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The modern theories of sexual selection predict that male sexual ornaments may have evolved as reliable signals of male fertilization efficiency. However, among the studies of fishes with external fertilization, the results have yielded ambiguous evidence. In the present study, we present data on the phenotypic relationships between red spawning coloration and ejaculate quality (spermatocrit, sperm motility) from Arctic charr, Salvelinus alpinus. We studied two generations (F1 and F2) of males from a large lake population, reared in a standardized hatchery environment, to determine whether differential hatchery history, or duration of hatchery selection, affected the variation in ejaculate characteristics or abdominal coloration. After controlling for body length, there was no difference between the hatchery generations in these traits. However, the degree of redness increased with fish size. We found a positive correlation between sperm velocity and sperm longevity, indicating a functional integration between these sperm features across generations. Sperm velocity was also positively correlated with male redness. Therefore, the finding obtained in the present study suggests that the carotenoid-based ornamentation in Arctic charr may provide information about differences between males in their fertilization potential. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802.
Content may be subject to copyright.
Spawning coloration and sperm quality in
a large lake population of Arctic charr
(Salmonidae: Salvelinus alpinus L.)
1Joensuu Game and Fisheries Research, Yliopistokatu 6, FI-80100 Joensuu, Finland
2University of Joensuu, Faculty of Biosciences, PO Box 111, FI-80101 Joensuu, Finland
3University of Tromsø, Department of Evolution and Ecology, Institute of Biology, 9037 Tromsø,
4University of Jyväskylä, Department of Biological and Environmental Science, PO Box 35, FI-40014
Jyväskylä, Finland
5Finnish Game and Fisheries Research Institute, Viikinkaari 4, PO Box 2, FI-00791 Helsinki,
Received 13 March 2009; accepted for publication 11 June 2009bij_1317794..802
The modern theories of sexual selection predict that male sexual ornaments may have evolved as reliable signals
of male fertilization efficiency. However, among the studies of fishes with external fertilization, the results have
yielded ambiguous evidence. In the present study, we present data on the phenotypic relationships between red
spawning coloration and ejaculate quality (spermatocrit, sperm motility) from Arctic charr, Salvelinus alpinus.We
studied two generations (F1and F2) of males from a large lake population, reared in a standardized hatchery
environment, to determine whether differential hatchery history, or duration of hatchery selection, affected the
variation in ejaculate characteristics or abdominal coloration. After controlling for body length, there was no
difference between the hatchery generations in these traits. However, the degree of redness increased with fish size.
We found a positive correlation between sperm velocity and sperm longevity, indicating a functional integration
between these sperm features across generations. Sperm velocity was also positively correlated with male redness.
Therefore, the finding obtained in the present study suggests that the carotenoid-based ornamentation in Arctic
charr may provide information about differences between males in their fertilization potential. © 2009 The
Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802.
ADDITIONAL KEYWORDS: ejaculate – ornamentation – sexual selection – sperm competition – teleost.
Conspicuous male ornaments during reproduction are
commonly found in various animal species. Especially
in species where males offer females gametes but
neither resources, nor parental care, indirect genetic
benefits to the offspring (i.e. good genes or compatible
genes; Mayrs & Hill, 2004; Neff & Pitcher, 2005) can
form a major selective force in the evolution of female
mate choice (Andersson, 1994; Møller & Alatalo, 1999;
Kokko et al., 2003). However, females could also
directly benefit from choosing more elaborately orna-
mented males if they thereby improve the changes of
mating with more fertile males. This assumption is
the background for the phenotype-linked fertility
hypothesis, which states that the male display of
sexual ornaments reliably advertises male fertility
via condition dependency of the ornaments and the
sperm (Sheldon, 1994).
Increasing attention has been recently devoted to
the idea of a phenotypic relationship between sexu-
ally selected characters and ejaculate quality (Pizzari,
*Corresponding author. E-mail:
Biological Journal of the Linnean Society, 2009, 98, 794–802. With 3 figures
© 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802794
Jensen & Cornwallis, 2004; Malo et al., 2005; Parker
et al., 2006; Rogers et al., 2008), although such
studies have yielded contradictory results. Among
fishes, there is ambiguous evidence for a linkage
between the expression of sexual ornaments and
various sperm quality indices. Positive correlations
have been found in some of the studies (Kortet et al.,
2004; Måsvær, Liljedal & Folstad, 2004; Locatello
et al., 2006; Pitcher, Rodd & Rowe, 2007), whereas
others have found no or even negative associations
(Liljedal, Folstad & Skarstein, 1999; Skinner & Watt,
2007; Liljedal, Rudolfsen & Folstad, 2008). Moreover,
there can be a significant intra-specific variation with
respect to which components of the male’s phenotype
potentially predict insemination success (Pitcher &
Evans, 2001). These findings may partly result from
the fact that such phenotypic relationships are often
tested in populations where varying environmental
effects may obscure the underlying genetic associa-
tions between male ornaments and fertilization
The prevalence of carotenoid-based ornaments, par-
ticularly in the versatile signalling of fishes and birds,
has made them an ideal study subject in the context of
sexual selection. Carotenoids usually appear as red–
yellows, and these integumentary colours in feathers
and skin are generally assumed to serve as reliable
signals of the bearer’s health, vigour, and genetic
quality (Olson & Owens, 1998; Møller et al., 2000).
Because primary and secondary sex traits are pro-
moted by the same sex hormones, namely androgens
(Folstad & Skarstein, 1997; Hillgarth, Ramenofsky &
Wingfield, 1997), the expression of carotenoid-derived
colour signals may be directly associated with the
males’ capacity for sperm production. Furthermore,
the allocation of carotenoids for ornamental purposes
might reflect low immune activity within the body as
well as the reduced exposure of ‘nonself’ sperm cells to
an autoimmune attack (Folstad & Skarstein, 1997;
Liljedal et al., 1999). Another explanation rests on the
role of carotenoids as antioxidants (i.e. functioning to
inactivate free radicals), which have a deleterious
effect on both sperm quality and the substrates
responsible for male ornamentation (von Schantz
et al., 1999; Blount, Møller & Houston, 2001). How-
ever, it has been recently suggested that carotenoid-
based sexual traits may rather signal the availability
of nonpigmentary antioxidants (Bertrand, Faivre &
Sorci, 2006; Pike et al., 2007; Pérez, Lores & Velando,
2008). Either way, intense carotenoid-dependent
ornamental traits may imply high body supplies of
antioxidants, which have a potential to reduce the
susceptibility of sperm to oxidative stress and thus
increase fertility (Greco et al., 2005).
The Arctic charr (Salvelinus alpinus L.) is a highly
suitable model species for studying the associations
between secondary sexual ornaments and sperm
traits (Måsvær et al., 2004). Charr males fertilize the
eggs externally, and neither males, nor females
provide parental care to offspring after spawning
(Sigurjónsdóttir & Gunnarson, 1989). Before and
during the breeding season, mature males form hier-
archical groups and develop a red abdominal orna-
mentation that is correlated with parasite intensities
and immune activity (Skarstein & Folstad, 1996;
Liljedal et al., 1999; Skarstein, Folstad & Liljedal,
2001). Previous studies from wild-caught charr have
revealed that the degree of carotenoid coloration also
may be related to male fertility traits. Måsvær et al.
(2004) found that redder males had higher sperm
production (i.e. testes mass, milt mass and sperm cell
numbers produced) than paler males; but see also
Liljedal et al. (1999). Yet a recent insemination
experiment demonstrated that more colourful male
charr have lower parentage success than their less
conspicuous rivals when ejaculates with equal sperm
numbers compete (Liljedal et al., 2008). This suggests
that the lower competitive ability of the ejaculates
from more intensively coloured males was a result of
sperm traits other than sperm numbers.
In the present study, we examined whether the two
important phenotypic traits, red spawning coloration
and body size, are correlated with appropriate mea-
sures of male reproductive quality (or primary sexual
traits) in a large lake Arctic charr (Lake Inari,
Finland) population, reared in a standard environ-
ment (fish hatchery). Both the first and the second
hatchery generations of wild-collected fish were used
to examine the alternative hypothesis that differen-
tial hatchery history had an effect on these traits.
The experiment was carried out in mid-October 2007
at the facilities of Sarmijärvi Aquaculture station
(Finnish Game and Fisheries Research Institute), in
north-eastern Finland. The charr were descended
from the nearby Lake Inari population and repre-
sented the first (F1) and second (F2) hatchery genera-
tions (year classes 2002 and 2001, respectively), both
of which had been produced by pairwise fertilizations
(F1:N=300 pairs; F2:N=76 pairs). Furthermore, the
F2group had been produced by specifically avoiding
matings between close relatives. The fish were reared
similarly in oblong outdoor tanks (area 200 m2, water
volume 200 m3) and fed continuously (ad libitum)
with carotenoid-rich salmonid food (Rehuraisio Emo-
Vital; astaxanthin content 80 mg kg-1). The tempera-
ture of the inflow water and the lightning conditions
both followed the natural rhythm.
© 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802
Prior to measurements, the fish were fasted for
more than 3 weeks. Twenty randomly chosen mature
males from both generations were stripped for all
available milt and placed into discrete group-specific
tanks for 5 days to prohibit spawning activity during
the replenishment of their sperm reserves. The anaes-
thetized fish (MS-222) were measured for total length
(LT) to the nearest millimetre and photographed on a
grey background under standardized light conditions
for subsequent analysis. Thereafter, each fish was
carefully dried around the genital pore to avoid
sample contamination and the produced milt was
collected in individual Petri dishes by pressing the
abdomen towards the vent.
Sperm quality parameters were quantified immedi-
ately after the stripping of males. Spermatocrit,
which is defined as the percentage of a given volume
of semen that is occupied by cells, was measured
by centrifuging a homogenized proportion of the
milt in a capillary tube for 3 min at 11 500 r.p.m.
(5396 g). with a mini-centrifuge (Compur-electronic
Gmbh). Computer-assisted sperm analysis was
employed to estimate variation in sperm velocity; for
a more detailed description of the method, see Rudolf-
sen et al. (2006). Briefly, sperm activity was initially
video-recorded for 40 s after activation, specifically,
the precise moment that the subsample of pure milt
was exposed to 4.5 mL of water on a cooled (approxi-
mately 5 °C) microscope slide (Leja Products BV).
Recordings were made using a CCD B/W video
camera (Sony XC-ST50CE PAL) attached to a nega-
tive phase-contrast microscope (Olympus CH30) with
a¥10 magnification objective. Video recordings were
later analysed using the HTM-CEROS sperm tracker
software (CEROS, version 12, Hamilton Thorne
Research). The parameters measured were: average
path velocity (VAP), straight line velocity (VSL), and
curvilinear velocity (VCL) (Rurangwa et al., 2004).
The velocity estimates were based on the mean veloc-
ity of all motile cells (i.e. those exceeding the pre-
determined threshold values VAP >10 mms
VSL >20 mms
-1) recorded at 10, 20, 30, and 40 s after
activation. The percentage of motile cells 40 s after
activation was used as an estimate of sperm longev-
ity. For statistical analysis, the average over two
replicates within each male was used for each motil-
ity measure. For four individuals, sperm swimming
speed could not be reliably quantified and, conse-
quently, they were excluded from final analyses.
To estimate the red spawning coloration on the
abdominal region, digital images were measured
using a graphical user interface designed for the
MATLAB environment (InFotonics Center, University
of Joensuu, Finland) to produce numerical estimates
for the red, green, and blue intensities in the RGB
mode (Stevens et al., 2007). The means of these colour
parameters were calculated for each fish within two
specified areas (Fig. 1), and the values were further
averaged. Red intensity was calculated according
to the formula: IR=red/(red +green +blue) (Liljedal
et al., 2008), and this measure was highly correlated
with two alternative colour measurements (i.e. hue
and saturation), defined in the converted HSV colour
model (r=-0.682, N=40, P<0.001 and r=0.973,
N=40, P<0.001, respectively). Unlike saturation, IR
showed normal sample frequencies and was therefore
selected along with hue for a colour variable. Hue is
expressed as an angle on a continuous circular scale
(0–360°), so that the hue scores closer to zero repre-
sent a higher degree of red coloration (Skarstein &
Folstad, 1996). It can be thus said to be a more
qualitative measure of redness.
We used SPSS, version 15.0, for Windows (SPSS Inc.)
for the statistical analysis. Variable distributions
were checked for normality and variance homogeneity
Figure 1. Fish illustration showing the abdominal areas from which the coloration was measured.
© 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802
to verify the assumptions of parametric statistics. The
arc-sine square-root transformation was applied to
sperm longevity and IRvariables to fulfil their nor-
mality assumption. Because there were no ovarian
fluid gradients that could have directed the course of
sperm cells (Urbach, Folstad & Rudolfsen, 2005), cell
trajectories were not expected to be linear and thus
the measures of the actual point-to-point track fol-
lowed by the cells (VCL) was expected to be the most
relevant indicator of sperm swimming speed. In addi-
tion, the two other velocity parameters were highly
correlated with VCL (both r>0.98, both P<0.001,
N=36) and so we omitted them in the analyses as
redundant variables.
To test whether hatchery generations differed in
their sperm or colour properties, we first used multi-
variate analysis of covariance in which the three
sperm measures or two colour measures were the
dependent variable(s), fish length was a covariate,
and generation was a fixed factor. To examine
whether the decrease in VCL differed between gen-
erations, we used a repeated measurements analysis
of variance (ANOVA), using measurements of sperm
velocity from 10–40 s after activation as the within-
subject variable. Otherwise, only the VCL 10 s post-
activation was included in the analyses because this
measurement is the one that is most likely to be
under selection (Levitan, 2000). Controlling for the
effect of male length (LT), partial correlation coeffi-
cients between sperm and colour variables were
formed. Sensu Nakagawa (2004), we did not use Bon-
ferroni or similar corrections for the multiple com-
parisons (N=10 pairwise tests), but present all test
probabilities as two-tailed. Because we did not obtain
the measures of sperm velocity parameters from all
males, sample sizes varied.
There was a significant difference in body size
between the hatchery generations as a result of their
different ages (mean length ± SE =48.7 ± 0.74 cm and
55.2 ± 1.19 cm for F1and F2generations, respectively;
t-test, t33 =–4.551, P<0.001). The sperm traits (sper-
matocrit, VCL, longevity) did not differ between the
hatchery generations [multivariate analysis of cova-
riance (MANCOVA), F3,31 =1.153, P=0.343], nor were
they related to male length (covariate: F3,31 =1.185,
P=0.332). However, the spermatocrit showed a nega-
tive relationship with fish length among the males
from the first hatchery generation (r=-0.540,
P=0.014, N=20), but not the second (r=0.189,
P=0.426, N=20). Sperm swimming speed declined
significantly from 10–40 s after sperm activation
(repeated measures ANOVA, time: F3,32 =165.01,
P<0.001), although there was no generation-specific
effect of the rate of decline (generation: F1,34 =0.008,
P=0.931; time ¥generation: F3,32 =1.275, P=0.300)
(Fig. 2).
There was no difference in the variation of red
coloration (IR, hue) between generations (MANCOVA,
F2,36 =1.056, P=0.220), when the effect of LTwas
taken into account (F2,36 =6.114, P=0.005). Redness
increased with male body length (Fig. 3A).
Because the two hatchery generations did not differ
from each other with respect to coloration or sperm
features, we combined the data for further partial
correlation analyses (for the respective correlation
coefficients, see Table 1). After controlling for male
body length, we found a strong positive correlation
between sperm longevity and VCL (P<0.001,
N=36).There were also moderate, although nonsig-
nificant, inter-relationships between spermatocrit
and both sperm motility traits (Table 1). VCL showed
a significant correlation with both red intensity
(P=0.004, N=36; Fig. 3B) and red hue (P=0.007,
N=36). The significant influence of redness on
VCL was also revealed by the univariate analyses
of covariance (IR=covariate: F1,32 =7.667, P=0.009;
IR¥generation: F1,32 =2.670, P=0.112, or, alterna-
tively, hue =covariate: F1,32 =5.688, P=0.023; hue ¥
generation: F1,32 =1.409, P=0.244).
The present study provides some evidence for the
phenotype-linked fertility hypothesis that sperm
velocity was positively associated with the degree of
male red spawning coloration among a large lake
population of Arctic charr, reared in a controlled envi-
Figure 2. Mean sperm velocity (VCL) among males of the
first (N=20) and second (N=16) hatchery generations
measured at different times after activation. Vertical bars
denote 95 % confidence intervals.
© 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802
ronment. Sperm motility has been found to predict
male fertilization success (Froman et al., 1999;
Rurangwa et al., 2004), and, under sperm competi-
tion, sperm velocity is probably the prime determi-
nant of paternity (Birkhead et al., 1999; Levitan,
2000; Gage et al., 2004; Liljedal et al., 2008; Rudolf-
sen et al., 2008; Fitzpatrick et al., 2009). Our obser-
vations are thus consistent with the phenotype-linked
fertility hypothesis (Sheldon, 1994): the expression of
a sexual ornament may signal a male reproductive
trait that potentially determines male fertility.
There are alternative mechanistic causes for the
general association between male fertility and orna-
mental traits. In wild Arctic charr populations, both
the males’ carotenoid-based coloration and fertilizing
potential can be mediated by the individual differ-
ences in resistance to parasitic infections (Skarstein
& Folstad, 1996; Liljedal et al., 1999; Måsvær et al.,
2004). Increased immune activity may canalize
resources away from ornamentation and sperm pro-
duction, as well as interfere with developing sperm
cells, which are regarded as nonself to the male
(Folstad & Skarstein, 1997; Hillgarth et al., 1997).
Hence, the males that are resistant or capable of
maintaining a low immunological defence against
pathogens and parasites before and during reproduc-
tion will have more intense carotenoid-based colora-
tion and higher sperm quality (Skarstein & Folstad,
1996; Liljedal et al., 1999). Because the fish in the
present study had been housed in a controlled envi-
ronment and fed with commercial food (i.e. there was
no parasite transmission through the diet), the dif-
ferences of intrinsic resistance may have been less
important for generating the between-individual vari-
ability in ornamental coloration and sperm quality.
Alternatively, males exhibiting carotenoid-rich colora-
tion may also be those with high body supplies of
sperm-protective antioxidants (von Schantz et al.,
1999; Blount et al., 2001). Carotenoids themselves
may not play an active role in mitigating oxidative
stress (Isaksson & Andersson, 2008), but, instead,
carotenoid-based ornaments could signal an individu-
al’s availability of a more general antioxidant defence
Figure 3. Relationship between the relative red intensity
(nontransformed) versus (A) fish total length and (B)
sperm velocity (VCL) 10 s after activation among individu-
als of the first (dark circles) and second (open circles)
hatchery generations. The curves were fitted by (A)
y=32.7 +24.7xand (B) y=88.8 +41.6x.
Table 1. Partial phenotypic correlations between red intensity (IR), red hue, spermatocrit, sperm velocity (10 s after
activation) and sperm longevity in sexually mature male Arctic charr when controlling for the effect of fish body length
Parameter Hue Spermatocrit VCL Sperm longevity
IR-0.682*** 0.168 0.475** 0.213
Hue -0.108 -0.449** -0.186
Spermatocrit 0.302 0.275
VCL 0.838***
Sample sizes are in the range 36–40. VCL, curvilinear velocity.
**P<0.01; ***P<0.001.
© 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802
(e.g. the dietary intake of vitamins A, C, and E)
(Hartley & Kennedy, 2004; Bertrand et al., 2006; Pike
et al., 2007; Pérez et al., 2008).
Previous studies of guppies (Poecilia reticulata
Peters) suggest that, independent of body size, caro-
tenoid pigmentation can be positively linked with
sperm movement (Locatello et al., 2006; Pitcher et al.,
2007), as well as with the number of sperm deposited
(Pilastro et al., 2002; Pitcher et al., 2007; but see also
Pitcher & Evans, 2001; Skinner & Watt, 2007). Inter-
estingly, our results revealed that male body length
(LT) was not a significant predictor of ejaculate char-
acteristics, whereas it did have a positive correlation
with male redness. Although there did not appear to
be a general trade-off between the attained body size
(or age) and ejaculate quality, we found a negative
correlation between spermatocrit and male length in
the first hatchery generation. This is likely to be
related to the differential social status of individuals
(Rudolfsen et al., 2006), which is determined by the
relative body size within the group of males present,
with larger males being more dominant (Gross, 1996;
in charr, see Sigurjónsdóttir & Gunnarson, 1989;
Blanchfield & Ridgway, 1999). Subordinate charr
males are known to rapidly invest more both in sperm
quantity and quality, presumably to compensate for
their disfavoured breeding position in relation to the
dominant males (Liljedal & Folstad, 2003; Rudolfsen
et al., 2006; Haugland et al., 2009). Additionally,
Liljedal et al. (2008) found that colourful males gain
lower parentage than their less ornamented counter-
parts when equal numbers of sperm from rival males
compete for fertilization. In their study, the authors
suspected that the more efficient sperm of the paler
males could result, at least in part, from their lower
social status. Also in the present study, the formation
of size-related social hierarchies during the few days
before the measurements is a potential confounding
factor affecting the observed within-group relation-
ships between coloration and sperm traits. The
smaller individuals, especially among the F1fish, may
have increased their ejaculate quality relatively (i.e.
both sperm density and motility) compared to the
larger, more colourful fish.
Consistent with the observations in roach (Rutilus
rutilus L.) (Kortet et al., 2004) and African cichlid
fishes (Cichlidae) (Fitzpatrick et al., 2009), we found a
positive correlation between spermatozoal velocity
and sperm longevity. A functional inter-dependence
between these features is a good reflection of the
metabolic performance of the sperm cells, and sug-
gests that sperm energetics have been the target of
particularly intense selection as a result of sperm
competition (Fitzpatrick et al., 2009). In a typical
spawning situation of Arctic charr where several
males simultaneously release their milt in close prox-
imity to eggs (Sigurjónsdóttir & Gunnarson, 1989),
initial sperm velocity may have precedence over
endurance in terms of fertilization success (Levitan,
2000; Liljedal et al., 2008; Fitzpatrick et al., 2009). In
addition, spermatocrit showed signs of covariance
with both sperm motility variables, implying that
these traits are phenotypically integrated to some
extent rather than representing totally independent
components of fertilizing efficiency. Unlike sperm
number and milt volume, sperm motility may be less
dependent on the intra-testicular steroid content, but
is mostly determined by the intra-cellular ATP stores
(Christen, Gatti & Billard, 1987; Cummins, 1998;
Froman et al., 1999, 2002). Because sperm motility is
susceptible to the activity of maternally-derived mito-
chondrial genes (Cummins, 1998; Pizzari & Birkhead,
2002), directional selection on sperm density and
sperm motility may not occur contemporaneously
(Froman et al., 2002; Pizzari & Birkhead, 2002); but
see also Fitzpatrick et al. (2009). It is also possible
that the mitochondrial genes themselves, or their
interaction with nuclear genes, mediate a relation-
ship between some male ornaments and sperm
quality (Pizzari et al., 2004).
Predicting the phenotypic linkage of primary and
secondary sex traits from captive-bred brood stocks
involves both advantages and drawbacks in compari-
son with wild fish. Most importantly, the culture
environment essentially reduces, although not totally
removes, the among-individual variation arising
from confounding environmental effects. Neverthe-
less, captive conditions are radically different from
natural habitats, which can easily alter and/or relax
the selective pressures operating on various pheno-
typic traits and thus ultimately reduce the frequency
of genotypes adapted to reproduce in the wild (Lynch
& O’Hely, 2001; Wedekind, 2002; Frankham, 2008).
Hatchery selection and inbreeding have been noted as
being among the major causes of the rapid genetic
divergence of hatchery fish from their wild ancestors
(Verspoor, 1988; Wang & Ryman, 2001; Wedekind
et al., 2007). Both hatchery generations in the present
study had been produced by a large number of pair-
wise fertilizations, which is presumably an effective
means to prevent the loss of genetic diversity, as well
as to prevent the selection for efficient sperm owing to
sperm competition. Furthermore, the possibility of
inbreeding among the F2fish had been minimized
with controlled matings, and thus inbreeding de-
pression (genetic load) for sexual coloration (van
Oosterhout et al., 2003) or fertility traits (Gomendio,
Cassinello & Roldan, 2000; Margulis & Walsh, 2002;
Gage et al., 2006) is unlikely in our sample. It
remains to be investigated, however, whether an
exposure to artificial selection over multiple genera-
tions would result in less clear phenotypic correla-
© 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 794–802
tions between sperm traits and sexually selected
In conclusion, the results obtained in the present
study provide some support for the idea that male
ornamental traits reveal information about primary
sexual traits. After controlling for environmental con-
ditions and body size, male abdominal redness was
positively correlated with sperm motility. Thus, the
spawning coloration of Arctic charr males may
provide information about differences in fertilization
potential between males.
We thank Sarmijärvi Aquaculture station (FGFRI) for
providing test fish and Kirsti Kyyrönen for drawing
the fish illustration. Ann Hedrick and two anonymous
reviewers gave constructive comments on the manu-
script. The research was funded by FGFRI (NP, MJ),
Jenny and Antti Wihuri Foundation (M.J.), the
University of Oulu (R.K.), and Academy of Finland
(J.K., project 121694; R.K., project 127398). G.R. and
L.F. received funding from the Norwegian Research
Council (177744/V40 and 166581/V40, respectively).
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... In fact, some studies have shown that sperm velocity in sneaker males, which experience greater sperm competition, was higher than in parental males (Burness et al. 2004;Locatello et al. 2007). Sperm velocity is thought to negatively affect sperm longevity; however, experimental and comparative analyses have resulted in inconsistent outcomes (negative: Neff et al. 2003;positive: Pitcher et al. 2009;Janhunen et al. 2009). ...
... In contrast to the numerous studies examining the associations between adult body size and sperm characteristics, few studies have focused on the associations of secondary sexual characters, such as breeding colour, snout length and hump length, with the sperm characteristics (M asvaer et al. 2004;Janhunen et al. 2009;Pitcher et al. 2009). The dominance hierarchy of Salmonidae within reproductive groups is determined not only by their body size but also by their secondary sexual characters (Fleming & Gross 1994). ...
... In this case, the range was specified as a circle with a five-pixel radius, and 10 circles were randomly superimposed on each photo so that they entirely covered the abdominal region displaying evident breeding colour (Fig. 1). In salmonids, the colours of this region are considered an ornament that signals important information in reproductive behaviour (M asvaer et al. 2004;Janhunen et al. 2009). In this study, three colour properties, hue (°), saturation (%) and brightness (%), were obtained as values of breeding colour (Liljedal et al. 1999;Pitcher et al. 2007). ...
In Salmonidae, subordinate males are exposed to higher risks of sperm competition than dominant males and thus are expected to improve the sperm characteristics (sperm concentrations, sperm velocity and sperm longevity). In this study, we investigated the relationships between body size and secondary sexual characters (breeding colour, hump height and snout length), and sperm characteristics of one-year-old (newly matured) Dolly Varden char. Small males displayed higher sperm concentrations than large males. Moreover, males with dull breeding colours, but not with lesser snout length and hump height, displayed an increased sperm velocity compared to males with bright colours, suggesting a trade-off between sperm quantity and the investment in breeding colour. In addition, sperm longevity decreased as sperm swimming velocity increased. These findings indicate that small males with dull breeding colours improve the quantity and quality of their sperm to a great extent to enhance their chances of reproductive success.
... In such contest, sperm quality parameters are known to respond with plasticity among males depending on age, length, dominance and other life-history variables (Fleming and Gross, 1994;Liley et al., 2002;Bozkurt, 2006;Bozkurt et al., 2006a;Rudolsen et al., 2006;Janhunen et al., 2009;Pitcher et al., 2009). ...
... Levitan (2000) observed that duration of motility is negatively correlated to spermatozoa velocity, assuming the existence of a trade-off between these two parameters. More recent discordant studies did not find negative correlations or evidence about trade-off between duration of motility and spermatozoa velocity in Atlantic salmon (Gage et al., 2004), or reported a positive relationship between the two considered parameters in Arctic charr (Janhunen et al., 2009) and Coho salmon (Pitcher et al., 2009). ...
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This research aimed to provide a characterization of fresh semen in wild and threatened Mediterranean brown trout (Salmo cettii), inhabiting the Biferno River basin and to study the variance of sperm parameters in a reproductive system with high male competition. The evaluated sperm quality parameters were: volume, density, viability, motility and sperm movement duration. High variability in sperm traits were found probably in response to the heterogeneity of individual condition, social status, spawning activity and migration costs. Duration of motility was positively correlated (P<0.05) with age class of breeders and motility. Stronger positive correlations (P<0.001) were observed between motility and viability and between sperm counts and viable sperms. This study reported the first data about semen quality of an Italian wild population of native trout. These results are useful for planning efficient artificial fertilization protocols in restoration programs involving supportive breeding together with other innovative conservation strategies as gamete cryopreservation. © Published by Central Fisheries Research Institute (CFRI) Trabzon, Turkey.
... However, differences in the timing of fertilization may also be caused by males. A positive relationship between carotenoid-based male ornamentation and sperm quality (velocity) has been reported in several species [27][28][29]. In fact, it is known that colorful male guppies produce faster sperm [30,31] (but see [32,33]). ...
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The trade-up hypothesis is a female behavioral strategy related to mating with multiple males. In this hypothesis, females can produce high-quality offspring while avoiding the risk of losing reproductive opportunities by non-selective mating with males at first mating and then re-mating with more attractive males. As an internal mechanism to realize this behavioral strategy, we predicted that females would immediately fertilize their eggs when they mated with attractive males, whereas females would delay fertilization when they mated with unattractive males to trade-up sires of offspring. The guppy ( Poecilia reticulata ) is an ovoviviparous fish with internal fertilization, and females show a clear mate preference based on the area of orange coloration on the bodies of males. In addition, it is known that females show a re-mating strategy consistent with the trade-up hypothesis. We tested whether the attractiveness of mated males affected the gestation period and the timing of fertilization. Females were paired with either colorful males or drab males, and the gestation periods (the number of days from mating to parturition) were compared. In addition, we dissected the abdomens of the females at intervals of several days after mating and observed whether the eggs were fertilized. The gestation period in females that were paired with attractive colorful males was significantly shorter than that in females that were paired with drab males. We found that females that mated with colorful males also had their eggs fertilized earlier than those that mated with drab males. Our findings show that differences in the timing of fertilization according to attractiveness of the mate increase the opportunity for cryptic female choice and trading up.
... The pattern in salmonids seems less 122 clear. Janhunen et al. (2009) found in a captive population of Arctic char that the intensity of 123 male coloration was positively correlated with sperm velocity (when tested in water) while 124 dominant males are expected to have reduced sperm velocity (Rudolfsen et al. 2006). 125 Combined, these findings suggest that male dominance and coloration are not necessarily 126 linked in char. ...
Fish often spawn eggs with ovarian fluids that have been hypothesized to support sperm of some males over others (cryptic female choice). Alternatively, sperm reactions to ovarian fluids could reveal male strategies linked to their likely roles during spawning. Sperm of males who would usually be close to females during spawning are then expected to be better adapted to the presence of ovarian fluids than to water only, while the reverse would be expected for males that typically spawn at larger distance to the females. We tested these predictions with gametes and ovarian fluids from wild-caught lake char (Salvelinus umbla). We found that sperm of more colorful males showed increased sperm velocity in diluted ovarian fluids while sperm of paler males were fastest in water only. We then let equal numbers of sperm compete for fertilizations in the presence or absence of ovarian fluids and used microsatellite markers to assign in total 1,464 embryos (from 70 experimental trials) to their fathers. Overall, sperm of more colorful males reached higher fertilization success than sperm of pale males. This difference was enhanced by the presence of ovarian fluids and best explained by the increased sperm velocity. Sperm competitiveness was not enhanced with decreasing male inbreeding coefficients or decreasing genetic distance to a given female, although parallel stress tests on embryos revealed that females would profit more from mating with least related males rather than most colored ones. We conclude that sperm of more colorful males are best adapted to ovarian fluids, and that the observed reaction norms reveal male strategies rather than cryptic female choice.
... To avoid including measurements taken of sperm cells moving due to drift or Brownian movement, threshold values for the only two optional settings defining static cells, that is, VAP and VSL, were set at 10 µm/s. The same method has successfully been used in previous studies (e.g., Janhunen et al., 2009;Liljedal et al., 2008;Urbach et al., 2005). The parameters assessed were average path velocity (VAP), straight-line velocity (VSL), and curvilinear velocity (VCL) (Rurangwa et al., 2004). ...
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Whether the ovarian fluid (OF) represents a selective environment influencing cryptic female choice was tested using an external fertilizer experiencing intense sperm competition and large effects of OF on sperm swimming behavior—the Arctic charr (Salvelinus alpinus). We physically separated the OF from the eggs of reproductively active females and reintroduced either their own OF or fluid from another female to the eggs. The eggs were then fertilized in vitro in a replicated split‐brood design with sperm from two males under synchronized sperm competition trials, while also measuring sperm velocity of the individual males in the individual OFs. We found large effects of males, but no effect of females (i.e., eggs) on paternity, determined from microsatellites. More important, we found no effect of OF treatments on the relative paternity of the two competing males in each pair. This experimental setup does not provide support for the hypothesis that OF plays an important role as medium for cryptic female choice in charr. Power analyses revealed that our sample size is large enough to detect medium‐sized changes in relative paternity (medium‐sized effect sizes), but not large enough to detect small changes in relative paternity. More studies are needed before a conclusion can be drawn about OF's potential influence on paternity under sperm competition—even in charr.
... Differences in flesh pigmentation also translate into differences in egg and spawning coloration (Withler 1986;Rajasingh et al. 2007;Lehnert et al. 2016b). Carotenoid pigments play an important role in salmonid fitness (Rajasingh et al. 2007) as carotenoids have been linked to salmon immune function (Amar et al. 2012), egg survival (Tyndale et al. 2008), mate choice (Fleming and Gross 1994;Skarstein and Folstad 1996;Craig and Foote 2001), and sperm quality (Ahmadi et al. 2006;Janhunen et al. 2009;Pitcher et al. 2009). However, despite this potential handicap to white Chinook salmon, both phenotypes persist in mixed populations in nature. ...
Post-copulatory processes, including sperm competition and cryptic female choice (CFC), can play important roles in the maintenance of polymorphisms. In Chinook salmon (Oncorhynchus tshawytscha), color morphs (red and white) exist due to genetic polymorphisms affecting carotenoid deposition in flesh, skin, and gametes. We investigated the role of post-spawning sexual selection in maintaining the polymorphism in a mixed population. First, we compared sperm velocity differences in water between morphs. Next, we measured color-based CFC via 2 methods: 1) sperm velocity in ovarian fluid and 2) in vitro competitive fertilization using paired red and white males. We found that red males had marginally faster sperm relative to white males in water, suggesting that carotenoid storage may affect sperm performance. However, ovarian fluid of red and white females influenced sperm velocity of red and white males differently, indicative of color-based CFC on sperm velocity. Furthermore, we found evidence of color-based CFC on paternity success during in vitro competitive fertilizations; however, sperm velocity in ovarian fluid did not predict results found under in vitro fertilization. Instead, in our study, sperm velocity in water was a significant predictor of fertilization success. When we accounted for this difference in sperm velocity (in water) between paired males, we partitioned the amount of variation in fertilization success that was attributed to individual level CFC (male pair × female) and male competitiveness (male pair) as 43% and 16%, respectively. In conclusion, post-spawning sexual selection processes represent important mechanisms contributing to the maintenance of the color polymorphism in nature.
... Colour is frequently a secondary sexual characteristic used to demonstrate fitness or aggression, as it signals better health (Ressel and Schall 1989;Olson and Owens 1998), higher reproductive performance (e.g., access to mates, Evans and Norris 1996; sperm velocity, Janhunen et al. 2009) and better access to critical resources (Luchiari et al. 2007) in a large range of taxa. In the study species, J. edwardsii, size and morph were not indicative of any dominance hierarchy, and size and colour do not influence survival in translocated SP J. edwardsii compared with resident LR 's ). ...
... The phenotype-linked fertility hypothesis (PLFH) predicts a positive relationship between sexual ornaments and male functional fertility (the success of ejaculates in fertilising eggs), and that females select highly ornamented males to guarantee increased fertilisation success (see Sheldon, 1994). For example, a study by Janhunen et al. (2009) showed that in male Arctic charr Salvelinus alpinus, the expression of the carotenoid-based red breeding coloration is positively correlated with sperm velocity and hence provides useful information to females concerning a male's sperm fertilisation ability. The relationship between male attractiveness (e.g., orange coloration) and sperm traits (e.g., velocity and morphology) has been well studied in guppies Poecilia reticulata, although these studies gave contradictory results; some findings support the PLFH (Locatello et al., 2006;Pitcher et al., 2007; resulting in a greater parentage of more colourful males: Evans et al., 2003), whereas others failed to show a positive relationship between sexually selected ornamentation and sperm quality traits (Skinner and Watt, 2007;Evans, 2010). ...
Full-text available
Recent studies have revealed that sexually selected traits may signal sperm quality and hence male fertilisation ability. There is also evidence that the expression of male sexual ornamentation and associated sperm characteristics depend on an individual's ability to cope with oxidative stress. Carotenoids are known for their antioxidant properties and carotenoid-based ornaments might represent honest signals as these pigments can be traded off between the investment in sexual ornamentation, sperm function as well as immune response. In this study, we examined the relationship between sexual ornamentation (breeding coloration) and sperm characteristics (e.g., velocity and morphology) in the three-spined stickleback Gasterosteus aculeatus, an externally fertilising fish species, in which sperm competition commonly occurs. During the breeding season males are sperm limited and develop a conspicuous carotenoid-based coloration, which is under strong pre-copulatory sexual selection due to female mate choice and male-male competition. The results of the present study show that the expression of stickleback male breeding coloration is significantly positively associated with the linearity of sperm movement, whereas sperm morphology (head length to tail length ratio) is significantly negatively related to the trajectory of sperm movement. Moreover, there is some support for the phenotype-linked fertility hypothesis as the intensity of male red breeding coloration is significantly positively correlated with sperm velocity, which is supposed to be an important determinant of fertilisation success in external fertilisers, indicating the honesty of the sexually selected nuptial red coloration.
... In Salmonidae, the nuptial colors of larger males tend to become brighter, so the larger males in our study might have had lower sperm speeds, since they invested more in nuptial color. However, the opposite result also exists, whereby sperm swimming speed is positively correlated with nuptial color in Arctic charr Salvelinus alpinus [31]. Unfortunately, nuptial colors were not quantified in this study. ...
Most comparative studies on the sperm traits (sperm concentration, swimming speed, and longevity) of salmonid fish involve males with alternative life histories (anadromous versus resident forms) that exhibit different reproductive strategies. However, males exhibit a dominance hierarchy within the same life history, in which smaller males have a tendency to be lower rank. This phenomenon prompted us to compare the sperm traits of large anadromous and small resident males in masu salmon Oncorhynchus masou, and to identify the size-dependent sperm traits within these two life history groups. We detected a significant difference in sperm concentration between the two groups, with resident males having higher sperm concentrations than anadromous males. For resident males, we detected a significantly negative correlation between body size and sperm swimming speed, i.e., faster sperm speed was associated with smaller body size. These findings support earlier data and suggest that smaller or younger males utilize more energy to produce high concentration and high speed sperms.
Reproductive Biology of Teleost Fishes is the first integrated review of the reproductive biology of the bony fishes, which are the most species-rich and diversified group of vertebrates. Teleosts display remarkable variation in their modes of reproduction, and this volume is intended to provide a framework for understanding the remarkable reproductive diversity of this group. It describes their reproductive biology using, wherever possible, phylogenetic analyses and life-history theory as a means to interpret the information. The book addresses the genetic, physiological, behavioural, ecological, evolutionary and applied aspects of teleost reproduction in a comparative framework that emphasises the adaptive basis of reproductive diversity. Reproductive Biology of Teleost Fishes provides a comprehensive synthesis of fish reproduction that will be of great interest to life scientists, particularly ecologists, evolutionary biologists, physiologists and advanced undergraduates, postgraduates and research workers requiring a comprehensive overview of fish reproduction. The book is suitable for courses in fish biology and ecology, reproductive physiology and reproductive genetics. It also addresses applied questions and will be of value for courses on fisheries science and aquaculture. Libraries in all universities and research establishments where biological sciences, fisheries science and aquaculture are studied and taught should have several copies of this important book on their shelves.
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Secondary sexual characters may signal parasite resistance because the development of such traits can have costs to immune functioning. Here we show that expression of red coloration in the salmonid Arctic charr is a sexually dimorphic character that reveals information of potential importance in sexual selection. Intensity of the carotenoid dependent coloration is in both sexes negatively related to lymphocyte counts. A causal mechanism for this relationship could be reduced availability of carotenoids for immunological application created by increased carotenoid requirements for ornamental development. Alternatively, if more ornamented individuals also have lower intensities of infection, the observed relationship might be explained by healthy individuals being both bright and having low antigen stimulation of lymphocyte transformation and proliferation. Parasite intensities also show relationships with intensity of coloration, and this is used to evaluate the latter explanation.
The aim of this study was to establish whether the mobility of sperm of the domestic fowl, as measured by an in vitro assay, predicted the outcome of sperm competition. Thirteen pairs of New Hampshire roosters, comprising one male categorized as having high-mobility sperm and the other as having average-mobility sperm, were used. Each male provided 25 times 106 sperm, which were mixed and artificially inseminated into between four and seven New Hampshire hens, each of which produced 2 to 11 offspring. The experiment was conducted twice, such that the same pair of males inseminated the same females. Paternity was assigned by using microsatellite markers. There was a clear effect of sperm-mobility phenotype on the outcome of sperm competition: in all 13 pairs the high-mobility male fathered the majority of offspring (73.3% overall; p < 0.0001). The proportion of offspring fathered by the high-mobility male within pairs varied significantly between male pairs (p < 0.0005). This effect was associated with the difference in sperm-mobility scores between males within pairs: there was a significant positive relationship between the proportion of offspring fathered by the high-mobility male and the ratio of mobility scores between males (p < 0.05). In addition, compared with their success predicted from the non-competitive situation, in the competitive situation high-mobility males were disproportionately successful in fertilizing eggs compared with average-mobility males. This may occur because female sperm storage is limited in some way and a greater proportion of high-mobility sperm gain access to the female's sperm storage tubules. There was no evidence that female effects accounted for any of the variation in paternity.
When females are inseminated by more than one male (polyandry) sexual selection continues after insemination in the form of sperm competition and cryptic female choice. The sexually-selected sperm hypothesis proposes that, under the risk of sperm competition, additive variation in male traits determining fertilising efficiency will select for female propensity to be polyandrous in order to increase the probability of producing sons with superior fertilising efficiency. Two factors complicate this prediction: sex-biased transmission of male fertilising efficiency traits and sexual antagonism of sex-limited traits. fostered by sex-biased inheritance. Here. we (i) review the evidence that male traits contributing towards fertilising efficiency are heritable through sex-biased mechanisms, and (ii) explore the evolutionary implications for male and female reproductive strategies caused by both sex-biased transmission and sexual antagonism of fertilising efficiency traits. Many male fertilising efficiency traits are heritable through sex-biased mechanisms and may not necessarily increase female fitness. The predictions of the sexually-selected sperm hypothesis change dramatically under these different mechanisms of inheritance of fertilising efficiency traits, and different fitness pay-offs derived by females from the expression of such traits. Both sex-biased control of fertilising efficiency and sexual antagonism may also be important in explaining the maintenance of the genetic variance and selection potential of fertilising efficiency. We propose that a useful approach to test the sexually-selected sperm hypothesis is to combine studies which identify behavioural and physiological mechanisms explaining variation in reproductive success with artificial selection experiments to infer the underlying evolutionary patterns.
Sperm competition occurs when sperm from more than one male compete for fertilizations [1]. This form of post-copulatory sexual selection is recognized as a significant and widespread force in the evolution of male reproductive biology and as a key determinant of differential male reproductive success 2 and 3. Despite its importance, however, detailed mechanisms of sperm competition at the gamete level remain poorly understood. Here, we use natural variation in spermatozoal traits among wild Atlantic salmon (Salmo salar), a species naturally adapted to sperm competition [4], to examine how the relative influences of sperm (i) number, (ii) velocity, (iii) longevity, and (iv) total length determine sperm competition success. Atlantic salmon fertilize externally, and we were therefore able to conduct controlled in vitro fertilization competitions while concurrently measuring spermatozoal traits within the aqueous micro-environment to which salmon gametes are naturally adapted 5, 6 and 7. Microsatellite DNA fingerprinting revealed that a male's relative sperm velocity was the primary determinant of sperm competition success. There was no significant relationship between fertilization success and either relative sperm number or total length; sperm longevity showed an inverse relationship with competition success. These relationships were consistent for two experimental repeats of the in vitro fertilization competitions. Our results therefore show, under the natural microenvironment for salmon gametes, that relative sperm velocity is a key spermatozoal component for sperm competition success. Atlantic salmon sperm can be considered to enter a competition analogous to a race in which the fastest sperm have the highest probability of success.
The fertility of males sometimes correlates with their ornamental display, but we do not have a mechanistic explanation to universally link these traits. We suggest that both sperm quality (fertility; integrity of DNA), and the substrates responsible for male ornamentation, may be vulnerable to free radical attack, which can be mitigated by antioxidants. Support for these ideas is at present weak, and requires validation in ecological contexts. We hypothesize that a link between ornamentation and sperm quality could arise if antioxidants are in limited supply, and the showiest males may be preferred because they are most likely to be fertile, or to provide sperm with undamaged genotypes that could give rise to fit offspring.
The idea that female mate choice might be adaptive is relatively easy to understand in species with resource-based mating systems in which females gain access to a territory, food, or other forms of parental care from the males with whom they mate. In contrast, the evolution of female mate choice in species exhibiting resource-free mating systems remains controversial. One such species in which males contribute nothing but sperm during mating is the guppy (Poecilia reticulata). Here, we examined whether female guppies can obtain information on male fertility (i.e., direct fertility benefits) via cues used during mate choice. Specifically, we examined whether male guppy colour patterns, body size, and mating behaviour signal their functional fertility, that is, their ability to supply a large number of sperm at copulation. We found significant correlations between male phenotype parameters and the number of sperm in male guppies originating from two wild Trinidadian populations. There were, however, significant interpopulation differences with respect to which traits were good predictors of sperm load. In the low-predation Paria River population, larger males and males with relatively more carotenoid colouration had significantly larger sperm loads, but mating behaviour (i.e., sigmoids) and melanin colouration were not good predictors of sperm load. In the high-predation Tacarigua River population, larger males, males that displayed more, and males with less yellow colouration had significantly more sperm, but other colour pattern components (area of orange and black colouration) were not good predictors of sperm load. Overall, our results suggest that there is the potential for direct fertility benefits through mate choice in the promiscuous, non-resource-based mating system of the guppy.
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.
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.
The relationships among the area, hue, saturation and brightness of orange colouration and sperm traits in the guppy Poecilia reticulata were investigated. Males with greater areas of orange colouration had significantly larger sperm loads, more motile sperm and longer sperm relative to males with relatively little orange colouration. Males with greater areas of orange colouration did not possess more viable sperm than males with relatively little orange colouration. There was no evidence that any of the sperm traits were related to the hue, saturation or brightness of the orange colouration. These results are discussed in the context of the roles that direct and indirect selection might play in maintaining female preference for male guppies with large areas of orange colouration.