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1.
A. Peters K. Delhey W. Goymann B. Kempenaers 《Behavioral ecology and sociobiology》2006,59(5):666-673
The proximate basis of sexual traits can suggest mechanisms maintaining honesty in signalling. A central role hereby has been
attributed to testosterone, although its importance for brightly coloured plumage has been questioned. We determined circulating
testosterone levels in male blue tits captured at the start of breeding and demonstrated an age-dependent relationship between
testosterone and male crown UV/blue coloration. In yearling males, testosterone increases with increasing ornamentation (higher
UV chroma, higher chroma, more UV-shifted hue), whereas in older males, this relationship is negative, with less UV-ornamented
males having higher testosterone. This pattern is robust since it occurred in 2 years, before and after egg laying, and in
males sampled during the day and during the night, despite a tenfold difference in testosterone levels. Since more UV-ornamented
young males gain higher within-pair paternity, while less UV-ornamented older males achieve more extra-pair matings, the results
imply that higher testosterone is associated with reproductive success and attractiveness in both age classes. We hypothesise
that this relationship could result from causal effects of testosterone on coloration or through associations with behaviour
and suggest ways to test these hypotheses. Our results caution against premature dismissal of a potential role for testosterone
in maintaining honesty of plumage signals. 相似文献
2.
Verena Dietrich-Bischoff Tim Schmoll Wolfgang Winkel Sven Krackow Thomas Lubjuhn 《Behavioral ecology and sociobiology》2006,60(4):563-571
Females of many socially monogamous bird species commonly engage in extra-pair copulations. Assuming that extra-pair males are more attractive than the females’ social partners and that attractiveness has a heritable component, sex allocation theory predicts facultative overproduction of sons among extra-pair offspring (EPO) as sons benefit more than daughters from inheriting their father’s attractiveness traits. Here, we present a large-scale, three-year study on sex ratio variation in a passerine bird, the coal tit (Parus ater). Molecular sexing in combination with paternity analysis revealed no evidence for a male-bias in EPO sex ratios compared to their within-pair maternal half-siblings. Our main conclusion, therefore, is that facultative sex allocation to EPO is absent in the coal tit, in accordance with findings in several other species. Either there is no net selection for a deviation from random sex ratio variation (e.g. because extra-pair mating may serve goals different from striving for ‘attractiveness genes’) or evolutionary constraints preclude the evolution of precise maternal sex ratio adjustment. It is interesting to note that, however, we found broods without EPO as well as broods without mortality to be relatively female-biased compared to broods with EPO and mortality, respectively. We were unable to identify any environmental or parental variable to co-vary with brood sex ratios. There was no significant repeatability of sex ratios in consecutive broods of individual females that would hint at some idiosyncratic maternal sex ratio adjustment. Further research is needed to resolve the biological significance of the correlation between brood sex ratios and extra-pair paternity and mortality incidence, respectively. 相似文献
3.
E. C. Pariser L. Gilbert N. Hazon K. E. Arnold J. A. Graves 《Behavioral ecology and sociobiology》2012,66(4):519-527
Females are expected to partition resources between offspring in a context-dependent way to maximise total fitness returns
from a reproductive attempt. Female zebra finches (Taeniopygia guttata) vary the allocation of yolk androgens and antioxidants among offspring. Importantly, the balance between androgens and antioxidants
in yolks may be more important than their independent absolute amounts in terms of fitness consequences for developing young.
Therefore, we tested whether the relative allocation of these two resources in yolks varies according to either the Trivers–Willard,
positive or compensatory maternal investment hypothesis. We manipulated male attractiveness using coloured leg bands (red-banded
males appear attractive; green-banded males, unattractive) and measured yolk androgens and antioxidants in each egg, egg sex,
clutch sex ratio and female condition. While female zebra finches manipulated the balance of androgens and antioxidants within
and between clutches in response to mate attractiveness, offspring sex and their own condition, they did not do so in a way
that consistently followed any of the hypotheses. Mothers paired with unattractive males allocated a larger antioxidant/androgen
ratio to daughters than sons. This pattern was reversed when paired to an attractive male; sons received a larger antioxidant/androgen
ratio than daughters. We also found offspring sex ratio decreased with increasing female condition for unattractive males,
but not for attractive males. However, without knowing the fitness consequences of the balance of different egg constituents,
it is difficult to interpret the patterns consistently in terms of the Trivers–Willard, compensatory and positive investment
hypotheses. 相似文献
4.
Elise D. Ferree 《Behavioral ecology and sociobiology》2007,62(1):109-117
Theory, empirical examples, and recently, proximate mechanisms point to the possibility of adaptive sex ratio adjustment in
various organisms. General predictions state that a female should adjust her offspring sex ratio to maximize the benefits
or minimize the costs of reproduction given her physical condition or current social and environmental conditions. I tested
for an influence of male attractiveness on brood sex ratio in a population of dark-eyed juncos (Junco hyemalis thurberi) by manipulating a male’s white outer tail feathers (“tail white”). Experimentally increasing male tail white did not significantly
affect sex ratio, nor was premanipulated male tail white significantly related to brood sex ratio. However, the amount of
white on the female’s outer tail feathers, independently of female condition, was positively related to the number of sons
in a brood. Determining how a female’s potential genetic contribution to her sons’ attractiveness influences offspring sex
ratio should be a priority for future research. 相似文献
5.
Brood sex ratio is dependent on female mating status in polygynous great reed warblers 总被引:2,自引:0,他引:2
Isao Nishiumi 《Behavioral ecology and sociobiology》1998,44(1):9-14
Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In
polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females,
females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed
warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding
effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we
would predict that females which start breeding first within harems might produce more sons than those which start breeding
later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females
mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of
primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer
food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females
modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably
stronger than the latter factor.
Received: 11 March 1998 / Accepted after revision: 23 May 1998 相似文献
6.
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
7.
Amy C. Dolan Michael T. Murphy Lucas J. Redmond Debbie Duffield 《Behavioral ecology and sociobiology》2009,63(10):1527-1537
Sex allocation theory predicts that if variance in reproductive success differs between the sexes, females who are able to
produce high-quality young should bias offspring sex ratio towards the sex with the higher potential reproductive success.
We tested the hypothesis that high-quality (i.e., heavy) female eastern kingbirds (Tyrannus tyrannus) that bred early in the breeding season would produce male-biased clutches. A significant opportunity for sexual selection
also exists in this socially monogamous but cryptically polygamous species, and we predicted that successful extra-pair (EP)
sires would be associated with an excess of male offspring. Although population brood sex ratio did not differ from parity,
it increased significantly with female body mass and declined with female breeding date, but was independent of the morphology
and display (song) behavior (correlates of reproductive success) of social males and EP sires. Male offspring were significantly
heavier than female offspring at fledging. Moreover, the probability that male offspring were resighted in subsequent years
declined with breeding date, and was greater in replacement clutches, but lower when clutch size was large. Probability of
resighting female offspring varied annually, but was independent of all other variables. Given that variance in reproductive
success of male kingbirds is much greater than that of females, and that male offspring are more expensive to produce and
have a higher probability of recruitment if fledged early in the season, our results support predictions of sex allocation
theory: high-quality (heavy) females breeding when conditions were optimal for male recruitment produced an excess of sons. 相似文献
8.
Joanna Rutkowska Tomasz Wilk Mariusz Cichoń 《Behavioral ecology and sociobiology》2007,61(8):1211-1217
There is accumulating evidence that maternal hormones may play a role in offspring sex adjustment, but little is known about
the costs of such hormone-mediated mechanisms. Recent studies have reported sex-specific effects of hormones on offspring
viability. Specifically, we previously found that elevating the plasma androgen level in mothers results in a male-biased
offspring primary sex ratio, but it affects the viability of sons negatively and daughters positively in zebra finches (Taeniopygia guttata; Rutkowska and Cichoń, Anim Behav, 71:1283–1288, 2006). In this study, we studied further fitness consequences of exposure
to elevated yolk androgen levels in zebra finches. We measured growth rate and cellular immune response of nestlings that
hatched from eggs laid by females injected with testosterone during egg laying and nestlings of unaffected control females.
We found that sons of testosterone-treated females grew slower in comparison to sons of control females. The significant interaction
between experimental group and offspring sex indicates that sons of testosterone-treated mothers suffered impaired immune
responsiveness while daughters seemed to benefit from elevated androgen level in terms of enhanced immune responsiveness.
We found no effects of androgens on offspring performance at adulthood—neither fecundity of females nor attractiveness of
males was affected. We conclude that the benefits of biasing sex ratio towards males by increasing androgen level in the yolk
may be limited due to negative effects on male offspring performance early in life. 相似文献
9.
Male dung beetles, Onthophagus taurus, are dimorphic for a secondary sexual trait, head horns. Horned males participate in the production of brood masses while
hornless male do not. Here we examine the reproductive performance of females mated with males exhibiting alternative horn
morphologies. We found that exposure to males may be costly for females in that it reduced the total number of brood masses
produced. However, females paired with horned males produced significantly larger brood masses than females paired with hornless
males or females producing broods alone. We discuss the possible selection pressures that may underly horn evolution in this
genus.
Received: 22 August 1997 / Accepted after revision: 19 January 1998 相似文献
10.
Apostolos Kapranas P. Pacheco L. D. Forster J. G. Morse R. F. Luck 《Behavioral ecology and sociobiology》2008,62(6):901-912
We examined whether several facultatively gregarious encyrtid (Hymenoptera: Encyrtidae) endoparasitoids of brown soft scale,
Coccus hesperidum L., manifest precise sex allocation under field conditions. Metaphycus luteolus (Timberlake), Metaphycus angustifrons (Compere), Metaphycus stanleyi (Compere), and Microterys nietneri (Motshulsky) evince brood sex ratios that are female-biased and extremely precise (low variance in the number of sons per
host). Typically, this sex allocation pattern is attributed to extreme local mate competition (LMC) in which only one foundress
exploits a patch of hosts and mating occurs mostly between her offspring. However, such a pattern of sex allocation was not
detected for Metaphycus helvolus (Compere). Also, a large proportion of the broods in all five species contained only daughters; thus, an excess of male-only
broods was expected if unmated females (i.e., females that can produce only sons) contribute offspring before mating. All-male
broods were rare in our samples. This finding coupled with the life history characteristics of these wasps, such as the exploitation
of aggregated hosts and the long life span and mobility of males, suggest that nonlocal mating is frequent. Our empirical
work suggests that it is advantageous to allocate precise sex ratios in cases in which mating opportunities for males are
not restricted to their natal host and/or when multiple foundresses exploit large patches of hosts. Limited theoretical work
also supports this prediction but more detailed studies of this taxon’s mating structure and other life history characteristics
are necessary to understand their sex allocation decisions. 相似文献
11.
Environmental effects on sex allocation are common, yet the evolutionary significance of these effects remains poorly understood.
Environmental effects might influence parents, such that their condition directly influences sex allocation by altering the
relative benefits of producing sons versus daughters. Alternatively, the environment might influence the offspring themselves,
such that the conditions they find themselves in influence their contribution to parental fitness. In both cases, parents
might be selected to bias their sex ratio according to the prevailing environmental conditions. Here, we consider sex allocation
in the citrus mealybug Planococcus citri, a species with an unusual genetic system in which paternal genes are lost from the germline in males. We test environmental
factors that may influence either female condition directly (rearing temperature and food restriction) or that may be used
as cues of the future environment (age at mating). Using cytological techniques to obtain primary sex ratios, we show that
high temperature, older age at mating and starvation all affect sex allocation, resulting in female-biased sex ratios. However,
the effect of temperature is rather weak, and food restriction appears to be strongly associated with reduced longevity and
a truncation of the usual schedule of male and offspring production across a female’s reproductive lifetime. Instead, facultative
sex allocation seems most convincingly affected by age at mating, supporting previous work that suggests that social interactions
experienced by adult P. citri females are used when allocating sex. Our results highlight that, even within one species, different aspects of the environment
may have conflicting effects on sex allocation. 相似文献
12.
Eugene S. Morton Bridget J. M. Stutchbury Ioana Chiver 《Behavioral ecology and sociobiology》2010,64(6):947-954
We investigated sexual conflict over parental care in blue-headed vireos (Vireo solitarius) and documented the first example of unvarying unisexual brood desertion in passerines. Females at all nests (N = 24) that were monitored closely near fledgling, deserted their broods on or near the day of fledging leaving males alone
to complete parental care of young. No males deserted. This observational evidence was confirmed with radiotracking of females
(2004, 2007) and both pair members (2008). Radiotracked females began visiting distant males 1–4 days before young left the
nest, subsequently paired with males 355–802 m away, and laid first eggs in new nests less than 5 days after deserting. In
contrast, females suffering nest predation did not desert and renested with the same male. We suggest equal parental care
(nest building, incubation, feeding) in the sexes, genetic monogamy, and an adult sex ratio biased towards males has led to
female control of brood desertion in this species. Unisexual desertion may be more important in altricial birds than generally
realized and we discuss prerequisites to predict its occurrence. One is genetic monogamy, which may be a female tactic that
reduces the likelihood of males evolving counter-adaptations to female desertion. 相似文献
13.
Adeline Loyau Michel Saint Jalme Robert Mauget Gabriele Sorci 《Behavioral ecology and sociobiology》2007,61(7):1043-1052
According to the differential investment hypothesis, females paired with attractive mates are expected to invest more in the
current reproduction relative to females paired with unattractive males. We experimentally tested this hypothesis in the peafowl
(Pavo cristatus) by providing females with males that differed in sexual attractiveness. In agreement with the differential allocation hypothesis,
females paired with more ornamented males laid larger eggs, and deposited higher amounts of testosterone into the egg yolk,
independently of the sex of the embryo. These results show that the association between paternal phenotype and offspring quality
could arise via a differential maternal investment. They also suggest that, if ornamented males do transmit good genes to
the progeny, the maternal differential investment can amplify the effect of such good genes on the offspring fitness. 相似文献
14.
Júlio M. Neto Bengt Hansson Dennis Hasselquist 《Behavioral ecology and sociobiology》2011,65(2):297-304
Sex allocation theory predicts that whenever the relative fitness of sons and daughters differ, females should invest more
in the sex with the greatest fitness return. In this study, we evaluated the influence of various ecological factors on the
brood sex ratio (BSR) of Savi’s warblers (Locustella luscinioides) across several breeding seasons. There was a slight but significant female production bias at the population level, which
is consistent with the ‘local resource competition’ hypothesis, as the breeding density is very high and females are more
prone to disperse. We found that there was a significant decline in BSR during the breeding season, but no influence of male
size, female size, social status nor extra-pair paternity were detected. The seasonal decline in BSR was further evaluated
by assessing the within- and between-female effects, which indicated that multiple factors were operating simultaneously in
our study population. First, there was a significant within-female decline in BSR, which was consistent with the decline in
female condition due to the reproductive effort associated with multiple brooding (supporting the Trivers and Willard hypothesis).
Second, a significant decline in BSR with the laying date of first clutches of different pairs indicated that male and/or
female qualities are also associated with the seasonal variation in BSR. Finally, a comparison between the sex of the youngest
nestling with the remaining ones did not suggest any bias, indicating that females do not compensate for the increased mortality
of the last nestling (caused by asynchronous hatching) by producing a male from the last laid egg. 相似文献
15.
Darrell J. Kemp Joseph M. Macedonia Tamara S. Ball Ronald L. Rutowski 《Behavioral ecology and sociobiology》2008,62(6):1017-1026
Female mate choice has been shown to provide direct mating benefits in several animal groups. In butterflies, for which there
are increasing reports of fine-scale color-based mate choice, the evolutionary benefits that accrue from such mating biases,
if any, are largely unknown. We addressed this issue in the butterfly Colias eurytheme, a species in which females choose mates on the basis of iridescent ultraviolet (UV) wing ornamentation and in which males
donate reproductively beneficial nuptial gifts. In the first experiment, we assessed the mass of gifts donated to 77 virgin
females by males sampled directly from a field encounter site. Despite large variance in the male adult phenotype and ejaculate,
no single aspect of dorsal wing coloration, including UV brightness, chroma, or hue, was related to ejaculate mass. There
was, however, an interesting interaction between the effects of male body size and copula duration upon ejaculate mass, with
size scaling positively with ejaculate mass among males involved in shorter copulations (those lasting <70 min) but negatively
among males in longer copulations. In the second experiment, we assessed the lifetime fecundity, fertility, and longevity
of 85 females mated under similar circumstances to free-flying wild males. Although several wing color parameters proved subtly
informative in more sophisticated multivariable models, no model predicted more than about 20% of the variation in any single
female fitness parameter. The duration of copulation, which ranged from 35 min to over 16 h and which carries putative costs
for females, was, again, only very weakly predicted by male wing color parameters (i.e., R
2 = 0.089). Given the overall minor predictive power of male wing coloration in general and of UV brightness in particular,
our results do not strongly support the hypothesis that female C. eurytheme prefer bright UV males to obtain direct benefits or to minimize the costs associated with lengthy copulations. 相似文献
16.
To better understand the attractiveness of host tree, Chinese white pines (Pinus armandi Fr.) to Chinese white pine beetle (Dendroctonus armandi Tsai and Li), the antennal responses of D. armandi to the host volatile, as well as the pure enantiomers and racemates of some monoterpenes, were examined using an electroantennogram
(EAG). EAG responses of male and female D. armandi to blended volatiles extracted from the host and some synthetic terpenes (α-phellandrene, (−)-β-pinene, (+)-α-pinene, (−)-α-pinene,
(−)-camphene, β-myrcene, (S)-(−)-limonene, (+)-camphene and (R)-(+)-limonene) showed significant variation due to different compound concentrations and sex of the beetles. EAG responses
to extracted blended volatiles were significantly greater in females than in males, but the EAG response was not always proportional
to the volatile concentration. At lower concentrations, females responded strongly to α-phellandrene and males to (−)-β-pinene,
while at higher concentrations, females responded most strongly to α-phellandrene and males to (+)-α-pinene. Females were
significantly responsive to (−)-α-pinene, α-phellandrene and (−)-camphene, while males were more responsive to (S)-(−)-limonene, (+)-α-pinene and (R)-(+)-limonene. The EAG responses of the female D. armandi to the volatile oil were significantly higher than that of the males, and the infested pine volatiles could evoke higher
EAG response. Most of the test compounds elicited similar responses, which suggested that several of the compounds may be
used in combination by D. armandi in habitat and/or host community location at the Qinling forest ecosystem. 相似文献
17.
Fisher’s 1930 theory of sex allocation predicts a population-wide 1:1 ratio of parental investment. We tested this prediction
in the European beewolf, a sphecid wasp that hunts for honeybees as larval food. Because the method to quantify parental investment
is of crucial importance, we compared the suitability of several different investment measures. Female/male cost ratios were
determined from a sample and the total investment in sons and daughters was calculated. In addition, the actual number of
prey items for sons and daughters was directly determined by excavating nests and counting the cuticle remains of the prey.
Though mortality was high (70%), it had only a weak effect on the estimate of the investment ratio. Based on commonly used
measures like fresh and dry weight of emerged adults, the investment ratio did not deviate from Fisher’s prediction of equal
investment. However, progeny weight considerably underestimates investment in males and investment in large progeny. Measures
that reflect the allocation of resources more directly (amount of provisions, brood cell volume) revealed a significant male
bias and thus contradicted Fisher’s theory. Three kinds of explanation are discussed. First, non-adaptive explanations are
unlikely. Second, from the spectrum of alternative adaptive theories, only models that assume a non-linear relationship between
amount of investment and progeny fitness seem to be relevant for the study species. Third, though the number of prey in a
brood cell seems to be a rather good measure of parental investment in European beewolves, some problems in measuring parental
investment remain. These problems are of broad significance.
Received: 17 June 1999 / Received in revised form: 6 July 1999 / Accepted: 11 July 1999 相似文献
18.
Brood sex ratios, female harem status and resources for nestling provisioning in the great reed warbler (Acrocephalus arundinaceus) 总被引:4,自引:0,他引:4
H. Westerdahl Staffan Bensch Bengt Hansson Dennis Hasselquist Torbjörn von Schantz 《Behavioral ecology and sociobiology》2000,47(5):312-318
The theory of parental investment and brood sex ratio manipulation predicts that parents should invest in the more costly
sex during conditions when resources are abundant. In the polygynous great reed warbler, Acrocephalus arundinaceus, females of primary harem status have more resources for nestling provisioning than secondary females, because polygynous
males predominantly assist the primary female whereas the secondary female has to feed her young alone. Sons weigh significantly
more than daughters, and are hence likely to be the more costly sex. In the present study, we measured the brood sex ratio
when the chicks were 9 days old, i.e. the fledging sex ratio. As expected from theory, we found that female great reed warblers
of primary status had a higher proportion of sons in their broods than females of lower (secondary) harem status. This pattern
is in accordance with the results from two other species of marsh-nesting polygynous birds, the oriental reed warbler, Acrocephalus orientalis, and the yellow-headed blackbird Xanthocephalus xanthocephalus. As in the oriental reed warbler, we found that great reed warbler males increased their share of parental care as the proportion
of sons in the brood increased. We did not find any difference in fitness of sons and daughters raised in primary and secondary
nests. The occurrence of adaptive sex ratio manipulations in birds has been questioned, and it is therefore important that
three studies of polygynous bird species, including our own, have demonstrated the same pattern of a male-biased offspring
sex ratio in primary compared with secondary nests.
Received: 1 June 1999 / Received in revised form: 10 January 2000 / Accepted: 12 February 2000 相似文献
19.
D. M. Shuker E. M. Sykes L. E. Browning L. W. Beukeboom S. A. West 《Behavioral ecology and sociobiology》2006,59(6):829-835
Sex allocation is an important reproductive decision for parents. However, it is often assumed that females have substantial
control over sex allocation decisions, and this is particularly true in haplodiploid insects, in which females apparently
determine sex by deciding whether to fertilise an egg (and produce a diploid daughter) or not (and produce a haploid son).
Mechanisms by which males may influence sex allocation are not so straightforward, and their potential influence on sex ratios
has been somewhat neglected. Here, we test whether males influence offspring sex ratios in the parasitoid wasp Nasonia vitripennis. We show that some of the variation in observed sex ratios can be attributed to males when comparing the affect of male strain
on sex ratio. We did not find among-male variation in sex ratio with a less powerful experiment using males from only one
strain or an effect of male mating environment. Our data suggest that males can influence female sex ratios and contribute
to the variation around the sex ratios optimal for females. However, the influence is not large, suggesting that females have
more influence on sex allocation than do males. We conclude by considering whether male influences on sex ratio represent
differences in male reproductive competence or deliberate attempts by males to increase their fitness by influencing daughter
production. 相似文献
20.
Masayo Soma Daichi S. Saito Toshikazu Hasegawa Kazuo Okanoya 《Behavioral ecology and sociobiology》2007,61(11):1695-1705
Maternal effects, such as investment in eggs, have profound effects on offspring fitness. Mothers are expected to skew their
investment depending on the laying order and sex when unequal sibling competition occurs within a brood because of sex-specific
vulnerability and age hierarchy caused by asynchronous hatching. The Bengalese finch hatches asynchronously and shows a moderate
reversed sexual size dimorphism. However, contrary to commonly accepted assumptions of size-dependent vulnerability, the smaller
sex (male) is more vulnerable to developmental stress caused by sibling competition. We investigated whether maternal investment
would be biased by the position in laying order and the sex of eggs, and also explored the possible differences in growth
patterns depending on sex, laying order, and age hierarchy by observing chicks fostered to experimentally manipulated broods
where brood composition was controlled and age hierarchy was more enhanced than in natural breeding conditions. We found that
overall patterns of maternal investment favored the disadvantageous sectors of sibling competition, i.e., eggs of later laying
order and sons over those of early laying order and daughters. We also examined the effect of laying order on adult body size
and sex differences in growth patterns. When reared in the subordinate age hierarchy, females could compensate for the deficit
of decreased growth rate by taking longer to mature, whereas males could not. We suggest that this sex-specific growth pattern
could be the cause of sex differences in vulnerability to early developmental stress. 相似文献