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Heterogeneity in male horn growth and longevity in a highly sexually dimorphic ungulate

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In sexually dimorphic ungulates, sexual selection favoring rapid horn growth in males may be counterbalanced by a decrease in longevity if horns are costly to produce and maintain. Alternatively, if early horn growth varied with individual quality, it may be positively correlated with longevity. We studied Alpine ibex Capra ibex in the Gran Paradiso National Park, Italy, to test these alternatives by comparing early horn growth and longevity of 383 males that died from natural causes. After accounting for age at death, total horn length after age 5 was positively correlated with horn growth from two to four years. Individuals with the fastest horn growth as young adults also had the longest horns later in life. Annual horn growth increments between two and six years of age were independent of longevity for ibex whose age at death ranged from 8 to 16 years. Our results suggest that growing long horns does not constrain longevity. Of the variability in horn length, 22% could be explained by individual heterogeneity, suggesting persistent differences in phenotypic quality among males. Research on unhunted populations of sexually dimorphic ungulates documents how natural mortality varies according to horn or antler size, and can help reduce the impact of sport hunting on natural processes.
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Heterogeneity in male horn growth and longevity in a highly sexually
dimorphic ungulate
P. Bergeron, M. Festa-Bianchet, A. von Hardenberg and B. Bassano
P. Bergeron (patrick.bergeron@usherbrooke.ca) and M. Festa-Bianchet, De
´
pt de Biologie, 2500 Boul. de l’Universite
´
, Univ. de Sherbrooke,
Sherbrooke, PQ, Canada, J1K2R1. A. von Hardenberg and B. Bassano, Alpine Wildlife Research Centre, Gran Paradiso National Park,
Degioz 11, IT-11010 Valsavarenche (Ao), Italy.
In sexually dimorphic ungulates, sexual selection favoring rapid horn growth in males may be counterbalanced by a
decrease in longevity if horns are costly to produce and maintain. Alternatively, if early horn growth varied with
individual quality, it may be positively correlated with longevity. We studied Alpine ibex Capra ibex in the Gran Paradiso
National Park, Italy, to test these alternatives by comparing early horn growth and longevity of 383 males that died from
natural causes. After accounting for age at death, total horn length after age 5 was positively correlated with horn growth
from two to four years. Individuals with the fastest horn growth as young adults also had the longest horns later in life.
Annual horn growth increments between two and six years of age were independent of longevity for ibex whose age at
death ranged from 8 to 16 years. Our results suggest that growing long horns does not constrain longevity. Of the
variability in horn length, 22% could be explained by individual heterogeneity, suggesting persistent differences in
phenotypic quality among males. Research on unhunted populations of sexually dimorphic ungulates documents how
natural mortality varies according to horn or antler size, and can help reduce the impact of sport hunting on natural
processes.
Male secondary sexual characters (SSC) may have evolved
through sexual selection to increase the attractiveness of
males as potential partners, their fighting ability, or both
(Darwin 1871, Andersson 1994). Many studies have
reported positive correlation between the size, color or
complexity of SSC and mating success (mammals: Kruuk
et al. 2002; birds: Hill 1991; fishes: Miller and Brooks
2005; arthropods: Mappes et al. 1996). SSCs are thought to
be energetically demanding to grow and maintain, and
there is often much variability in their expression within a
population, because only high-quality individuals can grow
large traits (Zahavi 1975). However, little is known about
what fitness tradeoffs they may involve (Reznick et al. 2000,
Kotiaho 2001).
Life history theory predicts that tradeoffs between
reproduction and survival should shape the evolution of
SSCs (Stearns 1992, Roff 2002). If SCCs are costly, a
positive selection on these characters (via increased fecund-
ity) could be counterbalanced by a negative effect on
survival (Møller 1989, Clinton and Le Boeuf 1993, Brooks
2000). According to this theory, males that quickly grow
large SSCs may reproduce at a young age, but because of
the energetic costs of reproduction (through combats or
courtship), they may suffer a decrease in survival. Males
with slower SSC growth may survive to reproduce at an
older age (Geist 1971). Alternatively, individual hetero-
geneity in the capacity to acquire nutrients and allocate
them to SSCs could lead to phenotypic variability in their
expression (van Noordwijk and De Jong 1986). High-
quality individuals could acquire more resources than their
conspecifics, and grow large SSCs without a tradeoff with
survival (Reznick et al. 2000, Service 2000). Therefore, size,
color or complexity of SSCs could be positively correlated
with other fitness-related traits (Kodric-Brown et al. 2006),
including survival (Møller and Alatalo 1999, Jennions et al.
2001).
In ungulates, much attention has been paid to the role of
horns and antlers as SSCs. In polygynous species, males
fight to obtain access to estrous females. In wild and feral
sheep, males with large horns usually dominate other males
and have a greater chance to reproduce (Ovis canadensis:
Coltman et al. 2002 ; O. aries: Preston et al. 2003,
Robinson et al. 2006). The reproductive advantage for
large-horned males is substantial. A dominant bighorn ram
can sire up to a third of all offspring during one mating
season (Coltman et al. 2002). Horns, however, are thought
to be costly because they require energy and nutrients to
grow, maintain (including heat loss during winter (Picard et
al. 1996)), and carry (Geist 1966a). Life history theory
would then predict that large horns should have a fitness
cost. On the other hand, heterogeneity in individual quality
could produce a positive relationship between horn growth
Oikos 117: 7782, 2008
doi: 10.1111/j.2007.0030-1299.16158.x,
#The authors. Journal compilation #Oikos 2007
Subject Editor: John Vucetich, Accepted 23 July 2007
77
and longevity (Reznick et al. 2000), because weaker
individuals may have small horns and die young (Service
2000, Cam et al. 2002).
Although Geist (1966a) suggested four decades ago that
horn growth rate and survival may be negatively correlated
in bighorn sheep, it is only recently that empirical studies
have looked for a survival cost of growing long horns
(Robinson et al. 2006, Loehr et al. 2007). In addition to
their fundamental value, such studies are important for
ungulate management because the selective effects of trophy
hunting (which increases the mortality of males with long
horns) may be reduced if hunting mimicked natural
mortality. In hunted populations, males with rapidly
growing horns are at risk of harvest at a young age (Festa-
Bianchet et al. 2004). However, the potential selective effect
of trophy hunting on early horn growth is controversial
(Coltman et al. 2003, Loehr et al. 2007), partly because
little is known about the relationship between horn growth
and longevity in the absence of hunting mortality. Under-
standing how natural mortality covaries with horn size is
central to test for tradeoffs between sexual and natural
selection in the evolution of SSCs, and to assess the
potential selective effects of hunting.
Here we explore the relationships between horn growth rate
and longevity in an unhunted population of Alpine ibex Capra
ibex. Ibex are long-lived and strongly sexually dimorphic, with
condition-dependent horn growth in males (Giacometti et al.
2002, von Hardenberg et al. 2004). Data on horn growth of
Alpine ibex males found dead from winter starvation for a
population protected since 1922 were analyzed by von
Hardenberg et al. (2004) who found that horn growth
decreased in the two years preceding death. Here we examine
the same sample to contrast the hypothesis that sexual selection
favoring rapid horn growth at young age is counterbalanced by
a decrease in longevity (Geist 1966a, Robinson et al. 2006,
Loehr et al. 2007), with the alternative that horn growth and
longevity are positively correlated because they both depend
on individual quality.
Material and methods
Between 1988 and 1997, park wardens in the Gran
Paradiso National Park (GPNP), Italian Alps (45826?N,
7808?E), collected all ibex skulls found during regular foot
patrols. No hunting is allowed in the Park and there are no
large predators. The main causes of death are winter
starvation, senescence or accidents such as avalanches.
Because park wardens frequently patrol their assigned
area, they find ibex carcasses in the year of death. Since
horn growth stops during winter forming a distinct growth
ring or annulus, it is possible to know age at death of each
individual by counting the annuli (Geist 1966b). Ibex skulls
were cleaned and annual horn growth increments measured
to the nearest 0.5 mm with a caliper along the center of the
posterior curvature. The first growth increment is often
worn or broken and it was excluded from analyses. Because
von Hardenberg et al. (2004) had shown a decline in
growth during the final two years of life, independently of
the age at death, we excluded from analyses horn
increments grown by each ibex in the two years before its
death. Similarly to von Hardenberg et al. (2004), we also
excluded individuals with unknown year of death and ibex
that had clearly died in avalanches. Less than 5% of ibex
appeared to have died in avalanches, and we excluded them
because avalanches may kill a random sample of ibex males.
von Hardenberg et al. (2004) provide more details on skull
collections and horn measurements.
A fundamental assumption of our study is that there are
no biases in skulls collection. Such biases are unlikely
because wardens systematically search the park to recover all
ibex skulls as part of their duties.
Statistical analyses
We used a linear regression model to test if the length of horn
grown between 24 years of age was correlated with horn
growth after age 5. Because horn length increases with age
and is correlated with longevity (Fig. 1a), we also included
log-transformed longevity as an explanatory variable in
the analysis. Thus, horn length grown after age 5 was a
relative measure, controlled for longevity (Fig. 2). A positive
correlation of horn length at 24 years of age and after age 5
would suggest persistent individual differences in phenotypic
quality. A negative correlation would indicate compensatory
Longevity
34567891011121314151617
)mm(htgnelnroH
0
100
200
300
400
500
600
700
800
(a)
(b)
n = 3 8 19 16 19 22 41 71 65 74 20 12 4 1
A
g
e
(y
ears
)
2 3 4 5 6 7 8 9 10 11 12 13 14 15
)mm(htgnelsulunnadegarevA
0
10
20
30
40
50
60
70
80
90
100
n = 375 379 372 356 340 319 297 253 184 112 41 8 5
Fig. 1. (a) Positive relationship between horn length (mm) and
age at death for 375 male ibex collected by Park Wardens in the
Gran Paradiso National Park, Italy, from 1988 to 1997. The first
and last annual horn growth increments are not included. (b)
Relationship between annual increment horn length and age (n
383, mean9SD). Sample sizes differ because eight individuals are
not included in (a) as not all of their increments were measured.
78
growth. We defined as ‘‘young age’’ horn growth between
two and four years of age because average increment length
increases slightly until age 4 and then decreases (Fig. 1b).
In a second analysis, we used a linear mixed effects model
(Pinheiro and Bates 2000) to test if longevity was related to
early annual horn growth for males that survived beyond
eight years of age. Survival of male ibex between two and 12
years of age is much higher than that of other ungulates, and
less than 15% of 2-year-old males die before eight years of age
(Toı¨go et al. 1997, Loison et al. 1999). In this analysis, we
used annual horn growth increments between two and six
years of age as a measure of ‘‘early horn growth’’ common to
our entire sample. We did not use age class 24 as in the
previous analysis because we wanted to consider all horn
increments grown two or more years before death by
individuals that survived to at least eight years of age. Of
383 ibex males in our sample, only 17% died before eight
years of age. To avoid pseudo-replication due to several
annual horn growth increments measured on the same horn
at different ages (Machlis et al. 1985), and to calculate the
variance in annual horn growth increments attributable to
individual ‘‘qualities’’, we fitted male identity (ID) as a
random term. We fitted the year during which each
increment was grown as a fixed term (18-level factor) to
account for year-specific environmental variability (Postma
2006) that can affect horn growth (Giacometti et al. 2002,
von Hardenberg et al. 2004). We also fitted age and longevity
as fixed predictor terms of annual horn growth increments
between two and six years of age. The significance of the fixed
terms was assessed with conditional F-tests. We used this
causal statistical approach because we could measure many
increments on a given male but had only one measure of
longevity per individual. Therefore, we cannot use mixed
models to estimate the proportion of variation in longevity
attributable to individual quality (Steele and Hogg 2003).
We assessed significance of the random term ID using a log-
likelihood ratio (LRT) test comparing models with and
without the term (Steele and Hogg 2003). We checked for a
possible bias for the LRT statistics under a x
2
distribution
(Pinheiro and Bates 2000) by comparing this model selection
for the random term with a model selection based on the
Akaike information criterion (AIC). We checked graphically
for normality of residuals and homogeneity of variance. We
conducted all analyses using the R 2.1.1 statistical package
using the restricted maximum likelihood estimation proce-
dure.
Results
Testing individual heterogeneity
Horn length grown after age 5, adjusted for longevity, was
weakly positively correlated with horn growth at 24 years
of age (b0.35, SE0.059 mm, t5.83, r
2
0.094, pB
0.001, Fig. 2). A comparison of total horn length grown
after age 3, adjusted for age at death, and increment length
at age 2 also revealed a positive correlation (b1.50, SE
0.218 mm, t6.89, r
2
0.127, pB0.001), confirming the
result obtained with age class 24. In the linear mixed
model of annual horn growth increments between two and
six years for individuals that survived beyond eight years,
the random term ID was highly significant (x
2
543.80,
DF1, pB0.001, n 318, AIC 11602.43 vs 12261.98
when removing ID from the model). ID explained 22% of
the between-males variance in annual horn growth ((s
2
ID
/
s
2
total
)100). For a given male, adding a first-order
autoregressive process of the within-subject error increased
substantially the fit of the model (r0.525, x
2
137.95,
DF1, pB0.001, AIC 11466.47 vs 11602.43 for the
same full model without the correlation structure), suggest-
ing that ibex with good growth one year were likely to have
above-average growth in other years.
Age-specific horn growth and longevity
We tested whether early annual horn growth increments
were related to longevity in a linear mixed effect model with
ID as a random term. In the final model, variation in
increment length between two and six years of age was best
explained by a quadratic relationship with age (age: b
7.600, SE1.054 mm, F
1,1244
11.164, pB0.001; age
2
:
b1.022, SE 0.128 mm, F
1,1244
73.274, pB
0.001, Table 1) and yearly differences (F
17,1244
5.501,
pB0.001). More importantly, after taking into account age
and year effects, longevity was independent of annual horn
Horn length between 2-4 years old (mm)
100
ytivegnolrofd
etsu
j
da)mm(5eg
aretfahtgnelnroH
-150
-100
-50
0
50
100
150
150 200 250 300 350
Fig. 2. Relationship between the relative measure of horn length
grown after age 5, controlled for longevity, and horn growth
between two and four years of age (n 328, r
2
0.094) for male
ibex from the Gran Paradiso National Park, Italy, 1988 to 1997.
Table 1. Linear mixed model of the effects of age and longevity on
horn growth between two and six years of age from 1581 annual
horn growth increments measured on 318 male ibex that survived to
at least eight years of age. We fitted ID as random term and year as
fixed term in both models. Wardens collected ibex skulls in the Gran
Paradiso National Park, Italy, from 1988 to 1997.
Terms DF Estimates SE F p
Full model
Age 1,1244 7.757 1.063 11.148 0.001
Age
2
1,1244 1.020 0.128 73.208 B0.001
Longevity 1,316 0.438 0.387 1.28 0.259
Final model
Age 1,1244 7.6 1.054 11.146 B0.001
Age
2
1,1244 1.023 0.128 73.201 B0.001
79
growth increments between two and six years, for indivi-
duals whose longevity ranged from eight to 16 years
(F
1,316
1.279, p0.259, Table 1). Figure 3 illustrates
this result by comparing individuals that died between eight
and 10 years with individuals that survived beyond that age.
Despite the marginal but consistently longer annual horn
growth between two and five years old for males that lived
between eight and 10 years, logistic regression (family
binomial with logit link function) suggested that the
probability of surviving past 10 years was not related to
the horn growth between two to five years of age (x
2
0.86, DF1, p0.36). Over this period, the mean
cumulative horn length only differed by 1.4% (4 mm)
between the two longevity classes.
Discussion
Using a large sample of unhunted wild polygynous
ungulates that died of natural causes, we tested two
opposing hypotheses relating early horn growth and long-
evity in males. We found persistent individual variation in
ability to grow horns. Our results suggest that males with
fast-growing horns early in life were able to grow longer
horns without any apparent longevity cost. Because male
ibex do not compensate for reduced horn growth at young
age by increasing growth in later years (Toı¨go et al. 1999),
persistent individual differences lead to much variability in
total horn length among mature males. After controlling for
age and the year when a horn increment was grown, about a
quarter of this phenotypic variability was explained by
individual quality.
It is likely that the length of ibex horns is correlated with
reproductive success, as reported for other polygynous
ungulates with a similar mating system (Coltman et al.
2002, Preston et al. 2003). Despite their association with
reproductive benefits, Pomiankowski and Møller (1995)
found that high variability in sexually selected traits is
common in nature. We also found much individual
heterogeneity in horn size, and some males were unable
to grow long horns independently of their longevity. Hence
we suggest that ibex horns could be an honest signal of
condition (Preston et al. 2003, von Hardenberg et al. 2004,
Malo et al. 2005 von Hardenberg et al. 2007). Assuming
that horn growth and maintenance are costly, our results
would also be consistent with the Handicap principle
(Zahavi 1975), which predicts a positive correlation
between the size, color or intensity of costly SSCs and the
quality of their bearer. Individuals could advertise their
quality if they are able to bear costly displays without
compromising their survival (Zahavi 1975). von Hard-
enberg et al. (2007) found that ibex horn growth was
positively correlated with multilocus heterozygosity and
suggested that long-horned males were of better genotypic
quality. Therefore, horn size could potentially guide mate
selection by females, or help establish dominance rank
among males while avoiding potentially costly fights
between males of different ‘‘quality’’ (Pelletier and Festa-
Bianchet 2006). Contrary to our expectation, however, we
found no relationship between early horn growth and
longevity. Males with slow-growing horns may increase
their survival by limiting their reproductive effort. As they
age, males with rapidly growing horns probably experience
an increase reproductive benefit (Coltman et al. 2002).
Our findings do not exclude the possibility that there
may be a survival cost for mature males with the largest
horns, after a few years of intense reproductive activity.
Geist (1966a, 1971) suggested that rapidly-growing males
would participate in rutting activities at a young age and
suffer increased mortality through injuries or exhaustion.
Recent suggestions that Dall’s sheep, Ovis dalli, rams with
rapidly-growing horns suffer a survival cost of reproduction
as young as 56 years (Loehr et al. 2007) ignore data on
age-specific reproductive behavior and reproductive success
of males of polygynous ungulates. Geist (1966a) suggested a
tradeoff between horn growth and longevity by comparing
bighorn rams that did and did not survive to 12 years of
age. We now know that 12-year-old bighorn rams are well
into survival senescence (Loison et al. 1999) and that
dominant rams obtain high reproductive success at 710
years of age (Coltman et al. 2002). In male ibex, survival
senescence becomes evident at about 1012 years of age and
the age-related decrease in survival is very rapid thereafter
(Toı¨go et al. 2007). We speculate that males with fast-
growing horns may make a strong reproductive effort when
aged 1014 years, possibly leading to increased mortality.
Such an age-dependent tradeoff may explain the weak trend
for males with the longest horns not to survive to the very
oldest ages (Fig. 1a). Because of the small sample of males
aged 12 years and older, we could not test statistically for
this age dependent tradeoff. It remains possible, however,
that for mature males with large horns that take an active
part in the rut, survival may both increase because of high
individual quality and decrease because of high reproductive
effort.
Our results underline the importance of studying
unhunted populations of ungulates to understand the
relationship between horn growth and natural mortality.
In feral sheep, Robinson et al. (2006) found that males with
larger horns gained in annual breeding success but suffered a
decrease in longevity. In that population, the largest male
lambs can participate in the rut but experience a survival cost
Age (years)
234567
Annulus length (mm)
67
68
69
70
71
72
73
74
75
76
77
78 longevity (8 -10 years)
longevity (11 years or more)
Fig. 3. Length (9SE) of the annual horn growth increments
grown between two and six years of age for 134 male ibex that died
when aged 8 to 10 years and 176 individuals that survived over 11
years of age in the Gran Paradiso National Park, Italy, 1988 to
1997.
80
(Stevenson and Bancroft 1995). Because Robinson et al.
(2006) did not look at age-specific costs of long horns, it
remains unclear whether this cost also affects adult rams.
Clinton and Le Boeuf (1993) reported that some male
elephant seals Mirounga angustirostris that attempted to
breed for the first time suffered a decrease in survival, and
found a positive, but not significant, relationship between
mating success and survival for ‘established’ breeding males.
Nonetheless, high-quality males enjoy high survival through
their prime reproductive years in many other polygynous
mammals. For example, Pelletier et al. (2006) found that
longevity was correlated with mating effort for bighorn rams
aged 25 years. Heavier young males participated more in
the rut than lighter males of the same age (Pelletier 2005). In
fallow deer Dama dama, mature males that reproduce are
larger (McElligott et al. 2001) and enjoy higher survival than
non-reproducers (McElligott et al. 2002).
In conclusion, we found significant individual hetero-
geneity in the capacity to grow horns but no effect of horn
growth on longevity. We suggest that age-specific horn
growth during young age is a correlate of individual quality.
This suggestion has substantial implications for ungulate
management and conservation, because of the potential
impact of artificial selection through trophy hunting (Loehr
et al. 2007). We suggest that any tradeoff between early horn
growth and longevity would only affect individuals that
survived past their prime reproductive years. Hunting
regulations that allow the harvest of males with large horns
when younger than about 10 years would not mimic natural
mortality and could select for small horn size (Coltman et al.
2003). Behavioral and paternity data are required to provide
a better understanding of the relationships between horn
size, reproductive effort and reproductive success, all of
which could affect the age-dependent tradeoff between horn
size and longevity.
Acknowledgements We thank D. Garant for help with statistical
analysis. Constructive comments from J.-M. Gaillard, F. Pelletier,
P. Bourgault, A. Mysterud, J. Vucetich and G. Yoccoz greatly
improved this manuscript. We are grateful to the many park
wardens who collected ibex skulls and to M. d. P. Zummel Arranz
and G. Bogliani for their help in measuring them. The Natural
Sciences and Engineering Research Council of Canada (scholar-
ship to P.B. and research grant to M.F.-B.) provided financial
support and GPNP provided logistical support.
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... In order to deepen our understanding of secondary sexual characters and reproduction, we investigated in this study (i) to what extent the age-specific total horn length in male Alpine ibex is associated with their behavioral reproductive effort during the current mating season, and (ii) if the behavioral reproductive effort itself is influencing subsequent age-specific horn growth during the following summer. Considering that horn size in male Alpine ibex covaries positively with the genetic and phenotypic constitution of individuals (Bergeron et al. 2008;Brambilla et al. 2015;von Hardenberg et al. 2007), we expected for males of a given age, that individuals with longer horns would invest more time into the acquisition of mating partners during the rut, than individuals with shorter horns. Furthermore, we predicted that reproductive effort during the mating season would negatively affect age-specific horn 1 3 growth during the following summer. ...
... Interestingly, no evidence was found that relatively large-horned male Alpine ibex would invest more time into reproduction than relatively short-horned individuals of a given age. Our results, therefore, suggest that investments into reproduction during the rut do not vary with the genetic and phenotypic quality of individuals (for which horn length was taken as an indicator; Bergeron et al. 2008;von Hardenberg et al. 2007). Instead reproductive effort appears to increase mainly with male age (see supplementary material), as is often the case in ungulates (Mysterud et al. 2004), and which has also previously been demonstrated for Alpine ibex (Willisch and Neuhaus 2009;Brivio et al. 2010). ...
... Indeed, previous observations confirm that dominant males can monopolize access to receptive females without effort, as subordinate males walk away from a female and stay at distance as soon as a more dominant individual approaches Neuhaus 2009, 2010). Whether the establishment of social relationships among competing males during the pre-rut season is a direct function of the presence of competitors in the area, as suspected by Festa-Bianchet (2012), and whether high-quality males are incurring higher costs (Bergeron et al. 2008;Toïgo et al. 2013), at least during that period of the year, remains open. ...
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Trade-offs between reproductive effort and subsequent growth in males are not well explored, despite their relevance in questions of individual energy allocation. Regarding the growth of sexual secondary characters in polygynous breeding male mammals, indeed, no conclusive studies exist. We investigated in male Alpine ibex ( Capra ibex ) the relationship between their behavioral reproductive effort, current horn size, and subsequent horn growth. While controlling for age, no evidence was found for male behavioral reproductive effort during the rut being affected by their horn size. On the other hand, reproductive effort significantly decreased age-specific horn growth during the following summer. Our study provides evidence that growth of secondary sexual characters is traded against behavioral investments in reproduction in a male mammal. It bears important implications for the understanding of energy allocation between various life-history components and the evolutionary ecology of secondary sexual characters.
... Growth patterns of secondary sexual characteristics such as ibex (Capra spp.) horns provide insight into a species natural history as well as relevant management data. Among polygynous species such as ibex, horn size is related to age, body size, social rank, and reproductive success (Bergeron et al. 2008(Bergeron et al. , 2010Willisch et al. 2012). Large horns provide high leverage and absorb force upon impact during bouts with other males (Alvarez 1990;Habibi 1994). ...
... The transverse ridges or knobs on ibex horns are believed to strengthen horns and reduce bending stress; facilitate lockup of impacting horns, allowing males to control opponents through pushing while minimizing sliding and accidental and dangerous skull clashes; and protect the horn by minimizing wear. Large horns also provide visual information regarding rank and degree of difficulty of a potential bout with an opposing male (Alvarez 1990;Bergeron et al. 2008;Geist 1966;Willisch et al. 2012). Moreover, females also use horns to assess mate quality (Bergeron et al. 2008;von Hardenberg et al. 2007). ...
... Large horns also provide visual information regarding rank and degree of difficulty of a potential bout with an opposing male (Alvarez 1990;Bergeron et al. 2008;Geist 1966;Willisch et al. 2012). Moreover, females also use horns to assess mate quality (Bergeron et al. 2008;von Hardenberg et al. 2007). Thus, maximizing horn growth and speed of development can be highly advantageous to the fitness of ibex. ...
Article
Documenting patterns of horn growth and horn-age relationships of Nubian ibex ( Capra nubiana ) can contribute to a more comprehensive understanding of their natural history, horn development in ibex in general, and future conservation of the species. Our specific objectives included (1) documenting age-horn growth patterns; (2) contrasting horn growth patterns of Nubian ibex with other ibex species; and (3) determining whether horn development accurately reflects age of Nubian ibex in Sinai, Egypt. As expected, all male and female horn measurements had significant relationships with age. Horn growth in males started plateauing at ca. age 7–8, whereas female horn growth started plateauing at ca. age 4–6. The extremely arid environment of Nubian ibex in the Sinai may account for the slowing of horn growth at a younger age than seen in populations of some other ibex species. We found a significant relationship between the number of horn ridges and age, indicating that counting horn ridges provides a viable method of aging males to within ±1 y. Thus counting horn ridges may be a useful and non-invasive method to determine age or age class, which can further our understanding of age structure, the natural history, and management of Nubian ibex populations.
... ; https://doi.org/10. 1101/2021 The fixed and random structures of the permuted GLMMs were selected using non-permuted GLMMs (lme4 package): each GLMM included as the dependent variable either strength centrality (modelled with a gaussian distribution) or eigenvector centrality (modelled with a binomial distribution) and, as fixed effects, the season and individual characteristics: age as a quadratic term (Bergeron et al., 2008) and the season preceding death (as a binary variable that indicated whether the animal died within that year of data collection or if it survived until the following year). The models also included year and individual identity (ID) as random effects. ...
... Because of their conservative life history strategy, adult survival is very high in Alpine ibex (Toïgo et al., 2007). Many males therefore reach senescence with progressively deteriorating body condition (Bergeron et al., 2008;Brambilla et al., 2015) and changes in activity rhythm and spatial behaviour, meaning they are less likely to remain central in the network. Our results suggests that social behaviour changes in Alpine ibex may occur as a result of senescence (Siracusa et al., 2022). ...
Article
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Despite its recognized importance for understanding the evolution of animal sociality as well as for conservation, long term analysis of social networks of animal populations is still relatively uncommon. We investigated social network dynamics in males of a gregarious mountain ungulate (Alpine ibex, Capra ibex) over ten years focusing on groups, sub‐groups and individuals, exploring the dynamics of sociality over different scales. Despite the social structure changing between seasons, the Alpine ibex population was highly cohesive: fission–fusion dynamics lead almost every male in the population to associate with each other male at least once. Nevertheless, we found that male Alpine ibex showed preferential associations that were maintained across seasons and years. Age seemed to be the most important factor driving preferential associations while other characteristics, such as social status, appeared less crucial. We also found that centrality measures were influenced by age and were also related to individual physical condition. The multi‐scale and long‐term frame of our study helped us show that ecological constrains, such as resource availability, may play a role in shaping associations in a gregarious species, but they cannot solely explain sociality and preferential association that are likely also to be driven by life‐history linked physiological and social needs. Our results highlight the importance of long‐term studies based on individually recognizable subjects to help us build on our understanding of the evolution of animal sociality.
... Empirical evidence for a negative relationship between horn growth and natural survival is scarce (see Table 1 in Lemaître et al., 2018). Previous studies have mainly focused on species with a high level of sexual dimorphism (e.g., Soay sheep, Robinson et al., 2006;bighorn sheep, Bonenfant, Pelletier, Garel, & Bergeron, 2009; Alpine ibex Capra ibex, Bergeron, Festa-Bianchet, Hardenberg, & Bassano, 2008;Toïgo, Gaillard, & Loison, 2013). Few studies have investigated similar relationships in species with low sexual size dimorphism, possibly because limited horn length is unlikely to impose major energetic costs. ...
... Together with this last study, our results support the idea that a negative relationship between weapon size and survival can arise in species where sexual selection is relatively weak. By contrast, early horn growth is generally not related to age-specific survival in highly sexually dimorphic ungulates (Bergeron et al., 2008;Bonenfant et al., 2009;Toïgo et al., 2013). The capacity to detect survival cost of growing long horns may depend more on environmental conditions experienced by the population than on intensity of sexual selection. ...
Article
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Abstract While all models of sexual selection assume that the development and expression of enlarged secondary sexual traits are costly, males with larger ornaments or weapons generally show greater survival or longevity. These studies have mostly been performed in species with high sexual size dimorphism, subject to intense sexual selection. Here, we examined the relationships between horn growth and several survival metrics in the weakly dimorphic Pyrenean chamois (Rupicapra pyrenaica). In this unhunted population living at high density, males and females were able to grow long horns without any apparent costs in terms of longevity. However, we found a negative relationship between horn growth and survival during prime age in males. This association reduces the potential evolutionary consequences of trophy hunting in male chamois. We also found that females with long horns tended to have lower survival at old ages. Our results illustrate the contrasting conclusions that may be drawn when different survival metrics are used in analyses. The ability to detect trade‐off between the expression of male secondary sexual traits and survival may depend more on environmental conditions experienced by the population than on the strength of sexual selection.
... Horn growth differed markedly among males of PTB. This is in line with previous studies on Iberian ibex relatives (Bergeron et al. 2008. For instance, individual heterogeneity accounted for approximately a quarter of the variability in horn length of Alpine ibex (Capra ibex; Bergeron et al. 2008) and for 17% of the variability in horn length of bighorn sheep (Ovis canadensis; Douhard et al. 2017). ...
... This is in line with previous studies on Iberian ibex relatives (Bergeron et al. 2008. For instance, individual heterogeneity accounted for approximately a quarter of the variability in horn length of Alpine ibex (Capra ibex; Bergeron et al. 2008) and for 17% of the variability in horn length of bighorn sheep (Ovis canadensis; Douhard et al. 2017). The absence of compensatory horn growth in the members of the tribe Caprini exacerbate the individual differences among mature males because individuals cannot compensate the growth depression after a period of nutritional deficit (Festa-Bianchet et al. 2004, Toïgo et al. 2013, Carvalho et al. 2017. ...
Article
Size‐selective harvesting of wild ungulates can trigger a range of ecological and evolutionary consequences. It remains unclear how environmental conditions, including changes in habitat, climate, and local weather conditions, dilute or strengthen the effects of trophy hunting. We analyzed horn length measurements of 2,815 male ibex (Capra pyrenaica) that were harvested from 1995 to 2017 in Els Ports de Tortosa i Beseit National Hunting Reserve in northeastern Spain. We used linear mixed models to determine the magnitude of inter‐individual horn growth variability and partial least square path models to evaluate long‐term effects of environmental change, population size, and hunting strategy on horn growth. Age‐specific horn length significantly decreased over the study period, and nearly a quarter (23%) of its annual variation was attributed to individual heterogeneity among males. The encroachment of pine (Pinus spp.) forests had a negative effect on annual horn growth, possibly through nutritional impoverishment. The harvesting of trophy and selective individuals (e.g., small‐horned males) from the entire population increased horn growth, probably because it reduced the competition for resources and prevented breeding of these smaller males. Local weather conditions and population size did not influence horn growth. Our study demonstrates how habitat changes are altering the horn growth of male ibex. We suggest that habitat interventions, such the thinning of pine forests, can contribute to securing the sustainability of trophy hunting. Even in situations where size‐selective harvesting is not causing a detectable phenotypic response, management actions leading to the expansion of preferred land cover types, such as grass‐rich open areas, can have a positive effect on ungulate fitness. Forest encroachment on open meadows and heterogeneous grasslands is pervasive throughout Mediterranean ecosystems. Therefore, our management recommendations can be extended to the landscape level, which will have the potential to mitigate the side effects of habitat deterioration on the phenotypic traits of wild ibex. © 2020 The Wildlife Society. The encroachment of coniferous forests and the consequent loss of natural pastures had a negative effect on the annual horn growth of male ibex inhabiting a Mediterranean ecosystem. The selective harvesting of small‐horned males had a positive effect on annual horn growth. The expansion of grass‐rich open areas should be prioritized to reduce the negative effects of habitat deterioration on the phenotypic traits of male ibex.
... Considering that the trophy hunting policy is a way of artificial selection, large-horned males are becoming targets and hunted (Bergeron et al., 2008;Büntgen et al., 2018;von Hardenberg et al., 2007). Ultimately, it is assumed that such a policy will jeopardize the survival of healthy genes and lower the group's evolutionary potential (Sarrazin and Barbault, 1996). ...
... Because this species is the primary prey for the endangered snow leopard in some regions (e.g., the Khunjerab National Park, Pakistan), trophy hunting in these areas would further reduce the food availability for snow leopard, which goes against the ultimate objective of endangered species conservation. Considering that the trophy hunting policy is a way of artificial selection, large-horned males are becoming targets and hunted (Bergeron et al., 2008;Buntgen et al., 2018;Von Hardenberg et al., 2007). Ultimately, it is assumed that such a policy will jeopardize the survival of healthy genes and lower the group's evolutionary potential (Sarrazin and Barbault, 1996). ...
Article
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The Asiatic ibex (Capra sibirica), the largest member of the genus Capra, is widely distributed in Central and South Asia. It is a primitive ibex species of the family Bovidae that is distinct from other ibex species. The Asiatic ibex is distributed in highland landscapes characterized by challenging terrains that have resulted in incomplete knowledge of this species. To understand the research advances in this species, this review summarizes the taxonomic position, global distribution, population size, foraging ecology, sexual segregation, health threat by diseases, and potential threats and conservation biology. Besides, this species is facing increasing impacts of anthropogenic activities and habitat loss induced by global climate change. It also proposes new research perspectives and priorities to understand the advanced ecology of the Asiatic ibex. We also highlight a suite of research gaps that require multidisciplinary approaches. These will increase understanding of the evolution, biology, ecology, and epidemiology of this species.
... On a behavioural point of view, the fact that 38% of the photographic observations of Alpine ibex occurred in the study area above 2,300 meters ( Fig. 1) might be due to social Biogeographia36: s003 Pellicioli & Cimberio, 2021 6 competition with other wild ungulates living at lower altitudes (Jaeggi et al., 2020). Also, the climate variations recorded in recent decades contributed to modifying the species behaviour (Grignolio et al., 2004, Paul et al., 2020, the use of grazing (Aubulet et al., 2009) and also the horn growth (Giacometti et al., 2002b;Bergeron, 2008). ...
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The Alpine ibex is one of the finest examples of how human’s attitude towards nature is changing by becoming aware of biodiversity conservation. On the 30th anniversary of the first Alpine ibex reintroduction in the OrobieAlps, a three year long Citizen Science Project started in June 2017 (‘Stambecco Orobie e Lombardia’). Nowadays, a complementary tool that can be used in data collection is citizen science; its use among scientific community is increasing and it is considered a new opportunity for the future of science. A three-year project (from 2017 to 2019) took place in the Orobie Alps (Bergamo, Italy), with the collection of 2,530 photographs of Alpine ibex (Capra ibex ibex). A total of 735 citizen scientists took part in the project by gathering data and collecting pictures (225 in 2017, 248 in 2018 and 262 in 2019). Photographs, complete with technical descriptions, were posted on the project’s Facebook page and the Instagram page and each one was georeferenced on the ArcGis platform and a web mapping application. The georeferenced images helped comparing the expansion zones of Lombard Alpine ibex colonies to the ones identified in a preliminary study. The images also turned out to be a useful tool in monitoring population health. These methods may help to avoid data dispersion and may raise public awareness of Alpine ibex conservation policies.
... The scarce empirical evidence available for a relationship between early-life growth and survival in harvested populations generally indicates that growing fast entails a cost, although there are notable exceptions (Table 1, Appendix S1). It is noteworthy that some studies have failed to detect a relationship between early-life growth and survival (e.g., Bergeron et al. 2008;Bonenfant et al. 2009), while others have found positive relationships (Chambellant et al. 2003;Beauplet et al. 2005;Nuñez et al. 2015). In these studies, high individual quality (with traits such as a heavy weight at birth) was strongly related to fast early-life growth and lower mortality rates. ...
Article
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From current theories on life-history evolution, fast early-life growth to reach early reproduction in heavily hunted populations should be favored despite the possible occurrence of mortality costs later on. However, fast growth may also be associated with better individual quality and thereby lower mortality, obscuring a clear trade-off between early-life growth and survival. Moreover, fast early-life growth can be associated with sex-specific mortality costs related to resource acquisition and allocation throughout an individual’s lifetime. In this study, we explore how individual growth early in life affects age-specific mortality of both sexes in a heavily hunted population. Using longitudinal data from an intensively hunted population of wild boar (Sus scrofa), and capture–mark–recapture–recovery models, we first estimated age-specific overall mortality and expressed it as a function of early-life growth rate. Overall mortality models showed that faster-growing males experienced lower mortality at all ages. Female overall mortality was not strongly related to early-life growth rate. We then split overall mortality into its two components (i.e., non-hunting mortality vs. hunting mortality) to explore the relationship between growth early in life and mortality from each cause. Faster-growing males experienced lower non-hunting mortality as subadults and lower hunting mortality marginal on age. Females of all age classes did not display a strong association between their early-life growth rate and either mortality type. Our study does not provide evidence for a clear trade-off between early-life growth and mortality.
Chapter
This comprehensive species‑specific chapter covers all aspects of the biology of Alpine ibex Capra ibex, including paleontology, physiology, genetics, life history, ecology, habitat, diet, and behavior. The economic significance and management of Alpine ibex and future challenges for research and conservation are addressed as well. The chapter includes a distribution map, a photograph of the animal, and a list of key literature.
Article
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Sexual traits are usually more phenotypically variable than non-sexual traits. We show that additive genetic variation is also higher in sexual traits, and often greater than in the same, non-sexually selected trait in females or other comparable traits in the same species. In contrast there is no difference in residual variation (environmental and non-additive) or heritability. The higher genetic variability of sexual traits is contrary to the expectations of the lek paradox. This hypothesis predicts that strong sexual selection, due to female choice, leads to fixation of most genetic variation in male sexual characters. High genetic variability in sexual traits can be explained if they are subject to directional selection that is greater than linear because this selects for greater phenotypic variation. It favours modifiers that increase the number of genes and the average contribution of a locus to phenotypic variance in sexual traits. These results provide a general resolution of the lek paradox.
Article
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According to the conditional handicap models females use male ornaments as honest signals of male viability. The assumptions for honest signalling are that the traits are costly and that they reflect male phenotypic condition, and hence optimal trait size is largest in the most viable males. However, experimental evidence for the costs of signalling are scarce. In this study we experimentally tested whether acoustic signalling, drumming, in a wolf spider Hygrolycosa rubrofasciata is a condition dependent, costly trait, and thus offers an honest signal of quality to females. Males of this species court females by drumming dry leaves with their abdomen. Females prefer to mate with males of high drumming rate, but body mass of males does not affect female choice. We manipulated phenotypic condition of males by keeping them in high, intermediate and low food levels. Males in a high food level treatment maintained their drumming rate at a high level, while males with intermediate and low food levels exhibited a reduction in drumming rates. Thus, phenotypic condition of the males affects their sexual signalling. We induced another set of males to increase their drumming activity by presenting females in proximity. These males suffered higher mortality and lost significantly more weight than other males, confirming that drumming is costly. However, within the increased treatment group males that drummed most actively survived better than less active males. Thus, males vary in their ability to bear the costs of drumming, which suggests that drumming is an honest signal of male quality (= conditional handicap) for females.
Article
The magnitude of the effect of good genes as a viability benefit accruing to choosy females remains a controversial theoretical and empirical issue. We collected all available data from the literature to estimate the magnitude of good-genes viability effects, while adjusting for sample size. The average correlation coefficient between male traits and offspring survival in 22 studies was 0.122, which differed highly significantly from zero. This implies that male characters chosen by females reveal on average 1.5% of the variance in viability. The studies demonstrated considerable heterogeneity in effect size; some of this heterogeneity could be accounted for by differences among taxa (birds demonstrating stronger effects), and by differences in the degree of mating skew in the species (high skew reflecting stronger effects). Although these results suggest that viability-based sexual selection is widespread across taxa, they indicate that the effect is relatively minor. Finally, there was also an effect of publication year in that the more recent studies reported reduced effects. This may reflect publication biases during paradigm shifts of this debated issue, but it should also be recalled that the studies have only partly estimated the full fitness consequences of mate choice for offspring.
Article
The magnitude of the effect of good genes as a viability benefit accruing to choosy females remains a controversial theoretica and empirical issue. We collected all available data from the literature to estimate the magnitude of good–genes viabilit effects, while adjusting for sample size. The average correlation coefficient between male traits and offspring survival i 22 studies was 0.122, which differed highly significantly from zero. This implies that male characters chosen by females revea on average 1.5%of the variance in viability. The studies demonstrated considerable heterogeneity in effect size; some of thi heterogeneity could be accounted for by differences among taxa (birds demonstrating stronger effects), and by difference in the degree of mating skew in the species (high skew reflecting stronger effects). Although these results suggest that viability–base sexual selection is widespread across taxa, they indicate that the effect is relatively minor. Finally, there was also a effect of publication year in that the more recent studies reported reduced effects. This may reflect publication biases durin paradigm shifts of this debated issue, but it should also be recalled that the studies have only partly estimated the ful fitness consequences of mate choice for offspring.
Book
Why have males in many species evolved more conspicuous ornaments and signals such as bright colours, enlarged fins, and feather plumes, as well as larger horns and other weapons than females? Darwin's explanation for such secondary sex traits, the theory of sexual selection, became his scientifically perhaps most controversial idea. It suggests that the traits are favoured by competition over mates. After a long period of relative quiescence, theoretical and empirical research on sexual selection has erupted during the last decades. This book describes the theory and its recent development, reviews models, methods, and empirical tests, and identifies many remaining open problems. Among the topics discussed are the selection and evolution of mating preferences; relations between sexual selection, species recognition, and speciation; constraints on sexual selection; the selection of secondary sex differences in body size, weapons, and in visual, acoustic, and chemical signals. The rapidly growing study of sexual selection in plants is also reviewed. Other chapters deal with alternative mating tactics, and with the relationships among sexual selection, parental roles, and mating systems. The present review of this very active research field will be of interest to students, teachers, and research workers in behavioural and evolutionary ecology, animal behaviour, plant reproductive ecology, and other areas of evolutionary biology where sexual selection is a potential selection factor. In spite of much exciting progress, some of the main questions in the theory of sexual selection yet remain to be answered.