Genetic status of the species

Following issues are the part of Action Plan:
Genetic Structure of the Species
Breeding Lines

Genetic Structure of the Species

All pure-bred European bison are the descendants of a basic group of 13 animals and represent a recombination of only 12 diploid sets of genes (Slatis 1960). Eleven of the 12 founder animals (all B. b. bonasus) originated solely from the Bia這wie瘸 Primeval Forest, from the Berlin and Budapest zoos and Pszczyna. One bull of B. b. caucasicus, born in 1907 in the Caucasus Mountains, was brought to Germany in 1908. Therefore, genetic problems can have a strong influence on the preservation of European bison, on long-term viability, and the adaptability of its populations. Two genetic lines are distinguished in recent populations of the species: The Lowland line (L or Bia這wie瘸 line) originates from only seven founders (4 males; 3 females) and includes pure animals of B. b. bonasus subspecies. A small, but important, part of this Lowland line included a group derived from a few animals brought from Bia這wie瘸 to Pszczyna in 1865 (1 bull and 3 cows) and supplemented throughout 1909 by five cows from Bia這wie瘸 and three other bulls. Three animals (2 males; 1 female) survived until 1922 (Czudek 1930; Pucek 1991). This group was later mixed (after World War II) together with original Bia這wie瘸 animals. The Lowland-Caucasian line (LC), (B. b. bonasus ?B. b. caucasicus) originate from all 12 founders (5 males; 7 females) including the bull of the Caucasian subspecies. Several studies proved small levels of genetic variability in Lowland European bison from the free-living population in the western part of the Bia這wie瘸 Forest (Poland). The average heterozygosity of proteins coded by 20 loci was indicated as 3.5 % (G瑿czy雟ki and Tomaszewska-Guszkiewicz 1987). Similar studies using electrophoresis of many more proteins at 69 structural loci showed the average heterozygosity equal to 1.2 % and only 5.8% of loci were polymorphic (Hartl and Pucek 1994). Genetic variability of European bison in the Lowland line from Bia這wie瘸 Forest (Belarus and Poland) and captive herds of the Lowland-Caucasian line (Prioksko-Terrasnyjj and Oka reserves) were studied. Variability and differentiation of proteins (22 loci, Sipko et al. 1997), blood group systems (9 systems, 57 antigens, Sipko et al. 1995), kappa-casein gene (Sipko et al. 1994; Burzy雟ka and Topczewski 1995), and the major histocompatibility complex class II DRB and DQB gene (Udina et al. 1994) were investigated. These studies generally show that genetic diversity within and among European bison lines is considerably lower in comparison to that within and among cattle breeds. From 57 antigens stated for European bison 28 (almost half) were widely distributed (in 94.6 %) but the other 29 antigens were only found in 5.4% of all animals tested (Sipko et al. 1996). The evidence of high inbreeding is connected with a very small polymorphism of molecular and biochemical markers, especially for the Lowland line (Sipko et al. 1997, 1999). In all studies, observed genetic diversity was lower in the Lowland line than the Lowland-Caucasian line. Sipko et al. (1997) calculated the level of heterozygosity for both lines, the Lowland line was equal to 1.2-3.8% and the Lowland-Caucasian line was higher at 4.4%. Asymmetry of non-metric characters of European bison skulls from different recent and sub-recent populations of European bison indicates an increase in indices of asymmetry with time. This increase of asymmetry is parallel with higher inbreeding values. The Lowland-Caucasian line shows lower indices of asymmetry than the Lowland line. The highest symmetry was observed in pure wild B. b. caucasicus whose skulls are preserved in museum collections (Rautian et al. 1998). It is obvious that genetic variation in the European bison has been seriously decreased by the historical population bottleneck; however, the presented studies were only conducted on a small part of the European bison population (10 % of free-living, and 1% of captive animals). Genealogical analysis can be an effective source for more complete information, because most captive European bison have known pedigrees (cf. European Bison Pedigree Book), including those released animals which founded free-living herds. This pedigree data enables the procurement of parameters, which explain the genetic structure of populations. One such parameter is the inbreeding coefficient, which shows the homozygosity of an individual. Mean kinship (mk) presents the relation of the individual within a population. The founder genome contribution and retention explain the gene pool structure. The values of those parameters for different herds are presented in Tables 6.1 - 6.4. Data sources for the European Bison Pedigree Book indicate that the world population of European bison is highly inbred. As found during the 1980s the average inbreeding coefficient for the world population was equal to 20.2%. The average inbreeding coefficient for live animals with full pedigree in the late 1990s was equal to 43.98% for the Lowland line; and was much smaller and equal to 26.28% for the Lowland-Caucasian line (Olech 1998). It is known, of course, that the Bia這wie瘸 population was isolated for a long time (at least since the 17th century) and these calculations can be made for the last five to six generations. The inbreeding depression has been shown to be very small in this species, but can influence stability of development and the demographic characteristics of the herd (Sipko et al. 1999). The only negative influence of inbreeding found up to now is in the viability of young animals (Slatis 1960; Olech 1987; Belousova 1993). Recent studies show significant positive correlations between the level of inbreeding and the mortality of young animals existing in the Lowland-Caucasian line. For living animals from the Lowland line with a much higher level of inbreeding, a relation between inbreeding and mortality was not found (Olech 1998). The estimated number of lethal equivalents in the captive group is very low (0.16 - Belousova 1993, 0.3 - Pucek et al. 1996) and lower than for other species (from 1.4-30.3 with a median of 3.1 - Ralls et al. 1988). Successful breeding of a species can be strongly associated with the maintenance of genetic diversity in a population. In the studies made in the Prioksko-Terrasnyjj reserve the harmful effect of low levels of genetic variability (founder genome equivalent /fge/ < 1.3) was shown in female fertility, the viability of calves, and young animals (Belousova 1999). Inbreeding has a depressive effect on skeletal growth, more expressed in females. Inbreeding in particular affects the skeletons of Lowland-Caucasian animals (Kobry鎍zuk 1985). Increased inbreeding causes neurocranium shortening and elongation of the skull basis, which results in elongation and narrowing of the splanchocranium. Furthermore, the skeleton of the distal appendage elements is also elongated, while the scapula is shortened. All these changes indicate that the skeleton of Lowland-Caucasian bison approaches that of pure B. b. caucasicus, as inbreeding towards the founder of this subspecies increases.

Origin and Genetic Characteristics of Breeding Lines

The Lowland line (L, or Bia這wie瘸 line) originates from Bia這wie瘸 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 (Table 6.1.). 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 (Table 6.1). 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 (Table 9.1). 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 Bia這wie瘸 Forest (fge=1.4) which were created during the first reintroduction. In the Polish part of the Bia這wie瘸 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) (Table 6.3). Other small herds, such as those in Wa販z forest (Poland) could be in a very similar situation from a genetic point of view. Only three herds (Puszcza Bia這wieska, "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 (Table 6.1). The Lowland-Caucasian line (B. b. bonasus ?B. b. caucasicus) (LC-line) [in older Russian literature also called Caucasian-Bia這wie瘸 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 (Table 6.2). 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 "Gatczina", 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% (Table 6.4). 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. The free-living part of the LC line world population is about 700 animals forming 19 isolated (free or semi-free) herds in the territory of Poland, Russia and Ukraine (Table 9.2) (cf. EBPB 2001). None of these free-living herds are safe (genetically or demographically) in the long-term. During the last few years, the Nadvirnjanska and Zalisska herds (Ukraine) have probably lost an essential part of their genetic variability because of the very small number of animals. Only one herd (Bukovynska, 138 animals) can be regarded as a genetically and demographically successful population (Table 9.2). The Cejjskijj herd (north- west Caucasian region, Russia) is rapidly disintegrating because of poaching and its future is unclear. Because of the unstable situation in this region, two other herds (about 60 animals in total) were exterminated in the last years. There are seven very small and unstable herds and four herds undergoing the first steps of reintroduction. The captive part of the Lowland-Caucasian line population is about 860 animals dispersed throughout 169 breeding centres and zoos. The captive population has lost a significant part of its gene pool in the first part of the species restitution and this process is continuing (Table 6.4). There is a successful breeding process in 71 larger captive groups (630 animals); 98 zoos have small groups (up to 4 individuals) only for demonstration purposes (225 animals); and 48 zoos did not send information to the European Bison Pedigree Book (EBPB) annually. In the last 10 years, more than 100 breeding centres and zoos were excluded from EBPB due to a lack of contact. That means that 730 animals from these breeding centres are not included in the only official register for pure European bison.

© Bison Specialist Group - Europe