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1.
Recent theoretical models predict that the relative allocation to advertisement and parental care depends on whether paternal
care is necessary for offspring survival: In species with exclusive male care, male investment in attraction is expected to
reliably indicate paternal care effort and male phenotypic quality. Previous research, yielding contrasting results, has considered
how one trait involved in mate attraction interacts with parental care or a specific aspect of male quality. In the blenny
Salaria pavo, we perform a comprehensive analysis of the interplay between overall male attractiveness and male quality, the latter in
terms of fertility, condition, and parental care. In this fish, males are larger than females, exhibit two sexually dimorphic
traits (head crest and anal glands), and solely care for eggs. We generated a male attractiveness index through principal
component analyses of morphological traits and quantified parental effort as the total time spent in egg care. In addition,
we analyzed the relationships between specific components of attractiveness and male qualities. In agreement with theory predictions,
we found that male overall attractiveness is a reliable indicator of fertility, in terms of sperm number, but is unrelated
to body condition and parental care effort, with males able to perform high levels of care regardless of their level of advertisement.
However, the relative expression of head crest area appears positively related to sperm number but is traded-off with parental
care effort. These findings underline the need, in addressing real patterns, to consider interactions between multiple aspects
of male display and quality. 相似文献
2.
Lisa A. Taylor David L. Clark Kevin J. McGraw 《Behavioral ecology and sociobiology》2011,65(5):1133-1146
In many animals, conspicuous coloration functions as a quality signal. Indicator models predict that such colors should be
variable and condition dependent. In Habronattus pyrrithrix jumping spiders, females are inconspicuously colored, while males display brilliant red faces, green legs, and white pedipalps
during courtship. We tested the predictions of the indicator model in a field study and found that male body condition was
positively correlated with the size, hue, and red chroma of a male’s facial patch and negatively correlated with the brightness
of his green legs. These traits were more condition dependent than non-display colors. We then tested a dietary mechanism
for condition dependence using two experiments. To understand how juvenile diet affects the development of coloration, we
reared juvenile spiders on high- and low-quality diets and measured coloration at maturity. To understand how adult diet affects
the maintenance of coloration, we fed wild-caught adults with high- or low-quality diets and compared their coloration after
45 days. In the first experiment, males fed high-quality diet had redder faces, suggesting that condition dependence is mediated
by juvenile diet. In the second experiment, red coloration did not differ between treatments, suggesting that adult diet is
not important for maintaining the color after it is produced at maturity. Diet had no effect on green coloration in either
experiment. Our results show different degrees of condition dependence for male display colors. Because red is dependent on
juvenile diet, it may signal health or foraging ability. We discuss evidence that green coloration is age dependent and alternatives
to indicator models for colorful displays in jumping spiders. 相似文献
3.
Facultative traits that have evolved under sexual selection, such as the acoustic ornaments present in the advertisement signals
of male túngara frogs (Physalaemus pustulosus), offer a unique opportunity to examine selection for trait exaggeration with a focus on individual differences amongst signalers.
By contrast, many studies of mate choice use experimental designs that obscure the inter-individual variation amongst signalers
available for selection to act on—through the use of “typical” or average signals from the population. Here, we use dichotomous
female phonotaxis choice tests to determine how the value of male call embellishment varies across 20 individual males frogs
recorded from the wild—a sample which captures the acoustic diversity present in the population. We tested 20 females for
each male call pair (i.e., 400 females). The results show widespread preference amongst females for ornamented calls (“whine–chucks”)
over simple calls (“whines”), yet also demonstrate substantial variation in the relative benefits for individual male frogs—some
males enjoy appreciable benefits by using ornaments while others (30% of males in this study) do not. We also show that the
relative amplitude of the chuck to the whine correlates positively with the value of call elaborations across these 20 males.
Finally, by manipulating the relative amplitude of whines and chucks using both natural and synthetic calls, we demonstrate
directly that this single call parameter is key to determining the relative value of call elaborations across males. 相似文献
4.
Henrik Brumm 《Behavioral ecology and sociobiology》2009,63(8):1157-1165
Bird song is a sexually selected multidimensional signal. A fundamental question regarding the evolution of sexually selected
signals is what information they convey and how their honesty is maintained. Song amplitude is a performance-related signal
trait that varies considerably between individuals, but this signal dimension has been neglected in past studies. I found
that median song amplitude in male nightingales (Luscinia megarhynchos) and zebra finches (Taeniopygia guttata) did not vary significantly with body size or residual body mass. In contrast, I found a significant negative correlation
between body size (and also residual mass) and the maximum song amplitude during interactive singing in nightingales. However,
the function of these more subtle differences in song amplitude remains to be investigated. By and large, the results of this
study suggest that mean song amplitude is unlikely to indicate a bird’s body size or current condition (measured as residual
mass). 相似文献
5.
Peter D. Dijkstra Renske Hekman Rüdiger W. Schulz Ton G. G. Groothuis 《Behavioral ecology and sociobiology》2007,61(4):599-609
The nature of the costs maintaining honesty of sexual signalling in inter- and intrasexual interactions remains a contentious
issue. For carotenoid-based colour ornaments, it has been hypothesized that the honesty of the signal is enforced when carotenoid
allocation to colour expression is traded off against carotenoid availability for immunocompetence. In addition, honesty is
enforced if androgens required for colour expression are immunosuppressive. We tested whether there is a trade-off between
colour expression and immunocompetence in a lek-breeding haplochromine cichlid fish, Pundamilia nyererei, from Lake Victoria with a carotenoid-based nuptial dress. First, we showed that expression of red nuptial colouration and
social rank in a group were positively correlated. We then successfully manipulated the level of colour advertisement by socially
stimulating individually housed males with a rival male: Stimulated males developed larger areas of red nuptial colouration
and had higher levels of circulating 11-ketotestosterone (11-KT) than non-stimulated males. We subsequently tested the humoral
immune response to a novel antigen (sheep red blood cells). There was no overall significant effect of social stimulation
on antibody production, but in the stimulated males, the degree of red colouration and the antibody response were negatively
correlated. This significant interaction between colour and treatment thus shows that the negative correlation between colouration
and antibody production is dependent on the (manipulated) social environment. This study provides correlational and experimental
evidence for a trade-off between expression of a sexual trait and one component of immune function in fish. We found no evidence
for a direct effect of 11-KT on antibody production, and we discuss alternative mechanisms that could mediate the trade-off. 相似文献
6.
Ectoparasites of house sparrows (Passer domesticus): an experimental test of the immunocompetence handicap hypothesis and a new model 总被引:2,自引:0,他引:2
Conspicuous secondary sexual traits may have evolved as handicap-revealing signals or as badges of status. We present results
of an experiment using males of the sexually dimorphic house sparrow (Passer domesticus), that support the idea that the male-specific bib can be both a handicap-revealing signal and a reliable badge indicating
the physical condition of the bird. In a test of the immunocompetence handicap hypothesis, wild-caught adult male house sparrows
were studied in captivity. Birds implanted with elevated doses of testosterone were more dominant, had higher circulating
levels of both testosterone and corticosterone and they also harboured relatively larger ectoparasite loads. Higher parasite
loads were also associated with individuals showing lower immunocompetence and larger changes in bib size. A new model for
immunocompetence effects in sexual selection is introduced, integrating actions that the hypothalamopituitary axis exerts
on gonads, adrenals and the thyroid gland. The ”integrated immunocompetence model” synthesizes both the ”handicap” (i.e. survival-decreasing)
and ”badge of status” (i.e. survival- enhancing) models for evolution of secondary sexual traits.
Received: 15 May 1999 / Received in revised form: 2 November 1999 / Accepted: 6 November 1999 相似文献
7.
Kathrin P. Lampert Ximena E. Bernal A. Stanley Rand Ulrich G. Mueller Michael J. Ryan 《Behavioral ecology and sociobiology》2006,59(6):796-804
In most sexually reproducing animals, the behavior of one or both sexes during courtship critically influences the success
at mating of the opposite sex. This behavior is often interpreted as “mate choice,” and there is great interest in why such
choices are exercised. The explanation for the evolution of mate choice that has received the most attention and generated
the most controversy is based on assumed genetic effects. In this study, we investigated whether female túngara frogs, which
choose mates based on acoustic cues, have a preference for genetically less related males. Specifically, we determine if there
is disassortive mating based on microsatellite markers, if there is information in the advertisement call that could be used
to assess genetic similarity, and if females exhibit acoustic-based mating preferences that would promote choice for genetic
diversity. Using seven microsatellite markers, we found no correlation of male call similarity and male genetic relatedness.
Female choice experiments showed no female preference for calls of less related males, and there was no evidence for inbreeding
avoidance in the field. Our results do not support the hypothesis of mate choice based on information about genetic relatedness
conveyed by acoustic signals in túngara frogs. 相似文献
8.
A large body of research has developed on male ornaments and their role in sexual selection while female ornaments have been less investigated. This study focused on the presence, function, and possible role of a sexually dimorphic nuptial trait as an indicator of female quality in a fish species presenting conventional sex roles: the yellow patch on the belly of Knipowitschia panizzae females. Aquarium spawning experiments demonstrated that this ornament is due to dermal pigments, is displayed only when the female is ready to spawn, and is switched off within minutes from the end of egg deposition. This sexual trait is variable in size among females and indicates female fecundity relative to her own body size. As a consequence, female yellow belly appears to be a reliable indicator of female quality as measured by current fecundity. Field data on natural nests highlights that males usually perform parental care on only one egg batch at a time. The modality of egg deposition suggests that males may be limited in their potential reproductive rates by environmental factors. Male limitations in egg care could favour male choosiness and the evolution of female nuptial displays.Communicated by R. Cattaneo-Vietti, Genova 相似文献
9.
Sex allocation theory predicts that female birds with high-quality mates will benefit from producing more sons, since sons
will inherit their father’s superior traits and enjoy a great reproductive success, whereas females with low-quality mates
will benefit from producing more daughters, since the variance in reproductive success among daughters is typically lower.
The male attractiveness hypothesis may apply to extra-pair paternity (EPP) because socially monogamous females routinely mate
with higher quality males outside the pair bond. We test these predictions using the Tibetan ground tit (Pseudopodoces humilis), a sexually monomorphic, socially monogamous, facultatively cooperative breeder. There was greater variation in actual reproductive
success among males than females due to EPP. An excess of sons was detected for bi-parental (i.e., non-cooperative) broods
wherein EPP was mainly sired by bi-parental males. The pattern was attributed to male-biased sex ratios produced for both
EPP and within-pair offspring within the same broods. The reason for the latter case might be a random allocation of more
offspring to sons by the potentially EPP-exposed females that have an inability to control fertilization by specific males.
In cooperative broods where EPP mostly resulted from within-group helpers of presumed low-quality, as indicated by their failure
in acquiring a social mate, there was a non-significant tendency for EPP offspring to be daughters and for within-pair offspring
in the same broods to be unbiased. These results support the EPP-related male attractiveness hypothesis especially in terms
of the overproduction of sons. Offspring produced through quasi-parasitism was unbiased towards either sex, suggesting a weak
female choiceness with respect to the quality of host males. 相似文献
10.
The honesty of ornamental signals of quality is often argued to be enforced via costs associated with testosterone. It is
still poorly understood, however, how seasonal variation of testosterone within individuals is related to the timing and extent
of ornament development. Here, we studied inter- and intra-individual variability of plasma testosterone levels in a population
of 150 captive male house sparrows (Passer domesticus) through the course of a full year. We further analyzed the relationship between plasma testosterone levels and two sexually
dimorphic ornaments: badge size and bill coloration. Also, because of a known negative relation between molt and circulating
testosterone levels, we analyzed the relationship between ornamentation and molt status during the fall. We found that testosterone
levels increased towards the breeding season and decreased before the onset of annual molt. However, within individuals, relative
testosterone titers demonstrated low repeatability between seasons. Plasma testosterone levels were not correlated with badge
size in any season but were correlated strongly with bill coloration during all periods, except the breeding season when variation
in bill color was low. Finally, we found that bill coloration strongly correlated with molt status during fall. Our results
indicate that bill coloration, not badge size, is the best ornamental indicator of a “running average” of male testosterone
in house sparrows and therefore the best potential indicator of qualities and/or behavioral strategies associated with testosterone. 相似文献
11.
Donald C. Dearborn Angela D. Anders Joseph B. Williams 《Behavioral ecology and sociobiology》2005,58(4):397-406
We used detailed time-budget observations, mark-resight data, and doubly labeled water estimates of energy expenditure to test whether energy spent on courtship display by male frigatebirds functions as a sexually selected handicap signal. During a 2-day period of time budget observations, males displayed on average 29.5% of the time (range 0–100% for 15 different males), and this value was correlated with an index of season-long display effort. Season-long display effort was strongly predictive of pairing success. Average field metabolic rate (FMR) during the 2-day time budget period was 676.5 kJ/day (range 464.8–1035.0), substantially lower than the mass-specific FMR predicted from studies of other seabirds during incubation or chick-rearing. Despite a low overall FMR, display effort could function as an energetic handicap, either if FMR correlates positively with the amount of courtship performed or if high-quality males display at a high rate because they pay a lower energy cost per unit of display than do low-quality males. We found no relationship between FMR and display rate, despite good power for doing so. We also did not find a significant difference in energy spent divided by courtship time for males that were or were not chosen by females (inferred to be high- and low-quality males, respectively), though the medians differed in the predicted direction (preferred males having lower relative costs than non-preferred males) and the confidence interval on the difference between groups was very wide. Thus, we found evidence that male courtship effort is predictive of pairing success, we rejected one mechanism by which energetic cost of display could function as a handicap, and our test of the alternate energetic handicap mechanism was equivocal. 相似文献
12.
Craig A. Walling Nick J. Royle Neil B. Metcalfe Jan Lindström 《Behavioral ecology and sociobiology》2007,61(7):1007-1014
It is well documented that poor early nutrition can have profound negative effects on adult life-history traits. However,
it has also been demonstrated that organisms can undergo compensatory resource allocation strategies (such as an accelerated
growth rate) if food availability improves, so as to mitigate the effects of the poor early conditions. Previous research
has indicated that elevated growth rates can incur costs in the longer term, such as an increased rate of senescence and shorter
lifespan. We tested whether a phase of compensatory growth after a period of reduced food availability earlier in life affected
the sexual attractiveness of adult male green swordtails Xiphophorus helleri, a species in which it has previously been documented that females prefer larger-bodied and longer-tailed males. The experiment
compared the attractiveness of size-matched brothers that had experienced contrasting growth trajectories as juveniles; the
experiments were initially conducted in the middle of a male’s sexually reproductive life and were then repeated towards the
very end of life. At both ages, males that had undergone compensatory growth were equally as attractive as their brothers
that had grown normally. These results suggest that the growth compensation benefits males through an increase in their attractiveness
over that which they would have had if they had remained on their original growth trajectory. The lack of change in relative
attractiveness with age indicates that the compensation does not cause greater deterioration in secondary sexual characters
at older ages than in continuously well-fed males. 相似文献
13.
Jeremy P. Bird Robert Martin H. Reşit Akçakaya James Gilroy Ian J. Burfield Stephen T. Garnett Andy Symes Joseph Taylor Çağan H. Şekercioğlu Stuart H. M. Butchart 《Conservation biology》2020,34(5):1252-1261
Birds have been comprehensively assessed on the International Union for Conservation of Nature (IUCN) Red List more times than any other taxonomic group. However, to date, generation lengths have not been systematically estimated to scale population trends when undertaking assessments, as required by the criteria of the IUCN Red List. We compiled information from major databases of published life-history and trait data for all birds and imputed missing life-history data as a function of species traits with generalized linear mixed models. Generation lengths were derived for all species, based on our modeled values of age at first breeding, maximum longevity, and annual adult survival. The resulting generation lengths varied from 1.42 to 27.87 years (median 2.99). Most species (61%) had generation lengths <3.33 years, meaning that the period of 3 generations—over which population declines are assessed under criterion A—was <10 years, which is the value used for IUCN Red List assessments of species with short generation times. For these species, our trait-informed estimates of generation length suggested that 10 years is a robust precautionary value for threat assessment. In other cases, however, for whole families, genera, or individual species, generation length had a substantial impact on their estimated extinction risk, resulting in higher extinction risk in long-lived species than in short-lived species. Although our approach effectively addressed data gaps, generation lengths for some species may have been underestimated due to a paucity of life-history data. Overall, our results will strengthen future extinction-risk assessments and augment key databases of avian life-history and trait data. 相似文献
14.
Oddmund Kleven Frode Jacobsen Rasa Izadnegahdar Raleigh J. Robertson Jan T. Lifjeld 《Behavioral ecology and sociobiology》2006,59(3):412-418
In socially monogamous species, extra-pair paternity has the potential to increase the variance in male reproductive success,
thereby affecting the opportunity for sexual selection on male extravagant ornamentation. In the European barn swallow (Hirundo rustica rustica), the tail streamer length is a sexually selected male ornament and an honest indicator of viability. The North American
barn swallow (Hirundo rustica erythrogaster) also shows sexual dimorphism in tail streamer length, but whether this trait holds the same signalling function in this
subspecies is a controversial issue, and the available literature is presently scarce. Here, we present data on paternity
in the North American barn swallow, including a complete sampling of extra-pair sires in four colonies. We analysed how extra-pair
paternity affected the variance in male fertilization success and examined whether male tail streamer (i.e. the outermost
tail feather) length correlated with fertilization success (n=86 males). Extra-pair paternity constituted 31% of all offspring and significantly increased the variance in male fertilization
success. The number of offspring sired by extra-pair males accounted for almost half of the total variance in male fertilization
success. Males with naturally long tail streamers had a higher fertilization success than males with shorter tail streamers,
and this pattern was mainly caused by a higher extra-pair success for males with long tail streamers. Males with long tail
streamers also paired with early breeding females in prime body condition. These results are consistent with the idea that
there is directional sexual selection on male tail streamer length, possibly mediated through male extra-pair mating success
or the timing of breeding onset. 相似文献
15.
For intersexual selection to occur, it is necessary that females choose between males. It is now well appreciated that constraints
exist, which preclude females sampling all the available males in a population. These constraints are likely to have caused
the evolution of sampling rules (such as the “best-of-n” rule) by which females sample males. Here we investigate the impact of female subsampling of the male population, not on
the evolution of sampling behaviour, but on the population-level correlation between a male trait and currencies such as reproductive
success. This study is important as it illustrates when population-level correlations can be safely used to infer the presence
and strength of sexual selection in the field. We find that the correlation between a male trait and a mate choice variable
rises steeply as the number of males sampled by each female increases, flattening above seven to ten males sampled. This shape
is found to be remarkably robust, and little affected by, for example, the mate choice variable used, by noise in assessment,
by sampling behaviour depending on female quality, or by population size. The only variable found to have a large impact is
male clumping according to their “quality”. If females are sampling about four males, the maximum correlation that can be
found at the population level is in the range 0.4–0.6, perhaps as little as 0.1 if males are strongly clumped. A recent review
of the literature suggests that four is the average number of males that females sample. Thus, the absence of a strong correlation
cannot by itself be used to infer that sexual selection is weak, as it may be due to females sampling few males.
Received: 18 May 1998 / Accepted after revision: 18 July 1998 相似文献
16.
Age at maturity is a particularly important life history trait, but maturational data are rare for males in natural populations of mammals. Here we provide information on three maturational milestones and their social and demographic correlates among 43 wild male baboons, Papio cynocephalus, in a natural population in Amboseli National Park, Kenya. We examined (1) age at testicular enlargement, which signals puberty and the onset of subadulthood, (2) age at attainment of adult dominance rank, which we consider to be the beginning of adulthood, and (3) age at first sexual consortship, which is the best measure available for age at first reproduction in male baboons. Testicular enlargement (median age = 5.69 years) occurred earlier among sons of high ranking mothers, and was not influenced by rainfall or seasonality. Attainment of adult dominance rank (median age = 7.41 years) was also accelerated among sons of high-ranking mothers, and among males whose mothers had died while the males were juveniles. First sexual consortship (median age = 7.92 years) was not influenced directly by maternal characteristics, but attainment of adult dominance rank always preceded first consortship. The lag time between attainment of adult rank and first consortship (median = 2.5 months; range = 5–526 days), was predicted by the number of sexually cycling females in the group when the male attained rank, and by how high ranking the male became in his first months as an adult. We suggest that the age at which a male baboon is ready to begin reproducing is influenced by a relatively stable maternal characteristic that exerts its influence early in development, but the timing with which this potential is realized depends on activation by more proximate, often stochastic triggers such as female availability. This two-level organization of influences is likely to contribute to the variance both in age at first reproduction and in lifetime fitness. Differences in the relative magnitude of the two levels will lead to both intra- and interspecific variability in the opportunity for maternal selection and sexual selection. 相似文献
17.
Sexual signalling and viability in a wolf spider (Hygrolycosa rubrofasciata): measurements under laboratory and field conditions 总被引:4,自引:0,他引:4
Janne S. Kotiaho Rauno V. Alatalo Johanna Mappes Silja Parri 《Behavioral ecology and sociobiology》1999,46(2):123-128
This study examined the crucial prediction of the conditional-handicap theory, the relationship between male sexual trait
size and male viability, in the wolf spider Hygrolycosa rubrofasciata. In this species, males court females by drumming dry leaves with their abdomen, and males with the highest drumming rate
enjoy highest mating success. We determined male drumming rate, body mass, and mobility, which reflects mate-searching activity,
in relation to male survival. Because it is often difficult to know how results obtained from laboratory studies reflect the
natural world, particularly when the measured variable is survival, we repeated our study in both laboratory and field conditions.
Males drumming at the highest rate survived better than males drumming at a lower rate in both laboratory and field conditions.
These results are in accordance with the predictions of conditional-handicap models of sexual selection. Survival was independent
of male body mass and there was no significant correlation between male drumming activity and body mass. However, large males
moved further than smaller males, and males moving longer distances lost less mass than those moving shorter distances. These
results suggest that, moving, and consequently mate-searching activity, may be a condition-dependent trait and that there
may be a advantage for large males in mate searching.
Received: 22 October 1998 / Received in revised form: 28 January 1999 / Accepted: 14 February 1999 相似文献
18.
The structure of male mating signals is often influenced by age. The causes and consequences of age-based signal variation
have been much studied in visual, acoustic, and chemical signaling modalities, but are less explored in species that use vibrational
signals for mate attraction. However, the complex structure of many vibrational signals makes them ideal for investigating
the relationships between age, signal variation, and patterns of female choice. In the thornbug treehopper, Umbonia crassicornis, females mate more often with older males, but the mechanism underlying older male mating success is unknown. Our goals in
this study were to determine whether male vibrational mate advertisement signals vary with age, and, if so, whether females
prefer the signals of older males. We recorded male signals over four consecutive weeks beginning at the onset of signaling
(a period spanning most of the male reproductive lifespan), and measured ten temporal, spectral, and energy-related parameters
from each signal. Several features of male signals changed markedly with age. However, females responded similarly to signals
representing males of different ages, indicating that they do not favor older males on the basis of long distance mate advertisement
signals. Nonetheless, the results reveal that even in short-lived, determinate growth species age can have surprisingly large
effects on mating signals, and we discuss some factors that may contribute to age-related signal variability in U. crassicornis. 相似文献
19.
The complex songs of songbirds are thought to have evolved through sexual selection. Sexually selected signals must be associated
with costs in order to ensure their honesty as indicator of male quality. Costs may relate to the development of the neural
substrate underlying song learning, which develops already very early in life. Song may, therefore, serve as an indicator
of the early developmental history. This nutritional stress hypothesis has initially been confirmed for a variety of species,
but recent studies using zebra finches as a model species reported somewhat inconsistent effects, and the functional consequences
of changes in adult song phenotype remain unclear. We tested the nutritional stress hypothesis in canaries by manipulating
either the brood size or the food quality postfledging. The brood size manipulation had a significant effect on early development,
and low food quality postfledging led to a transient reduction in body mass. However, we did not find evidence that any of
the song traits measured reflected the early developmental conditions, which is in conflict with the nutritional stress hypothesis.
Canaries may be less vulnerable to nutritional stress or are able to compensate stressful conditions during early development.
However, if males compensated, this compensation may have come at a survival cost. Female mate choice decisions were independent
of the developmental history of a male. Instead, females preferred males singing longer song bouts, a trait that may contain
a heritable component. 相似文献
20.
Kelly M. Proffitt Robert A. Garrott Jay J. Rotella 《Behavioral ecology and sociobiology》2008,62(10):1679-1687
The Trivers–Willard model predicts that in polygynous species, superior-quality females will maximize their fitness by producing
male offspring. Using a sample of 1,780 Weddell seal (Leptonychotes weddellii) pups recorded over 31 years, we investigated relationships between offspring sex ratio and maternal age, reproductive experience,
an index of maternal lifetime reproductive output, and annual environmental variations. We found evidence that females with
higher index of lifetime reproductive output were more likely to produce male than female offspring but found only weak evidence
that large-scale environmental variations influenced sex ratios. Our results suggest that mothers manipulate offspring sex
to maximize their own fitness, and inherent maternal quality may influence offspring sex. These findings support the Trivers–Willard
sex-allocation model.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献