Genetic variability in the European bison

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Bkbemkal Systematicsand Ecok.m, Vol. 15, No. 2, pp. 285-288,1987. Printed in Great Britain.

Genetic Variability in the European Bison MAREK GEBCZY&KI*

and KRYSTYNA TOMASZEWSKA-GUSZKlEWlCZt

Mammals Research institute, 17-230 Bidowieza, Poland; tlnstitute of Genetics and Animal Breeding, Jastrzebiec, 05-551 Mrokow, Poland

Key Word Index-&on

bonasus; European bison; electrophoretic polymorphism; genetic structure.

Abstract-In the European bison, Bison bonasus (L), 15 proteins coded by 20 loci have been studied. Two of these loci (Es-3 and Ca) are polymorphic and the remaining 18 are monomorphic. The average heterozygosity of bisons in Polish herds is 3.5%. The value does not differ from those found in populations of other large mammals in spite of restoration of the European bison population from a mere 13 individuals.

Introduction Some large mammals manifest rather low level of genetic variability if not uniformity. In the African blesbok, for example, individuals exhibit the same genetic pattern [l]. Similar situations have been reported for Mimunga leonina [2] and Cervus nippon [3]. The African elephant [l], the polar bear [4], the black bear [5], seven species of wild living carnivores [S], three species of seals [7], and the Atlantic walrus (81 show a low level of genetic variability. In some cervids, however, the variability may reach fairly high levels attaining in Odocoileus virginianus one of the highest values reported in mammals [9-V]. Nevertheless, it seems that in large mammals, except man, the average variability is lower than that in small mammals [12]. The explanation may be based on the ability of large mammals to cover large distances thus allowing easier contacts between individuals than among small mammals [13, 141. This explanation was challenged by Baccus et a/. [15] who, having studied 10 species of ungulates, maintains that the level of genetic variability does not appear to correlate with body size although it is generally lower than in other mammals. Yet another hypothesis, given by Bonnell and Selander [2], *Present address: University of Warsaw, Branch in BiaQtok, Institute of Biology, 15-887 Bialystok, Sosnowa 54, Poland. (Received 3 May 1986)

centres on the recurring drastic decreases in numbers of the species. Such drastic changes may occur in many populations of the species or may sometimes happen within the entire range of its distribution. Such bottlenecks cause depression or even disappearance of genetic variability. It should be noted that information about genetic structure of free-living large mammals (perhaps with exception of Odocoileus) are scarce, often based on few loci determined in small number of individuals. Additional troubles arise when the species under study happens to be an endangered one, and thus strictly protected. This was the case when the European bison Bison bonasus (L) was taken under consideration. This particular species survived extremely drastic reduction in numbers, All the lowland European bisons living now are descendants of a mere 13 individuals [16]. Recently (1978), after assiduous breeding efforts the number of bisons throughout the world reached 2111 individuals [17], out of which 547 lived in Poland. This increase has made possible the obtaining of more than 100 individuals for various research purposes. This paper describes measurements of the electrophoretic mobility of some proteins and the evaluation of the variability in the European bison bred in some Polish herds (Table 1). We also discuss the genetic variability in large mammals in comparison to B. bonasus. 285

286

MAREK

TABLE 1. NUMBER

OF THE EUROPEAN

BISONS

EXAMINED

GEBCZYtiSKI

AND KRYSTYNA

TABLE 3. PROTEINS

STUDIED.

USED, LOCI DETERMINING Herd

M&S

TOMASZEWSKA-GUSZKIEWICZ

TISSUE

AND/OR

THE PROTEIN,

BLOOD

FRACTIONS

AND NUMBER

OF ALLELES

Females Protein

Tissue

LOCUS

No. of alleles

N

LDH

Sl?r”m

Ldh-1

1

96

Ldh-2

1

9fi

Mdh-1

1

90

Mdh-2

1

90

Me-l

1

90

Me-2

1

90

Pgd

1

90 99

Free ranging Bialowieza

47

45

Borki

10

12

Reserves

MDH

PSXzY”a

3

4

Smardzewice

2

2

Niepottmice

2

3

MC?

Results and Discussion The results obtained for the European bison in electrophoretic analysis of enzymes and nonenzymatic proteins are given below (see Tables 2 and 3). Both plasma and liver tissue gave five-band zymograms for lactate dehydrogenase (LDH). No variation among bisons from various herds was found. Plasma revealed two zones of activity of malate dehydrogenase (MDH) each with one heavily stained band. No variation was found. Malic enzyme (Me) and 6-phosphogluconate dehydrogenase (6-PGD) also gave two-banded zymograms showing no variation. In the American bison, however, 6-PGD is polymorphic [18]. In 86 individuals studied, two were FF type homozygotes, 61 SS-homozygotes and 23 heterozygotes. Catalase (Cat) in red blood cells manifested strong activity. Only one thick band was found with no variation: the same is

TABLE 2. ENZYMES

ANALYSED,

NO.

REFERENCE

%%““l

FOR BUFFER SYSTEMS,

SW”l7-

6-PGD

erythrpcytes

Cat

erythrocytes

cat

1

PGM

erythrocytes

Pgm

1

90

Es-l

1

44

ES

liver

Am I

1

44

Es-3

2

44

Serum

A”l

1

90

Ca

erythrocytes

Ca

2

90

Hb

ewthrocytes

Hb

1

83

CP

serum

Cp

1

90

Alb

Serum

Alb

1

103

Pa

serum

Pa

1

103

Tf

Ser”“l

Tf

1

103

Average

heterozygosity

of polymorphic

of the European

loci equals

010.

bison is 0.035,

and average

number

proportion

of alleles

true of phosphoglucomutase (PGM) and phosphohexoseisomerase (PHI). Three zones of activity for esterases (Es) were found in liver tissue. Two of them correspond with B, (the fastest) and B, (the slowest) in humans [19], the middle one is close to B,. All were inhibited with alpha-napthyl propionate.

AND STAINING

PROCEDURES

Buffer system

Staining

procedure

1 .l .1.27

Lactate dehydrogenase

LDH

[14] No. 3

Cl41 overlay

1.1.1.37

Malate

MDH

[14] No 3

[141 overlay

1.1.1.40

Malic enzyme

Me

[14] No. 3

Cl41 overlay

1.1.1.44

6.Phosphogluconate

1331

[331

1.11.1.6

Catalase

2.7.5.1

Phosphoglucomutase

3.1 .l .l

Esterases

ES

3.2.1 1

a-Amylase

Aml

1211

4.2.1 .l

Carbonic

Ca

1341

w1

5.3.1.9

Phosphohexose

PHI

[331

1331

[14] No. 1

1141 1221

Nonenzymatic

Numbering

dehydrogenase

6-PGD

dehydrogenase

cat PGM

anhydrase isomerase

[14] No. 2

[I41

[331

[331

[14] No

2

v41 [211

proteins Hemoglobin

Hb

Ceruloplasmine

CP

Albumin

Al

WI [271

Postalbumine

Pa

~271

Transferrin

Tf

1271

of enzymes

recommended

by Commission

of Biological

per

locus is 1.10.

Abbreviation

Enzyme

ES-2

Nomenclature

(Enzyme

Nomenclature)

L271 [271 [271 after ref. [191

GENETIC

VARIABILITY

IN THE EUROPEAN

BISON

No variation was found in fast and middle zones whereas the slowest esterase was polymorphic with two alleles. One zone of activity with no variation was found for a-amylase (Am I). Mazumder and Spooner [20] found two amylase loci in cattie blood serum. The amylase band in the European bison corresponds to one of the phenotypes in cattle-the type called FF by Ashton [21]. There was only one locus of carbonic anhydrase (Ca), migrating anodally, at which polymorphism was found. In a total of 90 bisons, 32 individuals were heterozygotic, and 58 homozygotic, but only of the SS type. No FF type homozygotes were found. Also in the American bison polymorphism has been found in Ca locus with three alleles while in cattle only two alleles have been described [22]. In that study on the inheritance of carbonic anhydrase phenotypes in cattle, in total of 31 matings FSXSS there were 10 CaFs, 21 Cass and no CaFf phenotypes. However, another study carried out on 2 927 individuals of cattle of various breeds, likewise in the American bison, did not show any deviation from Hardy-Weinberg equilibrium. This may imply that the deviation observed in the European bison results from too small number of animals in the sample, or may stem from differentiated mortality in this species. There was only one two-band phenotype in the hemoglobin (Hb) locus showing on zymograms with no variation. A similar two-band phenotype was earlier found in the study carried out on four individuals of the European bison by Braend and Gasparski [23]. An identical situation (two loci, no variation) was found in the American bison [24]. Hence both species of Bison differ from cattle where hemoglobin gives a single band. More detailed chromatographic studies did, nevertheless, prove that hemoglobin was a product of two nonallelic Hb structural genes and their alleles [25]. This was indicated by the fact of various widths of respective bands. Similar differences in the width of bands appeared in our study but lack of chromatographic supplementary analysis did not allow the assumption that in the European bison Hb is a product of two codominant genes. Ceruloplasmine (Cp) was found to be monomorphic and showed a single band. This corres-

207

ponds to free fraction (BB) in cattle [26]. Albumin (Alb) also showed a single-band phenotype corresponding to A4 type in cattle [27], while postalbumine (Pa) had a two-band phenotype corresponding to BB phenotype in cattle [271. No variation was found in transferrin (Tf). The three-band fraction in the European bison corresponds to the AA type of Tf in cattle [27]. An earlier study [23] has also found a three-band phenotype in the European bison. So the picture resembles that in the American bison [24]. It should nevertheless be noted that such a threeband picture is characteristic for electrophoresis on starch gel. Separations carried out on polyacrylamide gel give a four-band phenotype. The European bison is a large even-toed ungulate with world total population not exceeding 2,400 animals [28]. The initial period of restitution effort has been carried out with a control of sexual selection [29]. The selection that now takes place within free-living herds is no longer disturbed by human influence. Within these herds the natural selection is stronger than in herds in captivity (enclosures, zoos), and is manifested by a smaller number of calves born per total number of adults in a herd [17]. It has, however, been found that high inbreeding in European bisons that manifested itself even by changes in skeleton proportions [30] does not effect their reproduction in any significant way [16, 311. A significant correlation was found, however, between degree of inbreeding and mortality among calves and young animals [32]. The results obtained in the study suggest that some individuals may be eliminated-as indicated by lack of homozygotes FF in locus Ca. In many breeds of cattle the frequency of allele F is as low as that in the European bison [22]. Very high variability in this locus in the American bison is quite surprising. The frequency of the fastest allele is 0.35. The locus Es-3 in the European bison conforms to the Hardy-Weinberg equilibrium. Moreover in a surprising development the European bisons retained their heterozygosity despite drastic reduction in numbers in the not very distant past. In another species--Mimunga leonina-that underwent similar drastic reduction followed by revival the heterozygosity dropped 121.The average heterozygosity in the European bisons 3.5% falls still within the range

288

of fi found (from 0 to 3.5%) in the species of Artiodactyla studied so far (for detailed refs see [15]). It is therefore less than in small mammals where it stands at about 5% [12]. It should be nevertheless noted that among Artiodactyla this index is extremely variable. In some populations of Odocoileus virginianus, for example n attains values over 12% [I51 while in other populations of this species it varies between 8 and 10% [9]. In the European bison the value of the index remained similar to that of the American bison in spite of the fact that the latter was not subjected to such a drastic drop in numbers as underwent its European counterpart. Thus the numerical bottleneck did not cause disappearance of genetic variability in the European bison.

Experimental All the bisons used for this study were separated from their respective herds and shot after a careful selection. The selection procedures (carried out by the Commission of the State Council for Nature Conservation) aim at elimination of animals of poor physical condition and at calves that have not grown properly, or have been born outside the normal breeding season, etc. The numbers of animals available from various breeding centres varied (Table 1). All the animals, however, were related, as they originate from Bidowieza population. The histon/ of main herds and description of breeding methods applied have been given earlier [29, 301. Blood samples were collected within a few minutes after shooting the animal. The 50 ml blood sample with the erythrocytes separated was collected into heparinized vessels [33]. A second sample (about 150 ml, for blood serum) was left for several hours to allow separation of clots. A liver tissue sample was also collected from the same animal, and kept, until use, at -20”. The samples were analyzed by starch gel electrophoresis for 15 proteins; references for the buffer systems and staining procedures are given in Table 2. Acknowledgements-The technical assistance of U. Niedzielska, J. Lipinska, M. Szuma and J. Dackiewicz is acknowledged by M. G.; that of K. Olbrycht by K. T.-G. We thank Professor 2. Pucek for comments.

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