Do peahens not prefer peacocks with more elaborate trains?
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Do peahens not prefer peacocks with more elaborate trains?
AD ELIN E L OYA U , MA RION PE TR IE †, M ICH E L S AIN T J AL M & G AB RI E L E SORC I§
*Station d’Ecologie Expe´rimentale du CNRS a` Moulis, CNRS UMR 2936
yEvolutionary Biology Group, Newcastle University
zMuse´um National d’Histoire Naturelle (MNHN), UMR 5173
xBioge´osciences, CNRS UMR 5561, Universite´ de Bourgogne
(Received 17 June 2008; initial acceptance 9 July 2008;
ﬁnal acceptance 23 July 2008; published online 7 September 2008; MS. number: D-08-00401)
Keywords: female mate choice; interpopulation variability; ornament; Pavo cristatus; peafowl
Ever since , the peacock’s train has been
population can be misleading if generalized to the whole
cited as the icon of an extravagant conspicuous second-
ary sexual trait that has evolved through female mate
The peacock’s train is a complex structure that cannot
be summarized with only three morphological traits
lenged this idea. They monitored female mate choice
(number of eyespots, train symmetry and train length).
during 7 years in a feral peafowl, Pavo cristatus, popula-
Two previous studies showed that the density and the
tion in Japan and found no correlation between male
coloration and iridescence of eyespots in the train have
mating success and three morphological train traits.
the potential to be involved in mate choice
They concluded that ‘combined with previous results,
our ﬁndings indicate that the peacock’s train is not cur-
cannot discard the possibility that they did not measure
rently the universal target of female choice’ and pro-
elements of the signal most relevant for female mate
posed ‘that the peacock’s train is an obsolete signal for
choice. Their main concern was the absence of correla-
which female preference has already been lost or weak-
tions between the number of eyespots and mating suc-
cess, consistent over the 7 years of their study. One
their conclusions are far too strong, particularly since
explanation for this absence of correlation could be
three independent studies have found a relationship be-
that, in the Japanese population, the train contains
tween train features and mating success (
a trait preferred by the females that is not always posi-
tively correlated with the number of eyespots. Hence,
it would not be possible to detect whether the train
fore to draw attention to alternative explanations and
contains a signal under sexual selection. On the basis
conclusions that are essential for the understanding of
the complexity of mate choice. We ﬁrst suggest some
that train symmetry and train length were not compo-
possible nonadaptive and adaptive explanations for the
nents of the signal received by the females. However,
reported differences in female preferences in the peafowl.
does that mean that no signal exists? More recently,
We then show that plasticity in mate choice is a wide-
a correlational study suggested that females may use
spread phenomenon across a large spectrum of species.
Therefore, we suggest that ﬁndings based on a single
than the number of eyespots, perhaps because thisfeature is more quickly assessed. This ﬁnding is notinconsistent with the fact that experimentally reducingthe number of eyespots in the train decreased mating
Correspondence: A. Loyau, Station d’Ecologie Expe´rimentale du CNRS a`
Moulis, CNRS UMR 2936, 09200 Saint Girons, France (email:
). M. Petrie is at the School of Clinical Medical
Sciences, William Leech Building, Newcastle University, Newcastle-
tions between eyespot number, train length and mating
upon-Tyne NE1 4HH, U.K. M. Saint Jalme is at the Muse´um National
success, although the relationship between eyespot
d’Histoire Naturelle (MNHN), UMR 5173, MNHN-CNRS-Paris 6,France. G. Sorci is at Bioge´osciences, CNRS UMR 5561, Universite´ de
number and train length was negative in a sample of
culled birds from one lek, all shot on the same day
Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
density was the trait with the highest coefﬁcient of vari-
Takahashi and colleagues may be able to test for an
ation (10.3%) while the coefﬁcient of variation of the
effect of eyespot density, since they measured the
number of eyespots and the train length of 24 pea-
It is unfortunate that Takahashi et al. did not provide
cocks for 3 years. This would be a valuable addition
the pattern of variation of the eyespot density in their
to our understanding of how the various components
population. Low variation in train morphology could
of the signal in the male’s train affect female mate
arise if genetic variability is low. Consideration of varia-
all the studies of peahen mate choice were carried
between studies and suggested that missed observations
out in an unnatural environment. Apart from the obvi-
of mating and small sample sizes of previous studies
ous problem that feral populations of peafowl do not un-
may play a part, claiming that their study had ‘the lon-
dergo the same selection pressures as wild populations,
gest observation with the largest sample size among pea-
these populations were established outside the original
distribution range of the species several centuries ago,
that the number of copulations observed is critical to
usually using a small number of individuals which could
a meaningful analysis of variance in mating success.
have created a strong genetic bottleneck. Isolated small
populations are expected to have reduced genetic vari-
tions in 7 years, which amounts to ca. 38 copulations
ability because of a combination of founder effects, in-
per annum from 20 to 37 territorial males observed in
a number of instances where the conspicuous coloration
116 copulations in 1 year (1989) from observations of
of mainland birds has been lost on small island popula-
30 territorial males (almost three times as many). We sus-
tions and genetic drift is often cited as a cause
pect the difference in the number of copulations ob-
and references therein). Another possibility is
served may be caused by a difference in population size
that, in some captive populations, not all founders
and in particular the number of reproductively active
have come from the same place in the native range of
hens observed. The Japanese study reported a total pop-
the species, resulting in a higher genetic diversity. There-
fore, isolation combined with relaxed or modiﬁed selec-
stated is male biased, whereas the Whipsnade population
tion pressures and/or mixed origins of founders could
was estimated at 179 birds. Unfortunately, watching the
explain why Takahashi et al. found different results to
same small population for a number of years does not
overcome the problem of error associated with small
Reasons for the discrepancy between Takahashi et al.’s
sample size, as the dependent variable is the number of
results and previous studies may not only reﬂect differ-
copulations per male per annum; the possibility there-
ences in methodology. There are several other explana-
fore remains that there may be insufﬁcient observations
tions for what might be called plastic female choice.
of copulations to detect an effect in the Japanese study.
Indeed, divergence in behaviour among populations
There are other possible explanations for the discor-
of a given species is widespread ; see also
dance between studies, including uncontrolled variation
as a result of small methodological differences. For
example, train length was measured ‘in early spring’ in
In particular, there is a growing body of evidence demon-
beginning to the peak of the mating season in Japan.
strating a signiﬁcant variation in male traits and female
This could confound the relationship, as there is marked
variation in the timing of the start and length of time
a wide range of taxa including insects, amphibians, ﬁshes
over which feathers drop. The number of feathers lost
by the end of the season could relate to performance
during the mating season, if expenditure on reproductive
guppies, Poecilia reticulata, among 11 populations in Tri-
effort or mating success leads to an earlier or compressed
nidad and showed that mate preferences varied in inten-
sity, direction and the number of traits used. In this
species, females also differ in the relative importance
male mating success. The most successful male obtained
that they place on male orange coloration or iridescence
only 14.9e31.4% of copulations per year whereas in ear-
lier studies these values were consistently higher (36.4%
Regardless of methodological differences (as suggested
by ) or small sample sizes (as suggested by
by Takahashi et al. there appeared to be a low consensus
tions can arise by several mechanisms. Populations might
among females about whom to mate with, an unusual
differ in the amount of genetic variation for the trait of
ﬁnding in a lekking species. Could that be a result of
interest because of a founder effect and/or a genetic drift.
low variation in train morphology which does not allow
Geographical variation in selection pressures can also pro-
peahens to distinguish between the different potential
duce genetic structuring among populations (e.g.
mates? In the French population, we found that eyespot
genetic differences may account for the differences of pat-
is a galliform bird, the train is likely to develop in the
cost of trait expression may vary with environmental con-
absence of oestrogen and consequently is unlikely to be
ditions such as climate, predation risk, pathogen preva-
lence, conspeciﬁc density and sex ratio (e.g.
Therefore, they expected females to discard this trait in
A given trait within one environment may not
reliably indicate mate quality in another environment
male preference for the male’s train is supposed to have
been ‘lost or weakened’. If so, it implies that this prefer-
in female mate choice is thought to result from spatial
ence existed at some point and thus may still exist. Eye-
and temporal variation in environmental conditions
spots have independently evolved in several taxa (birds
and butterﬂies) and it is likely that such a trait originally
evolved through the exploitation of a sensory bias (
). A spectacular illustration of the concept of
) which would also account for the ‘hypnotic effect’
adaptive plasticity in female mate choice has been re-
of the train on peahens described by .
The coexistence of the heritability of female preference
ting, Calamospiza melanocorys, sexual selection on male
(through the sensory bias) and the heritability of the
traits can vary dramatically across years and even show re-
versals in the direction of a single trait. Importantly, in
support for the idea that the train evolved through Fish-
a given year, these changes usually favour male traits
er’s runaway process (). At some point, as the
that correlate with the highest reproductive success
train became an extreme trait, it presumably crossed
a threshold and started to impose costs on the bearer,
that a seemingly inconsistent female mate choice across
with only the better quality males being able to grow
years in fact targets the male phenotype that within
and display the more ornamented trains. Some results al-
each year provides the best reproductive output. Even
though different selection mechanisms may arise for
temporal and spatial variation, this example illustrates
has evolved as a Fisherian trait and is maintained as
that, if temporal differences can be found within a given
a good genes indicator, whatever the hormonal control.
population, it is not surprising to ﬁnd differences
In other galliform species the development of the train
between geographically distinct populations. Finally,
may never have reached the threshold, leading to
variation in male traits and female preferences can
a loss of ornamental traits and associated display
account for learning and cultural transmission. Indeed,
male bowerbirds may copy peers when building bowers
not see why the form of hormonal control of train
and this would explain interpopulation differences in
expression negates previous ﬁndings and know of no
evidence to suggest why it should. The peahens may
brown-headed cowbirds, Molothrus ater, are a conse-
‘appear to be quite exceptional if they indeed select
quence of complex interactions between male learning
and population differences in female preferences (re-
page 1215). However, the existence of secondary sexual
ornaments and display behaviours as complex and
inﬂuences such as sexual imprinting and mate choice
extravagant as the peacock’s train and display is itself
copying can induce variation in female preferences
male song can be inﬂuenced by social experience in
it is important to publish negative results, and hopefully
female zebra ﬁnches, Taeniopygia guttata, and canaries,
further such studies will be published so that a more
meaningful meta-analysis can be carried out. However,
Taken together, these examples highlight the fact that
the failure to detect evidence of mate choice in one
great caution is required when generalizing results from
study based on a limited array of traits does not mean
a single population to the whole set of populations of
that females do not prefer males with more elaborate
a given species, as already pointed out by
trains. Only a very strict experimental study across
several captive and wild populations could demonstrate
by three independent groups on three independent pop-
that. To date, only one study on peafowl mate choice
and, unfortunately, the number of eyespots was not re-
elaboration in mate choice, it is thus rather surprising
corded. Further studies of wild populations with natural
levels of genetic variation will be particularly useful
proposed that ‘the peacock’s train is an obsolete sig-
in extending our understanding of peahen mating
nal for which female preference has already been lost or
We thank Dirk S. Schmeller, Alexis S. Chaine, L. Morris
the peacock’s train might be an indicator of good genes,
Gosling and Jean Clobert who provided valuable com-
despite strong evidence supporting that hypothesis
ments and discussion and two anonymous referees who
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I dette notat gives en række råd vedrørende forstørret prostata – opdelt i svagt, moderat og stærkt forstørret prostata – samt prostatakræft. De givne råd er baseret på indtagelse af almindelige fødemidler, urtedrikke, plantemedicin samt homøopatisk, antroposofisk og ayurvedisk medicin. Notatet indeholder ingen generelle anatomiske eller fysiologiske oplysninger om prostata og sygd
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