The origin of the species
The general assumption is that the genus Bison (H. Smith, 1827) has its origin in southern Asia. From the late Pliocene of India (Sivalik) deposits of Probison dehmi (Sahmi et Kahn, 1968) are known, while Protobison kushkunensis (Burtschak-Abramowitsch, Gadziev et Vekua, 1980) comes from the late Pliocene of Trans-Caucasia. According to Flerov (1979) Bison sivalensis (Lydekker, ex Falconer, 1878) can be traced from the first of these forms. Late Pliocene Bison paleosinensis (Teilhard de Chardin et Pivetau, 1930) is probably a representative of B. priscus (Bojanus, 1829) (McDonald 1981). During the late Pliocene and early Pleistocene bison were widely spread throughout the temperate zones of Asia and Europe (cf. Figure 3.1). They also crossed the Bering Strait to North America (Flerov 1979). Forms reaching from Asia to Eastern Europe (near the Black Sea and the south Ukraine) during Villafranchium were relatively short-horned. Longhorn forms (B. priscus) developed in large areas of Europe and Asia, from England to Manchuria during the mid- Pleistocene.
With the cessation of glaciation bison became smaller in size, especially in Western Europe, with shorter horns (cf. B. priscus mediator) as compared with East Europe and Asia (B. priscus gigas). During the early Holocene bison were still widespread but still did not inhabit northern Europe. At the end of the Würm (15,000 - 10,000 BP), a transitory form appeared between B. priscus and B. bonasus, described as B. bonasus major (Hilzheimer, 1918). B. bonasus did not occur in central Europe until the late Holocene. During the last glaciation (c.10,000 BP) B.bonasus appeared in Denmark, Sweden and in the Caucasian region. (cf. reviews in Pucek 1986; Bauer 2001). Flerov (1979) claims that both the European bison Bison bonasus and the wood bison Bison bison athabascae come from the Palearctic B. priscus. McDonald (1981) and some other authors claim, that the European bison may be derived from late Pleistocene re-emigrants from North America. Craniometrical research by van Zyll de Jong (1986) reveals a great similarity between Holocene and late Pleistocene bison of Eurasia and North America, which makes an earlier hypothesis of a common ancestor very probable (cf. Skinner and Kaisen 1947; Bohlken 1967). Most recent authors, on the base of significantly different morphotypes and extreme disjunctive distribution continue to give the European bison and North American bison the status of a separate species, disregarding their interbreeding (cf. Wilson and Reeder 1993). In this review, European bison Bison bonasus is treated as a separate species. This conclusion is significant when considering problems of genetic purity of Lowland European bison, B. b. bonasus and its crossbreeds with Caucasian subspecies B. b. caucasicus (Lowland-Caucasian line) as well as their hybrids with North American bison Bison bison.
European bison Bison bonasus (Linnaeus, 1758) belong to the Family Bovidae (Gray, 1872), Subfamily Bovinae (Gray, 1821), Genus Bison (H. Smith, 1827). Sometimes it is treated as a synonym of Bos (Linnaeus, 1758) according to Groves (1981). Three subspecies are recognized (but see Rautian et al. 2000): B. b. bonasus (Linnaeus, 1758) - (from Bialowieza Forest) B. b. hungarorum (Kretzoi, 1946) - Carpathian Mountains and Transylvania, Extinct B. b. caucasicus (Turkin et Satunin, 1904) - Caucasus region, Extinct.
Distribution of the species in historical times
In historical times the range of European bison covered western, central and south-eastern Europe, extending up to the Volga River and the Caucasus.
European bison probably also occurred in the Asiatic part of the Russian Federation, but reconstruction of this range requires further research (Strategy 2002). There is a consistent opinion that the shrinkage of the European bison range on the continent was caused by the progress of civilization and that protective actions could not effectively protect the species. The process of extinction started from the west, the south and the north. Bison in Gallia were the first to die out (8th century). In the north of Sweden bison only survived until the 11th century. In the 7th century, the European bison's existence was reported from the north-east of France. In the Ardennes and in the Vogues these animals survived until the 14th century. In Brandenburg by the 16th century, they were already kept, and bred in enclosures. At the end of the 17th century (1689) an attempt was undertaken in Mecklenburg to release European bison from enclosures, however, this was unsuccessful. In the 12th century, the existence of European bison was reported from the Usocin Forest on the Oder River, near Szczecin. Bison existed in West Pomerania until the year 1364. Thanks to the protective actions of Wilhelm I, bison survived relatively long in eastern Prussia. In 1726, their number was estimated at 117 individuals (Genthe 1918), but in 1755 the last two animals were killed by poachers between Labiau (today Polesk) and Tilsit (today Sovetsk) (Karcov 1903; Heptner et al. 1966). From Prussia and Poland, European bison were transported to Saxony in the 16th century, and kept in enclosures. In the years of 1733 to 1746 these animals were set free. They survived in enclosures in Kreyern and later in Liebenwerda until 1793. In the 16th century bison became extinct in Hungary, although free animals survived a relatively long time in Transylvania. The last individual was poached in 1790. In Romania, the last European bison was killed in the Radnai Mountains in 1762. In Poland, by the 11th and 12th centuries bison populations were limited to larger forest complexes, where they were protected as the royal game. In the 15th century, they were found in Bialowieza Forest, Niepolomicka Forest, Sandomierska Forest, near Ratna on the Pripet River and in Volhynia (Sztolcman 1924). In the Kurpiowska Forest, they became extinct in the 18th century.
The last European population in Bialowieza Forest was protected until its extinction in the spring of 1919 (Genthe 1918; Sztolcman 1924; Wróblewski 1932; Okolów 1966; Krysiak 1967). There is direct and indirect evidence of the European bison's existence within the former Soviet Union until the 17th and 18th century. Along the River Don, European bison was preserved until 1709, in Moldova up to 1717. The last free population survived in the Caucasus until 1927 (Heptner et al. 1966; Kirikov 1979). It can be assumed that in historical times the European bison was subject to gradual shrinkage and fragmentation of the range, decreasing numbers and increasing isolation of sub-populations leading to extinction. An interesting theory refers to the effect of climate on the range of bison. According to Heptner et al. (1966), the depth of snow cover (50cm-thick snow cover limited the species' spread to the north) determined the northern border of the species range (see also Vereshchagin and Baryshnikov 1985). In many regions inhabited by bison in historical times, the thickness of snow cover exceeded that value (e.g., within the last 50 years in the Bialowieza Forest the monthly maximum depths of snow cover approached that value in five years, exceeding it considerably in two years - 1970 and 1979). This could be a significant factor hindering the bison's survival in that part of its range
Origin of Breeding Lines
The Lowland line (L, or Bialowieza line) originates from Bialowieza Primeval Forest and includes animals of B. b. bonasus. It is managed as a separate (closed) population. This line, derived from seven founders, lost the majority of its genetic diversity during the first period of the species restitution. The effective founder number decreased rapidly at the beginning of the restitution and in 1945 was very small (fge=1.7). Presently the level of genetic diversity is lower in the captive world population (fge=1.37) than it was in free-living herds at the moment of their creation (fge=1.6). Over 55 years (between 1945 and 2000) the loss of genetic variability within captive groups continued. This is not only expressed by the founder genome equivalent (fge) which changed from 1.7 in 1945 to 1.37 in 2000, but also by the fact that the relationships between animals increased (average mean kinship mk changed from 30.3%-36.5 %) (Belousova 1999; Olech 2002). The value of mean kinship for animals within recent populations ranges from 26.7%-65.9% (Olech 2002) and shows that the Lowland line is very homogenous. Genes of two founders (male 45, "Plebejer" and female 42, "Planta") are over-represented; their genetic contribution in the Lowland line gene pool is higher than 84%. The rest of the founders made a very small contribution; for four founders, it was no higher than 3%. The same situation concerns the retention of founder genes. Only two founders (No.s 45 and 42) saved more than 50% of their genotype in the living Lowland line. Between 17%-34% of the other five founder's genes were saved in the actual population. The contribution of founder's genes is fairly stable, but the retention of each of the founder's genes is decreasing. Due to the bottleneck between 1940 and 1945, the present world population of the Lowland line has copies of the same Y-chromosome from the founder No. 45 "Plebejer". The number of European bison of the Lowland line living in free-ranging herds is close to 900 distributed in 12 herds over the territories of Poland, Belarus, and Lithuania. The genetic variability of those herds, at the time of their founding (starting in 1952), was very low (Belousova 1999). The highest initial variability was found in European bison herds in Bialowieza Forest (fge=1.4) which were created during the first reintroduction. In the Polish part of the Bialowieza herd the participation of founders is very interesting because there is a lower contribution from founders 42 and 45. Two herds in Borisovskijj leskhoz (Belarus) and Panevezys-Pasiliu Stumbrynas (Lithuania) went through very serious founder bottlenecks and had very low genetic variability ( fge=1.2). Other small herds, such as those in Walcz forest (Poland) could be in a very similar situation from a genetic point of view. Only three herds (Puszcza Bialowieska, "Belovezhskaya Pushcha", Puszcza Borecka, about 630 animals in total) are estimated to be genetically and demographically successful populations. In fact, no free-living herd is safe (genetically or demographically) in the long term because of the low level of variability from the start.
The captive part of the Lowland line population numbers about 295 animals dispersed throughout 43 breeding centres and zoos. In half of the herds (240 animals in 22 herds) animals of only the Lowland line can be found, but in other herds, animals of both lines are kept together. Animals of the Lowland line are found in all captive herds in Poland (c.170) (EBPB 2001). All Polish captive herds are treated as one population by a special breeding programme that includes a system of animal exchange (Olech 1997). Genetic variability estimated on pedigrees has decreased very slowly in the last few years . The Lowland-Caucasian line (B. b. bonasus × B. b. caucasicus) (LC-line) [in older Russian literature also called Caucasian-Bialowieza line] has always been managed as an open population and sometimes mixed with the Lowland line. The LC-line contains genes of one B. b. caucasicus bull (No. 100 "Kaukasus") and of all 11 founders of B. b. bonasus (4 males and 7 females). The main part of the line's gene pool and genetic variability were lost at the beginning of the species restitution, a process continuing to this day. The founder genome equivalent for the captive part of the Lowland-Caucasian line is decreasing rapidly, from fge=4.5 in 1945 to 3.1 in 2000. The contribution of No. 100 "Kaukasus" and four females (No.s 96 "Gatczyna", 95 "Garde", 35 "Plewna", 46 "Placida") which did not participate in the other line is decreasing because of the Lowland line influence. At the same time, the contribution of seven founders common to both lines is increasing. The value of mean kinship has increased, especially in the last five years. The founder genome equivalent is much lower in free-living herds (fge = 2.0) than in the captive part of the world population (fge=3.5) (Belousova 1999). Not all twelve founders are represented in free-living herds. Founder No. 46 "Placida" has not contributed to any herd, and in some herds the genes of founders No.s 35 "Plewna" and 147 "Bismarck" are not found. Consequently, the genetic diversity within free-ranging herds is less than for animals in captivity. The retention and participation of the genes of five founders characteristic for this line is very small for free-living herds. This was due to the practice of mixing both lines when these herds were created. For example, the western part of the Bieszczady herd is closer to the Lowland line in its genetic characteristics (Olech and Perzanowski 2002). In this part of the Bieszczady herd the contribution of founders (No. 42 and 45) reached 83%. The founder's Y-chromosomes are not equally spread in the recent world population. The Y-chromosome of founder No. 45 "Plebejer" is most common in both free-living herds and captive groups. The Y-chromosome of founder No. 100 "Kaukasus" can be found in the Bieszczady free-living herd and in some captive groups. The Y-chromosome of founders No. 15 "Begrunder" and No. 147 "Bismarck" were lost during the breeding process during 1945 to 1997. The last male descendant of founder 87 "Bill" died childless in 1935 (Sipko et al. 1999). In conclusion three of five Y-chromosomes were lost.
Text is a part of European bison Action Plan.