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1.
Uller T Massot M Richard M Lecomte J Clobert J 《Evolution; international journal of organic evolution》2004,58(11):2511-2516
Maternal effects and early environmental conditions are important in shaping offspring developmental trajectories. For example, in laboratory mammals, the sex ratio during gestation has been shown to influence fitness-related traits via hormonal interaction between fetuses. Such effects have the potential to shape, or constrain, many important aspects of the organism's life, but their generality and importance in natural populations remain unknown. Using long-term data in a viviparous lizard, Lacerta vivipara, we investigated the relationship between prenatal sex ratio and offspring growth, survival, and reproductive traits as adults. Our results show that females from male-biased clutches grow faster, mature earlier, but have lower fecundity than females from female-biased clutches. Furthermore, male reproduction was also affected by the sex ratio during embryonic development, with males from male-biased clutches being more likely to successfully reproduce at age one than males from female-biased clutches. Thus, the sex ratio experienced during gestation can have profound and long-lasting effects on fitness in natural populations of viviparous animals, with important implications for life-history evolution and sex allocation. 相似文献
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V. N. Evdokimova T. V. Nikitina I. N. Lebedev N. N. Sukhanova S. A. Nazarenko 《Russian Journal of Developmental Biology》2000,31(4):204-210
The problem of the functioning specificity of sex chromosomes during the early stages of embryogenesis in man and the associated
problem of the sex ratio in spontaneous and induced abortions, as well as in newborns, remains open. We have conducted a cytogenetic
examination of 342 spontaneous abortions divided into three clinical groups on the basis of the severity of the developmental
disturbances of the embryo: spontaneous abortionssensu stricto with a developed embryo without any significant intrauterine delay of development (n=100), nondeveloping pregnancies (n=176), and anembryonic fetuses (n=66). The frequency of chromosomal mutations in these groups was 22.0, 48.3, and 48.5%, respectively. Statistical analysis
has demonstrated significant differences between the studied groups in the frequencies of the normal and abnormal karyotypes:
the major contributions to these differences were associated with autosomal trisomy, triploidy, and the 46.XY karyotype. The
presence of 46.XY may reflect the specific genetic mechanisms of the prenatal mortality of embryos with the normal karyotype,
associated with sex and/or with the imprinting of X-chromosomes. The sex ratio in spontaneous abortions with the normal karyotype
was as follows: 0.77 for spontaneous abortions with well-developed embryos without any significant intrauterine delay of development;
0.60 for nondeveloping pregnancies; and 0.31 for anembryonic fetuses. An analysis of DNA from the embryos and their parents
has demonstrated a low probability of contamination of cell cultures with mother cells as a possible source of the prevalence
of embryos with the 46.XX karyotype among spontaneous abortions. Nondeveloping pregnancies and anembryonic fetuses showed
statistically significant differences in the sex ratio from the control group consisting of medical abortions (1,11). Differences
in the sex ratio were due to an increasingly lower proportion of embryos with karyotype 46.XY (relative to the expected one)
among the fetuses with an increased severity of developmental disturbances. The statistical “chances ratio” index also provided
evidence that embryos with the 46.XY karyotype had a higher propensity to produce a well-formed fetus as compared with the
female embryos. We propose that the expression of genes of the maternal X-chromosome in XY embryos supports a more stable
development during early embryogenesis as compared with XX embryos. In the latter case, normal development is coupled with
the operation of an additional mechanism for compensation of the dose of X-linked genes. Operation of this mechanism increases
the probability of disturbances in female embryos. A higher viability of XY embryos during the early stages of ontogenesis
in man appears to explain their underrepresentation in samples of spontaneously aborted embryos and appears to be the major
factor responsible for the deviation of the sex ratio from the theoretically expected value. 相似文献
4.
Adam J. Lawrance-Owen Gary Bargary Jenny M. Bosten Patrick T. Goodbourn Ruth E. Hogg J. D. Mollon 《Human genetics》2013,132(4):415-421
Men and women differ statistically in the relative lengths of their index and ring fingers; and the ratio of these lengths has been used as a biomarker for prenatal testosterone. The ratio has been correlated with a wide range of traits and conditions including prostate cancer, obesity, autism, ADHD, and sexual orientation. In a genome-wide association study of 979 healthy adults, we find that digit ratio is strongly associated with variation upstream of SMOC1 (rs4902759: P = 1.41 × 10?8) and a meta-analysis of this and an independent study shows a probability of P = 1.5 × 10?11. The protein encoded by SMOC1 has recently been shown to play a critical role in limb development; its expression in prostate tissue is dependent on sex hormones, and it has been implicated in the sexually dimorphic development of the gonads. We put forward the hypothesis that SMOC1 provides a link between prenatal hormone exposure and digit ratio. 相似文献
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In hermaphroditic fishes, the initiation of sex reversal by male removal explains the replacement of lost males but does not explain how the number of males in a group may increase. Since numerous species apparently cannot produce primary males, a second means of initiating sex reversal must exist. In the present study we formulate a model which suggests the existence of an additional mechanism governing sex change: as soon as the ratio of adult females to males within a group exceeds a certain threshold value, a female changes sex even though no male has been removed. This process is inferred from comparison of data collected in the Red Sea and the western Indian Ocean with the model's predictions concerning size at sex reversal and the sex ratio of groups. The results suggest how several ecological factors may influence the occurrence rate of sex reversal and the development and growth of social groups. 相似文献
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Secondary sex ratio in mice 总被引:1,自引:0,他引:1
9.
J. Timson 《Genetica》1970,41(1):457-465
It is shown that the well known excess of females in anencephalic births is statistically significant when compared with (a) the general population and (b) their normal sibs.There is also a statistically significant difference between the sex ratio of anencephalic births and that of spina bifida births which suggests that there is a definite difference in the genetic component of their aetiology.These results are discussed with reference to the genetics of anencephaly and spina bifida and a genetic model of the inheritance of the genetic component of anencephaly is given. The significance of a possible cytoplasmic factor is also considered. 相似文献
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Abstract 1. Hylaeus alcyoneus is an endemic solitary bee common on coastal heaths of Western Australia. The bee is unusual in that males are larger than females. This size dimorphism presents an opportunity to test the theory of resource-dependent sex allocation, in which theory predicts that when resources are low the sex ratio should be biased towards the smaller sex. In most bees, females are larger than males and, in line with theoretical prediction, sex ratios are male biased when resources are scarce.
2. The emerging sex ratio and brood mass from a natural population of H. alcyoneus using trap nests was studied over two seasons (1999, 2000). A switch from a male- to a female-biased sex ratio through the season was found, which was related to a reduced floral resource.
3. Fisherian sex ratio theory predicts that total investment in each sex throughout a season should be equal and that the sex ratio should be biased towards the smaller sex. By measuring the mass of the emerging progeny, the total investment was found to favour males. Possible explanations for this bias in investment are discussed. 相似文献
2. The emerging sex ratio and brood mass from a natural population of H. alcyoneus using trap nests was studied over two seasons (1999, 2000). A switch from a male- to a female-biased sex ratio through the season was found, which was related to a reduced floral resource.
3. Fisherian sex ratio theory predicts that total investment in each sex throughout a season should be equal and that the sex ratio should be biased towards the smaller sex. By measuring the mass of the emerging progeny, the total investment was found to favour males. Possible explanations for this bias in investment are discussed. 相似文献
12.
Intragenomic conflict produces sex ratio dynamics that favor maternal sex ratio distorters
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Maternal sex ratio distorters (MSDs) are selfish elements that enhance their transmission by biasing their host's sex allocation in favor of females. While previous models have predicted that the female‐biased populations resulting from sex ratio distortion can benefit from enhanced productivity, these models neglect Fisherian selection for nuclear suppressors, an unrealistic assumption in most systems. We used individual‐based computer simulation modeling to explore the intragenomic conflict between sex ratio distorters and their suppressors and explored the impacts of these dynamics on population‐level competition between species characterized by MSDs and those lacking them. The conflict between distorters and suppressors was capable of producing large cyclical fluctuations in the population sex ratio and reproductive rate. Despite fitness costs associated with the distorters and suppressors, MSD populations often exhibited enhanced productivity and outcompeted non‐MSD populations in single and multiple‐population competition simulations. Notably, the conflict itself is beneficial to the success of populations, as sex ratio oscillations limit the competitive deficits associated with prolonged periods of male rarity. Although intragenomic conflict has been historically viewed as deleterious to populations, our results suggest that distorter–suppressor conflict can provide population‐level advantages, potentially helping to explain the persistence of sex ratio distorters in a range of taxa. 相似文献
13.
Miguel A. Toro 《Journal of theoretical biology》1982,95(2):305-311
Using precise genetic models, the evolution of the sex ratio in a population in which interactions between siblings exist but these interactions are not symmetrical with respect to the sexes has been studied. Some interesting differences between co-operative and aggressive models have emerged. 相似文献
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Hormonal control of sex ratio 总被引:6,自引:0,他引:6
W H James 《Journal of theoretical biology》1986,118(4):427-441
It has been hypothesized that the maternal gonadotrophin level at the time of conception is causally related to the sex of the resultant human zygote, high levels of hormone being associated with the production of female offspring. In this note, evidence for and against this hypothesis is reviewed. There seems so much evidence in its favour that one might conclude that it contains at least a kernel of truth. It is suggested here that of the components of gonadotrophin, the active one in this hypothesized sex-selective process is luteinizing hormone, rather than follicle-stimulating hormone. The hypothesis is nevertheless unable to accommodate several well-established sets of data. Accordingly it is suggested that other hormones, oestrogen and testosterone, have sex-selective properties too, high levels being associated with male offspring. This elaboration of the hypothesis, if it were true, would explain most, if not all, of the epidemiological data on the human secondary sex ratio. In particular it would explain Guerrero's data which have hitherto resisted explanation of any kind. No suggestion is made about possible mechanisms underlying these hypothesized sex-selective properties. But it seems that sex-selective abortion is not the only one. It is hoped that other workers may be stimulated not only to test the hypothesis as outlined here, but--if it survives this testing--to suggest such mechanisms. 相似文献
16.
The allocation of resources to male and female progeny is a major component of the reproductive strategies of all sexual plants and animals. Over the past 30 years there has been intensive theoretical and experimental investigation of how natural selection moulds the sex ratio. Here, we discuss recent exciting developments and new applications of sex allocation theory and highlight some unresolved issues. 相似文献
17.
Nandan G 《BMJ (Clinical research ed.)》1993,306(6874):353
18.
To our knowledge, there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, more males hatch at low incubation temperatures and more females hatch at high temperatures, whereas the proportion is 1:1 at the average temperature found in natural mounds. Chicks from lower temperatures weigh less, which probably affects offspring survival, but are not smaller. Megapodes possess heteromorphic sex chromosomes like other birds, which eliminates temperature-dependent sex determination, as described for reptiles, as the mechanism behind the skewed sex ratios at high and low temperatures. Instead, our data suggest a sex-biased temperature-sensitive embryo mortality because mortality was greater at the lower and higher temperatures, and minimal at the middle temperature where the sex ratio was 1:1. 相似文献
19.
The sex ratio in ectoparasitic insects 总被引:2,自引:0,他引:2
ADRIAN G. MARSHALL 《Ecological Entomology》1981,6(2):155-174
Abstract. 1. The sex ratio in 379 collections, each consisting of more than 100 individuals, of 250 different species of ectoparasite belonging to seven orders of insects is recorded. The data are gathered from a broad survey of published literature.
2. In general, ectoparasitic insects emerge as adults in equal numbers of each sex, although there are certain exceptions.
3. The sex ratio in natural populations may alter with numerous factors, but in general it is unbalanced, females usually predominating. Out of 359 collections from the host's body or home, the sex ratio of 30% showed no significant departure from unity, 63% contained significantly more females, and 7% significantly more males.
4. These imbalances could be due to sampling methods but this is rare. Generally they are due to one sex, usually the male, being shorter lived than the other. This may be because males are often more active and smaller than females, and thus more likely to be separated from the host's body or home, succumb to host predation, or be killed by adverse climatic or nutritional conditions. 相似文献
2. In general, ectoparasitic insects emerge as adults in equal numbers of each sex, although there are certain exceptions.
3. The sex ratio in natural populations may alter with numerous factors, but in general it is unbalanced, females usually predominating. Out of 359 collections from the host's body or home, the sex ratio of 30% showed no significant departure from unity, 63% contained significantly more females, and 7% significantly more males.
4. These imbalances could be due to sampling methods but this is rare. Generally they are due to one sex, usually the male, being shorter lived than the other. This may be because males are often more active and smaller than females, and thus more likely to be separated from the host's body or home, succumb to host predation, or be killed by adverse climatic or nutritional conditions. 相似文献
20.
J. Timson 《Genetica》1969,40(1):427-433
It is shown that the well known excess of females in spina bifida children is statistically significant when they are compared with (a) the general population and (b) their sibs.Although there is a small excess of males amongst the sibs this is not statistically significant when compared with the general population and when all the children in these families are considered they appear to have a sex ratio very similar to that general population. The sibs of the parents of spina bifida children show a statistically significant excess of females.These findings are discussed with particular reference to the genetics of spina bifida. 相似文献