Animal Genetics, Zebu-taurine variation in Y ...
Animal Genetics,
Zebu-taurine variation in Y chromosomal DNA:
1994257-12
a sensitive assay for genetic introgression in
West African trypanotolerant cattle populations
D G Bradley, D E MacHugh, R T Loftus, R S Sow, C H Hoste,
E P Cunningham
Summary
millenia (Epstein 1971; Epstein & Mason 1984).
Crossbreeding is a recurring theme in the history
Owing to increasing scientific and agricultural
of African breeds and it is suspected that
interest in the disease-resistant (trypanotoler-
virtually a11 the modern humped cattle of Africa
ant), indigenous cattle breeds of West and
are products of some degree of hybridization
Central Africa, there is a need for a rational
between early migrant zebu and indigenous
genetically based description of populations in
humpless breeds (Loftus 1992).
the region. The greatest threat to the invaluable
The two cattle subspecies inhabit ecologically
genetic resource represented by these animals is
distinct, but overlapping, regions of West Africa
that of extensive genetic introgression of dis-
(Fig. 1; Trail et al. 1980; Hoste et a]. 1988; Lhoste
tantly related zebu cattle from northern popula-
1991). Zebu animals are predominant in the dry
tions which do not share their inherited
Northern, Sahelo-Sudanian regions where their
tolerances. Southern blotting with a chromo-
natural adaptations to heat, poor fodder and long
some Y-specific probe, btDYZ-1 (locus DYZl) is
migrations allow them to prevail. However, these
shown to be a sensitive assay to detect such
cattle are susceptible to trypanosomiasis and
introgression. Evidence of historical crossbreed-
other diseases fostered by a damp environment,
ing is reported in two important N’Dama popula-
such as blood and gastrointestinal parasitism,
tions previously classed as purely taurine.
and skin and tick-borne diseases. Taurine cattle
Keywords: cattle, disease resistance, trypanoso-
form the majority of herds in the southern, more
miasis, genetic introgression
humid, zones which are infested with tsetse fly
(the vector for trypanosomiasis). Breeds such as
Domestic cattle populations in West Africa exhi-
the N’Dama have evolved a tolerance of this and
bit a unique, ancient interface between two
other endemic diseases (Murray et al. 19823,
subspecies, Bos taurus (taurine) and Bos indicus
perhaps because of their association with local
(zebu). These two subspecies seem to have arisen
challenges over several millenia. In traditional
through separate domestication events (Loftus
husbandry systems these animals thrive in
1992; Loftus et al. 1992). Taurine animals in
regions where zebu and exotic breeds may only
Africa are believed to represent the descendants
be sustained with the expensive application of
of the herds maintained by the earliest hus-
chemical prophylaxis a n d vector
control
banders in the continent, having emerged from
measures.
the domestication centres of the Middle East
West African taurine populations, although
some 7000 years BP (Epstein 1971). The N’Dama
composed of smaller, largely unimproved,
breed, centred in Guinea and representing some
animals, form a valuable genetic resource. With
D G Bradley
50% of populations of this type, bears some
the use of these animals, the potential pasture of
D E MacHugh
resemblance to artistic representations of the
over one-third of the continent presently infested
R T LofIus
longhorn animals of the Hamitic peoples of
E P Cunningham
with tsetse fly may become amenable to cattle
ancient Egypt and to paintings discovered on the
Department of Genetics,
production. Indeed, N’Dama have already been
Trinity College,
Bauchi plateau in Nigeria. Other taurine
the basis of successful exportations to Zaire,
Dublin 2, Ireland
shorthorn breeds first appear more recently in the
Gabon and Nigeria, and may be used in ranching,
RSSow
archaeological record, around 4700 years BP
Centre de Recherche
agropastoralism or breeding in palm plantations
(Payne 1970; Epstein 1971). Zebu cattle are more
Zootechnique, Dahra,
(Shaw & Hoste 1987, 1991). However, with
BP
recent migrants to Africa, most populations
1, Sénégal
ecological and agricultural changes in recent
C H Hoste
apparently arising from the major Arab expan-
decades, the genetic integrity of humpless cattle
International Service for
sions into the continent within the last two
in West Africa has been threatened with erosion
National Agricultural
Research, PO Box
Correspondence:
Daniel G Bradley.
by crossbreeding with southerly migrating zebu
93375,2509 AJ The
herds (Lhoste 1991; Bradley 1992). A com-
Hague, the Netherlands
Accepted 10 August 1993
prehensive knowledge of the extent of B. indicus
8
/
i
Brodley, MacHugh,
Loftus, Sow, Hoste,
MAURITANIA
i
C u n n i n g h a m
Fig. 1. Map showing the geographical origins for six West African cattle populations. Three zebu breeds. Gobra,
White Fulani and Sokoto Gudali, are denoted by filled squares and the taurine N’Dama populations are marked by
unfilled circles. The origins of European taurine and East African zebu breeds are not given.
genetic introgression into the trypanotolerant
lack of sequence variability compared with other
populations should be an invaluable genetic
regions of the genome (Ellis et al. 1990; Spurdle &
ba :is for the choice of candidate populations for
Jenkins 1991).
experimental, breeding and conservation pro-
This paper describes two major RFLP patterns
grammes aimed at the preservation and exploit-
achieved by probing B. taurus and B. indicus
ation of the region’s unique resources (Soller &
DNA with btDYZ-1 and discusses how the dis-
Beckmann 1987; Bradley 1992).
tribution of these two types in West Africa
Two major types of Y chromosome have been
provides evidence for historical crossbreeding in
revealed by cytogenetic studies of domestic
the N’Dama herds of the Gambia and Guinea
cattle (Kieffer & Cartwright 1968). The typical B.
Bissau.
taurus Y chromosome morphology is subme-
tacentric, while that of B. indicus is acrocentric.
Both types have been found in African cattle
Materials and methods
(reviewed in Halnan 1989). Also, several Y-spe-
cific DNA sequences
have been cloned, chiefly as
Sampling
a result of research directed at developing sexing
The West African male animals selected for
procedures for preimplantation bovine embryos,
analysis formed part of population samples (50
but only one of these has been reported as
animals each) collected in the Gambia, Nigeria,
detecting polymorphism (Leonard et al. 1987;
Sénégal, Guinea Bissau and Guinea for a com-
Perret et al. 1990; Matthews & Reed 1991,1992).
prehensive survey of bovine genetic variation in
Clone btDYZ-1, containing 60 tandem repe-
the region. Locations of the herds from which the
titions of a motif estimated to occur on the bovine
samples were drawn are shown in Fig. 1 and are
Y chromosome in approximately 6 X 104 copies
listed in Table 1. Animals were chosen from
has revealed restriction fragment length poly-
either recently established large herds, where the
m o r p h i s m s (RFLPs) w h e n h y b r i d i z e d t o
geographical origins of individuals were known,
Southern blots of Belgian Blue cattle (Perret et al.
or from typical members of village herds within
1990). No studies comparing populations have
defined areas. The cosampling of closely related
been published using this or other bovine Y-spe-
animals was avoided by selecting individuals
cific markers. Something of the ancestry of
knowu not to share grandparents. Typically, 2-5
human Y chromosomes has been elucidated
animals were sampled from herds of size 20-150.
using a repetitive DNA probe but additional
European samples were obtained from bulls in
investigation has been hampered by the marked
Irish artiticial insemination centres and here
9
Table 1. Listing of the populations investigated, their country and area of origin and the numbers of taurine and
Zebu-taurine
zebu Y chromosome haplotypes detected in each sample
variation
No. taurine
No. zebu
Breed
Country
Sampling areas
haplotypes
haplotypes
N’Dama
Guinea
Boké
35
0
N’Dama
Guinea Bissau
Bafata, Gabu
16
5
N’Dama
The Gambia
McCarthy Island region
0
26
Gobra
Sénégal
Diourbel Ferlo, Fleuve
0
23
White Fulani
Nigeria
Zaria, Kaduna
1
1 5
Sokoto Gudali
Nigeria
Sokoto
0
14
East African Zebu
Sudan
Shukaba
0
3
European Taurine
Ireland
I’edigree A.I. Stations
44
0
pedigrees were consulted to achieve a minimum
genomic
D N A p r o d u c e d a male-specific
amount of relatedness (Loftus 1992). These
fingerprint as detailed by Perret et al. (1990). No
included 8 Aberdeen Angus, 3 Jersey, 8 Hereford,
hybridization was apparent in three females
1 Kerry, 10 Charolais, 10 Friesian and 4 Simental.
tested. Examples of fingerprint patterns are given
Three East African zebu samples were individ-
in Fig. 2. Two major patterns of hybridization
uals of the Sudanese Kenana and Butana breeds.
were obvious: one corresponding to that
Samples consisted of 20ml of peripheral blood
published previously for Belgian Blue cattle and
collected in 1Oml lithium heparin vacutainer
shared by a11 European cattle tested here; and one
tubes and subsequently stored and transported at
differing markedly from this and occurring
ambient temperatures for up to 10 days. After 10
chiefly in zebu bulls. Seven consistent differ-
days a Sharp fa11 in the quality and yield of
ences from the European pattern are arrowed in
extracted DNA was observed.
Fig. 2. These bands were either a11 present or a11
absent and were taken as diagnostic for assigning
either a zebu or taurine Y-haplotype status to a
DNA extraction
given
animal.
O t h e r , m i n o r differences
Differential lysis of red blood cells was per-
(examples shown) involving higher-molecular-
formed by addition of 1.5 volumes of 10mM
weight autoradiographic bands were observed
KHC03, 150mM NH&l, @lmM EDTA pH 8.0.
within both lineages but were not used as criteria
After 15 min at room temperature white blood
for excluding a given animal from either classifi-
cells were pelleted by centrifugation in a bench
cation. The particular taurine variant pattern
centrifuge at 2OOOg. These were then treated with
described previously (Perret et al. 1990) was not
standard proteinase K digestion, phenol/chloro-
observed.
form extractions and ethanol precipitation. Afri-
The numbers of zebu and taurine Y-haplotypes
cari samples were processed in the Centre de
in each test population are given in Table 1, Al1 B.
Recherche Zootechnique (Kolda, Sénégal], the
indicus animals, with the exception of one Niger-
University of Ibadan (Nigeria) and the National
ian White Fulani bull, showed definitive zebu
Dairy Research Institute (Wad Medani, Sudan).
patterns. Al1 European animals, together with
each of 3.5 Guinean N’Dama bulls, gave taurine
hybridization patterns. However, two morpholo-
Southern blotting
gically B. taurus populations, the N’Dama from
Plasmid btDYZ-1 was kindly donated by Dr
central Guinea Bissau and the N’Dama from the
Michel Georges, Genmark, Salt Lake City, and
McCarthy Island administrative region of Eastern
was used to probe Southern blots of HoeIII
Gambia, showed the presence of zebu haplo-
digested genomic DNA. Gel electrophoresis was
types. The Guinea Bissau sample yielded five
performed at a constant current of 40mA over
zebu from a total of 21 Y chromosomes and,
24h. Southern blots and hybridizations were
surprisingly, a11 of 28 Gambian bulls tested
carried out u s i n g s t a n d a r d protocols a n d
showed a B. indicus Y pattern.
stringencies. a-P32 dCTP and nick translation
(Amersham, UK) were used for plasmid
labelling.
Discussion
Previously, sequencing of the mitochondrial
Results
D-loop of African, Indian and European cattle
Southern hybridizations of btDYZ-1 to total
revealed a grouping of a11 variants into two major
10
lineages. These results are also consistent with
Bradley, MacHugh,
cytogenetic studies which have revealed a major
Loftus, Sow, Hoste,
dichotomy in cattle Y chromosome morphology.
C u n n i n g h a m
mtDNA phylogeny pointed towards a fun-
damental B. indicuslB. taurus division as the
source of genetic dichotomy. This is supported
here and by previous data involving cytogenetic
and protein polymorphism technology (Manwell
& Baker 1980; Graml et al. 1986; Halnan 1989).
However, in African cattle a contrast is evident in
patterns of variation. The present study suggests
that zebu Y chromosomes are introgressing into
taurine populations at a faster rate than other B.
indicus features.
The morphologically taurine N’Dama popula-
tions taken from the Gambia and Guinea Bissau
each show the presence of zebu Y haplotypes,
exclusively SO in the former and at a frequency of
5121 in the latter. Both populations have been
classed as purely taurine previously (Trail et al.
1980), although the Gambian region chosen was
adjacent to one in which some crossbreeding had
been suspected and perhaps should not be inter-
preted as typical of that country. Additionally,
examination of autosomal variation using micro-
satellite markers has yielded estimates for the
extent of zebu genetic influence of 20 and 4% for
these Gambian and Guinea Bissau populations
respectively (Bradley et al. 1992; D. MacHugh,
unpublished). This assymetrical dissemination
of genetic variation is most easily explained as
the result of predominantly male-mediated
Fig. 2. Examples of zebu and taurine restriction frag-
introgression of zebu genes in both recent and
ment length polymorphism (RFLP) patterns achieved
historical times. As a result, Y chromosome
by probing Southern blots of HaeIIT-digested bovine
DNA with Y-specific probe, btDYZ-1. Seven clear band
polymorphism provides the most sensitive assay
differences, which are absent or altered in taurine bulls
for the detection of historical crossbreeding in
and present in a11 zebus tested, are arrowed to the right.
the populations of the region. It is suspected that
Other, additional but less uniform band size variations
the single Nigerian White Fulani zebu exhibiting
are also obvious in the animals chosen. Zebu animals
a taurine pattern is a result of recent crossing
are labelled Zl, 22 and taurine individuals Tl-T3. The
with an imported N’Dama herd.
size markers indicated to the left correspond to frag-
The drought in West Africa between 1972 and
ments of HindIII-digested A phage.
1983, together with changes in agropastoral prac-
tices, has led to major changes in cattle densities
lineages which were interpreted as the results of
in many regions. The four Sahelian countries,
two primary domestication events of different
Mali, Mauritania, Sénégal and Niger, bave, on
subspecies of the wild progenitor, the aurochs
average,
experienced a decrease in cattle
(Loftus 1992; Loftus et al. 1992). The Y chromo-
numbers of 15% in the decade between 1970 and
some data presented here, also reveal a grouping
1981 (Hoste et al. 1988; Lhoste 1991). In 11 more
of variants into two main classifications, where
southerly West African countries numbers have
the bulk of variation occurs between, rather than
increased on average by 16% over the same
within, categories. Through phylogeny construc-
period. Southward migrations of northern zebu
tion, and calibration using two methods, the
breeds such as the Gobra of Sénégal, and
mtDNA common ancestor was estimated to have
consequent
crossbreeding, are threatening the
lived 0.21-1.00 million years BP. Such temporal
genetic integrity of many taurine populations.
calibration of data of the nature presented here is
The Guinean N’Dama exhibit negligible intro-
not possible, but these results would seem
gression probably as a result of the recent politi-
compatible with a comparatively ancient, i.e.
cal situation in that country. Under a previous
predomestic, divergence of the two bovine male
head of state, Sekou Touré, livestock owners
11
were discouraged from remaining and cattle left
Epstein H., Mason I.L. (1984) Cattle. In: Evolution of
Zebu-taurine
instead of entering the jurisdiction. However,
Domesticated Animais (ed. I.L. Mason), pp. 6-27.
variation
this is no longer the case and these populations
Longman, New York.
may be under threat in the near future.
Graml Von R., Ohmayer G., Pirchner F., Erhard L.,
It is generally desirable to preserve the bio-
Buchberger J. & Mostageer A. (1986) Biochemical
diversity of livestock populations (Hall 1990),
polymorphism in Egyptian Baladi cattle and their
which may only be achieved by maintaining
relationship with other breeds. Animal Genetics 17,
their discreteness, and the trypanotolerant cattle
61-76.
Hall S.J.G. (1990) Genetic conservation of domestic
of West Africa represent a particularly important
livestock. Oxford Reviews of Reproductive Biology
genetic resource. International perception of
12,289-318.
these animals has changed in recent decades,
Halnan C.R.E. (1989) Karyotype and phenotype in
from regarding them as interesting but unimpor-
cattle and hybrids of the genus. In: Cytogenetics of
tant historical remnants, to recognizing their
Animals (ed. C.R.E. Halnan), pp. 235-56. CAB Inter-
potential for exploitation of the vast tracts of
national, Wallingford, UK.
tsetse-infested Africa (Trail et al. 1980). They are
Hoste CH., Chalon E., D’Iteren G. & Trail J.C.M. (1988)
increasingly the focus for breeding, experimental
Le bétail trypanotolérant en Afrique occidentale et
and conservation programmes which concen-
centrale, Vol. 3. Bilan d’une décennie. FAO Animal
trate on their natural resistances.
The choice of
Production and Health Paper No. 20/3.
animals for future conservation and utilization
Kieffer N.M. & Cartwright T.C. (1968) Sex chromosome
should be facilitated by genetic characterization
polymorphism in domestic cattle. Journal of
Heredity 56, 3.8-7.
such as that presented here.
Leonard H., Kirszenbaum M., Cotinot C., Chesne P.,
Heyman Y., Stinnakre M.G,, Bishop C., Delouis C.,
Acknowledgements
Vaiman M. & Fellous M. (1987) Sexing bovine
embryos using Y specific DNA probes. Theriongo-
The authors thank Dr Michael J. Stear, Professor
logy27,248.
Max Murray (University of Glasgow), Dr Arouna
Lhoste P. (1991) Cattle genetic resources of West Africa.
Gueye, Dr Adama Faye and Dr Abdou Fall (ISRA
In: Catt!e Genetics Resources, pp. 73-88 (ed. C.G.
Sénégal), Benoît Sauveroche, Hans Wagner
Hickman). Elsevier, Amsterdam.
and Trevor Wilson (FAO regional project, Banjul,
Loftus R.T. (1992) Mitochondrial DNA phylogeny of
the Gambia) and Professor Livy 0. Ngere (Uni-
European, African and Indian cattle breeds. PhD
thesis, University of Dublin.
versity of Ibadan), for their help in the planning
Loftus R.T., MacHugh D.E., Bradley D.G., Sharp P.M. &
and
conducting of
sampling
missions.
Cunningham E.P. (1992) Mitochondrial DNA and
Additional assistance was rendered by Dr M.
inferred relationships between European, African
Dia110 (Boké, Guinea), Dr B. Fye (Gambia), Dr H.
and Asian cattle. Animal Genetics 23 (Suppl. l), 65.
Djata (Guinea Bissau) and the International
Manwell C. & Baker C.M.A. (1980) Chemical classifi-
Trypanotolerance Centre, Gambia. Michel
cation of cattle 2. Phylogenetic tree and specific
Georges (Genmark) kindly provided probe
status of the Zebu. Animal Blood Groups and Bio-
btDYZ-1. This research was funded under Con-
chemical Genetics 11, 151-62.
tract No. TS3*-CT91-0009 of the Science and
Matthews M.E. & Reed K.C. (1991) A DNA sequence
Technology in Developing Countries Programme
that is present in both sexes of Artiodactyla is
of the European Communities.
repeated on the Y chromosome of cattle, sheep and
goats. Cytogenetics and Ce11 Genetics 56,40-4.
Matthews M.E. & Reed K.C. (1992) Sequences from a
References
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Murray M., Morrison WI. & Whitelaw D.D. (1982) Host
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Payne W.J.A. (1970) General introduction to breeds and
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characterisation of indigenous cattle breeds: first
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FAO Animal Production and Health Paper No. 110.
(1990) A polymorphie satellite sequence maps to the
Ellis N., Taylor A., Bengtsson B.O., Kidd J., Rogers J. &
pericentric region of the bovine Y chromosome.
Goodfellow P. (1990) Population structure of the
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Shaw A.P.M. & Hoste CH. (1991) Les échasngees
p@a detects complex PvuII haplotypes and many
Bradley, MacHugh,
internaux de bovins trypanotolérants. 1. Hisotrique
new TaqI haplotypes in Southern African popula-
Loftus, Sow, Hoste,
et synthése. Revue d’Elevage et de Médécine
tions. American journal of Human Genetics 50,
C u n n i n g h a m
Vétérinaire des Pays Tropicales 44,221-8.
107-25.
Soller M. & Beckmann J.S. (1987) Toward an under-
Trail J.C.M., Hoste C.H., Wissocq Y.J., Lhoste P. &
standing of the genetic basis for trypanotolerance in
Mason I.L. (1980) Trypanotolerant livestock in West
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Spurdle A. & Jenkins T. (1991) Y chromosome probe
Zebu-taurine variation in Y chromosomal DNA:
1994257-12
a sensitive assay for genetic introgression in
West African trypanotolerant cattle populations
D G Bradley, D E MacHugh, R T Loftus, R S Sow, C H Hoste,
E P Cunningham
Summary
millenia (Epstein 1971; Epstein & Mason 1984).
Crossbreeding is a recurring theme in the history
Owing to increasing scientific and agricultural
of African breeds and it is suspected that
interest in the disease-resistant (trypanotoler-
virtually a11 the modern humped cattle of Africa
ant), indigenous cattle breeds of West and
are products of some degree of hybridization
Central Africa, there is a need for a rational
between early migrant zebu and indigenous
genetically based description of populations in
humpless breeds (Loftus 1992).
the region. The greatest threat to the invaluable
The two cattle subspecies inhabit ecologically
genetic resource represented by these animals is
distinct, but overlapping, regions of West Africa
that of extensive genetic introgression of dis-
(Fig. 1; Trail et al. 1980; Hoste et a]. 1988; Lhoste
tantly related zebu cattle from northern popula-
1991). Zebu animals are predominant in the dry
tions which do not share their inherited
Northern, Sahelo-Sudanian regions where their
tolerances. Southern blotting with a chromo-
natural adaptations to heat, poor fodder and long
some Y-specific probe, btDYZ-1 (locus DYZl) is
migrations allow them to prevail. However, these
shown to be a sensitive assay to detect such
cattle are susceptible to trypanosomiasis and
introgression. Evidence of historical crossbreed-
other diseases fostered by a damp environment,
ing is reported in two important N’Dama popula-
such as blood and gastrointestinal parasitism,
tions previously classed as purely taurine.
and skin and tick-borne diseases. Taurine cattle
Keywords: cattle, disease resistance, trypanoso-
form the majority of herds in the southern, more
miasis, genetic introgression
humid, zones which are infested with tsetse fly
(the vector for trypanosomiasis). Breeds such as
Domestic cattle populations in West Africa exhi-
the N’Dama have evolved a tolerance of this and
bit a unique, ancient interface between two
other endemic diseases (Murray et al. 19823,
subspecies, Bos taurus (taurine) and Bos indicus
perhaps because of their association with local
(zebu). These two subspecies seem to have arisen
challenges over several millenia. In traditional
through separate domestication events (Loftus
husbandry systems these animals thrive in
1992; Loftus et al. 1992). Taurine animals in
regions where zebu and exotic breeds may only
Africa are believed to represent the descendants
be sustained with the expensive application of
of the herds maintained by the earliest hus-
chemical prophylaxis a n d vector
control
banders in the continent, having emerged from
measures.
the domestication centres of the Middle East
West African taurine populations, although
some 7000 years BP (Epstein 1971). The N’Dama
composed of smaller, largely unimproved,
breed, centred in Guinea and representing some
animals, form a valuable genetic resource. With
D G Bradley
50% of populations of this type, bears some
the use of these animals, the potential pasture of
D E MacHugh
resemblance to artistic representations of the
over one-third of the continent presently infested
R T LofIus
longhorn animals of the Hamitic peoples of
E P Cunningham
with tsetse fly may become amenable to cattle
ancient Egypt and to paintings discovered on the
Department of Genetics,
production. Indeed, N’Dama have already been
Trinity College,
Bauchi plateau in Nigeria. Other taurine
the basis of successful exportations to Zaire,
Dublin 2, Ireland
shorthorn breeds first appear more recently in the
Gabon and Nigeria, and may be used in ranching,
RSSow
archaeological record, around 4700 years BP
Centre de Recherche
agropastoralism or breeding in palm plantations
(Payne 1970; Epstein 1971). Zebu cattle are more
Zootechnique, Dahra,
(Shaw & Hoste 1987, 1991). However, with
BP
recent migrants to Africa, most populations
1, Sénégal
ecological and agricultural changes in recent
C H Hoste
apparently arising from the major Arab expan-
decades, the genetic integrity of humpless cattle
International Service for
sions into the continent within the last two
in West Africa has been threatened with erosion
National Agricultural
Research, PO Box
Correspondence:
Daniel G Bradley.
by crossbreeding with southerly migrating zebu
93375,2509 AJ The
herds (Lhoste 1991; Bradley 1992). A com-
Hague, the Netherlands
Accepted 10 August 1993
prehensive knowledge of the extent of B. indicus
8
/
i
Brodley, MacHugh,
Loftus, Sow, Hoste,
MAURITANIA
i
C u n n i n g h a m
Fig. 1. Map showing the geographical origins for six West African cattle populations. Three zebu breeds. Gobra,
White Fulani and Sokoto Gudali, are denoted by filled squares and the taurine N’Dama populations are marked by
unfilled circles. The origins of European taurine and East African zebu breeds are not given.
genetic introgression into the trypanotolerant
lack of sequence variability compared with other
populations should be an invaluable genetic
regions of the genome (Ellis et al. 1990; Spurdle &
ba :is for the choice of candidate populations for
Jenkins 1991).
experimental, breeding and conservation pro-
This paper describes two major RFLP patterns
grammes aimed at the preservation and exploit-
achieved by probing B. taurus and B. indicus
ation of the region’s unique resources (Soller &
DNA with btDYZ-1 and discusses how the dis-
Beckmann 1987; Bradley 1992).
tribution of these two types in West Africa
Two major types of Y chromosome have been
provides evidence for historical crossbreeding in
revealed by cytogenetic studies of domestic
the N’Dama herds of the Gambia and Guinea
cattle (Kieffer & Cartwright 1968). The typical B.
Bissau.
taurus Y chromosome morphology is subme-
tacentric, while that of B. indicus is acrocentric.
Both types have been found in African cattle
Materials and methods
(reviewed in Halnan 1989). Also, several Y-spe-
cific DNA sequences
have been cloned, chiefly as
Sampling
a result of research directed at developing sexing
The West African male animals selected for
procedures for preimplantation bovine embryos,
analysis formed part of population samples (50
but only one of these has been reported as
animals each) collected in the Gambia, Nigeria,
detecting polymorphism (Leonard et al. 1987;
Sénégal, Guinea Bissau and Guinea for a com-
Perret et al. 1990; Matthews & Reed 1991,1992).
prehensive survey of bovine genetic variation in
Clone btDYZ-1, containing 60 tandem repe-
the region. Locations of the herds from which the
titions of a motif estimated to occur on the bovine
samples were drawn are shown in Fig. 1 and are
Y chromosome in approximately 6 X 104 copies
listed in Table 1. Animals were chosen from
has revealed restriction fragment length poly-
either recently established large herds, where the
m o r p h i s m s (RFLPs) w h e n h y b r i d i z e d t o
geographical origins of individuals were known,
Southern blots of Belgian Blue cattle (Perret et al.
or from typical members of village herds within
1990). No studies comparing populations have
defined areas. The cosampling of closely related
been published using this or other bovine Y-spe-
animals was avoided by selecting individuals
cific markers. Something of the ancestry of
knowu not to share grandparents. Typically, 2-5
human Y chromosomes has been elucidated
animals were sampled from herds of size 20-150.
using a repetitive DNA probe but additional
European samples were obtained from bulls in
investigation has been hampered by the marked
Irish artiticial insemination centres and here
9
Table 1. Listing of the populations investigated, their country and area of origin and the numbers of taurine and
Zebu-taurine
zebu Y chromosome haplotypes detected in each sample
variation
No. taurine
No. zebu
Breed
Country
Sampling areas
haplotypes
haplotypes
N’Dama
Guinea
Boké
35
0
N’Dama
Guinea Bissau
Bafata, Gabu
16
5
N’Dama
The Gambia
McCarthy Island region
0
26
Gobra
Sénégal
Diourbel Ferlo, Fleuve
0
23
White Fulani
Nigeria
Zaria, Kaduna
1
1 5
Sokoto Gudali
Nigeria
Sokoto
0
14
East African Zebu
Sudan
Shukaba
0
3
European Taurine
Ireland
I’edigree A.I. Stations
44
0
pedigrees were consulted to achieve a minimum
genomic
D N A p r o d u c e d a male-specific
amount of relatedness (Loftus 1992). These
fingerprint as detailed by Perret et al. (1990). No
included 8 Aberdeen Angus, 3 Jersey, 8 Hereford,
hybridization was apparent in three females
1 Kerry, 10 Charolais, 10 Friesian and 4 Simental.
tested. Examples of fingerprint patterns are given
Three East African zebu samples were individ-
in Fig. 2. Two major patterns of hybridization
uals of the Sudanese Kenana and Butana breeds.
were obvious: one corresponding to that
Samples consisted of 20ml of peripheral blood
published previously for Belgian Blue cattle and
collected in 1Oml lithium heparin vacutainer
shared by a11 European cattle tested here; and one
tubes and subsequently stored and transported at
differing markedly from this and occurring
ambient temperatures for up to 10 days. After 10
chiefly in zebu bulls. Seven consistent differ-
days a Sharp fa11 in the quality and yield of
ences from the European pattern are arrowed in
extracted DNA was observed.
Fig. 2. These bands were either a11 present or a11
absent and were taken as diagnostic for assigning
either a zebu or taurine Y-haplotype status to a
DNA extraction
given
animal.
O t h e r , m i n o r differences
Differential lysis of red blood cells was per-
(examples shown) involving higher-molecular-
formed by addition of 1.5 volumes of 10mM
weight autoradiographic bands were observed
KHC03, 150mM NH&l, @lmM EDTA pH 8.0.
within both lineages but were not used as criteria
After 15 min at room temperature white blood
for excluding a given animal from either classifi-
cells were pelleted by centrifugation in a bench
cation. The particular taurine variant pattern
centrifuge at 2OOOg. These were then treated with
described previously (Perret et al. 1990) was not
standard proteinase K digestion, phenol/chloro-
observed.
form extractions and ethanol precipitation. Afri-
The numbers of zebu and taurine Y-haplotypes
cari samples were processed in the Centre de
in each test population are given in Table 1, Al1 B.
Recherche Zootechnique (Kolda, Sénégal], the
indicus animals, with the exception of one Niger-
University of Ibadan (Nigeria) and the National
ian White Fulani bull, showed definitive zebu
Dairy Research Institute (Wad Medani, Sudan).
patterns. Al1 European animals, together with
each of 3.5 Guinean N’Dama bulls, gave taurine
hybridization patterns. However, two morpholo-
Southern blotting
gically B. taurus populations, the N’Dama from
Plasmid btDYZ-1 was kindly donated by Dr
central Guinea Bissau and the N’Dama from the
Michel Georges, Genmark, Salt Lake City, and
McCarthy Island administrative region of Eastern
was used to probe Southern blots of HoeIII
Gambia, showed the presence of zebu haplo-
digested genomic DNA. Gel electrophoresis was
types. The Guinea Bissau sample yielded five
performed at a constant current of 40mA over
zebu from a total of 21 Y chromosomes and,
24h. Southern blots and hybridizations were
surprisingly, a11 of 28 Gambian bulls tested
carried out u s i n g s t a n d a r d protocols a n d
showed a B. indicus Y pattern.
stringencies. a-P32 dCTP and nick translation
(Amersham, UK) were used for plasmid
labelling.
Discussion
Previously, sequencing of the mitochondrial
Results
D-loop of African, Indian and European cattle
Southern hybridizations of btDYZ-1 to total
revealed a grouping of a11 variants into two major
10
lineages. These results are also consistent with
Bradley, MacHugh,
cytogenetic studies which have revealed a major
Loftus, Sow, Hoste,
dichotomy in cattle Y chromosome morphology.
C u n n i n g h a m
mtDNA phylogeny pointed towards a fun-
damental B. indicuslB. taurus division as the
source of genetic dichotomy. This is supported
here and by previous data involving cytogenetic
and protein polymorphism technology (Manwell
& Baker 1980; Graml et al. 1986; Halnan 1989).
However, in African cattle a contrast is evident in
patterns of variation. The present study suggests
that zebu Y chromosomes are introgressing into
taurine populations at a faster rate than other B.
indicus features.
The morphologically taurine N’Dama popula-
tions taken from the Gambia and Guinea Bissau
each show the presence of zebu Y haplotypes,
exclusively SO in the former and at a frequency of
5121 in the latter. Both populations have been
classed as purely taurine previously (Trail et al.
1980), although the Gambian region chosen was
adjacent to one in which some crossbreeding had
been suspected and perhaps should not be inter-
preted as typical of that country. Additionally,
examination of autosomal variation using micro-
satellite markers has yielded estimates for the
extent of zebu genetic influence of 20 and 4% for
these Gambian and Guinea Bissau populations
respectively (Bradley et al. 1992; D. MacHugh,
unpublished). This assymetrical dissemination
of genetic variation is most easily explained as
the result of predominantly male-mediated
Fig. 2. Examples of zebu and taurine restriction frag-
introgression of zebu genes in both recent and
ment length polymorphism (RFLP) patterns achieved
historical times. As a result, Y chromosome
by probing Southern blots of HaeIIT-digested bovine
DNA with Y-specific probe, btDYZ-1. Seven clear band
polymorphism provides the most sensitive assay
differences, which are absent or altered in taurine bulls
for the detection of historical crossbreeding in
and present in a11 zebus tested, are arrowed to the right.
the populations of the region. It is suspected that
Other, additional but less uniform band size variations
the single Nigerian White Fulani zebu exhibiting
are also obvious in the animals chosen. Zebu animals
a taurine pattern is a result of recent crossing
are labelled Zl, 22 and taurine individuals Tl-T3. The
with an imported N’Dama herd.
size markers indicated to the left correspond to frag-
The drought in West Africa between 1972 and
ments of HindIII-digested A phage.
1983, together with changes in agropastoral prac-
tices, has led to major changes in cattle densities
lineages which were interpreted as the results of
in many regions. The four Sahelian countries,
two primary domestication events of different
Mali, Mauritania, Sénégal and Niger, bave, on
subspecies of the wild progenitor, the aurochs
average,
experienced a decrease in cattle
(Loftus 1992; Loftus et al. 1992). The Y chromo-
numbers of 15% in the decade between 1970 and
some data presented here, also reveal a grouping
1981 (Hoste et al. 1988; Lhoste 1991). In 11 more
of variants into two main classifications, where
southerly West African countries numbers have
the bulk of variation occurs between, rather than
increased on average by 16% over the same
within, categories. Through phylogeny construc-
period. Southward migrations of northern zebu
tion, and calibration using two methods, the
breeds such as the Gobra of Sénégal, and
mtDNA common ancestor was estimated to have
consequent
crossbreeding, are threatening the
lived 0.21-1.00 million years BP. Such temporal
genetic integrity of many taurine populations.
calibration of data of the nature presented here is
The Guinean N’Dama exhibit negligible intro-
not possible, but these results would seem
gression probably as a result of the recent politi-
compatible with a comparatively ancient, i.e.
cal situation in that country. Under a previous
predomestic, divergence of the two bovine male
head of state, Sekou Touré, livestock owners
11
were discouraged from remaining and cattle left
Epstein H., Mason I.L. (1984) Cattle. In: Evolution of
Zebu-taurine
instead of entering the jurisdiction. However,
Domesticated Animais (ed. I.L. Mason), pp. 6-27.
variation
this is no longer the case and these populations
Longman, New York.
may be under threat in the near future.
Graml Von R., Ohmayer G., Pirchner F., Erhard L.,
It is generally desirable to preserve the bio-
Buchberger J. & Mostageer A. (1986) Biochemical
diversity of livestock populations (Hall 1990),
polymorphism in Egyptian Baladi cattle and their
which may only be achieved by maintaining
relationship with other breeds. Animal Genetics 17,
their discreteness, and the trypanotolerant cattle
61-76.
Hall S.J.G. (1990) Genetic conservation of domestic
of West Africa represent a particularly important
livestock. Oxford Reviews of Reproductive Biology
genetic resource. International perception of
12,289-318.
these animals has changed in recent decades,
Halnan C.R.E. (1989) Karyotype and phenotype in
from regarding them as interesting but unimpor-
cattle and hybrids of the genus. In: Cytogenetics of
tant historical remnants, to recognizing their
Animals (ed. C.R.E. Halnan), pp. 235-56. CAB Inter-
potential for exploitation of the vast tracts of
national, Wallingford, UK.
tsetse-infested Africa (Trail et al. 1980). They are
Hoste CH., Chalon E., D’Iteren G. & Trail J.C.M. (1988)
increasingly the focus for breeding, experimental
Le bétail trypanotolérant en Afrique occidentale et
and conservation programmes which concen-
centrale, Vol. 3. Bilan d’une décennie. FAO Animal
trate on their natural resistances.
The choice of
Production and Health Paper No. 20/3.
animals for future conservation and utilization
Kieffer N.M. & Cartwright T.C. (1968) Sex chromosome
should be facilitated by genetic characterization
polymorphism in domestic cattle. Journal of
Heredity 56, 3.8-7.
such as that presented here.
Leonard H., Kirszenbaum M., Cotinot C., Chesne P.,
Heyman Y., Stinnakre M.G,, Bishop C., Delouis C.,
Acknowledgements
Vaiman M. & Fellous M. (1987) Sexing bovine
embryos using Y specific DNA probes. Theriongo-
The authors thank Dr Michael J. Stear, Professor
logy27,248.
Max Murray (University of Glasgow), Dr Arouna
Lhoste P. (1991) Cattle genetic resources of West Africa.
Gueye, Dr Adama Faye and Dr Abdou Fall (ISRA
In: Catt!e Genetics Resources, pp. 73-88 (ed. C.G.
Sénégal), Benoît Sauveroche, Hans Wagner
Hickman). Elsevier, Amsterdam.
and Trevor Wilson (FAO regional project, Banjul,
Loftus R.T. (1992) Mitochondrial DNA phylogeny of
the Gambia) and Professor Livy 0. Ngere (Uni-
European, African and Indian cattle breeds. PhD
thesis, University of Dublin.
versity of Ibadan), for their help in the planning
Loftus R.T., MacHugh D.E., Bradley D.G., Sharp P.M. &
and
conducting of
sampling
missions.
Cunningham E.P. (1992) Mitochondrial DNA and
Additional assistance was rendered by Dr M.
inferred relationships between European, African
Dia110 (Boké, Guinea), Dr B. Fye (Gambia), Dr H.
and Asian cattle. Animal Genetics 23 (Suppl. l), 65.
Djata (Guinea Bissau) and the International
Manwell C. & Baker C.M.A. (1980) Chemical classifi-
Trypanotolerance Centre, Gambia. Michel
cation of cattle 2. Phylogenetic tree and specific
Georges (Genmark) kindly provided probe
status of the Zebu. Animal Blood Groups and Bio-
btDYZ-1. This research was funded under Con-
chemical Genetics 11, 151-62.
tract No. TS3*-CT91-0009 of the Science and
Matthews M.E. & Reed K.C. (1991) A DNA sequence
Technology in Developing Countries Programme
that is present in both sexes of Artiodactyla is
of the European Communities.
repeated on the Y chromosome of cattle, sheep and
goats. Cytogenetics and Ce11 Genetics 56,40-4.
Matthews M.E. & Reed K.C. (1992) Sequences from a
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