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1.
Parental investment, adult sex ratios, and sexual selection in a socially monogamous seabird 总被引:7,自引:0,他引:7
Although most birds are monogamous, theory predicts that greater female parental investment and female-biased adult sex ratios
will lower the polygyny threshold. This should result in polygynous mating, unless obligate biparental care or the spatial
and temporal distribution of fertilizable females constrains a male’s ability to take advantage of a lowered polygyny threshold.
Here we present data on the extent of male sexually dimorphic plumage, adult sex ratios and breeding season synchrony in three
populations of a socially monogamous seabird, the brown booby Sula leucogaster. For one of these populations, San Pedro Mártir Island, we also present data on differences in male and female parental investment,
mortality and probability of pairing. The extent of plumage dimorphism varied among populations. Sex ratios were female biased in all populations. On San Pedro
Mártir Island, parental investment was female biased, females failed more often than males to find a mate, but there was no
polygyny. We suggest that on San Pedro Mártir: (1) a period of obligate biparental care coupled with a relatively synchronous
breeding season constrained the ability of males to take advantage of a high environmental polygamy potential and (2) the
resulting socially monogamous mating system, in combination with the female-biased adult sex ratio, caused females to be limited
by the availability of males despite their greater parental investment.
Received: 18 November 1999 / Accepted: 24 January 2000 相似文献
2.
Several small populations of Hawaiian monk seals ( Monachus schauinslani ) exhibit male-biased adult sex ratios and "mobbing," an aggressive behavior in which adult males injure and often kill adult females and immature seals of both sexes during mating attempts. Mobbing appears to be limiting the growth of some populations of this endangered species. The frequency of mobbing deaths appears to increase as a population's sex ratio becomes increasingly male-biased, although the exact relationship between these two variables (the mobbing response) is unknown. We developed a stochastic demographic model of a small Hawaiian monk seal population using several different assumptions about the mobbing response. We used the model to explore the origins of male-biased sex ratios in monk seal populations and to determine whether it was possible, given the lack of data on the mobbing response, to evaluate the probable effects of alternative management strategies to address the mobbing problem. Small populations (100 to 200 seals) and those with slower growth rates were more likely to develop male-biased adult sex ratios. Almost all of our modeling scenarios supported the immediate removal of males from populations where mobbing occurs. Our conclusions were relatively unaffected when the assumptions regarding the mobbing response were varied. Thus, a model was helpful even when apparently crucial data were unavailable. 相似文献
3.
The host size model, an adaptive model for maternal manipulation of offspring sex ratio, was examined for the parasitoid
wasp Spalangia endius. In a Florida strain, as the model predicts, daughters emerged from larger hosts than sons, but only when mothers received
both small and large hosts simultaneously. The pattern appeared to result from the mother's ovipositional choice and not from
differential mortality of the sexes during development. If sex ratio manipulation is adaptive in the Florida strain, it appears
to be through a benefit to daughters of developing on large hosts rather than through a benefit to sons of developing on small
hosts. Both female and male parasitoids were larger when they developed on larger hosts. For females, developing on a larger
host (1) increased offspring production, except for the largest hosts, (2) increased longevity, (3) lengthened development,
and (4) had no effect on wing loading. For males, development on a larger host had no effect on any measure of male fitness
– mating success, longevity, development duration, or wing loading. In contrast, a strain from India showed no difference
in the size of hosts from which daughters versus sons emerged, although both female and male parasitoids were larger when
they developed on larger hosts. These results together with previous studies of Spalangia reveal no consistent connection between host-size-dependent sex ratio and host-size-dependent parasitoid size among strains
of S. endius or among species of Spalangia.
Received: 28 October 1998 / Received in revised form: 20 May 1999 / Accepted: 30 May 1999 相似文献
4.
Learning and natal host influence host preference,handling time and sex allocation behaviour in a pupal parasitoid 总被引:6,自引:0,他引:6
The host choice and sex allocation decisions of a foraging female parasitoid will have an enormous influence on the life-history
characteristics of her offspring. The pteromalid Pachycrepoideus vindemiae is a generalist idiobiont pupal parasitoid of many species of cyclorrhaphous Diptera. Wasps reared in Musca domestica were larger, had higher attack rates and greater male mating success than those reared in Drosophila melanogaster. In no-choice situations, na?ve female P. vindemiae took significantly less time to accept hosts conspecific with their natal host. Parasitoids that emerged from M. domestica pupae spent similar amounts of time ovipositing in both D. melanogaster and M. domestica. Those parasitoids that had emerged from D. melanogaster spent significantly longer attacking M. domestica pupae. The host choice behaviour of female P. vindemiae was influenced by an interaction between natal host and experience. Female P. vindemiae reared in M. domestica only showed a preference among hosts when allowed to gain experience attacking M. domestica, preferentially attacking that species. Similarly, female parasitoids reared on D. melanogaster only showed a preference among hosts when allowed to gain experience attacking D. melanogaster, again preferentially attacking that species. Wasp natal host also influenced sex allocation behaviour. While wasps from
both hosts oviposited more females in the larger host, M. domestica, wasps that emerged from M. domestica had significantly more male-biased offspring sex ratios. These results indicate the importance of learning and natal host
size in determining P. vindemiae attack rates, mating success, host preference and sex allocation behaviour, all critical components of parasitoid fitness.
Electronic Publication 相似文献
5.
The caterpillars of Eucheira socialis westwoodi cooperatively spin and maintain a hollow silken nest and an elaborate network of silken foraging trails on their host plant,
madrone (Arbutus spp.: Ericaceae). Nests typically contain several hundred larvae. Two populations are known to harbor a sex ratio distorter.
The primary sex ratio in these two populations for four generations has been exceedingly male biased (64–79% male). Lepidoptera
larvae are easily sexed using external morphology, allowing us to uniquely mark male and female larvae and to assemble larval
groups of particular sex ratios. We report here the results of experiments on sex-specific larval behavior and physiology
and the effect of colony sex ratio on individual behavior. We found that male larvae spent more time spinning silk on the
nest and less time feeding than female larvae. Males were the first to emerge from the nest and the first to venture out along
trails to feed. Male-biased nests had a significantly greater amount of silk deposited on their surfaces than female-biased
nests. In the field, male-biased nests produced heavier male and female pupae than female-biased nests. Male and female larvae
in 75% male nests became active earlier than males and females in other sex ratio treatments.
Received: 11 September 1998 / Received in revised form: 24 February 1999 / Accepted: 27 March 1999 相似文献
6.
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
7.
Bertanne Visser Cécile Le Lann Helen Snaas Ian C. W. Hardy Jeffrey A. Harvey 《Behavioral ecology and sociobiology》2014,68(1):105-113
Population-wide mating patterns can select for equal parental investment in both sexes, but limiting resources, such as mates or developmental substrates, can increase competition leading to biased sex ratios in favor of either sex. Such competition for resources typically occurs in spatially structured populations, where dispersal is limited. In this laboratory study, we investigate if and how resource competition affects sex allocation, discriminative behaviors and competitive interactions of the wingless hyperparasitoid Gelis acororum, which exploits patchily distributed hosts. We show that G. acororum sex ratios are male-biased and that this is not a consequence of constrained reproduction by virgin females. Our results suggest that this pattern of reproductive investment, which is only rarely observed in parasitoids, is a consequence of resource limitation, in terms of hosts rather than mates. Further, G. acororum appears not to respond to intrinsic host quality or to prior oviposition in its host. When competing inter-specifically for host resources, G. acororum outcompetes its congener Gelis agilis, but does so mainly when ovipositing on the host first. Overall, our results suggest that host resource limitation could be an important environmental factor shaping sex allocation in G. acororum, with competition taking place both intra- and inter-specifically. 相似文献
8.
Sexual selection and cuckoldry in a monogamous songbird: implications for sexual selection theory 总被引:11,自引:0,他引:11
Geoffrey E. Hill Robert Montgomerie Christina Roeder Peter Boag 《Behavioral ecology and sociobiology》1994,35(3):193-199
Sexual selection is generally assumed to be weaker in monogamous than in polygynous animals. Recently, though, extra-pair fertilizations have been hailed as an important force in generating variance in reproductive success among males in socially monogamous species, thereby increasing the intensity of sexual selection. To see if extra-pair copulations contribute to variance in male reproductive success in the house finch (Carpodacus mexicanus), we used DNA fingerprinting to determine the paternity of chicks from 35 nests. This species is a socially monogamous passerine in which plumage brightness serves as a sexually selected indicator of male quality. Out of 119, nestlings 10 (8.3%) were fathered by a male other than the attending male, but cuckoldry occurred randomly with respect to the plumage colouration, size, or age of the attending male. Thus extra-pair fertilizations do not generate variance in male reproductive success with respect to plumage colour. On the other hand, a strongly male-biased sex ratio and asynchronous breeding by females may generate substantial variance in male reproductive success and could explain the evolution of ornamental colouration. 相似文献
9.
The local resource enhancement (LRE) model predicts that in cooperatively breeding species, sex ratios will be biased in favor
of the more helpful sex. In this study, we assess the assumptions underlying the LRE model in a population of cooperatively
breeding wild dogs (Lycaon pictus) in Northern Botswana monitored over a 15-year period. In this population, litter size and pup survival to 1 year are strongly
affected by pack size and the breeding female’s age, but adult males have a stronger and more linear effect on females’ reproductive
performance than do adult females. This asymmetry in the benefits derived from male and female helpers is reflected in male-biased
sex ratios in litters at the time pups emerge from the den. Sex ratio biases are most pronounced in the litters of the youngest
mothers who live in significantly smaller packs than older females. The presence of potential rivals for the dominant female’s
position depresses pup production at the time of emergence, suggesting that competition among females for breeding positions
may also contribute to the selective forces affecting birth sex ratios. 相似文献
10.
J. Antonio Baeza 《Marine Biology》2008,153(3):387-395
A previous study predicted the evolution of monogamy in symbiotic crustaceans inhabiting scarce, relatively small hosts in
tropical environments where predation risk away from hosts is high. This prediction was tested in the shrimp Pontonia margarita, which inhabits the pearl oyster Pinctada mazatlanica. A total of 68 oysters were collected from the intertidal and shallow subtidal at two islands (Islas Secas [N 27° 55′, W
82° 03′] and Isla de La Coiba [N 27° 50′, W 97° 03′]) off the eastern tropical Pacific coast on 15 and 17 March 2007, respectively.
The population structure, distribution, male-female association pattern, and relative growth of the major claw and pleura
of the second abdominal segment of each shrimp retrieved were examined. Shrimps were found as heterosexual pairs in the mantle
cavity of hosts more frequently than would be expected by chance alone. Males occurred with females in the same host, independent
of the reproductive condition of the female or the stage of development of brooded embryos. This observation, and strong correlations
between the host and shrimp body size in both males and females suggest a long-term association between males and females
in each host. Sexual dimorphism in body size was minor, with males being just slightly smaller than females. In agreement
with predictions for monogamous species, the major claw of males did not display positive allometry, which has been generally
reported for polygamous shrimps. In turn, the pleura of the second abdomen presented negative allometry in males but positive
allometry in females. All available information suggests that Pontonia margarita has a socially monogamous mating system with males and females forming exclusive pairs in their hosts. 相似文献
11.
Hana Patzenhauerová Josef Bryja Radim Šumbera 《Behavioral ecology and sociobiology》2010,64(5):757-767
The African mole-rats (Bathyergidae, Rodentia) are subterranean rodents that have evolved a wide range of social organisations
varying from solitary to eusocial. Due to some unusual features of their breeding and social systems, much attention has been
focused on social species, with solitary species being virtually ignored. Here, we present the first genetic study on the
mating system of any solitary mole-rats, the silvery mole-rat (Heliophobius argenteocinereus) - a species which is assumed to be monogamous. Microsatellite markers were used to analyse the mating system and the kinship
structure in populations in southern Malawi. Isolation by distance between individuals was apparent in two studied populations,
but not in the third, probably, as a result of barriers limiting dispersal in the latter population. Polygyny was found to
be a mating system in this population, where a strongly female-biased adult sex ratio was present. In this case, large distances
between the burrow systems of mating partners exclude the possibility of belowground searching for mates, suggesting that
the males might seek females aboveground. Interestingly, among analysed litters from various localities, one multiple-sired
litter was found. Therefore, the results suggest that the mating system in potentially monogamous solitary subterranean rodents
may be much more variable than expected and can differ among populations. 相似文献
12.
In behavioral ecology it is generally assumed that behavior is adaptive. This assumption is tested here for sex ratio manipulation in response to host size in the parasitoid wasp Spalangia cameroni. Females produce a greater proportion of daughters on larger hosts. If this behavior is adaptive, it is not through a positive effect of host size on the fitness of daughters, as theory suggests and as found for other species. Females that developed on larger hosts were not more successful at drilling into hosts, were not more successful at interspecific competition for hosts, and did not have greater dispersal ability as measured by wing loading (weight/area of wing and thorax). The possibility that S. cameroni's sex ratio manipulation may be adaptive through a negative effect of host size on the fitness of sons cannot be ruled out. Relative to males from larger hosts, males from smaller hosts had lower wing loading and thus potentially greater dispersal ability. The actual effect of wing loading on fitness remains to be tested. 相似文献
13.
Julie E. Elie Nicolas Mathevon Clémentine Vignal 《Behavioral ecology and sociobiology》2011,65(12):2197-2208
Same-sex sexual behaviors are well documented in both captive and wild animals. In monogamous species, these behaviors are
often exclusive, each individual having only one same-sex partner. A bias in sex ratio has been proposed as a social context
yielding same-sex pair-bonding, but this hypothesis has rarely been tested. Focusing on a life-long pair-bonding songbird,
the zebra finch Taeniopygia guttata, we tested whether same-sex pairing results from a shortage of individuals of the opposite sex. By experimentally skewing
the sex ratio towards members of one sex, we observed a greater proportion of same-sex pair-bonds of that sex. Moreover, we
assessed whether the quality and stability of social interactions were equivalent in same-sex and male–female pairs. Male–male
and female–female same-sex bonds display the same behavioral characteristics as male–female ones: they are intense, highly
selective, and stable affinitive relationships involving the same behavioral displays already described in wild birds. Moreover,
same-sex male bonds were sufficiently strong not to split up when individuals were given the opportunity to reproduce with
females. Because the pair-bond in socially monogamous species represents a partnership that may give advantages for survival
(e.g., resources defense, fighting against predators, etc.), we propose that same-sex pairing in the zebra finch may result
from the pressure to find a social partner. 相似文献
14.
Haruna Amano Toshiaki Fujita Naoshi Hiramatsu Sayumi Sawaguchi Takahiro Matsubara Craig V. Sullivan Akihiko Hara 《Marine Biology》2007,150(6):1215-1225
Coralliophila abbreviata (Lamarck) is a corallivorous gastropod that lives and feeds on several species of scleractinian coral in the Western Atlantic
and Caribbean. Previous studies of C. abbreviata have revealed that snails on branching acroporid corals are larger and consume more tissue than those on massive and plating
corals. To ascertain whether snail life-history and fitness are differentially affected by the coral host, an analysis of
the age structure and female reproductive output of snail populations on three coral host taxa (Acropora palmata, Diploria spp., and Montastraea spp.) was conducted at four shallow (2–7 m depth) reef sites off Key Largo, Florida in June through August, 2004. Snails
were, on average, almost twice as large on A. palmata than on Diploria spp. and Montastraea spp., averaging 30.3 mm shell length, compared to 17.2 and 17.6 mm, respectively. Brood size increased as a power function
with female shell length. Females on A. palmata were significantly larger than females on the other two hosts and, therefore, produced more offspring per female. The number
of growth striae on the inner surface of the operculum was used to estimate snail age. Estimates of growth rate were obtained
by fitting the Gompertz growth function to size-at-age plots and mortality was estimated using growth parameters and size-frequency
data. The data suggest that C. abbreviata inhabiting A. palmata are larger than on alternative hosts due to a combination of a faster growth rate and longer life-span. The species is believed
to be a protandrous hermaphrodite. The timing of sex change varied among hosts; snails on A. palmata changed sex later at larger sizes relative to those on the other two hosts. Based on these results, it seems probable that
C. abbreviata has developed reaction norms for life-history traits, allowing snails to adjust and maximize fitness in the different environments
associated with various coral hosts. 相似文献
15.
Ludivine de Menten Denis Fournier Colin Brent Luc Passera Edward L. Vargo Serge Aron 《Behavioral ecology and sociobiology》2005,58(6):527-533
Social Hymenoptera are general models for the study of parent-offspring conflict over sex ratio, because queens and workers frequently have different reproductive optima. The ant Pheidole pallidula shows a split distribution of sex ratios with most of the colonies producing reproductives of a single sex. Sex ratio specialization is tightly associated with the breeding system, with single-queen (monogynous) colonies producing male-biased brood and multiple-queen (polygynous) colonies female-biased brood. Here, we show that this sex specialization is primarily determined by the queens influence over colony sex ratio. Queens from monogynous colonies produce a significantly more male-biased primary sex ratio than queens from polygynous colonies. Moreover, queens from monogynous colonies produce a significantly lower proportion of diploid eggs that develop into queens and this is associated with lower rate of juvenile hormone (JH) production compared to queens from polygynous colonies. These results indicate that queens regulate colony sex ratio in two complementary ways: by determining the proportion of female eggs laid and by hormonally biasing the development of female eggs into either a worker or reproductive form. This is the first time that such a dual system of queen influence over colony sex ratio is identified in an ant. 相似文献
16.
Heterospecific matings are generally assumed to be unconditionally disadvantageous due to reduced viability or fertility of
hybrid offspring. For female collared flycatchers (Ficedula albicollis) mated to male pied flycatchers (Ficedula hypoleuca), the cost of heterospecific pair formation is reduced due to high levels of conspecific extra-pair paternity and a male-biased
offspring sex ratio. In order to investigate whether these cost-reducing mechanisms are the result of female mating strategies,
rather than being a by-product of species incompatibilities, we manipulated the plumage of male collared flycatchers before
pair formation to make them resemble male pied flycatchers. Since species incompatibilities are absent in this design, any
systematic effect of manipulation on sex ratio or paternity would indicate a role of female mating strategy. Paternity was
determined by means of a likelihood approach that controls the errors made in assigning a chick to be ‘within-pair’ or ‘extra-pair’.
Neither the sex ratio nor the male share of paternity was affected by the manipulation in a systematic manner. We therefore
conclude that our experimental data provide no support for the suggestion that female behavioural strategies are markedly
adjusted in response to formation of mixed-species pairs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
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
18.
Michler SP Nicolaus M Ubels R van der Velde M Komdeur J Both C Tinbergen JM 《Behavioral ecology and sociobiology》2011,65(10):1975-1986
An individual’s decision to disperse from the natal habitat can affect its future fitness prospects. Especially in species
with sex-biased dispersal, we expect the cost–benefit balance for dispersal to vary according to the social environment (e.g.,
local sex ratio and density). However, little is known about the social factors affecting dispersal decisions and about the
temporal and spatial patterns of the dispersal process. In our study, we investigated experimentally the effects of the social
environment on post-fledging dispersal of juvenile great tits by simultaneously manipulating the density and sex ratio of
fledglings within forest plots. We expected young females in the post-fledging period mainly to compete for resources related
to food and, as they are subordinate to males, we predicted higher female dispersal from male-biased plots. Juvenile males
compete for vacant territories already in late summer and autumn; thus, we predicted increased male dispersal from high density
and male-biased plots. We found that juvenile females had a higher probability to leave male-biased plots and had dispersed
further from male-biased plots in the later post-fledging phase when juvenile males start to become territorial and more aggressive.
Juvenile males were least likely to leave male-biased plots and had smallest dispersal distances from female-biased plots
early after fledging. The results suggest that the social environment differentially affected the costs and benefits of philopatry
for male and female juveniles. The local sex ratio of individuals is thus an important social trait to be considered for understanding
sex-specific dispersal processes. 相似文献
19.
The operational sex ratio (OSR) may influence the intensity of competition for mates and mate choice and is therefore thought
to be a major factor predicting the intensity and direction of sexual selection. We studied the opportunity for sexual selection,
i.e., the variance in male reproductive success and the direction and intensity of sexual selection on male body mass in bank
vole (Clethrionomys glareolus) enclosure populations with experimentally manipulated sex ratios. The opportunity for sexual selection was high among male-biased
OSRs and decreased towards female-biased OSRs. Paradoxically, selection for large male body mass was strongest in female-biased
OSRs and also considerable at intermediate OSRs, whereas at male-biased OSRs, only a weak relationship between male size and
reproductive success was found. Litters in male-biased OSRs were more likely to be sired by multiple males than litters in
female-biased OSRs. Our results suggest that the intensity and direction of sexual selection in males differs among different
OSRs. Although the direction of sexual selection on male body mass was opposite than predicted, large body mass can be favored
by sexual selection. Naturally varying OSRs may therefore contribute to maintain variation in male sexually selected traits. 相似文献
20.
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