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1.
Engelhardt A Fischer J Neumann C Pfeifer JB Heistermann M 《Behavioral ecology and sociobiology》2012,66(1):121-134
Primates are unusual in that many females display sexual signals, such as sex skin swellings/colorations and copulation calls,
without any sex role reversal. The adaptive function of these signals remains largely unclear, although it has been suggested
that they provide males with information on female reproductive status. For sex skin swellings, there is increasing evidence
that they represent a graded signal indicating the probability of ovulation. Data on the functional significance of copulation
calls are much scarcer. To clarify the information content of such calls, we recorded copulation calls in wild long-tailed
macaques (Macaca fascicularis) and analysed the structure of these calls during the ovarian cycle. Specifically, we correlated selected call parameters
with the female oestrogen to progestogen ratio (obtained from faecal samples), which are known to be elevated during the female's
fertile phase. In addition, we ran a general linear mixed model for these call parameters, testing factors (cycle phase, occurrence/absence
of ejaculation, male dominance status, occurrence/absence of mate guarding) which potentially influence female copulation
calls in primates. Our results show that copulation calls of female long-tailed macaques signal mating outcome and rank of
the mating partner, but not female reproductive status. They also show for the first time on primates that copulation calls
can convey information on whether a female is mate guarded or not. We suspect that the function of these calls is manipulation
of male mating and mate-guarding behaviour and that in this way the degree of sperm competition and ultimately male reproductive
success is influenced. 相似文献
2.
Joanna M. Setchell Marie J. E. Charpentier Issa-Ben Bedjabaga Patricia Reed E. Jean Wickings Leslie A. Knapp 《Behavioral ecology and sociobiology》2006,61(2):305-315
Honest advertisement models of sexual selection propose that exaggerated secondary sexual ornaments are condition-dependent, and that only individuals with superior disease resistance will be able to express costly ornamentation. Studies of secondary sexual ornamentation and their maintenance by sexual selection tend to focus on males. However, females may also possess showy ornaments. We investigated whether female ornaments, in the form of sexual swellings, reliably signal female fitness in a semifree-ranging colony of mandrills (Mandrillus sphinx) at the Centre International de Recherches Médicales, Franceville (CIRMF), Gabon. We measured swelling height and width using photographs of periovulatory females over three mating seasons and compared swelling size with parasitism (using fecal analysis over one annual cycle), immune status (ratio of lymphocytes to neutrophils in blood smears made during captures), and genetic diversity (microsatellite heterozygosity). Swelling size varied by up to 10% between cycles in individual females, giving some support to the hypothesis that size differences may indicate the quality of individual swelling cycles. However, there was no significant difference in swelling size between conceptive and nonconceptive cycles. Measures of swelling size varied more between females than within females across swelling cycles, implying that swelling size was a relatively consistent characteristic of individual females. Swelling size was not significantly related to either general measures of parasitism and immune status, or to the closest available measures to each swelling cycle. Nor was swelling size significantly related to genetic diversity. The healthy, provisioned nature of the colony and problems associated with observational, correlational studies restrict interpretation of our data. However, in combination with previous findings that females of higher reproductive success do not show larger swellings, and that males do not allocate mating effort as a function of swelling size, these results imply that sexual swelling size does not indicate female quality in these semifree-ranging mandrills. 相似文献
3.
Maturity,fecundity, and reproductive cycle of the spotted ratfish, <Emphasis Type="Italic">Hydrolagus colliei</Emphasis> 总被引:1,自引:1,他引:0
Lewis A. K. Barnett Ryan L. Earley David A. Ebert Gregor M. Cailliet 《Marine Biology》2009,156(3):301-316
Size at maturity, fecundity, and reproductive periodicity were estimated for the spotted ratfish, Hydrolagus colliei (Lay and Bennett, 1839), off the coast of California, Oregon, and Washington. Maximum body size and size at median maturity
were greater for females than males. Skeletal muscle concentrations of the steroid hormones testosterone (T) and estradiol
(E2) predicted similar, but slightly smaller sizes at maturity than the morphological criterion. Stage of maturity for males
was estimated identically using internal organs or external secondary sexual characters, thus allowing non-lethal maturity
assessments. Size at median maturity was greater north of Point Conception for females, and north of Cape Mendocino for males.
Peak parturition occurred from May to October, with increased concentrations of E2 in skeletal muscle of females correlating with ovarian recrudescence during November to February. No significant seasonal
trends in female T were apparent, but mean female 11-ketotestosterone (11KT) was 300% greater in April than any other month
during the parturition season. There was a marginal evidence for increased number and size of ova with maternal size. Extrapolation
of the hypothesized 6 to 8-month egg-laying season to observed mean parturition rates of captive specimens yielded an estimated
annual fecundity of 19.5–28.9 egg cases. Differences in fecundity among higher taxonomic classifications of chondrichthyans
were detected with chimaeriform fishes more fecund than lamniform, myliobatiform, squaliform, and rhinobatiform fishes, and
less fecund than rajiform fishes.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
5.
A fundamental question of sexual selection theory concerns the causes and consequences of reproductive skew among males. The
priority of access (PoA) model (Altmann, Ann NY Acad Sci 102:338–435, 1962) has been the most influential framework in primates living in permanent, mixed-sex groups, but to date it has only been
tested with the appropriate data on female synchrony in a handful of species. In this paper, we used mating data from one
large semi-free ranging group of Barbary macaques: (1) to provide the first test of the priority-of-access model in this species,
using mating data from 11 sexually active females (including six females that were implanted with a hormonal contraceptive
but who showed levels of sexual activity comparable to those of naturally cycling females) and (2) to determine the proximate
mechanism(s) underlying male mating skew. Our results show that the fit of the observed distribution of matings with sexually
attractive females to predictions of the PoA model was poor, with lower-ranking males mating more than expected. While our
work confirms that female mating synchrony sets an upper limit to monopolization by high-ranking individuals, other factors
are also important. Coalitionary activity was the main tactic used by males to lower mating skew in the study group. Coalitions
were expressed in a strongly age-related fashion and allowed subordinate, post-prime males to increase their mating success
by targeting more dominant, prime males. Conversely, females, while mating promiscuously with several males during a given
mating cycle, were more likely to initiate their consortships with prime males, thus reducing the overall effectiveness of
coalitions. We conclude that high-ranking Barbary macaque males have a limited ability to monopolize mating access, leading
to a modest mating skew among them. 相似文献
6.
Male seahorses (genus Hippocampus) provide all post-fertilization parental care, yet despite high levels of paternal investment, these species have long been
thought to have conventional sex roles, with female mate choice and male–male competition. Recent studies of the pot-bellied
seahorse (Hippocampus abdominalis) have shown that sex-role reversal occurs in high-density female-biased populations, indicating that male mating preferences
may lead to sexual selection on females in this species. Egg size, egg number, and offspring size all correlate positively
with female body size in Hippocampus, and by choosing large mating partners, male seahorses may increase their reproductive success. While male brood size is
also positively correlated with body size, small H. abdominalis males can carry exceptionally large broods, suggesting that the fecundity benefits of female preference for large partners
may be limited. We investigated the importance of body size in reproductive decisions of H. abdominalis, presenting focal individuals of both sexes with potential mating partners of different sizes. Mating preferences were quantified
in terms of time spent courting each potential partner. Male seahorses were highly active throughout the mate-choice trials
and showed a clear behavioral preference for large partners, while females showed significantly lower levels of activity and
equivocal mating preferences. The strong male preferences for large females demonstrated here suggest that sexual selection
may act strongly on female body size in wild populations of H. abdominalis, consistent with predictions on the importance of female body size for reproductive output in this species.
An erratum to this article can be found at 相似文献
7.
Life-history theory predicts that individuals should increase their reproductive effort when the fitness return from reproduction is high. Females mated with high-quality males are therefore expected to have higher investment than females mated with low-quality males, which could bias estimates of paternal effects. Investigating the traits females use in their allocation decisions and the aspects of reproduction that are altered is essential for understanding how sexual selection is affected. We studied the potential for differential female allocation in a captive population of a precocial bird, the Chinese quail, Coturnix chinensis. Females paired with males with large sexual ornaments laid larger, but not more, eggs than females paired with males with small sexual ornaments. Furthermore, female egg mass was also significantly positively affected by male testis size, probably via some unknown effect of testis size on male phenotype. Testis size and ornament size were not correlated. Thus, both primary and secondary male sexual traits could be important components of female allocation decisions. Experimental manipulation of hormone levels during embryonic development showed that both male and female traits influencing female egg size were sensitive to early hormone exposure. Differences in prenatal hormone exposure as a result of maternal steroid allocation to eggs may explain some of the variation in reproductive success among individuals, with important implications for non-genetic transgenerational effects in sexual selection.Communicated by C. Brown 相似文献
8.
The primates of Madagascar (Lemuriformes) are unusual among mammals in that polygynous species lack sexual dimorphism, and
females dominate males socially in most species. Moreover, lemur groups are relatively small and characterized by even adult
sex ratios despite the fact that one male should be able to exclude other males from the group. One hypothesis to explain
this combination of behavioral, morphological, and demographic traits (the “lemur syndrome”) postulates that male–male competition
is relaxed and, hence, variance in male reproductive success is low. Reproductive skew theory provides a framework for testing
this and several related predictions about lemur social evolution. Specifically, low reproductive skew is also predicted if
dominant males or adult females make reproductive concessions to subordinates or if the latter group successfully pursues
alternative reproductive tactics. However, suitable data on paternity, demography, and behavior for a conclusive test of these
predictions have not been available in the past. In this paper, we show that male reproductive success in ten groups of Verreaux’s
sifakas (Propithecus verreauxi) was extremely skewed in favor of the dominant male over 9 years. Our genetic analyses also revealed that more than a third
of all groups are effectively harem groups because only one male was unrelated to the resident female(s). In groups with two
or more non-natal males, the dominant sired 91% of 33 infants. Together, males pursuing one of several alternative reproductive
tactics, such as roaming among several groups or immigrating peacefully, sired only 11% of infants. Thus, female sifakas do
not control group composition by offering reproductive opportunities to subordinate males as staying incentives, intrasexual
selection is not relaxed, and dominant males prevail in a tug-of-war over subordinate males. Because male reproductive skew
in sifakas is even more pronounced than in harem-living anthropoids studied to date, intrasexual selection is clearly not
relaxed, and the lemur syndrome is more puzzling than ever. 相似文献
9.
Melissa Emery Thompson Martin N. Muller Richard W. Wrangham 《Behavioral ecology and sociobiology》2014,68(12):1973-1983
Sexual conflict develops when the optimal reproductive strategy for one sex inflicts fitness costs upon the other sex. Among species with intense within-group feeding competition and high costs of reproduction, females are expected to experience reduced foraging efficiency by associating with males, and this may compromise their reproductive ability. Here, we test this hypothesis in chimpanzees, a species with flexible grouping patterns in which female avoidance of large subgroups has been attributed to their relatively high costs of grouping. In an >11-year study of the Kanyawara community of East African chimpanzees (Pan troglodytes schweinfurthii) in the Kibale National Park, Uganda, the availability of sexually receptive females was a key determinant of the number of males in parties. In turn, females experienced significantly lower C-peptide of insulin levels, indicative of reduced energy balance, during periods when they associated with more males. Female associates did not produce the same negative effect. C-peptide levels positively and significantly predicted female ovarian steroid production, indicating that the costs of associating with males can lead to downstream reproductive costs. Therefore, we conclude that Kanyawara chimpanzees exhibit sexual conflict over subgroup formation, with the large groupings that allow males to compete for mating opportunities inflicting energetic and reproductive costs on females. Because association with males is central to female chimpanzees’ anti-infanticide strategy, and males may confer other benefits, we propose that reproductive success in female chimpanzees hinges on a delicate balance between the costs and benefits of associating with male conspecifics. 相似文献
10.
Infanticide by males is common in mammalian species such as primates in which lactation lasts much longer than gestation.
It frequently occurs in one-male groups following male takeovers and is likely a male reproductive strategy. Reported female
countertactics include abrupt weaning of infants, dispersal, or paternity confusion. Here, we estimated costs of female countertactics
in terms of weaning ages and interbirth intervals. We observed a population of white-headed leaf monkeys (Trachypithecus leucocephalus) in Nongguan Nature Reserve, China (1995–2006) mainly composed of one-male groups. Takeovers (N = 11) coincided with the peak conception period. Detailed data are presented for five takeovers (34 females, 29 infants,
and 47 group-years) leading to six infant disappearances (42.9% of infant mortality). All presumed infanticides were in accordance
with the sexual selection hypothesis. Following a takeover, females without infants or with old infants stayed with the new
males, incurring no or low costs (via abrupt weaning). Females with young infants dispersing with the old males also experienced
low costs. High costs (due to infant loss) were incurred by pregnant females and those with young infants who stayed with
the new males indicating that paternity was not confused. Costs in terms of long interbirth intervals were also high for females
leaving with the old males to later join the new males, despite infant survival. Female countertactics reflected female philopatry
mediated by infant age. Presumably due to the seasonal timing of takeovers, most countertactics seemed successful given that
32.3% of females apparently incurred no costs and 41.2% incurred only low costs. 相似文献
11.
Female choice and male–male aggression are two modes of sexual selection that can lead to elaboration of male morphological
and behavioral traits. In lek-mating species, male mating success is often strongly skewed, and it is puzzling why variation
in male traits is still observed given directional female choice. If male traits correlated with reproductive success are
honest signals of male quality, there may be survival costs associated with the expression of those traits. In this study,
we examined whether morphological, behavioral, and territorial traits are correlated with male mating success and survival
in the lek-mating greater prairie-chicken (Tympanuchus cupido). We introduce a novel application of multinomial discrete choice models for analysis of female mate choice behavior. We
found that behavioral and territorial attributes showed 6.5 times more variability among males than morphological traits.
Both display and aggressive behaviors were strong predictors of male mating success, suggesting that both female choice and
male–male aggression were important in determining mating success among male greater prairie-chickens. Moreover, annual survival
of male prairie-chickens was independent of mating success and male traits. Females appear to be choosing males based on behavioral
traits where large variation exists between males (coefficient of variation >30%). Behavioral traits were the most important
factor in determining mating success of male prairie-chickens, but the mechanism underlying this relationship is unknown.
In the future, experimental manipulations of male hormones or parasite loads could bridge the proximate mechanisms and ultimate
consequences of factors mediating male mating success in lek-mating grouse. 相似文献
12.
Summary Ten years of data collected from a population of savanna baboons, Papio cynocephalus anubis, residing near Gilgil, Kenya were analyzed to ascertain the extent to which social and ecological factors influence reproductive maturation in females. First sexual swelling occurred at an average age of 4.79 years and first birth occurred at an average age of 6.92 years. Age at first menses was significantly correlated with age at first sexual swelling, but age at first sexual swelling was not a good predictor of age at first birth. The amount of rainfall in the 6 months preceding first sexual swelling and resource availability were significantly correlated with age at first sexual swelling. When ecological factors were taken into account, dominant females had an earlier age at onset of puberty, but not an earlier age at first birth, than did subordinate females. We suggest that nutritional and social stress operate at the same physiological level to disrupt GnRH pulsatility and retard reproductive maturation in some females. Given that socioecological variables modify the timing of life history events related to fitness in female baboons, the task for the future is to unravel how socioecological factors influence different life history components and generate variation in lifetime reproductive success.
Correspondence to: F.B. Bercovitch 相似文献
13.
Michael J. Young Leigh W. Simmons Jonathan P. Evans 《Behavioral ecology and sociobiology》2010,64(6):915-925
Sexual selection can act through female choice and male–male competition. Although both processes can act simultaneously,
they are typically studied independently. Here, we adopt a more integrated approach to studying sexual selection by incorporating
measures of both processes using the western rainbowfish Melanotaenia australis, a freshwater fish endemic to northwestern Australia. We assessed male–male competition and female choice separately while
measuring the performance of individual males under both processes and used paternity analyses to estimate male reproductive
success. We then related the performance of males during each of these stages to their phenotype, which was described using
linear measures of size and color pattern traits, and spectrographic measures of the reflectance of color patches. We found
that female choice favored relatively large males and that these preferences were consistent within individual females and
repeatable between different females. Larger males were also more dominant in the competition trials and sired the majority
of offspring produced when females spawned. There was little evidence to suggest that sexual selection acted on male color
patterns either via female choice or male contest competition or during subsequent post-mating episodes of sexual selection.
We conclude, therefore, that male–male competition and female choice act concordantly to favor relatively large males and
that these patterns of mating success are reflected during post-mating episodes of sexual selection. 相似文献
14.
The aim of this study was to investigate reproductive strategies and their consequences in gray mouse lemurs (Microcebus murinus), small solitary nocturnal primates endemic to Madagascar. Previous reports of sexual dimorphism in favor of males and females,
respectively, a high potential for sperm competition and pheromonal suppression of mating activity among captive males, led
us to investigate mechanisms of intrasexual competition in a wild population. Based on 3 years of mark-recapture data, we
demonstrate that sexual dimorphism in this species fluctuated annually as a result of independent changes in male and female
body mass. Male body mass increased significantly prior to the short annual mating season. Because their testes increased
by 100% in the same period and because their canines are not larger than those of females, we suggest that large male size
may be advantageous in searching for estrous females and in enabling them to sustain periods of short-term torpor. In contrast
to reports from captive colonies, we found no evidence for two morphologically distinct classes of males. Finally, we also
show that most adult males are active throughout the cool dry season that precedes the mating season, whereas most adult females
hibernate for several months. This is in contrast to other solitary hibernating mammals, where males typically emerge 1–2
weeks before females. Thus, this first extended field study of M.␣murinus clarified previous conflicting reports on sexual dimorphism and male reproductive strategies in this primitive primate by
showing that their apparent deviation from predictions of sexual selection theory is brought about by specific environmental
conditions which result in sex-specific life history tactics not previously described for mammals. A general conclusion is
that sexual selection can operate more strongly on males without resulting in sexual dimorphism because of independent selection
on the same traits in females.
Received: 6 July 1997 / Accepted after revision: 28 March 1998 相似文献
15.
Palestina Guevara-Fiore Jessica Stapley Penelope J. Watt 《Behavioral ecology and sociobiology》2010,64(10):1665-1672
Males vary in the degree to which they invest in mating. Several factors can explain this variation, including differences
in males’ individual condition and the fact that males allocate their energy depending on the context they face in each mating
attempt. Particularly, female quality affects male reproductive success. Here, we studied whether male guppies (Poecilia reticulata) strategically allocated more mating effort, in terms of mating behaviour and male–male competition, when they were matched
with a receptive (R) female than a non-receptive one. In accordance with our prediction, we found that males increased their
mating behaviour when they were with a receptive female. Even though male guppies can inseminate non-receptive females, we
only found high levels of courtship between males that were with a receptive female rather than a non-receptive one. Although
there was little affect of female receptivity on male–male competition, we found that males chased and interrupted courtships
more with receptive females than with non-receptive females regardless of odour. Finally, we also studied whether the sexual
pheromone produced by receptive female guppies is a cue that males use in order to increase their mating effort. We found
that males were more attracted to a female when they perceived the sexual pheromone, but only increased their mating and aggressive
behaviours when females showed receptive behaviour. This strategic increase in mating effort could result in higher male reproductive
success because mating attempts towards receptive females are likely to be less costly and males could have a greater probability
of fertilisation. 相似文献
16.
Larissa Swedell Liane Leedom Julian Saunders Mathew Pines 《Behavioral ecology and sociobiology》2014,68(2):263-273
Fundamental reproductive interests dictate that females generally benefit most from mate selectivity and males from mate quantity. This can create conflict between the sexes and result in sexual coercion: male use of aggression to garner mating success at a cost to females. Potential fitness costs of sexual coercion, however, can be difficult to measure. Here, we demonstrate benefits to males and costs to females of female defense polygyny in wild hamadryas baboons, cercopithecoid primates in which females are coercively transferred among social units by males, restricting both female choice and bonding among female kin. Of all coercive transfers (takeovers) of females with young infants, 67 % were followed by infant mortality, which was significantly more likely to occur after takeovers than at other times. As expected, infant mortality decreased time to subsequent conception but lengthened intervals between surviving infants. Following infant survival, whether a female had experienced a takeover after the previous birth was a significant predictor of subsequent interbirth interval, with interbirth intervals of females remaining with the same male between births being significantly shorter than those of females incurring takeovers between births. Together, these results reveal that takeovers increase the chance of infant mortality while delaying subsequent conception. Male-driven female defense polygyny in this species is thus costly to females in two ways. These results demonstrate that reproductive strategies benefitting males can evolve despite substantial costs to females. These costs may be mitigated over the long term, however, by female counterstrategies and protective behavior by males. 相似文献
17.
The determination of reproductive status and the reconstruction of individual reproductive histories are central to many ecological
studies. In cetaceans, it has been assumed that ovarian scars accumulate with age and provide a lifetime record of female
reproductive history. If ovarian scars persist, the number of scars should increase with age after puberty. To test this,
we examined age, reproductive status and ovarian scars from 187 short-beaked common dolphins (Delphinus delphis) from the eastern North Atlantic. The number of Corpus Albicans (CA) present in ovaries did not increase with age after age
at sexual maturity (ASM), suggesting that ovarian scars are not persistent and that their number at any one time would be
a function of rates of ovulation and healing, the latter being defined here as the resorption or disintegration of CA tissue.
Since female mammals stop ovulating when pregnant, inferences about healing rates could be made by using pregnant females.
Pregnant females had ca. 40% fewer scars than non-pregnant females. This suggests that most CAs would heal quickly, with a
half-life of less than 1 year, although larger scars may persist longer. Therefore, counting CAs would have limited potential
for reconstructing individual reproductive lifetime histories in the common dolphin. A reassessment of the use of ovarian
scars to reconstruct individual life reproductive histories in cetaceans is suggested. 相似文献
18.
Martin N. Muller Melissa Emery Thompson Sonya M. Kahlenberg Richard W. Wrangham 《Behavioral ecology and sociobiology》2011,65(5):921-933
The extent to which active female mating preferences influence male reproductive success in mammals is unclear, particularly
for promiscuously breeding species like chimpanzees (Pan troglodytes). Previous studies from multiple long-term study sites have shown that female chimpanzees mate more restrictively around
ovulation, and this has been taken as evidence for female choice. However, none of these studies rigorously evaluated the
alternative hypothesis that restrictive mating results not from unconstrained choice, but in response to coercive mate guarding,
in which males use punishment and intimidation to reduce female promiscuity and promote their own mating interests. Nor did
they consider evidence for the potential genetic or phenotypic benefits that females might be choosing. Using 11 years of
data from the Kanyawara community in Kibale National Park, Uganda, we previously demonstrated that males achieve elevated
mating success with those females toward whom they direct high levels of aggression. Here we extend those findings to show
that even female copulatory approaches, which have previously been attributed to female choice, are correlated with male aggression.
Specifically, individual females at our site initiated periovulatory copulations most frequently with the males who were most
aggressive toward them throughout their cycles. Those males showed high rates of aggression toward females throughout estrus,
despite achieving high copulation rates, demonstrating a continuing conflict of interest over the exclusivity of mating access.
Because sexual coercion is potentially widespread in primates and other mammals, our results stress the importance of considering
the influence of male aggression in studies of female choice. 相似文献
19.
Clare C. Rittschof Swetapadma Pattanaik Laura Johnson Luis F. Matos Jérémie Brusini Marta L. Wayne 《Behavioral ecology and sociobiology》2013,67(4):529-540
The risk of disease transmission can affect female mating rate, and thus sexual conflict. Furthermore, the interests of a sexually transmitted organism may align or diverge with those of either sex, potentially making the disease agent a third participant in the sexual arms race. In Drosophila melanogaster, where sexual conflict over female mating rate is well established, we investigated how a common, non-lethal virus (sigma virus) might affect this conflict. We gave uninfected females the opportunity to copulate twice in no-choice trials: either with two uninfected males, or with one male infected with sigma virus followed by an uninfected male. We assessed whether females respond behaviorally to male infection, determined whether male infection affects either female or male reproductive success, and measured offspring infection rates. Male infection status did not influence time to copulation, or time to re-mating. However, male infection did affect male reproductive success: first males sired a significantly greater proportion of offspring, as well as more total offspring, when they were infected with sigma virus. Thus viral infection may provide males an advantage in sperm competition, or, possibly, females may preferentially use infected sperm. We found no clear costs of infection in terms of offspring survival. Viral reproductive success (the number of infected offspring) was strongly correlated with male reproductive success. Further studies are needed to demonstrate whether virus-induced changes in reproductive success affect male and female lifetime fitness, and whether virus-induced changes are under male, female, or viral control. 相似文献
20.
Lifjeld JT Kleven O Jacobsen F McGraw KJ Safran RJ Robertson RJ 《Behavioral ecology and sociobiology》2011,65(9):1687-1697
When males become more ornamented and reproduce more successfully as they grow older, phenotypic correlations between ornament
exaggeration and reproductive success can be confounded with age effects in cross-sectional studies, and thus say relatively
little about sexual selection on these traits. This is exemplified here in a correlative study of male fertilization success
in a large colony of American barn swallows (Hirundo rustica erythrogaster). Previous studies of this species have indicated that two sexually dimorphic traits, tail length and ventral plumage coloration,
are positively correlated with male fertilization success, and a mechanism of sexual selection by female choice has been invoked.
However, these studies did not control for potential age-related variation in trait expression. Here, we show that male fertilization
success was positively correlated with male tail length but not with plumage coloration. We also show that 1-year-old males
had shorter tails and lower fertilization success than older males. This age effect accounted for much of the covariance between
tail length and fertilization success. Still, there was a positive relationship between tail length and fertilization success
among older males. But as this group consisted of males from different age classes, an age effect may be hidden in this relationship
as well. Our data also revealed a longitudinal increase in both tail length and fertilization success for individual males.
We argue that age-dependent ornament expression and reproductive performance in males complicate inferences about female preferences
and sexual selection. 相似文献