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Genetic consequences of hunting: What do we know and what should we do



Possible evolutionary consequences of sport hunting have received relatively little con -sideration by wildlife managers. We reviewed the literature on genetic implications of sport hunting of terrestrial vertebrates and recommend research directions to address cur -rent uncertainties. Four potential effects can be ascribed to sport hunting: 1) it may alter the rate of gene flow among neighboring demes, 2) it may alter the rate of genetic drift through its effect on genetically effective population size, 3) it may decrease fitness by deliberately culling individuals with traits deemed undesirable by hunters or managers, and 4) it may inadvertently decrease fitness by selectively removing individuals with traits desired by hunters. Which, if any, of these effects are serious concerns depends on the nature and intensity of harvest as well as the demographic characteristics and breeding system of the species at issue. Undesirable genetic consequences from hunting have been documented in only a few cases, and we see no urgency. However, studies specif -ically investigating these issues have been rare, and such consequences require careful analysis and long time periods to detect. Existing information is sufficient to suggest that hunting regimes producing sex-and age-specific mortality patterns similar to those occur -ring naturally, or which maintain demographic structures conducive to natural breeding patterns, will have fewer long-term evolutionary consequences than those producing highly uncharacteristic mortality patterns.
Wildlife Society Bulletin 2002, 30(2):634–643Peer edited
Genetic consequences of hunting: what do we know
and what should we do?
Richard B. Harris, William A. Wall, and Fred W. Allendorf
AbstractPossible evolutionary consequences of sport hunting have received relatively little con-
sideration by wildlife managers. We reviewed the literature on genetic implications of
sport hunting of terrestrial vertebrates and recommend research directions to address cur-
rent uncertainties. Four potential effects can be ascribed to sport hunting: 1) it may alter
the rate of gene flow among neighboring demes, 2) it may alter the rate of genetic drift
through its effect on genetically effective population size, 3) it may decrease fitness by
deliberately culling individuals with traits deemed undesirable by hunters or managers,
and 4) it may inadvertently decrease fitness by selectively removing individuals with traits
desired by hunters. Which, if any, of these effects are serious concerns depends on the
nature and intensity of harvest as well as the demographic characteristics and breeding
system of the species at issue. Undesirable genetic consequences from hunting have
been documented in only a few cases, and we see no urgency. However, studies specif-
ically investigating these issues have been rare, and such consequences require careful
analysis and long time periods to detect. Existing information is sufficient to suggest that
hunting regimes producing sex- and age-specific mortality patterns similar to those occur-
ring naturally, or which maintain demographic structures conducive to natural breeding
patterns, will have fewer long-term evolutionary consequences than those producing
highly uncharacteristic mortality patterns.
Key wordsalleles, effective population size, evolution, gene flow, genetics, heterozygosity, hunting,
Wildlife managers have historically placed great
emphasis on demographic issues and relatively lit-
tle on how hunting influences genetic characteris-
tics or the evolution of populations (Rhodes and
Smith 1992). However, speaking as hunters as well
as biologists, we value hunting as an experience of
the wild, which in our view is linked inextricably to
the forces of natural selection that have produced
our native species. Few hunters would find interest
or fulfillment in stalking animals housed in a zoo;
similarly, we believe our descendents deserve
opportunities to interact with species shaped prin-
cipally by their native environments, rather than
artificially molded in adaptation to human desires.
In our opinion, integrity of a wild speciesgene
pool deserves respect similar to that accorded to
maintenance of its natural habitat.
Unlike in fisheries, however (e.g., Sutherland
1990, Stokes et al. 1993, Law 2000), North American
game managers have paid little attention to the
Commentary • Harris et al.635
long-term effects hunting may have on the genetic
makeup of game species. This is surprising because
sport hunting alters population density, sex ratio, and
age distribution (Wall 1989, Ginsberg and Milner-
Gulland 1994, Solberg et al. 2000), all of which
potentially influence the genetics of populations.
We addressed four questions relating to common
sport hunting practices and their long-term genetic
consequences: 1) Can hunting alter natural patterns
of gene flow among demes? 2) Can hunting lower
genetic variation, through increasing genetic drift
caused by reduction of effective population size?
3) Can deliberate selection against traits viewed as
undesirable by hunters or managers reduce fitness?
and 4) Can unintentional selection pressures, usual-
ly arising from management based on demographic
criteria alone, have unintended consequences? We
reviewed the existing literature to examine these
questions, and provide some interpretations and
suggest areas where further research is needed.
Hunting and gene flow
Genetic procedures recently described genetic
differentiation within populations that appear mor-
phologically uniform. Localized genetic differentia-
tion has been documented for many hunted
species, including pronghorn antelope (Antilo-
capra americana, Lee et al. 1989), mouflon (Ovis
gmelini, Petit et al. 1997), red deer (Cervus ela-
phus, Strandgaard and Simonsen 1993), red fox
(Vulpes vulpes, Frati et al. 1998), ring-necked pheas-
ants (Phasianus colchicus, Warner et al. 1988,
Robertson et al. 1993), and bobwhite quail (Colinus
virginianus,Nedbal et al. 1997). In white-tailed
deer (Odocoileus virginianus), considerable differ-
entiation exists among neighboring subpopulations
on a genetic level (Sheffield et al. 1985, Scribner et al.
1997). It appears that local differences in white-
tailed deer are maintained by philopatry among
females, but subpopulations are prevented from
becoming too subdivided by male dispersal
(Mathews and Porter 1993, Purdue et al. 2000; see
Cronin et al. 1991 for similar findings in mule deer,
O. hemionus). If males become rare through hunt-
ing, one concern is that the existing level of gene
flow may be reduced further, strengthening popula-
tion differentiation at the expense of genetic vari-
ability within localized demes (Ellsworth et al. 1994).
Conversely, for species that are naturally
philopatric or territorial, local genetic adaptations
might be lost if gene flow among demes is
increased due to the alteration of social structure
caused by hunting. Kurt et al. (1993) examined
populations of European roe deer (Capreolus
capreolus) living in both forested and open habi-
tats. In forest habitats, male roe deer were territo-
rial, controlled access to a number of females, and
variance of reproductive success among males was
high. In open habitats, males were more migratory,
a larger proportion of adult males succeeded in
breeding, and genetic mixing within populations
was greater. These differences evidently reflected
adaptive responses to the variability of environ-
mental resources, and were maintained locally by
low levels of gene flow. However, under high hunt-
ing rates, gene flow between the 2 social systems
increased, and this differentiation began to break
Similarly, among territorial greywing francolin
(Francolinus africanus), Little et al. (1993) found
no difference in heterozygosity (H, the percentage
of loci that are heterozygous in an average individ-
ual) between hunted and unhunted populations,
but higher levels of inbreeding in unhunted popu-
lations. They concluded that any reduction in H
caused by lower population size was compensated
by greater gene flow within the hunted population.
The net effect on Hwas neutral (i.e., higher migra-
tion rates were balanced by fewer potential
migrants), but hunting clearly had contributed to a
breakdown in the usual territorial structure.
Frati et al. (2000) interpreted lower genetic vari-
ability among unhunted populations than hunted
populations of red fox in Europe as reflecting
changes in fox social structure following the loss of
larger predators. Historically, with the presence of
wolves (Canis lupus), leopards (Panthera pardus),
and lynx (Lynx lynx, L. pardinus), fox social struc-
ture was flexible and outbreeding common. They
suggested that hunting, by increasing turnover and
decreasing inbreeding, could partially mimic the
effects of predation pressure under which foxes
had evolved.
Hogg (2000) found that mid-ranking male
bighorn sheep (Ovis canadensis) from an unhunt-
ed population made temporary migrations during
rut to an adjacent hunted population. These rams
faced less competition for mates from the relatively
few high-ranking males in the hunted population
and enhanced their breeding opportunities by mov-
ing. Here, gene flow from one deme to another was
again increased, but in this case the probable deter-
minant was not hunting per sebut rather the
abrupt contrast in density of older, larger-horned
males between adjacent demes.
636Wildlife Society Bulletin 2002, 30(2):634–643
The available evidence suggested to us that alter-
ations in naturally occurring patterns of gene flow
would seem possible from any type of hunt; some
level of social disruption must accompany any
removal of individuals. We found this troublesome
only when locally adapted gene complexes were
compromised by hunting-induced gene flow,
where gene flow would otherwise be discouraged
by social behaviors. As the red fox example sug-
gested, a hunting-induced increase of gene flow
among adjacent demes may help mitigate other
man-made reductions of gene flow.
Hunting and genetic drift
Genetic drift is the random change in gene fre-
quencies caused by sampling (via sexual reproduc-
tion) from a finite population. Genetic drift occurs
in all populations, but its effects become pro-
nounced only if effective population size (N
) is
small. N
is the number of individuals in an ideal
population expected to lose genetic variation at the
same rate as the census population (N) (Wright
1969, Harris and Allendorf 1989). With small N
, H
is expected to decline, rare alleles are expected to
be lost, and alleles may become fixed regardless of
their effect on fitness.
Relevant questions were whether N
eof hunted
populations might be small enough for drift to be a
legitimate concern, and whether hunting regimes
further reduce it. Concern about small N
expressed for introduced herds of bighorn sheep
(Fitzsimmons et al. 1997) and upland birds (Little et
al. 1993). Ryman et al. (1981) simulated moose
(Alces alces) and white-tailed deer populations, cal-
culating N
based on various approximations from
demographic statistics. They found that N
likely to be much lower than N, even in a popula-
tion exposed to no selective hunting. N
were additionally reduced under most hunting sce-
narios simulated. Although reductions in N
under hunting were not large, Ryman et al. (1981)
did not simulate hunts featuring extreme selection
for males. They found N
/Nratios as low as 0.2 (i.e.,
a population of 100 would experience genetic drift
at the rate of an ideal population of 20), but point-
ed out that extreme selectivity for males in the hunt
could further reduce this ratio.
Harris and Allendorf (1989) varied hunting
regimes for hypothetical grizzly bear (Ursus arctos)
populations, finding relationships between the type
of hunt and N
. In some cases, N
/Nincreased from
the nonhunted situation, because reproductive suc-
cess among males became more equitable.
However, in hunting scenarios where the number
of males became limiting, N
/Ndeclined from its
unhunted level.
Wall (1989) examined demographics and het-
erozygosity of white-tailed deer populations in
Texas exposed to hunts with differing selectivities.
Although he was unable to estimate variation in
reproductive success, an important determinant in
e(Harris and Allendorf 1989), Wall (1989) com-
pared “maximum N
among populations based on
the demographic parameters and assuming no dif-
ferences in variance of reproductive success.
Variable hunting strategies had profound effects on
/N. However, because those hunting regimes
reducing N
/Noften were designed to keep Nhigh,
generally varied less than did N
/N. For exam-
ple, populations exposed to buck-only harvest had
low N
/N(because few bucks dominated breed-
ing), but high N
(because census population size
remained high, being primarily a female popula-
tion). In contrast, hunting regimes with a relatively
high female harvest (and more equitable sex ratios)
had the highest N
/Nratios, but lower N
the total population was lower). His sampling of
genetic attributes suggested, however, that genetic
drift (as documented by H) was a substantial con-
cern only in the smallest, most isolated population.
Concerns about low N
have been appropriately
focused on small or declining populations
(Allendorf and Ryman 2002) rather than on the
larger populations typically subjected to sport
hunting. Managers of sport hunts should be mind-
ful, however, of the potential for undesirable genet-
ic consequences of low N
ewhere high harvest
rates produce severely skewed sex ratios. Sex ratios
of about 1 adult male:10 adult females were docu-
mented for elk (Cervus elaphus, Leptich and Zager
1991, Noyes et al. 1996) and mule deer (Scribner et
al. 1991), and are probably common in other
species where males are selectively hunted. We
agree with Scribner et al. (1991) that large popula-
tion size substantially reduces the concern about
genetic drift. Nevertheless, smaller breeding
groups of related individuals may occur within larg-
er populations because of strong site fidelity by
females (Scribner et al. 1991). Therefore, highly
skewed sex ratios may increase the frequency of
inbreeding even in the presence of little popula-
tion-wide genetic drift. Most managers of ungulate
populations attempt to prevent adult sex ratios
from reaching such extremes in order to maintain
normal breeding behavior. We believe that loss of
Commentary • Harris et al.637
genetic variability, even if nested within a larger
population, is another reason to avoid highly
skewed sex ratios.
Hunting and deliberate selection
Many European wildlife managers have tradition-
ally attempted to alter antler or horn characteristics
of artiodactyls by selectively culling those consid-
ered inferior (Webb 1960, Taber 1961, Hartl 1991,
Sforzi and Lovari 2000). Culling of yearling white-
tailed deer with poor antler development was also
suggested in the southeast United States (Harmel
1983, Cook 1984, Newsome 1984, but see Lukefahr
and Jacobson 1998). Although such management
might be seen as a partial correction to practices
where only the largest animals are taken, it is not
without risks. By selecting for one particular trait
of perceived value to humans, we believe it likely
that management simultaneously (if inadvertently)
selects against other traits potentially of adaptive
significance for the species (Voipio 1950, Klein et
al. 1992). In particular, relatively rare alleles that
might be important in a long-term evolutionary per-
spective are vulnerable to loss when such selection
for other traits takes place.
Research on red deer in Europe provided com-
pelling evidence that deliberate selection could
have unintended consequences. In France, Hartl et
al. (1991, 1995) found that alleles at loci Idh-2, Me-
1, and Acp-1were associated with body and antler
size in red deer. Deliberate culling of yearling bulls
with undesirable antler characteristics rapidly
increased the frequency of an allele (Idh-2
) pos-
itively correlated with number of antler points.
Importantly, Pemberton et al. (1988) found that
juvenile survival among juvenile female red deer in
Scotland heterozygous at this same Idh-2locus was
higher than among homozygous individuals. Thus,
by selectively removing males with small antlers
and thus reducing the frequency of the alternate
allele at Idh-2, it appeared that French hunters may
have also unwittingly selected for poor juvenile sur-
vival (Hartl 1991). In general, when one phenotyp-
ic trait is maximized other traits are inevitably (and
probably unknowingly) affected because life-histo-
ry strategies inevitably involve trade-offs among
various fitness components related to demographic
equilibrium (Pemberton et al. 1991). Thus, human
attempts to “improvehunted species through
selective culling seem certain to produce unfore-
seen consequences. Similarly, releasing penned
deer bred specifically for antler growth (Cook
1984) into the wild (to produce large “super
bucks”) seems to us careless disregard for this fun-
damental concept.
Hunting and unintentional selection
North American managers have often down-
played possible genetic consequence of selective
hunting, focusing instead on maximizing yield
either of total animals or of trophy males. However,
harvest regimes that are focused on removing large
males risk producing inadvertent directional selec-
tion against the very characteristics (usually large
antlers or horns in artiodactyls) that hunters desire.
We distinguished the effects that selective hunting
may have on genetic diversity generally (as indicat-
ed by H) from those leading to loss of specific alle-
Selective hunting and H
His often (albeit not universally) thought to be
related to fitness in natural populations (Allendorf
and Leary 1986, Britten 1996, Coltman et al. 1999).
In white-tailed deer, studies have reported positive
correlations between Hand twinning (Johns et al.
1977, Chesser and Smith 1987), fetal growth
(Cothran et al. 1983), body weight (Smith et al.
1982), body size (Chesser and Smith 1987), and
antler size (Scribner et al. 1989). The last-named
authors considered it likely that higher Hresulted
in higher metabolic efficiency, and thus decreased
maintenance-energy requirements, leading to larger
antlers. Fitzsimmons et al. (1995) found slightly
greater yearly horn growth among >
bighorn sheep rams that were heterozygous at >
loci than among those heterozygous at a zero or
one locus.
However, other studies have found no correla-
tions between Hand body mass or number of
antler points in white-tailed deer (Sheffield et al.
1985) and red deer (Hartl et al. 1991). Chesser and
Smith (1987) reported negative as well as positive
correlations between Hand components of repro-
duction related to fitness. Further, the relationships
involving antler or horn growth observed by
Scribner et al. (1989) and Fitzsimmons et al. (1995)
occurred only for older age-classes. Because the
majority of antler and horn growth occurred in
younger classes (for which no correlation with H
was found), the total amount of variation attributa-
ble to Hclass was low. Antler and horn growth also
are known to respond to environmental factors
(and the largest single determinant of size usually is
638Wildlife Society Bulletin 2002, 30(2):634–643
age class), so it is difficult to distinguish the effects
of Hon horn or antler size.
Can selection imposed by hunting reduce H?
Fitzsimmons et al. (1995) voiced concerns that
selectively removing the largest rams by hunting
would, perhaps unintentionally, reduce genetic
variability in such populations. Although not specif-
ically designed to examine such a possibility, the
work of Wall (1989) provided some insight.
Despite widely varying hunting regimes (and thus
standing age structures), he found no differences in
H, as measured by allozymes from harvested deer,
among populations examined. If antler quality
were related to H, we might expect hunter-harvest-
ed samples from those hunts featuring the greatest
selectivity for trophies to exhibit higher Hthan
those from less selective hunts.
We found that the evidence for selective removal
of relatively more heterozygous individuals within
natural populations was weak. Perhaps more
importantly, loss of Hcaused by removal of individ-
uals that tend to be heterozygous at specific loci is
a reversible process. That is, even if heterozygotes
were selectively removed, heterozygous progeny
would be regenerated the next generation by mat-
ings between individuals that are homozygous for
different alleles (Mitton 1997). Thus, although pos-
sible deleterious effects from selective removal of
heterozygous individuals bears monitoring, it does
not appear to be a serious problem.
Selective hunting and changes in allele
A slightly different mechanism may come into
play where hunter selectivity is based on pheno-
typic traits such as horns or antlers. Such hunts
may unintentionally select against those very traits
by reducing the life span (and thus the reproduc-
tive contribution) of individuals carrying specific
alleles. Festa-Bianchet (2002) suggested that heavy
hunting can alter selective pressures of female
artiodactyls from those favoring high survival and
low maternal investment per litter to those favoring
early reproduction and lower survival. We share
with Festa-Bianchet (2002) additional concerns
about long-term genetic consequences of trophy
hunts on phenotypic characteristics of males.
The empirical literature is ambiguous on
whether hunting regimes focused on taking males
with large horns or antlers unintentionally alters
allele frequencies (as evidenced by phenotypic
changes). Dubas and Jezierski (1989) documented
declining antler quality and carcass weight by age
over a 6-year time period in European red deer,
speculating that selective hunting may have played
a part. However, population density also increased
during their study, confounding interpretation
(Clutton-Brock et al. 1982). Ludwig and Hoefs
(1995) discounted hunting as a possible factor in
their finding that Dall sheep (Ovis dalli) in a hunt-
ed population had shorter horns than did those in
the adjacent (unhunted) Kluane National Park
despite similar age distributions (horn circumfer-
ences in the 2 populations did not differ). Solberg
and Sæther (1994) reported no decline in antler
size over a 23-year period of moose harvest. In con-
trast, Shea and Vanderhoof (1999) observed a reduc-
tion in antler size of 2.5-year-old white-tailed deer 5
years after initiation of a hunting regime intended
to increase antler size by prohibiting harvest of
small-antlered bucks. They attributed the unex-
pected reduction to “high-grading(i.e., selective
killing) of bucks born earlier during their year of
birth. Their data also showed that early birth was
associated with larger antlers, leaving predominant-
ly late-born bucks to survive to 2.5 years. Shea and
Vanderhoof (1999) evidently did not examine the
genetic basis of these changes, but selective hunt-
ing of larger bucks may have changed frequencies
of alleles that contributed to antler size.
In most cases hunters prefer to harvest large
artiodactyls, and horn or antler size is generally cor-
related with male fitness. However, it does not fol-
low that hunting removes relatively more fit indi-
viduals in all cases. Artiodactyl males begin with
small horns or antlers that become progressively
larger with age. Hunters selecting for individuals
with the largest horns or antlers remove primarily
old individuals, not necessarily those with genomes
conducive to producing large secondary sexual
characteristics. Changes in allele frequencies
caused by selective hunting of large males may be
buffered by the genetic contributions of females,
which will have most of the same alleles as males
but are likely to be subject to differing selective
pressures. Finally, other factors may affect vulnera-
bility to hunting independent of hunter selectivity.
For example, DuFour et al. (1993) found that mal-
lards in poorer body condition were more vulnera-
ble to hunting than those in better condition.
Given these complexities and ambiguities, we
believe the simulation model constructed by
Thelen (1991; see also Hundertmark et al. 1993,
1998) currently provides the best indication of
how selective hunting might unintentionally alter
the genetic constitution of big game populations.
Commentary • Harris et al.639
Thelen (1991) assumed that antler characteristics of
elk were polygenic traits, inherited in simple
Mendelian fashion but with no dominance or epis-
tasis. Antler size increased with age, but antler char-
acteristics were also assumed to be an additive func-
tion of multiple loci (i.e. the greater the number of
alleles favorable for large antlers, the larger the
antlers). Heritability, the proportion of variation in
antler size attributable to genotype, varied from 25%
to 75%. Breeding success was controlled by both
age and antler size. Age-specific survival of bulls was
also negatively correlated with antler size (i.e., a sur-
vival cost of carrying heavy antlers was assumed).
Hunting strategies were modeled to reflect various
possible management objectives. Hunting regimes
that specified minimum antler sizes always reduced
the frequency of large antler alleles in modeled pop-
ulations. When heritability of antler traits was mod-
eled as 50%, allele frequencies were altered by
approximately 10–20% after 50 years. When heri-
tability was assumed to be 75%, the 50-year reduc-
tion in favorable allele frequency was on the order
of 20–25%; with heritability of 25%, the 50-year
reduction was about 10% (Figure 1).
By contrast, other hunting regimes had little
effect on the frequency of existing alleles in the
population. A nonrestricted harvest strategy, in
which the sex and age of individuals harvested was
directly proportional to their abundance in the
population, had little effect on allele frequency
after 50 years. The nonrestricted hunting regime
also resulted in relatively high yield overall, but low
yield of trophy males. But a split hunting regime, in
which spike (mostly yearling) and >
5 point (tro-
phy) males were legally taken (but 2–4 point males
protected) resulted simultaneously in moderate
overall harvest, moderate harvest of trophy males,
and little change in large-antler alleles (Figure 1).
It is likely not coincidental the mortality pattern
produced by the split hunting regime resembled
that of an ungulate population experiencing only
nonhunting mortality (high mortality in young age
classes, low among mature animals, high again as
animals senesce). Thelen’s (1991) model suggested
the possibility of achieving a sustainable harvest
(including of trophy males) while avoiding sub-
stantial alterations in allele frequencies, by moder-
ating hunting pressure focused on large males and
simultaneously harvesting young males vulnerable
to natural mortality. Klein et al. (1992) also recom-
mended a split hunting regime as one that would
produce a good compromise between hunter satis-
faction and long-term evolutionary concerns.
Thelen’s results were sensitive to heritability of
antler size (Figure 1). There is little doubt that
antler characteristics are heritable traits (Harmel
1983, Williams et al. 1994, Lukefahr and Jacobson
1998, Wang et al. 1999). However, all studies to date
have estimated heritability under captive condi-
tions, thus the “unexplainedportion of antler vari-
ability (i.e., that remaining after inheritance is
explained) has been low. In the wild, we would
expect age-specific antler size to vary considerably
with nutritional status as well as with genotype
(Brown 1990).
An additional, important factor in such models is
the strength of reproductive advantage enjoyed by
males with desired traits. Conventional wisdom
suggests that males with the largest horns and
antlers have the highest reproductive success
(Solberg and Sæther 1994). But just how much
higher? The rate of loss of alleles affecting horn and
antler size on the population caused by hunter
selection of large males would be higher if males
vulnerable to hunting dominate the breeding, and
lower if smaller males (which would presumably
survive a selective hunt) also make substantial con-
tributions under natural conditions.
In unhunted red deer, paternity data showed not
only that dominant bulls had greater reproductive
Figure 1. Percent change after 50 years in frequency of alleles
modeled as favorable for large antler formation in elk, under 4
alternative hunting strategies, and assuming antler heritability
of 25%, 50%, and 75%. Under “nonrestricted” hunts, bulls
were killed in the simulated hunt in proportion to their abun-
dance; under “2-” and 4-point minimum” hunts, only bulls
with these antler characteristics were killed; “spike and 5+
points” hunts protected males with 2–4 points from hunting
mortality. Adapted from Thelen (1991).
640Wildlife Society Bulletin 2002, 30(2):634–643
success than did subordinates, but also that their
relative success was even greater than had been
estimated from behavioral data (Pemberton et al.
1992). Younger, smaller, or less dominant bulls did
relatively little breeding. In contrast, paternity data
on bighorn sheep in two intensively studied popu-
lations showed that high-ranking rams, while still
more successful than lower ranking rams, fathered
fewer lambs than would have been estimated from
only observing their success at tending estrous
ewes (Hogg and Forbes 1997). Rams using “uncon-
ventionalcourting tactics associated with lower
rank were surprisingly effective in contributing
their genes to subsequent generations. Thus, a vari-
ety of alleles in bighorns may be transmitted to sub-
sequent generations by smaller, younger rams that
would be unaffected by strongly selective hunts.
We suspect that long-term changes in allele fre-
quencies are a common attribute of terrestrial pop-
ulations subjected to strongly selective hunting. It
is difficult to see how it could be otherwise, given
that hunting often constitutes the largest source of
mortality (Festa-Bianchet, 2002). However, because
age and environment exert major influences on
size, mating systems are often flexible, gene flow
among adjacent populations that vary in mortality
patterns may replenish vulnerable alleles, heritabil-
ities of phenotypic traits observable to hunters may
be low, and offtake rates usually are moderated in
the most strongly selective hunts, we expect such
changes to occur gradually and to be undetectable
for many generation lengths.
Research directions
Research into genetic effects of hunting has been
much less common than research into demograph-
ic and behavioral effects of hunting. Several impor-
tant questions remain unanswered: 1) under what
conditions is the alteration of gene flow among
population subdivisions resulting from hunting of
sufficient magnitude to cause problems? 2) does
selective hunting preferentially take more het-
erozygous individuals than would a random hunt,
and if so, does this reduce heterozygosity in the
population? and 3) how much breeding is con-
ducted by subordinate males, and how does that
change under various hunting regimes? Answers to
these questions are likely to vary by species, and
perhaps also geographically.
Now that genetic techniques allow paternity
determination (e.g., Hogg and Forbes 1997, Cronin
et al. 1999), researchers are in a much better posi-
tion to understand male reproductive success, its
correlates, and its variance. Understanding patterns
of male reproductive success has implications for
the survival effects on other age classes of remov-
ing dominant males, influences of removing domi-
nant males on breeding activity of females, and of
the effects of management on genetically effective
population size (N
), which, in turn, tells us about
the magnitude of genetic drift. It is most useful to
add paternity studies to populations already under
intensive demographic study, but where these con-
ditions exist, the laboratory expenses usually will
be justified by the insight gained. Where paternity
studies are conducted and phenotypic information
also obtained, the opportunity exists to document
the heritability of secondary male sexual character-
istics of interest to hunters (usually horns or
antlers) under wild conditions. The strength of her-
itability remains a critical, but largely unknown,
piece of the puzzle in considering the long-term
evolutionary consequences of selective hunting in
ungulates (Rèale et al. 1999, Kruuk et al. 2000).
Indirect information on possible directional
selection of genomes can also be obtained from
existing data sources (e.g., hunter check-stations)
by careful examination of long-term data sets com-
paring hunting intensity to trends in horn/antler
size by age. Confounding effects, such as popula-
tion density and varying environmental conditions,
will need to be carefully considered. Further labo-
ratory analyses (e.g., using carcasses at hunter
check-stations) correlating the presence of specific
alleles, as well as estimates of H, with male charac-
teristics (coupled with sampling of unhunted indi-
viduals) would further elucidate whether selective
hunting has disruptive effects on Hand allelic
We began by expressing concern about the long-
term genetic consequences of hunting, but our
review of the literature suggested little empirical
evidence of such consequences. We have hypothe-
sized a number of characteristics of hunting and
hunted species that may act to mitigate expected
negative effects. However, we found no grounds for
complacency; studies designed to quantify genetic
effects have been rare, and the effects eliciting our
greatest level of concern are subtle and difficult to
detect without long-term monitoring.
We stress that demographic and genetic changes
occur on different time scales. Demographic
Commentary • Harris et al.641
effects are often immediate and easily recognized;
genetic changes occur over evolutionary time
scales of many generations. Thus, although short-
lived actions are unlikely to have genetic effects
over the long term, any genetic changes will be dif-
ficult to detect because of the time scale over
which they occur. For example, it would require
careful study to detect the effects of a hunting man-
agement scheme that decreased mean antler size
by 4% per generation (i.e., 1% reduction/yr in a
species where the mean age of reproduction was 4
years). However, such a rate of change may have
substantial effects over the long term. For example,
this rate of change would reduce mean antler size
by 30% in 50 years.
We urge managers to consider not only the main-
tenance of genetic diversity, but also whether the
primary selective forces influencing adaptations in
hunted populations have become artificial rather
than natural. Where concern is justified, it is pru-
dent to manage hunting such that the age-specific
survival pattern (and thus age-specific breeding
structure) emulates that occurring in the absence
of hunting (Klein et al. 1992, Hundertmark et al.
1993). Such hunting regimes will generally pro-
duce little alteration in allele frequencies, have low
chance of causing extinction of rare alleles, mini-
mize extremely skewed sex ratios (and thus have
less effect on N
),and still allow for the hunting
opportunities we cherish.
Acknowledgments. We thank P. Voipio for pro-
viding a copy of his classic monograph on the
genetic effects of game management. M. S. Boyce,
W. J. Sutherland, W. M. Ford, M. A. Cronin, J. T. Hogg,
and 2 anonymous reviewers suggested improve-
ments to earlier versions of this manuscript.
Funding for R. B. Harris during initial portions of
this work was provided by Safari Club
International. We thank J. Hensiek and P. Sandstrom
for translation help, and the staff at the Maureen
and Mike Mansfield Library at the University of
Montana for assistance.
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Address for Richard B. Harris:Wildlife Biology Program, School
of Forestry, University of Montana, Missoula, MT 59812, USA;
e-mail: Address for William A. Wall:
Safari Club International, 441-E Carlisle Dr., Herndon, VA
20170, USA. Address for Fred W. Allendorf: Division of
Biological Sciences, University of Montana, Missoula, MT
59812, USA.
Richard B. (Rich) Harris(photo) is research associate in the
Wildlife Biology Program at the University of Montana, and also
serves as editor of the journal Ursus. He received his Ph.D.
from the University of Montana and later worked as program-
matic biologist for the Montana Department of Natural
Resources and Conservation. His research interests include
enhancing incentives for local people to conserve wildlife in
western China, where he has conducted surveys and worked
with hunting programs since 1988. William A. (Bill) Wallcur-
rently is senior scientist for wildlife conservation for Safari Club
International Foundation. He received his Ph.D. from Stephen
F. Austin State University in Nacogdoches, TX. He currently is
developing conservation hunting programs for argali sheep in
Central Asia. Fred W. Allendorfis professor of biology at the
University of Montana. His primary research interest in the
application of genetic principles to problems in the conserva-
tion and management of natural populations.
... Trophy hunting is considered as a selective factor, selective in relation to the phenotype or sex of animals; for this reason, it has become the object of scientific studies (Harris et al., 2002;Allendorf and Hard, 2009;etc.). However, it is hardly possible to talk about any selectivity in relation to the wolf. ...
... However, it is hardly possible to talk about any selectivity in relation to the wolf. At the same time, a change in the population structure, a loss of genetic diversity, and evolution as a result of selection (for example, a significant change in the frequencies of alleles in the population associated with one trait or another, for which intensive selection occurs due to hunting) were identified among the consequences of hunting (Harris et al., 2002;Allendorf et al., 2008). In relation to the Finnish population, poaching and legal hunting were determined as the main factors that regulate modern population dynamics (Kaartinen et al., 2015;Suutarinen and Kojola, 2017). ...
... The consequences of hunting pressures on genetic diversity of ungulates have been investigated for regulated hunting. Harris et al. (2002) summarizes that gene flow among hunted populations may be hindered (e.g., decrease in number of dispersing sex) or promoted (e.g., breakdown of territorial structure and decreased competition for mates between populations) because of hunting pressure, and these changes may be parallel to natural responses of the populations to drastic changes. The authors indicated that hunting may lead to increased genetic drift in smaller populations, greater selection pressure and subsequent loss of desirable alleles and increase of undesirable alleles. ...
... Studies in other mammal groups indicate that unregulated indiscriminate hunting can lead to increase in inbreeding, hybridization due to decreased availability of mating partners, as well as reduction in reproductive potential (Allendorf et al., 2008;Moura et al., 2014). Hunting when excessive or selective can also introduce skewed sex ratios into populations of species with sexual dimorphism and therefore alter gene flow rates in ungulates (Harris et al., 2002;Marealle et al., 2010). ...
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Genetic diversity is a fundamental measure of a populations ability to adapt to future environmental change. Subpopulations may carry unique genetic lineages that contribute to fitness and genetic diversity of species across their distribution range. Therefore, considerations, or lack thereof, of genetic diversity in wildlife management practices may result in either population persistence or extinction over time. Some management tools may pose a greater risk to a species' survival than others when populations are impacted. In South Africa, there has been great interest to translocate animals, sometimes with little consideration to the potential impacts on the species and/or populations survival. Thus, there is a need to collate scientific information to better inform decision‐making and review these management practices and their effects on populations. Here, we focus on three antelope species, the blue duiker (Philantomba monticola), oribi (Ourebia ourebi), and tsessebe (Damaliscus lunatus). We review the genetic status of each species across South Africa, with regards to taxonomy, genetic diversity and population structure, threats that may compromise the genetic diversity within species and across populations, conservation management actions and how they may compromise or benefit the genetic status and lastly make recommendations on possible alternative management actions and future research to inform conservation policy and sustainable management practice. In South Africa, there has been great interest to translocate animals, sometimes with little consideration for the genetic integrity of the species. Thus, in this review, we collate scientific information to better inform decision‐making and review these management practices and their effects on species integrity.
... Population size reductions in harvested wildlife species have disrupted their geographical distribution, increased their isolation, and reduced gene flow (Allendorf et al., 2008). Under this metapopulation dynamic scenario, persistent harvest may further exacerbate the loss of genetic variability (Harris, Wall & Allendorf, 2002). The Montezuma quail (Cyrtonyx montezumae Vigors 1830) is a small game bird with limited dispersal by flight, that has a naturally disjointed geographic distribution. ...
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... It is also, on the average, almost 15 times heavier than the European roe deer, which is regarded as a relatively small cervid species. Owing to slower life histories and larger home ranges, larger mammals have always been disproportionately affected by human overharvesting in comparison to smaller mammals [43] and thus their populations are likely to have undergone genetic drift events [44]. Our results revealed contrasting patterns of genetic structure of the two studied New World deer species from Belarus. ...
... Selective harvesting is known to induce phenotypic changes (Allendorf & Hard, 2009;Coltman et al., 2003;Fenberg & Roy, 2008;Grift et al., 2003;Jeke et al., 2019;Proaktor et al., 2007; although see Festa-Bianchet, 2017 for the limitations of hunting-induced evolution). Furthermore, selective harvesting can unintentionally select for or against other heritable traits or genetic variants that might be important for population persistence (Harris et al., 2002). For example, in bighorn sheep (Ovis canadensis), the selective harvesting of trophy rams has been associated with declines not only in horn size, but also in body weight (Coltman et al., 2003;Hedrick, 2011;Pigeon et al., 2016;Schindler et al., 2017). ...
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... Males are often targeted for their ornaments, such as horns and tusks (Holmern et al., 2006;Chiyo, Obanda, & Korir, 2015). Skewed sex ratios can lead to demographic shifts including changes in effective population sizes, leading to loss of genetic diversity and an increase in inbreeding as well as conflict over mates (Harris, Wall, & Allendorf, 2002;Charlesworth, 2009;Wedekind, 2012;Rosche et al., 2018). These impacts can be particularly detrimental for threatened species due to their small population sizes and low genetic variability (Grayson et al., 2014;Willoughby et al., 2015). ...
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... As previously discussed, selective removal of wild populations can influence the mating structure, leading to genetic changes [44]. Small effective population sizes can lead to a decline in heterozygosity and the loss of rare alleles [45]. ...
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... In many studies investigating genetic structure across introduced populations, the structure detected is typically attributed to multiple founding events (Lecis et al. 2008;Brown and Stepien 2009;Zalewski et al. 2010;Bai et al. 2012). Given that the Victorian population of hog deer has likely arisen from a single founding event, genetic drift may alternatively be responsible for much of the structure observed, which is commonly exacerbated by low effective population sizes (N e ) (Harris et al. 2002). Low N e causes allele frequencies to change at a much faster rate due to genetic drift, which can cause populations to lose genetic diversity and become genetically distinct over a relatively short period of time (Masel 2011). ...
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Techniques are described that define contiguous genetic subpopulations of white-tailed deer (Odocoileus virginianus) based on the spatial dispersion of 4,749 individuals that possessed discrete character values (alleles or genotypes) during each of 6 years (1974-1979). White-tailed deer were not uniformly distributed in space, but exhibited considerable spatial genetic structuring. Significant non-random clusters of individuals were documented during each year based on specific alleles and genotypes at the Sdh locus. Considerable temporal variation was observed in the position and genetic composition of specific clusters, which reflected changes in allele frequency in small geographic areas. The position of clusters did not consistently correspond with traditional management boundaries based on major discontinuities in habitat (swamp versus upland) and hunt compartments that were defined by roads and streams. Spatio-temporal stability of observed genetic contiguous clusters was interpreted relative to method and intensity of harvest, movements, and breeding ecology.
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Genetic variation and differentiation in 326 white-tailed deer (Odocoileus virgin-ianus) from Allegany and Garrett counties, Maryland, were examined by horizontal starch gel electrophoresis. Of 57 loci examined, 18 were polymorphic. Patterns of frequency distribution of alleles at polymorphic loci indicate considerable genetic heterogeneity within deer from western Maryland; differentiation of deer populations was observed over short geographical distances. The genetic character of the deer of western Maryland is thought to be strongly influenced by natural selection, genetic drift, and the hunting regime.
The survival of red deer (Cervus elaphus L.) calves to two years of age was examined in relation to electrophoretic variation in a population on the Scottish island of Rhum. Survival was analyzed using logistic analysis in which the "phenotypic" factors birth weight, birth date, subdivision of the study area, cohort, and sex, which affect the probability of a calf's survival, were taken into account. All three polymorphic loci examined, Mpi, Idh-2, and Trf (each with two detected alleles) are significantly associated with juvenile survival. At Mpi, there is selection against one allele, f (or an allele at a linked locus), and there are indications that this effect is stronger in females than males. For Idh-2, overall, the heterozygote class survives better than the two homozygotes, which survive equally well. However, again there is a difference between the sexes; female heterozygotes survive much better than homozygotes, whereas male homozygotes survive better than heterozygotes, and the difference in survival is smaller. Furthermore, there is an interaction involving Mpi, Idh-2, and survival in which Mpi(f) carriers that are also Idh-2 homozygotes survive very badly compared with other Mpi-Idh-2 combinations, which all survive equally well. For Trf, the heterozygote class survives best, and there is also a difference in survival between the two homozygote classes. Genotype frequencies in the adult population are consistent with the results for calf survival, in that the Mpi(f) frequency is lower in succeeding cohorts of surviving adults, whereas no significant gene frequency change is apparent for Idh-2 or Trf.
In individually monitored red deer (Cervus elaphus) living in the North Block of the Isle of Rhum, Scotland, juvenile survival is related to the genotype at the enzyme loci Mpi and Idh-2 (each with two alleles, f and s). To establish whether other fitness components also are related to genetic differences, we examined whether age at first breeding, fecundity, and adult survival of females were related to genotype at the same loci. Fertility in females shot outside the study area was also analyzed in relation to Mpi and Idh-2 genotype. The analyses controlled for phenotypic and environmental factors affecting female reproductive performance. At Mpi, f-carrying females in the study area bred earlier than ss individuals and tended to be more fecund. However, no association was found between Mpi genotype and adult survival. In culled females, Mpi f-carriers were more likely to be pregnant than ss females. At Idh-2, homozygous females in the study area started breeding earlier than heterozygous females. Idh-2 fs and ss females were more fecund than ff females though this relationship was complicated by an interaction with spring temperature in the year of birth. When the population was at high density, adult survival of Idh-2 ss females was better than survival of ff females, which was, in turn, better than survival of fs females. No association was found between Idh-2 genotype and fertility in culled females. Overall, the associations found in female reproductive measures favor those genotypes that survive particularly badly over the first two years of life. This result supports the idea that countervailing selection in different fitness components (antagonistic pleiotropy) is a common and powerful force maintaining polymorphism in natural populations. It may also explain how fitness components can have large heritabilities while overall fitness may have a low heritability.
Meta-analyses of published correlation coefficients between multilocus heterozygosity (MLH) and two fitness surrogates, growth rate and fluctuating asymmetry, suggested that the strength of these correlations are generally weak. A variety of plants and animals was included in the meta-analyses. A statistically homogeneous group of MLH-growth rate correlation coefficients that included both plants and animals yielded a common correlation of rz = 0.133. A common correlation of rz = -0.170 was estimated for correlations between MLH and fluctuating asymmetry in three species of salmonid fishes. These results suggest that selection, including overdominance, has at most a weak effect at allozyme loci and cast some doubt on the widely held notion that heterozygosity and individual fitness are strongly correlated.
We examined genetic variability and spatial heterogeneity of maternally (mtDNA) and biparentally (allozymes) inherited genes for a large, widely distributed mammal. White-tailed deer (Odocoileus virginianus) in 6 populations from the coastal plain in Georgia and South Carolina showed high levels of variability and spatial heterogeneity for mtDNA and allozymes. There was little sharing of mtDNA variants among samples separated by 30 to 100 km, and 12 of 13 allozyme loci showed significant differentiation among populations. Spatial genetic heterogeneity was positively correlated with geographical distance as predicted in Wright's isolation by distance model. High spatial heterogeneity is surprising considering the species' physical capacity for moving great distances. Dispersal must be limited, but more so in females because they accounted for only an estimated 13% of total dispersal. Social factors must strongly Limit dispersal in white-tailed deer and probably many other mammals.
Based on previously published eletrophoretic data on genetic variability in 31 roe deer populations, the proportion of loci polymorphic (P), average heterozygosity (H), and the inbreeding coefficient (FIS) were examined for relationships with the social structure displayed in the various populations. The hypothesis was that genetic variability is lower and FIS-values are more positive in populations where males maintain a stable pattern of territories during the rutting season (forest dwelling roe deer) than in those characterized by pronounced fluctuations in population structure, both within and among seasons (field or mountain dwelling roe deer). P and H did not show differences among those two groups. FIS was significantly more positive in "forest' roe deer than in the more migratory "type', but only when populations subjected to high culling rates were excluded from the analysis. Highly negative FIS-values in forest populations with high culling rates suggested that considerable perturbations of population structure may be caused by hunting. The "forest' roe deer and the "field' roe deer do not represent two distinct ecotypes with a particular genetic integrity, but rather reflect the considerable behavioural plasticity of the species. -from Authors
Relationships between electrophoretically determined genetic variation and physical characteristics were examined for pregnant white-tailed deer and their fetuses. Fetal growth was significantly increased by higher fetal and maternal heterozygosity and maternal weight; the number of in utero fetuses had the opposite effect. Maternal weight was also positively associated with maternal heterozygosity within each age class. Fetal and maternal heterozygosity were positively correlated, but fetal heterozygosity was significantly lower than maternal heterozygosity A significant interaction effect of maternal and fetal heterozygosity on fetal growth was found and indicates that the relationship between fetal heterozygosity and fetal growth varied over the different levels of maternal heterozygosity Differences in fetal growth rate related to heterozygosity were attributed to differences in the degree to which the individuals were inbred. Inbreeding is probably a result of the subdivision and social structure of the deer population. Inbreeding affects the level of genetic variation which alters the strategy for optimizing the partitioning of energy into the secondary productivity processes of growth and reproduction.