2) habitat isolation (the residual ponds are surrounded by hostile agricultural habitats), (3) fish introduction (many ponds are colonized by bluegills, catfishes, all heavy predators of early larval stages), (4) introduction of bullfrogs and exotic crayfish. The well known and also relatively abundant populations reproducing in the ricefields of Novara surroundings suffered in the last years a constant lowering due to the evident change of agricultural practice (many ricefields were replaced by Soya fields, the others were made more “regular” and less deep). In some cases the residual breeding sites are surrounded by houses and are also filled with materials for building. To contrast this tendency and possible population reduction the Italian subspecies has been declared “asterisked taxon” in the Habitat Directive. Furthermore it has been object of a conservation campaign of WWF Italia. This campaign had – among its concrete programs – the attempts of captive breeding for reintroduction. Anyhow, despite the good results in documenting the breeding behavior, little results were until now obtained in the sense of population reintroduction and reinforcement.
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Written by Sergius L. Kuzmin and Franco Andreone (ipe51 AT yahoo.com and f.andreonelibero.it), Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow
First submitted 1999-10-06
Edited by Meredith J. Mahoney (2008-01-05)
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