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Molecular Ecology (2001)
10
, 1959–1966
© 2001 Blackwell Science Ltd
Blackwell Science, Ltd
Y chromosome haplotyping in Scandinavian wolves
(
Canis lupus
) based on microsatellite markers
A.-K. SUNDQVIST,* H. ELLEGREN,* M. OLIVIER† and C. VILÀ*
*
Department of Evolutionary Biology, Uppsala University, Norbyvägen 18 D, SE-752 36 Uppsala, Sweden,
†
Stanford
Human Genome Center, Department of Genetics, Stanford University School of Medicine, 975 California Avenue, Palo Alto,
CA 94304, USA
Abstract
The analysis of mitochondrial DNA sequences has for a long time been the most extensively
used genetic tool for phylogenetic, phylogeographic and population genetic studies. Since
this approach only considers female lineages, it tends to give a biased picture of the popu-
lation history. The use of protein polymorphisms and microsatellites has helped to obtain
a more unbiased view, but complementing population genetic studies with Y chromosome
markers could clarify the role of each sex in natural processes. In this study we analysed
genetic variability at four microsatellite loci on the canid Y chromosome. With these four
microsatellites we constructed haplotypes and used them to study the genetic status of the
Scandinavian wolf population, a population that now contains 60–70 animals but was
thought to have been extinct in the 1970s. In a sample of 100 male wolves from northern
Europe we found 17 different Y chromosome haplotypes. Only two of these were found in
the current Scandinavian population. This indicates that there should have been at least two
males involved in the founding of the Scandinavian wolf population after the bottleneck
in the 1970s. The two Scandinavian Y chromosome haplotypes were not found elsewhere
in northern Europe, which indicates low male gene flow between Scandinavia and the
neighbouring countries.
Keywords
: grey wolf, haplotype, isolation, microsatellites, migration, Y chromosome
Received 7 November 2000; revision received 22 March 2001; accepted 27 March 2001
Introduction
The grey wolf (
Canis lupus
) was once spread all over North
America, Europe and Asia (Mech 1970), but in the early
Middle Ages extermination of wolves began in central and
northern Europe (Carbyn
et al
. 1995). Today, wolves have
disappeared from most of Europe, USA, Mexico and
southern and eastern Asia (Mech 1970). In Scandinavia,
wolves were common until the mid-19th century (Wabakken
et al
. 1992). In 1966, legal protection of the wolf was
introduced in Sweden, but only a few years thereafter the
species was thought to be extinct from the Scandinavian
Peninsula (Naturvårdsverket 2000). However, in 1980, a
few wolves were seen in southern Sweden, in the county of
Värmland, and in southern Norway (Fig. 1; Wabakken
et al
. 1992). These animals formed a stable pack and since
1983 breeding has taken place almost every year in this
area, and the population size has increased. The wolf
population on the Scandinavian Peninsula was estimated to
be about 50–72 individuals in 1998 (Wabakken
et al
. 2001).
As there is no regular occurrence in northern Scandinavia,
the population may be isolated (Fig. 1). The management
situation is complicated since the population, though
small, causes large economic losses to sheep and reindeer
breeders (Naturvårdsverket 2000). Three alternatives have
tentatively been suggested to explain the origin of the
population (Ellegren
et al
. 1996; Wabakken
et al
. 2001):
immigrants from neighbouring populations (e.g. Finland
and Russia), release from captive populations, or survival
of a few individuals during the demographic bottleneck.
The current Scandinavian wolf population has low
levels of genetic variability. A study by Ellegren
et al
. (1996)
showed that all modern Scandinavian wolves analysed
(
n
= 12) shared the same mitochondrial DNA (mtDNA)
haplotype, and that the heterozygosity at 12 microsatellite
Correspondence: Carles Vilà. Fax: + 46–(0)18 4716310; E-mail:
carles.vila@ebc.uu.se
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1960
A.-K. SUNDQVIST
ET AL.
© 2001 Blackwell Science Ltd,
Molecular Ecology
, 10, 1959–1966
loci had decreased over time after recolonization. Addi-
tional analyses, totalling over 30 individuals, have failed to
find additional mtDNA lineages (Vilà
et al
. in preparation).
All the current animals may be descendants of the indi-
viduals that founded the population in the early 1980s
and extensive inbreeding can be expected (Ellegren 1999).
Unless genetic contact can be established with more eastern
wolf populations, a continuous loss of genetic variability
may be inevitable. Inbreeding depression has been reported
in a study of captive wolves from Swedish zoos, e.g. reduction
in juvenile weight, as well as impaired reproduction and
longevity (Laikre & Ryman 1991). Moreover, a hereditary
form of blindness frequently appeared in the same captive
population as a result of inbreeding (Laikre
et al
. 1993). The
founders of the Swedish zoo population were two Swedish
and Finnish full-sib pairs captured in 1950–60 (Ellegren
et al
. 1996). The existence of deleterious alleles in the zoo
founders suggests that Scandinavian wolves have not been
purged of deleterious alleles and therefore that such alleles
might also be present in the contemporary wild popula-
tion. Furthermore, such alleles may currently exist at high
frequencies due to founding effects, potentially causing
inbreeding depression.
Population genetic studies have been greatly facilitated
during the last 10–15 years by the introduction of new
DNA-based approaches. Sequence analysis of mtDNA and
genotyping of highly variable nuclear microsatellites have
become the two standard tools in most genetic surveys in
animals, allowing inferences to be made on phylogenetic
relationships and maternal gene flow (mtDNA), phylogeo-
graphic patterns and levels of genetic variability (mtDNA
and microsatellites), and fine-scale population structure
(mainly microsatellites). Recent advances in human genome
analysis (Lahn & Page 1997) and in human population
genetics (Casalotti
et al
. 1999; Hurles
et al
. 1999; Pritchard
et al
. 1999; Su
et al
. 1999; Thomas
et al
. 2000) now suggest
that Y chromosome haplotyping may develop to become
the third main tool in the next generation of genetic studies
of natural populations. Y chromosome analysis has the
obvious advantage that it specifically follows paternal gene
flow, thus complementing studies of maternal gene flow
based on mtDNA. Several features make the Y chromo-
some a suitable target for population genetics analysis.
Although not having the high mutation rate characteristic
of mtDNA (Seielstad
et al
. 1999), the Y chromosome offers an
essentially inexhaustible source of polymorphisms given
that its size is several orders of magnitude larger than that
of mtDNA and that most of the chromosome, in contrast to
mtDNA, consists of noncoding DNA. Moreover, it repres-
ents a single segregating unit, i.e. being a nonrecombining
chromosome (with the exception of the very small pseudo-
autosomal region), and haplotypes composed of a very
large number of segregating sites can thus be constructed.
In the case of the Scandinavian wolf population, analysis
of Y chromosome haplotypes can, among other things,
provide information on the number of founding males.
There should have been at least as many male founders as
the number of Y chromosome haplotypes present in the
population, assuming no mutation. Additionally, the com-
parison of haplotypes in different populations can be used
to trace the origin of the Scandinavian wolf population. It
can also be used to reconstruct male migration patterns
between populations in northern Europe. Migration of
wolves from other populations (in Finland and Russia;
Fig. 1) might be the only natural way to restore the genetic
diversity in Scandinavian wolves and management
decisions are, and will be, taken depending on the exist-
ence of possible migration (Naturvårdsverket 2000). To
establish a system for Y chromosome haplotyping in wolf
populations we report here the development of locus-
specific microsatellite markers on the wolf Y chromo-
some, based on sequence data presented by Olivier &
Lust (1998) and Olivier
et al
. (1999). We also describe an
initial characterization of their variability in a haplotypic
context. Moreover, we apply these markers to the Scandin-
avian wolf population to address questions about founding
and migration pertinent to conservation issues.
Fig. 1 Present distribution of wolves in Scandinavia and sur-
rounding areas (shaded area). The location of the first appear-
ance of wolves in the early 1980s is indicated with an asterisk
(adapted from Wabakken et al. 2001).
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Y CHROMOSOME MICROSATELLITES IN SCANDINAVIAN WOLVES
1961
© 2001 Blackwell Science Ltd,
Molecular Ecology
, 10, 1959–1966
Materials and methods
Strategy for the development of locus-specific markers
Olivier
et al
. (1999) identified two different microsatellite
sequences (termed MS34 and MS41) from the canine Y
chromosome using a random amplified polymorphic
DNA (RAPD) approach (Olivier & Lust 1998). When
primers for polymerase chain reaction (PCR) amplification
flanking these microsatellite sequences were constructed,
however, none of the primer pairs revealed locus-specific
amplification in dogs. In both cases two fragments,
normally of different size, were obtained from amplification
of male dog DNA, while no amplification was obtained
from females (Olivier
et al
. 1999). We obtained a similar
pattern when we used the primers for amplification of
wolf DNA (data not shown). Since duplication of DNA
sequences is a common event on the Y chromosome
(Jobling
et al
. 1996; Lahn & Page 1997; Tilford
et al
. 2001),
this observation suggests that both these microsatellites
had been duplicated during the evolution of the canine
Y chromosome. To test for this possibility and, if correct,
to be able to develop locus-specific markers that sub-
sequently could be integrated to allow Y chromosome
haplotyping, we cloned amplification products obtained
from wolf DNA with the original primers reported by
Olivier
et al
. (1999) and screened the clones with single-
strand conformation polymorphism (SSCP).
DNA extraction and amplification
DNA was initially extracted from tissue samples from
two male wolves from different populations in Europe
(Latvia and Spain). A modified phenol/chloroform
protocol (Sambrook
et al
. 1989) was used, after digestion
with proteinase K. DNA was dissolved in water and the
concentration was measured with a fluorometer (Hoefer).
The specific canine Y chromosome primers MS34F plus
MS34R and MS41F plus MS41R, developed by Olivier
et al
.
(1999), were used to amplify the corresponding fragments
initially from the two male wolves. PCR reactions included
1
×
PCR buffer II (Perkin Elmer), 0.4 m
m
dNTPs, 0.5
µ
m
of
each primer, 5 mg/mL bovine serum albumin and 0.02 U
Ampli
Taq
Gold polymerase (Perkin Elmer). For MS34
3 m
m
MgCl
2
was used and for MS41 2 m
m
MgCl
2
. The
reactions were run in a total volume of 10
µ
L with 10–50 ng
DNA as template.
The PCR profile for MS34 included an initial denaturation
step at 95
°
C for 10 min, 14 touchdown cycles with 30 s at
95
°
C, annealing at 72
°
C for 30 s and decreasing 0.5
°
C each
cycle, and 1 min at 72
°
C, followed by 25 cycles of 95
°
C for
30 s, 65
°
C for 30 s and 72
°
C for 1 min. An extension step
of 10 min at 72
°
C was added after the last cycle. For MS41
the PCR profile was a similar touchdown reaction but
starting at a lower temperature, i.e. six cycles with
annealing at 68
°
C and decreasing 0.5
°
C each cycle,
followed by 32 cycles as above.
Cloning and sequencing
After PCR, the products were purified with QIAquick
PCR Purification Kit (Qiagen). Ligation of PCR products
into a pUC18 vector was performed at room temperature
for 2 h using the ‘New improved 2*Rapid ligation’ kit
(Promega). Plasmids were introduced into competent
cells by electroporation at 1800 V. Cells were incubated
at 37
°
C over night on agar plates containing X-gal and
IPTG. To be able to discriminate, in the ligations, between
the different Y chromosome fragments containing the
duplicated microsatellites, single strand conformation
polymorphism (SSCP; Hayashi 1991) analysis was used.
Cloned inserts were PCR amplified with the same primers
used previously and PCR products were denatured
and run in 12% acrylamide gels at 3 W for 16 h at 20
°
C.
Afterwards DNA was visualized using silver staining
(Bassam
et al
. 1991). Clones identified as containing
different inserts on the SSCP gel were selected for sequenc-
ing and template DNA was prepared with a QIAquick
PCR Purification Kit. Sequencing was performed using
BigDye terminator cycle sequencing chemistry on an ABI
377 instrument (Perkin Elmer). The corresponding protocols
recommended by the manufacturer were used.
Primer design and microsatellite amplification
New forward primers were designed from the obtained
sequences (see Results), in order to be able to amplify
independently individual copies of the duplicated frag-
ments. These primers were labelled with different fluor-
escence labels (6-FAM and TET) to allow them to be run
together in the same PCR reaction. The four microsatellite
loci identified by this procedure were named MS34A,
MS34B, MS41A and MS41B, and a corresponding nomen-
clature was used for the new forward primers.
The PCR mix for MS34A and MS34B included 1
×
PCR
buffer (Qiagen), 4 m
m
MgCl
2
, 0.8 m
m
dNTPs, 0.5
µ
m
forward primer A, 0.5
µ
m
forward primer B, 1.0
µ
m
reverse
primer and 0.02 U Hot Star
Taq
polymeras (Qiagen). The
PCR profile was 10 min at 95
°
C, followed by 35 two-step
cycles with 30 s at 95
°
C and 45 s at 72
°
C, and was com-
pleted with 10 min at 72
°
C.
The PCR mix for MS41A and MS41B included 1
×
PCR
buffer, 1.5 m
m
MgCl
2
, 0.8 m
m
dNTPs, 0.4
µ
m
forward primer
A, 0.5
µ
m
forward primer B, 0.9
µ
m
reverse primer and
0.02 U Ampli Taq Gold (Perkin Elmer). The PCR profile
included an initial denaturation step at 95
°
C for 10 min
and eight touchdown cycles, with 95
°
C for 30 s, 54
°
C for
30 s decreasing 0.5
°
C each cycle, and 72
°
C for 1 min,
MEC1326.fm Page 1961 Monday, July 23, 2001 5:24 PM
1962
A.-K. SUNDQVIST
ET AL.
© 2001 Blackwell Science Ltd,
Molecular Ecology
, 10, 1959–1966
followed by 35 cycles of 95
°
C for 30 s, 50
°
C for 30 s and
72
°
C for 1 min. An extension step of 72
°
C for 10 min was
added at the end.
Comparison of populations and data analyses
For population comparisons DNA was extracted from
male wolves originating from several populations in
northern Europe. Fourteen wild wolves from Scandinavia
and 13 wolves from the Swedish zoo population identified
as males by the collector and verified by us using ampli-
fication of the SRY gene (Meyers-Wallen
et al
. 1995) were
analysed. Additionally, 16 male wolves from Finland, 26
from Russia and 31 from the Baltic States were genotyped,
to be able to study the relationship between Scandinavian
wolves and animals from neighbouring populations. The
samples were genotyped on an ABI 377 instrument (Perkin
Elmer) and data were analysed using the software programs
genscan
and
genotyper
(Perkin Elmer).
Since the four markers analysed are located in the
nonrecombining region of the canine Y chromosome (see
Results), they can be combined into haplotypes. We used
the number of haplotypes in different populations as a
measure of genetic diversity. Because mutations in micro-
satellite loci are normally produced by the addition or
deletion of one or two repeat units (Ellegren 2000a), two
haplotypes that differ at multiple microsatellite loci or
by multiple repeat units are not likely to have recently
derived from each other.
Results
In order to isolate locus-specific markers from the Y
chromosome microsatellites amplified by two pairs of
primers reported by Olivier
et al
. (1999), we cloned PCR
products obtained in amplification with these primers on
male wolves (see Materials and methods). Two different
types of clones, within each individual, were identified for
MS34. Both types were about 330 base pairs (bp) in length,
and after sequencing they were found to differ by three
point mutations and one insertion/deletion of 2 bp in the
microsatellite flanking regions (Fig. 2a). They varied also
in the number of CA repetitive elements. Similarly, for
MS41 two different types of clones were identified within
each individual. These differed by two point mutations in
the c. 238 bp region amplified, one interrupting the repeat
array in the middle of the microsatellite, and one imme-
diately flanking it (Fig. 2b). Again, the number of CA
repeats was also different between the types. To allow
locus-specific amplification of the different microsatellites,
we used the deletion in MS34 and the point mutation
immediately adjacent to the microsatellite in MS41 to
design, for each marker, two new forward primers to be
used with original reverse primers (Fig. 2). These four new
primer pairs detecting the MS34A, MS34B, MS41A and
MS41B loci all yielded single fragments in amplification of
male wolf DNA. Since no amplification was still obtained
from female DNA (
n
= 138), we conclude that four locus-
specific microsatellite markers had been developed for
the nonrecombining region of the canid Y chromosome.
The four microsatellites were genotyped in 14 males
from the wild Scandinavian wolf population, in 13 males
from the Swedish zoo population and in 73 males from
other north European wolf populations. All markers were
polymorphic with two to nine alleles seen among the 100
male wolves analysed (Table 1). In a preliminary analysis
of haplotype diversity among north European (including
Scandinavian) wolves, 17 different haplotypes were found
Fig. 2 DNA sequences obtained for MS34
(a) and MS41 (b). Identical positions are
indicated with dots, and gaps in the
alignment are indicated with dashes.
Specific forward primers designed to
amplify independently each copy are
indicated by underlined sequences.
Microsatellite sequences are inside the
boxes.
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Y CHROMOSOME MICROSATELLITES IN SCANDINAVIAN WOLVES
1963
© 2001 Blackwell Science Ltd,
Molecular Ecology
, 10, 1959–1966
(Table 2). Three of these haplotypes (A, B and C) were seen
in wild Scandinavian wolves, and a fourth one (D) was
found fixed in the Swedish zoo population (Table 3). A and
B differed by three repeat units at one locus (MS41B) but
were otherwise identical. C differed from A and B at three
loci (MS34B, MS41A, MS41B) by a total of nine and six repeat
units, respectively (Table 2). A total of four haplotypes were
observed in Finland, nine in Russia and 10 in the Baltic
States (Table 3). Haplotypes A, B and D were not found
outside Scandinavia, but haplotype C was also found in the
Baltic States. The haplotypic diversity is lower in Scandinavia
than in the other populations. The number of haplotypes
found per sample analysed was 0.21 in Scandinavia (0.15
excluding haplotype C, see below), and 0.25, 0.35 and 0.32
for Finland, Russia and Baltic States, respectively.
The temporal occurrence of haplotypes A, B and C in
Scandinavian male wolves is shown in Table 4. Haplotype
A was found in three animals collected during the period
1993–99, haplotype B was found in a total of 10 animals
collected during 1984–2000, while haplotype C was only
found in a single individual killed in 1977 in northern
Sweden.
Table 1 Characteristics of four wolf Y chromosome microsatellites
Microsatellite Primer sequence No. alleles Observed length (bp)
MS34A MS34AF 5′-AGCCATTCCTGGCCGAGTGG-3′4 172–178
MS34R 5′-GGTCCCCTTTTGCCATAGTGT-3′
MS34B MS34BF 5′-AGCCATTCCTGGCCGAGTCC-3′5 174–182
MS34R, as above
MS41A MS41AF 5′-TCCTCTAATTTTCCCCTCTA-3′2 208–210
MS41R 5′-CTGCTCGACCCTCTTCTCTG-3′
MS41B MS41BF 5′-TCCTCTAATTTTCCCCTCTC-3′9 212–228
MS41R, as above
Table 4 Time distribution of haplotypes A, B and C in the
Scandinavian wolf population. Each year corresponds to the date
when individual male wolves were killed
Haplotype A Haplotype B Haplotype C
1977
1984
1986
1986
1989
1992
1992
1993
1996
1997
1998
1999
2000
2000
Table 2 Y chromosome haplotypes found in the North European
wolves and allele sizes at four microsatellite loci (in base pairs)
Haplotype MS34A MS34B MS41A MS41B
A 172 182 208 214
B 172 182 208 220
C 174 178 208 226
D 172 180 208 216
E 178 176 208 216
F 176 176 208 218
G 176 178 208 222
H 174 178 208 228
I 172 180 208 212
J
172 180 208 214
K 178 176 208 218
L 174 178 208 222
M 176 178 210 224
O 172 182 208 216
P 178 174 208 216
Q 174 176 208 220
R 174 178 208 214
Table 3 Distribution of Y chromosome haplotypes across wolf
populations in northern Europe
Haplotype
Scand.
(14)
Zoo
(13)
Finland
(16)
Baltic states
(31)
Russia
(26)
A3
B10
C1 3
D13
E656
F53
G211
H332
I1
J
4
K510
L4
M41
O1
P1
Q1
R1
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1964
A.-K. SUNDQVIST
ET AL.
© 2001 Blackwell Science Ltd,
Molecular Ecology
, 10, 1959–1966
Discussion
The isolation and characterization of polymorphic
microsatellite markers on the Y chromosome can help
explain the recovery of the Scandinavian wolf population
during the last decades. One important question is the
number of males that founded the population in the 1980s.
In this study we found three Y chromosome haplotypes
(A, B and C) among modern Scandinavian wolves.
Haplotype C, however, was only found in one individual
from northernmost Sweden killed in 1977. This was before
wolves re-appeared in southern Sweden and this particular
animal, and its relatives, were excluded as founders of
the extant population based on data from mtDNA and
autosomal microsatellite loci (Ellegren
et al
. 1996). Our
results therefore suggest that there could have been as few
as two males involved in the founding of the current
Scandinavian population, given that we only identified
two different Y chromosome haplotypes (A and B) in
samples from southern Scandinavia collected after 1983.
Together with the observation of a fixed mtDNA variant in
the population (Ellegren
et al
. 1996), a minimum of three
founders is suggested (two males and one female). This
agrees with the interpretation derived from the presence
of a maximum of five alleles at autosomal microsatellite
loci (Ellegren
et al
. 1996). Of course, the observation of
two paternal lineages only provides an absolute min-
imum number of male founders, given that multiple
males with identical Y chromosome haplotypes may have
been involved. Similarly, the presence of a fixed mtDNA
variant in Scandinavia represents a minimum number
of founding females because that variant is also very
common outside Scandinavia (Vilà
et al
. in preparation).
We cannot distinguish between the scenarios of two
males founding the population in the early 1980s and only
one early male founder and the other lineage being intro-
duced later. Haplotype A was first seen in a sample from
1993, which might be indicative of a relatively recent
recruitment. However, the limited sample size of males from
before 1993 precludes strong conclusions on this point.
Related to the question of the number of founders is the
origin of founders. If the current Scandinavian wolf popu-
lation descends from immigrants from northern Europe,
e.g. from Finland, Russia, or the Baltic States, we would
have expected to find haplotypes A and B also in these
populations. However, these haplotypes were not seen in any
of our 73 male samples from other north European coun-
tries. Assuming that these samples are from wolves of a
single panmictic population, for any haplotype present in
a frequency of 5% in this population the probability of
being missed in a sample of 73 is lower then 0.025. How-
ever, our preliminary data using mtDNA sequences and
microsatellites suggest that some fragmentation between
north European wolf populations exists (Vilà
et al
. in
preparation). In light of this, although our results are not
evidence of immigration from other North European
populations, it is probably premature to exclude other north
European wolf populations as the origin of the current
Scandinavian population.
The sudden appearance of wolves in southern Scandinavia
in the early 1980s, at least 1000 km from the closest regular
occurrence of Finnish or Russian wolves, led to speculation
about a possible origin from a release from the captive zoo
population (see Ellegren
et al
. 1996). According to the
pedigree for the Swedish zoo population only one sur-
viving paternal lineage should be expected. Indeed, all 13
zoo males analysed in this study shared the same haplo-
type (D), not found in the wild population. From this we
conclude that the paternal lines in the wild Scandinavian
wolf population cannot originate from the Swedish zoo
population.
The presence of Y chromosome lineages in the wild
population not observed in captive or in neighbouring
populations is compatible with the hypothesis that the
extant population could have been derived from some
Scandinavian male wolves surviving during the bottle-
neck. However, we cannot provide any direct support
for this idea. The analysis of these markers in ancient
wolf samples, collected before the population decline
in Scandinavia, could help to address the question.
The three haplotyes found in Scandinavia (A, B and C)
are not likely to have arisen from each other by mutation
in recent times. Assuming that mutations in microsatellite
sequences are normally produced by the addition or deletion
of one or, rarely, two repeat units (Ellegren 2000a), the dif-
ferences between these haplotypes correspond to several
mutational steps. The average mutation rate for human Y
chromosome microsatellites is in the order of 0.2% per
generation (Ellegren 2000b; Jobling & Tyler-Smith 2000).
If this figure is roughly applicable to other mammals and
considering that only a few generations have passed since
wolves reappeared in Scandinavia (mean generation time
of 3 years; Mech & Seal 1987), it indeed seems unlikely
that one of these haplotypes has recently derived from
another. A similar reasoning can be made for excluding a
recent mutational origin of the haplotype found in the
zoo population (D), which differed from the haplotypes
found in Scandinavia at two (A and B; totalling two and
three repeat units, respectively) or three (C; seven repeat
units) microsatellite loci.
The captive and wild Scandinavian wolf populations
show similarly low levels of genetic variability at auto-
somal markers (Ellegren 1999). Our results also indicate
relatively low diversity of Y chromosome haplotypes, con-
sistent with the low diversity of mtDNA variants (Ellegren
et al
. 1996; Vilà
et al
. in preparation). This reduced genetic
variability could be the result of the demographic bottle-
necks. Consequently, the establishment of gene flow with
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1965
© 2001 Blackwell Science Ltd,
Molecular Ecology
, 10, 1959–1966
other populations that could allow the recovery of some
variability is important for the long-term survival of the
Scandinavian wolf population. Our results indicate that
immigration of males might not be taking place and, until
more complete genetic evidence is available, effort should
be allocated to allow gene flow.
This study represents one of the first reports of Y chro-
mosome microsatellites in a wildlife species and their
application for fine-scaled Y chromosome haplotyping in a
natural population. We anticipate that more studies of this
kind will follow. Since dispersal patterns in many organ-
isms are characterized by pronounced differences between
sexes (Greenwood 1980, 1983), the ability to study specific-
ally gene flow in both sexes is highly warranted and will
add to the study of the effects of such differences on phylo-
geographic patterns. Moreover, since variation in male
reproductive success is often higher than that among
females (a consequence of the prevailing direction of sexual
selection, Andersson 1994), the ability to follow patrilines
can be particularly important in studies of social structures
and mating systems. Y chromosome haplotyping obviously
also represents a fast method to exclude possible fathers in
paternity studies and to determine multiple paternities in
single litters or clutches.
Admittedly, however, the use of Y chromosome haplo-
typing in population genetic studies of natural populations
is still often hindered by lack of sequence information
necessary for polymorphism screening. Identification of Y
chromosome microsatellites or single nucleotide poly-
morphisms (SNPs) should thus be given high priority in
population genetic studies. The combined use of SNPs and
microsatellites in Y chromosome haplotyping should allow
both deep-rooted events (slowly evolving SNPs) and more
recent population differentiation (fastly evolving microsat-
ellites; see de Knijff 2000; Forster
et al
. 2000) to be followed.
Acknowledgements
Samples for this study were kindly provided by Zanete Andersone,
Adriano Casulli, Inge Gade-Jørgensen, Ilpo Kojola, Rie Stagegaard,
Harri Valdmann and the Swedish National Veterinary Institute.
We wish to acknowledge Dr Jennifer Seddon, and two anonymous
reviewers for their helpful comments on the manuscript. This
research has been supported by Direktoratet for Naturforvaltning
(Norway), Swedish Environmental Protection Agency, the
Swedish Research Council for Agriculture and Forestry, the
Swedish Hunting Association, the Nordic Arctic Research Program,
and by the Olle Engkvist, Carl Trygger, Oscar and Lili Lamms,
and the Sven and Lilly Lawskis foundations. H.E. is a Royal
Academy of Sciences Research fellow supported by a grant from
the Knut and Alice Wallenberg foundation.
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This study was part of a larger project analysing the genetic
diversity of Scandinavian carnivores that is being done at the
Department of Evolutionary Biology, Uppsala University. Within
this project, led by Hans Ellegren, Anna-Karin Sundqvist (PhD
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Michael Olivier’s PhD Research at Cornell University.
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