Normal development of fetuses resulting from Holstein semen processed for sex separation

Semen from two high fertility Holstein bulls with extensive histories in artificial insemination was specially processed for the purpose of sexing and then frozen. The semen was used to inseminate 200 open crossbred beef heifers carefully selected for reproductive soundness from a much larger group. Animals were inseminated alternately with the semen from one of the two bulls and subsequently slaughtered. There were 96 fetuses, ranging in age from 63 to 88 days, which were carefully examined for general appearance, fetal crown-rump length and body weight. There was no effect of sire on fetal size, but the difference between fetal sexes was significant, with the male fetus being appreciably heavier. The regression of fetal length on fetal age was linear and the regression of fetal weight on fetal age was curvilinear. Fetal age accounted for 92% to 96% of the variation in fetal weight and also in crown-rump length.     

Experimental demonstration that pre- and post-conceptional mechanisms influence sex ratio in mouse embryos

Previously we have demonstrated in two monotocous species (bovine and sheep), a relationship between time of insemination, moment of ovulation, and embryo sex ratio. Here, we have analyzed in a polytocous specie (mice) if in addition to pre-conceptional mechanisms, also post-conceptional ones affect the offspring sex ratio. To verify this hypothesis we carried out two experiments. In the first experiment, we analyzed the effect of mating dynamics on the sex ratio of mice with synchronic male and female embryo development. Females were mated before and after ovulation and sacrificed 13 days later for sex determination of embryos and reabsorptions. A decreased litter size, and an increased offspring sex ratio in matings occurring later in oestrus, supported the view that a biased sex ratio may occur as the result of behavioral differences between the populations of X- or Y-bearing spermatozoa. In the second experiment, embryos developmentally synchronic and asynchronic with the recipient female endometrium were transferred, and again, 13 days later, females were sacrificed for sex determination of embryos and reabsorptions. The male proportion per litter found, indicated that our developmentally asynchronic transfers favored a sex ratio disbalance at birth. When combined, these results become the first experimental evidence supporting the view that both pre- and post-conceptional mechanisms of sex ratio distortion in polytocous species are not mutually exclusive and both may explain, under different conditions, sex ratio deviations at birth.     

Altered sex ratio of live young after transfer of fast- and slow-developing mouse embryos

We cultured eight-cell mouse embryos to blastocyst stage, divided them into three groups according to the time of blastocoel formation, and transferred them separately into recipients. The proportion of live young from the fast-developing embryos was slightly high (49%) but not significantly different from those of other embryos (38% and 39%). However, the sex ratio of live young from the fast- and slow-developing embryos was significantly shifted toward the male (71%) and to the female (80%), respectively.     

蜜蜂性别决定与性比调控机理研究

叙述了 4个主要蜜蜂性别决定机理的假说 :即性位点假说、基因平衡假说、蜜蜂性别决定综合假说和性基因数量决定假说。然后就蜜蜂性比由蜂王操纵 ,或是由工蜂操纵进行了论述 ,并对蜜蜂性比调控机理研究提出了一些建议     

Long-term fitness benefits of egg sex modification by the Seychelles warbler

Sex-ratio theory states that if the fitness costs to the parents of producing one offspring's sex relative to the other are higher, parents should discount these costs by producing fewer individuals of the more costly sex. In the co-operatively breeding Seychelles warbler (Acrocephalus sechellensis) mothers adaptively modify the sex of their single egg toward daughters, the helping sex, when living on territories with rich resources where helpers increase parental reproductive success, but toward sons, the dispersing sex, when living on territories where resources are scarce and/or no helping benefits accrue. By modifying offspring sex ratio, parents maximize their inclusive fitness benefits. Pairs in high-quality territories gained significantly more inclusive fitness benefits (through helping and reproducing offspring) from the production of daughters than from sons, and vice versa in low-quality territories (through reproducing offspring). Experimental manipulation of the offspring's sex shows that the consequences of sex allocation are adaptive for parents on high-quality territories. On high-quality territories with female production, breeding pairs raising step-daughters gained significantly higher inclusive benefits (through indirect and direct fitness gains) than by raising step-sons.     

Whisker exploration behaviours in the 5xFAD mouse are affected by sex and retinal degeneration

Active whisking in mice and rats is one of the fastest behaviours known in mammals and is used to guide complex behaviours such as exploration and navigation. During object contact, whisker movements are actively controlled and undergo robust changes in timing, speed and position. This study quantifies whisker movements in 6‐ to 7‐month old male and female 5xFAD mice, and their C57/SJL F1 wild‐type (WT) controls. As well as genotype, we examined sex differences and the effects of retinal degeneration (rd). Mice were filmed using a high‐speed video camera at 500 frames per second (fps), under infrared light while behaving freely in three tasks: object exploration, sequential object exploration and tunnel running. Measures of whisker position, amplitude, speed and asymmetry were extracted and analysed for each task. The 5xFAD mice had significantly altered whisker angular positions, amplitude and asymmetry during object contacts and female 5xFAD mice with rd had lower mean angular positions during object contact. There were no significant effects of genotype on sequential object exploration or on tunnel running but differences due to sex and rd were found in both tasks, with female mice making larger and faster whisker movements overall, and mice with rd making larger and faster whisker movements during object contact. There were sex differences in whisker movements during sequential object exploration and females with rd had higher whisker retraction speeds in tunnel running. These data show that measuring whisker movements can quantify genotype and sex differences and the effects of rd during exploratory behaviour in these mice.     

Heritable variation of sex ratio in a polychaete worm

Ophryotrocha labronica is a gonochoristic polychaete worm whose sex determining mechanism and sex ratio control are supposed to be polygenic. From a lab population, whose sex ratio (i.e., proportion of males) was 0.5, the estimate of sex ratio heritability by offspring-father regression was 0.54 ± 0.15 and by offspring-mother regression was not significantly different from 0. Estimate of sex ratio repeatability between successive broods of a pair was 0.64 ± 0.33. Since female parents do not contribute in any way to the variability of sex ratio, sex ratio variation seems to be largely a paternal character. On the basis of these estimates we advance the hypothesis that in this species sex is determined by a multilocus genetic system, allowing the combined effects of a female major sex gene (which could give rise to a form of female heterogamety) and masculinizing modifiers. The hypothesis that the male sex has the least canalised sexual differentiation is supported by the observation that some old males developed oocytes.     

Developmental appearance of proteins identified by two-dimensional gel electrophoresis in mouse gonadal tissue

Gonadal protein patterns of the mouse were studied during fetal development by two-dimensional gel electrophoresis. Fetal mice at days 8.5, 10.5, 12.5, and 14.5 post-coitum were analyzed for male or female specific proteins. Although no sex specific proteins were found, several proteins were found which were expressed in significantly different amounts in the two sexes at about the time of gonadal differentiation. Hence, quantitative differences, rather than qualitative ones, could be related to the initiation of testis or ovary development.     

A model for environmental sex reversal in fish

A mathematical model is presented which combines genetic XX-female/XY-male sex determination with environmental pressure for phenotypic sex reversal. This may occur when fishes are exposed to endocrine disrupters, specifically masculinization by exposure to androgens and feminization by exposure to estrogens. A generic model is derived for the sex ratio in successive generations and three special cases, with chronic and constant pressure to sex reverse, are discussed in detail. These show that, with extreme environmental pressure to masculinize, the male genotype is at risk of dying out but with less extreme pressure, masculinization will not be detectable since the proportion of phenotypic males becomes one-half. With feminization at any pressure to sex reverse, the male and female genotypes will be maintained in a stable sex ratio in which the proportion of genotypic males exceeds one-half and is close to one-half if YY offspring (eggs) are not viable. In converse, the model is also applicable to the genetic ZZ-male/ZW-female system of sex determination in fish. At present suitable data are not available with which to validate the model, but proposals are made for relevant experimental studies.     

Intragenomic conflict produces sex ratio dynamics that favor maternal sex ratio distorters

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.     

Environmental sex reversal,Trojan sex genes,and sex ratio adjustment: conditions and population consequences

The great diversity of sex determination mechanisms in animals and plants ranges from genetic sex determination (GSD, e.g. mammals, birds, and most dioecious plants) to environmental sex determination (ESD, e.g. many reptiles) and includes a mixture of both, for example when an individual’s genetically determined sex is environmentally reversed during ontogeny (ESR, environmental sex reversal, e.g. many fish and amphibia). ESD and ESR can lead to widely varying and unstable population sex ratios. Populations exposed to conditions such as endocrine‐active substances or temperature shifts may decline over time due to skewed sex ratios, a scenario that may become increasingly relevant with greater anthropogenic interference on watercourses. Continuous exposure of populations to factors causing ESR could lead to the extinction of genetic sex factors and may render a population dependent on the environmental factors that induce the sex change. However, ESR also presents opportunities for population management, especially if the Y or W chromosome is not, or not severely, degenerated. This seems to be the case in many amphibians and fish. Population growth or decline in such species can potentially be controlled through the introduction of so‐called Trojan sex genes carriers, individuals that possess sex chromosomes or genes opposite from what their phenotype predicts. Here, we review the conditions for ESR, its prevalence in natural populations, the resulting physiological and reproductive consequences, and how these may become instrumental for population management.     

About the sex ratio in connection with early embryonic mortality in man

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.     

Complex sex allocation in the laughing kookaburra

In groups of the cooperatively breeding laughing kookaburra(Dacelo novaeguineae), offspring sex varied with the type ofsocial group and with hatch rank. Groups with female helpers,especially if all helpers were female, had male-biased clutchand fledging sex ratios. Groups without female helpers (unassistedpairs or male-only helpers) had female-biased clutch and fledgingsex ratios. Breeding females responded facultatively to increasesin the number of female helpers in their group by producingmore male eggs. These biases may occur if breeding femalestry to limit the number of daughters recruited into their groupbecause unlike male helpers, female helpers depress the breedingsuccess of their parents. Across all nests, two-thirds of first-hatchedyoung were male, two-thirds of second-hatched young were female, and the sex ratio of third-hatched young was even. Hatch ranksex ratios also varied dramatically between different typesof social groups, from 16.7% for second-hatched nestlings ofunassisted pairs to 100% for first-hatched nestlings of groupswith only female helpers. A corollary of the relationship betweenhatch rank and sex was that hatching sex sequences were distributed nonrandomly: all groups avoided hatching a daughter first followedby a son (FM). Sibling competition is aggressive and sometimesfatal. Since females grow to be 15% larger than males the hatchingsequence of sexes could affect nestling growth and mortality.However, an exhaustive analysis found little evidence thatgrowth or survival of males was compromised if hatched aftera sister. The small number of FM sequences may only have occurredin nests that were able to ameliorate any negative consequences.Alternatively, when clutch size is small and fledging successunpredictable because of brood reduction, the preferred broodsex ratio may be contingent on the number of fledged young,making it advantageous to order the sexes in the brood.     

Sex choice in plants: facultative adjustment of the sex ratio in the perennial herb Begonia gracilis

Sex allocation theory predicts that reproducing individuals will increase their fitness by facultatively adjusting their relative investment towards the rarer sex in response to population shifts in operational sex ratio (OSR). The evolution of facultative manipulation of sex ratio depends on the ability of the parents to track the conditions favouring skewed sex allocation and on the mechanism controlling sex allocation. In animals, which have well-developed sensorial mechanisms, facultative adjustment of sex ratios has been demonstrated on many occasions. In this paper, we show that plants have mechanisms that allow them to evaluate the population OSR. We simulated three different conditions of population OSR by manipulating the amount of pollen received by the female flowers of a monoecious herb, and examined the effect of this treatment on the allocation to male vs. female flowers. A shortage of pollen on the stigmas resulted in a more male-skewed sex allocation, whereas plants that experienced a relatively pollen rich environment tended to produce a more female-skewed sex allocation pattern. Our results for Begonia gracilis demonstrate that the individuals of this species are able to respond to the levels of pollination intensity experienced by their female flowers and adjust their patterns of sex allocation in accordance to the expectations of sex allocation theory.     

Hyperglycemia-induced apoptosis affects sex ratio of bovine and murine preimplantation embryos

The effect of glucose in the medium used during in vitro culture on both cell death by apoptosis and the sex ratio of bovine blastocysts derived from in vitro-matured and in vitro-fertilized oocytes was evaluated. Oocytes were matured, inseminated, and cultured in vitro in mSOF medium with 10% FCS with or without glucose supplementation. Exposure to high concentrations of glucose (10, 20, and 30 mM) during bovine embryo development in vitro from zygote to blastocyst resulted in a decrease in the number of cells per embryo and an increase in the frequency of apoptotic cells. A significantly higher proportion of females was found among those embryos that developed under hyperglycemic conditions in vitro. Moreover, both murine and bovine blastocysts incubated for 6 hr in 20 mM glucose had a significantly higher number of apoptotic cells in comparison to control. In this study, we also determined whether blastocyst production of the X-linked inhibitor of apoptosis protein (XIAP) differs between the sexes. Our results show that female bovine blastocysts produce significantly higher amounts of XIAP mRNA than males and this could be crucial in explaining the higher proportion of female blastocysts observed following in vitro culture under hyperglycemic conditions which induce apoptosis. Moreover, a higher proportion of female murine blastocysts cultured under hyperglycemic conditions were implanted in the uterus (65.3 of implantations from embryos cultured with 20 mM of glucose are females vs. 49% in control). This mechanism provides an explanation for the significant reduction of male children born to diabetic mothers.     

Brood sex ratio determination by flow cytometry in ants

Sex ratio variations during brood development have important implications for the study of sex allocation in haplodiploid insects. So far, few studies have addressed this question because of the difficulty to determine the sex of the brood. We used flow cytometry to differentiate haploid males from diploid females in the ant Linepithema humile. Our data show that flow cytometry can be used successfully to distinguish between male and female brood on the basis of their DNA content, from the very first larval stage. Moreover, we show that flow cytometry allows sex brood determination in other ant species, as well as in nonsocial Hymenoptera.     

Biased sex ratios in the dioecious annual Croton texensis (Euphorbiaceae) are not due to environmental sex determination

At Arapaho Prairie, in the sandhills of western Nebraska, the dioecious annual Croton texensis (Euphorbiaceae) exhibits biased sex ratios. Moreover, the direction of bias changes from year to year: in 1994 the study population was significantly female biased, in 1995 and 1996 it was significantly male biased, and in 1997 and 1998 the sex ratio did not differ from 1 : 1. Such variation in the observed sex ratio in plants is frequently attributed to environmental sex determination (ESD), which is favored by natural selection if the rate of fitness gain across an environmental gradient is greater for one sex than the other. We performed experiments to determine: (1) whether variation in the sex ratio is correlated with environmental conditions, as would be expected if ESD is operating, and (2) whether ESD, if present, would be favored by natural selection. In a common garden experiment in which water and fertilizer were manipulated the sex ratio was marginally male biased in treatments in which water was added, but not different from 1 : 1 in other treatments. In field plots into which seeds were planted none of several soil characteristics, nor overall plot quality for C. texensis (measured as average plant biomass) were correlated with plot sex ratio. However, plots in which a large number of planted seeds emerged tended to be female biased. These results provide very weak evidence for sex ratio bias across an environmental gradient, and thus provide little evidence for ESD. Moreover, sex-by-environment interactions for fitness, which are required for the evolution of ESD, were absent for all measured variables. Thus, ESD does not appear to be favored by natural selection in this population. Instead, these biases may have been caused by differences between the sexes in germination and/or early mortality.     

Precision in sex allocation is influenced by mate choice in Drosophila melanogaster

Theory predicts that a 1 : 1 sex ratio is favoured in the absence of countervailing selection pressures. In an experiment with Drosophila melanogaster, we found significantly greater variation in the offspring sex ratios of freely mated flies than would be expected by the binomial distribution. In a surprise result, control flies given no mate choice exhibited significant under-dispersal in their sex ratio variation, possibly from sperm limitation. Both treatments, however, produced populations with a 1 : 1 sex ratio. This supports the hypothesis that sexually antagonistic selection for reproductive success in sons, and fecundity in daughters, may overcome selection for an equal sex ratio. Such precision in sex allocation may allow for the maintenance of genetic variation underlying trade-offs between male and female reproductive success.     

Reproducing lizards modify sex allocation in response to operational sex ratios

Sex-allocation theory suggests that selection may favour maternal skewing of offspring sex ratios if the fitness return from producing a son differs from that for producing a daughter. The operational sex ratio (OSR) may provide information about this potential fitness differential. Previous studies have reached conflicting conclusions about whether or not OSR influences sex allocation in viviparous lizards. Our experimental trials with oviparous lizards (Amphibolurus muricatus) showed that OSR influenced offspring sex ratios, but in a direction opposite to that predicted by theory: females kept in male-biased enclosures overproduced sons rather than daughters (i.e. overproduced the more abundant sex). This response may enhance fitness if local OSRs predict survival probabilities of offspring of each sex, rather than the intensity of sexual competition.     

Heritability of sex tendency in a harpacticoid copepod,Tigriopus californicus

Abstract.— Systems with genetic variation for the primary sex ratio are important for testing sex-ratio theory and for understanding how this variation is maintained. Evidence is presented for heritable variation of the primary sex ratio in the harpacticoid copepod Tigriopus californicus. Variation in the primary sex ratio among families cannot be accounted for by Mendelian segregation of sex chromosomes. The covariance in sex phenotype between full-sibling clutches and between mothers and offspring suggests that this variation has a polygenic basis. Averaged over four replicates, the full-sibling heritability of sex tendency is 0.13 ± 0.040; and the mother-offspring heritability of sex tendency is 0.31 ± 0.216. Genetic correlations in the sex phenotype across two temperature treatments indicate large genotype-by-temperature interactions. Future experiments need to distinguish between zygotic, parental, or cytoplasmic mechanisms of sex determination in T. californicus.