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1.
Diego Rubolini Maria Romano Roberta Martinelli Nicola Saino 《Behavioral ecology and sociobiology》2006,59(3):344-352
Androgen hormones of maternal origin contained in the eggs of avian species are considered to have positive effects on offspring
characteristics and performance. However, negative consequences have also been reported, suggesting that mothers may experience
a trade-off between beneficial and detrimental effects of egg androgens to offspring fitness. We studied the effects of elevated
yolk testosterone (T) concentration on survival, development and phenotype of male and female yellow-legged gull (Larus michahellis) chicks by injecting egg yolks with physiological doses of the hormone. Elevated yolk T resulted in a male-biased post-hatching
sex ratio, T-treated clutches producing a greater proportion of males compared to control ones at day 4 post-hatching, likely
resulting from a reduction of female embryonic survival, whereas no effect of hormone treatment on hatching success or short-term
chick survival was observed. In addition, T depressed post-hatching body mass in both sexes but had no effects on the intensity
of the cell-mediated immune response or skeletal growth. No sex differences in egg characteristics or chick phenotype were
detected. Time to hatching was not affected by T, but females originating from first laid eggs hatched earlier than males
of the same laying order, independently of hormone treatment. However, the implications of sex differences in hatching times
are unclear in the study species. Taken together, our results suggest that female yellow-legged gulls may be constrained in
transferring androgens to their eggs by negative consequences on the viability of female offspring and growth of chicks of
the two sexes. 相似文献
2.
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
3.
Life history theory predicts that parents will have lower Darwinian fitness if they tend clutches that are above or below the size they naturally produce. We experimentally tested for relationships between fitness and clutch size in Tree Swallow (Tachycineta bicolor) offspring and parents. Over 130 trios of nests initiated on the same day were randomly divided among reduce (-3 eggs), control (3 eggs picked up and replaced), or add (+3 eggs) manipulations. Pre-manipulation modal clutch size was six eggs (range before manipulations was 1-10; afterwards, it was 1-11). Hatching took longer in larger clutches, but the proportion of eggs hatching and fledging was similar for clutches from 4 to 10, so that clutches of 10 produced the maximum number of fledgling. Parental feeding rates were higher for larger broods, but per capita feeds to nestlings were fewer, and nestlings were smaller. Nonetheless, survival of both young and adults, based on recaptures in subsequent years, was not significantly affected by manipulations. Manipulations also had no significant effect on subsequent reproduction, including the number of fledglings produced by either local recruits or returning breeders. Collectively, our results failed to detect fitness costs associated with tending larger clutches for either parents or the offspring reared and suggested directional selection for larger clutch size. However, because clutches that hatch later produce fewer recruits, the extra days required to lay more eggs and to fledge extra young may eliminate a large part of the advantage that would accrue to parents producing enlarged clutches. For example, our data suggest that there may be less than a 16% benefit to producing nine instead of six eggs, rather than 50%, as is suggested by experimentally manipulated egg numbers alone. Thus, time, rather than costs of reproduction, may be the crucial constraint selecting against Tree Swallows laying larger clutches. 相似文献
4.
Diego Rubolini Roberto Ambrosini Maria Romano Manuela Caprioli Mauro Fasola Andrea Bonisoli-Alquati Nicola Saino 《Behavioral ecology and sociobiology》2009,63(12):1809-1819
Non-random sex allocation may occur whenever the expected reproductive value of sons and daughters differs, as is the case when the sexes differ in susceptibility to environmental conditions or maternal effects (e.g. egg size and hatch order). Under such circumstances, covariation between egg and clutch characteristics and egg sex may be expected, and this covariation should vary with maternal state or ecological conditions. In this 2-year study (2007–2008), we examined sex allocation in relation to egg and clutch traits in the yellow-legged gull Larus michahellis, a species where male chicks are larger and more susceptible to harsh rearing conditions than female ones. In 2008, eggs were more likely male early in the season in two- but not three-egg clutches, and large eggs were more likely males late in the season. No egg/clutch traits predicted egg sex in 2007. Within-clutch egg mass asymmetry (the difference in egg mass between the first- and last-laid eggs) predicted sex in both years. In 2007, clutches with smaller egg mass variation were more likely to contain males, while in 2008 this relationship held for the last-laid egg and was reversed for the preceding egg(s). Laying order and sex of the previous egg did not predict egg sex, providing no evidence of sex-specific oocyte clustering. Thus, the relationships between egg sex and egg/clutch traits differed among years, suggesting a phenotypically plastic response of females to extrinsic conditions, and involved within-clutch egg mass asymmetry, a trait likely reflecting variation in maternal quality and/or reproductive tactics, which has been largely neglected in previous studies of sex allocation. 相似文献
5.
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
6.
Laaksonen T Adamczyk F Ahola M Möstl E Lessells CK 《Behavioral ecology and sociobiology》2011,65(2):257-264
Female birds might be able to manipulate the parental effort of their male partner through elevated transfer of hormones to
the eggs, since these hormones affect many chick traits that males might use as cues for adjusting the level of their investment.
We experimentally studied whether female pied flycatchers Ficedula hypoleuca could manipulate male investment via yolk androgens. There is much more variation in yolk androgen levels between females
than within clutches, and in order to change the androgen levels of the eggs, we swapped whole clutches between nests. To
estimate the androgen levels of the clutch, we measured the androgen content of a single egg per clutch. Females did not succeed
in manipulating male effort using yolk androgens, since there was no relationship between the division of parental care within
a pair and either original or foster egg androgen levels. One of these relationships should have occurred if females were
manipulating males. The proportion of feeding visits by the male was higher when the male was old (55%) than when he was young
(45%) and females laid eggs with higher androgen levels when mated with a young male. Young males did not exhibit any responses
to yolk androgen levels either, which indicates that females cannot exploit their effort more than that of old males. We suggest
that females may allocate yolk androgens to adjust the growth trajectories of the chicks to poor growing conditions when mated
with young males that are poor providers or occupying a poor territory. 相似文献
7.
Cor Dijkstra Bernd Riedstra Arjan Dekker Vivian C. Goerlich Serge Daan Ton G. G. Groothuis 《Behavioral ecology and sociobiology》2010,64(9):1393-1402
When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio
of their offspring to maximize their fitness (Trivers and Willard, Science 179:90–92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring
sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early
in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating
the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species.
Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock
pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific
age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early
and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced
clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study
presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an
endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism. 相似文献
8.
Liliana D’Alba Matthew D. Shawkey Peter Korsten Oscar Vedder Sjouke A. Kingma Jan Komdeur Steven R. Beissinger 《Behavioral ecology and sociobiology》2010,64(6):1037-1045
Female birds can influence offspring fitness by varying the relative quantities of egg components they deposit within and
between clutches. Antimicrobial proteins (lysozyme, ovotransferrin, and avidin) are significant components of the avian albumen
and likely aid in defense of embryos from microbial infection. Within clutches, females may enhance antimicrobial defense
of early-laid eggs to protect them from the high risk of infection incurred before the onset of incubation. Among entire clutches,
females may invest more resources in young sired by more attractive males because they have higher reproductive value. We
tested these hypotheses by quantifying antimicrobial protein distribution within and among clutches in blue tit eggs. Contrary
to our hypothesis, clutches showed no differential deposition of lysozyme or avidin within clutches, but eggs laid in the
middle of the sequence had higher concentrations of ovotransferrin than eggs in the beginning and end. Consistent with our
second hypothesis, we found that females produced eggs with higher concentrations of lysozyme (although not ovotransferrin
or avidin) when mated to more attractive (more UV-reflective) males. Furthermore, females mated to polygynous males deposited
less lysozyme than those mated to monogamous males. These data suggest that allocation of lysozyme at the clutch level may
be a maternal effect mediated by male qualities. 相似文献
9.
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
10.
Ummat Somjee Kelly Ablard Bernard Crespi Paul W. Schaefer Gerhard Gries 《Behavioral ecology and sociobiology》2011,65(5):1071-1077
Local mate competition (LMC) occurs when brothers compete with each other for mating opportunities, resulting in selection
for a female-biased sex ratio within local groups. If multiple females oviposit in the same patch, their sons compete for
mating opportunities with non-brothers. Females, in the presence of other females, should thus produce relatively more sons.
Sex ratio theory also predicts a more female-biased sex ratio when ovipositing females are genetically related, and sex-ratio
responses to foundress size if it differentially affects fitness gains from sons versus daughters. The mating system of the
parasitoid wasp Ooencyrtus kuvanae meets assumptions of LMC. Females insert a single egg into each accessible egg of gypsy moth, Lymantria dispar, host egg masses. Wasps complete development inside host eggs and emerge en masse, as sexually mature adults, resulting in
intense competition among brothers. We tested the hypothesis that O. kuvanae exhibits LMC by manipulating the number of wasp foundresses on egg masses with identical numbers of eggs. As predicted by
LMC theory, with increasing numbers of wasp foundresses on an egg mass, the proportions of emerging sons increased. In contrast,
the presence of a sibling compared to a non-sibling female during oviposition, or the size of a female, did not affect the
number or sex ratio of offspring produced. The O. kuvanae system differs from others in that larvae do not compete for local resources and thus do not distort the sex ratio in favor
of sons. With no resource competition among O. kuvanae larvae, the sex ratio of emergent son and daughter wasps is due entirely to the sex allocation by ovipositing wasp foundresses
on host egg masses. 相似文献
11.
Intra-specific interactions influence egg composition in the lesser black-backed gull (Larus fuscus)
Nanette Verboven Neil P. Evans Liliana D’Alba Ruedi G. Nager Jonathan D. Blount Peter F. Surai Pat Monaghan 《Behavioral ecology and sociobiology》2005,57(4):357-365
Egg composition, which is under maternal control, can have a profound effect on offspring fitness. The presence of maternal testosterone and carotenoids in avian egg yolk, for example, is thought to enhance the development and competitive ability of the offspring and protect the hatching and growing chick against oxidative stress. Egg quality often differs between females and such variation can be due to differences in maternal social environment, e.g. breeding density. However, this is confounded by the possibility that the quality of individuals breeding in high- or low-density areas may vary. We tested if maternal social environment influences egg composition in a colonial seabird, the lesser black-backed gull (Larus fuscus). To control for confounding effects of female quality, we experimentally manipulated maternal social environment during egg formation. We increased the frequency of intra-specific interactions (i.e. aggressive encounters with conspecifics other than nest mates) in which the females were involved, by placing an elevated platform in their territory. Females that took part in more intra-specific interactions produced a heavier last egg, but the yolk testosterone concentration in eggs laid by control and experimental females did not differ. Differences in yolk testosterone concentration in relation to embryo sex were found neither in the control nor in the experimental group. In contrast, within the control group, eggs with a male embryo contained more carotenoids than eggs with a female embryo. Moreover, experimental females that had been involved in more intra-specific interactions produced female eggs with higher carotenoid levels compared to female eggs of control birds. An experimental increase in carotenoid levels was not observed in eggs containing a male embryo. Our results suggest that intra-specific interactions experienced by female birds during egg formation can influence conditions for embryonic development.Communicated by J. Graves 相似文献
12.
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
13.
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
14.
János Török Rita Hargitai Gergely Hegyi Zoltán Matus Gábor Michl Péter Péczely Balázs Rosivall Gyula Tóth 《Behavioral ecology and sociobiology》2007,61(4):541-550
Birds may influence the fitness of their offspring by transmission of different amounts of carotenoids to their eggs. Carotenoids
play crucial roles in antioxidant protection and immune defence mechanisms, but they may be available to females in limiting
amounts. Therefore, their allocation to the eggs may be influenced by the female’s condition, age and environmental circumstances.
Furthermore, the quality of the male parent, which affects the reproductive value of the offspring, may also influence this
investment. In this correlational study, we investigated proximate and ultimate factors that may lead to variation in yolk
lutein, zeaxanthin and β-carotene concentrations among and within clutches of a wild passerine, the collared flycatcher (Ficedula albicollis). We found that carotenoid concentration was positively associated with caterpillar supply at the time of egg formation,
which suggests a proximate constraint of carotenoid availability on yolk composition. Neither female condition, body size,
age, nor male plumage ornamentation, age and body size correlated with carotenoid deposition. Yolk β-carotene concentration
was found to be positively linked to yolk testosterone concentration. We suggest that females allocated more β-carotene to
their eggs to mitigate the potentially detrimental effects of elevated steroid concentration. We found that concentration
of β-carotene increased with laying order. The possible function of this pattern may be to enhance the resistance to oxidative
stress and pathogens of the disadvantaged last-hatching nestling, suggesting that collared flycatchers pursue a compensatory,
“brood survival” strategy. 相似文献
15.
Carotenoid-based ornaments (many yellow–orange–red colourations) may signal the genetic or parental quality of the bearer. Thus, their expression could influence the amount of resources/energy that the mate will invest in the production of offspring, thereby optimising its reproductive fitness. The differential allocation hypothesis (DAH) predicts that females mated with more attractive males should lay more and better eggs. This has been explored only in few bird species with carotenoid-based traits. We tested this hypothesis in the red-legged partridge (Alectoris rufa), a gallinacean with very variable laying capacity. Both sexes display carotenoid-based ornamentation that gradually fades throughout the laying period. Here, the redness of beak and eye rings of captive males was intensified after mating by means of paint. The proportion of females that laid eggs did not differ between treatments. Amongst laying females, those mated with colour-enhanced males (experimental females) tended to lay earlier and produced significantly more eggs than controls, but of similar quality (egg mass and composition). We additionally investigated whether male attractiveness influenced egg components depending on the clutch size and laying sequence. The testosterone level in eggs from experimental females was positively related to the laying order, whereas control eggs did not show any trend. Our results provided mixed support for the DAH, but nevertheless revealed that female red-legged partridges may adjust their breeding investment according to male carotenoid-based ornamentation. 相似文献
16.
Rebecca J. Safran Kevin M. Pilz Kevin J. McGraw Stephanie M. Correa Hubert Schwabl 《Behavioral ecology and sociobiology》2008,62(3):427-438
Recently, evidence is mounting that females can adaptively engineer the quality of their offspring via the deposition of yolk
compounds, including carotenoids and androgens. In this study, we simultaneously consider how both carotenoids and androgens
in egg yolk relate to parental quality in barn swallows (Hirundo rustica erythrogaster). First, we found no relationship between concentrations or amounts of yolk androgens and carotenoids. Yolk carotenoids decreased
with laying order, whereas we found no relationship between yolk androgens and laying order. Second, we tested the Investment
Hypothesis, which predicts that high-quality females or females paired to high quality mates, allocate differentially more
of these yolk compounds to their offspring. For carotenoids, we mostly found evidence to counter predictions of the Investment
hypothesis: (1) Carotenoid concentrations varied among females, (2) heavier eggs contained lower carotenoid concentrations,
although heavier yolks contained greater amounts of carotenoids, (3) eggs of earlier-laying females had lower concentrations
in their eggs, and (4) yolk carotenoids were not correlated with clutch size or male plumage ornamentation. For androgens,
we found weak support for the Investment Hypothesis: (1) Yolk androgens varied among females, (2) heavier eggs and yolks contained
greater amounts, although not concentrations of androgens, (3) females paired to more colorful males laid eggs with greater
concentrations of androgens, and (4) no effects of laying date or morphological correlates of female quality on androgen concentrations
in egg yolks. Overall, these findings suggest that each yolk compound may have different functions and therefore may be regulated
by different mechanisms. 相似文献
17.
José M. Aparicio 《Behavioral ecology and sociobiology》1997,41(2):129-137
Lesser kestrels (Falco naumanni) lay clutches which appear excessive as only 3% of them yield as many young as eggs laid. Four hypotheses may explain the
adaptive value of producing surplus eggs: (1) the bet-hedging hypothesis assumes that the environment varies unpredictably
and surplus eggs serve to track uncertain resources; (2) the ice-box hypothesis suggests that surplus offspring serve as a
reserve food during a period of shortage; (3) the progeny choice hypothesis says that parents produce surplus offspring in
order to choose these with higher fitness; and (4) the insurance-egg hypothesis proposes that extra eggs are an insurance
against the failure of any egg. To test the significance of this strategy in the lesser kestrel, an experiment manipu-lating
brood size at hatching was carried out over 2 years, with good and bad feeding conditions. The experiment consisted of adding
a chick to experimental broods where one egg failed to hatch or removing a randomly selected chick from experimental broods
where all eggs had hatched. Independently of annual food availability, pairs with brood sizes reduced by one chick fledged
more nestlings than pairs with brood size equalling their clutch sizes. Body condition of young was also better in the former
group, but only in 1993 (a high-food year). Independently of year, mean local survival of parents with complete broods at
hatching was lower than for parents raising reduced broods. These results supported only the insurance-egg hypothesis which
says that surplus eggs may be an insurance against the failure of any egg, but parents may suffer reproductive costs when
all eggs hatch.
Received: 17 January 1997 / Accepted after revision: 27 April 1997 相似文献
18.
Diego Rubolini Maria Romano Roberta Martinelli Barbara Leoni Nicola Saino 《Behavioral ecology and sociobiology》2006,59(4):549-560
Mothers may profoundly affect offspring phenotype and performance by adjusting egg components, including steroid hormones.
We studied the effects of elevated prenatal testosterone (T) exposure in the ring-necked pheasant on the expression of a suite
of male and female traits, including perinatal response to stress, immune response, growth, and secondary sexual traits. Prenatal
T levels were increased by injecting the yolk of unincubated eggs with physiological doses of the hormone. Yolk T injection
resulted in a reduced length of male tarsal spurs, a trait which positively predicts male success in intra- and intersexual
selection and viability, whereas no direct effect on male wattle characteristics or plumage traits of either sex was observed.
Female spur length was also negatively affected by T, but to a lesser extent than in males. In addition, the covariation between
male secondary sexual traits, which are reliable quality indicators, differed between T and control males, suggesting that
the manipulation may have altered the assessment of overall male quality by other males and females. In conclusion, the negative
effects of elevated yolk T on spur length, a trait which positively predicts male fitness, coupled with the lack of effects
on growth or other traits in both sexes, provided limited evidence for mothers being subjected to a trade-off between positive
and negative consequences of yolk T deposition on offspring traits and suggest that directional selection for reduced yolk
T levels may occur in the ring-necked pheasant. 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.
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