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PubMed1994

Gene-culture coevolution and sex ratios: the effects of infanticide, sex-selective abortion, sex selection, and sex-biased parental investment on the evolution of sex ratios.

The evolutionary consequences of culturally transmitted practices that cause differential mortality between the sexes, thereby distorting the sex ratio (e.g., female infanticide and sex-selective abortion), are explored using dynamic models of gene-culture coevolution. We investigate how a preference for the sex of offspring may affect the selection of genes distorting the primary sex ratio. Sex-dependent differences in mortality have been predicted to select for a male- or female-biased primary sex ratio, to have no effect, or to favor either under different circumstances. We find that when a mating pair's behavior modifies mortality rates in favor of one sex, but does not change the number of offspring produced in the mating, the primary sex ratio will evolve a bias against the favored sex. However, when the total number of offspring of a mating pair is significantly reduced as a consequence of their prejudice, the primary sex ratio will evolve to favor the preferred sex. These results hold irrespective of whether the sex ratio is distorted by the mother's, the father's or the individual's own autosomal genes. The use of dynamic models of gene-culture coevolution allows us to explore the evolution of alleles which distort the sex ratio, as well as the final equilibrium states of the system. Gene-culture interactions can provide equilibria different from those in purely genetic systems, slow the approach to these equilibria by orders of magnitude, and move the primary (PSR) and the adult sex ratio (ASR) away from any stable equilibrium for hundreds of generations.

Abortion, Induced↗

PubMed2001

Sex chromosomes, sex-linked genes, and sex determination in the vertebrate class amphibia.

In this chapter the different categories of homomorphic and heteromorphic sex chromosomes, types of sex-determining mechanisms, known sex-linked genes, and data about sex-determining genes in the Amphibia have been compiled. Thorough cytogenetic analyses have shown that both XY/XX and ZW/ZZ sex chromosomes exist in the order Anura and Urodela. In some species quite unusual systems of sex determination have evolved (e.g. 0W-females/00-males or the co-existence of XY/XX and ZW/ZZ sex chromosomes within the same species). In the third order of the Amphibia, the Gymnophiona (or Apoda) there is still no information regarding any aspect of sex determination. Whereas most species of Anura and Urodela present undifferentiated, homomorphic sex chromosomes, there is also a considerable number of species in which an increasing structural complexity of the Y and W chromosomes exists. In various cases, the morphological differentiation of the sex chromosomes occurred as a result of quantitative and/or qualitative changes to the repetitive DNA sequences in the constitutive heterochromatin of the Y and W chromosomes. The greater the structural differences between the sex chromosomes, the lesser the extent of pairing in meiosis. No dosage compensation of the sex-linked genes in the somatic cells of the homogametic (XX or ZZ) individuals have been detected. The genes located to date on the amphibian sex chromosomes lead to the conclusion that there is no common ancestral or conserved sex-linkage group. In all amphibians, genetic sex determination (GSD) seems to operate, although environmental factors may influence sex determination and differentiation. Despite the accumulated evidence that GSD is operating in Anura and Urodela, there is little substantial information about how it functions. Although several DNA sequences homologous to the mammalian ZFY, SRY and SOX genes have been detected in the Anura or Urodela, none of these genes is an appropriate candidate to explain sex determination in these vertebrates.

Amphibians↗

PubMed1994

Effects of sex and sex roles on avoidance of same- and opposite-sex touch.

Touch and touch avoidance are important facets of interpersonal relations. Touch avoidance has been related to sex, but the relationship between touch and sex roles has not been widely substantiated. 259 undergraduate students participated in a procedure designed to test the relationship between sex, sex roles, and same-sex and opposite-sex touch avoidance. Significant differences were reported between men and women on same-sex touch avoidance but not on opposite-sex touch avoidance. Participants high on androgyny reported less same-sex and opposite-sex touch avoidance than did subjects low on androgyny. No interactive effect between sex and androgyny was found for either same-sex or opposite-sex touch avoidance. Regression procedures indicated predictive models for sex and androgyny in relation to same-sex and opposite-sex touch avoidance. Specific conclusions regarding the relationships among sex, androgyny, and touch avoidance were stated.

Female↗

PubMed1994

Sex differences, sex ratios and sex roles.

Sexual selection theory predicts that sex roles will be determined by the operational sex ratio (OSR), the sex ratio among individuals searching for mates at any given time. There are two predictions: (i) the sex which is in 'excess' will be the more competitive sex with respect to access to mates; and (ii) the sex of which there is a 'shortage' will be the more choosy with respect to potential partners. We examine the second prediction and find that current OSR theory does not consider an important factor which affects mate choice. This factor is sex differences in variation in mate quality. Hence, we develop a new model of mate choice which shows that the parameter which should be optimized during mate choice is the trade-off between reproductive rate and mate quality. If mate choice is too lax, reproductive rate may be high but partners will be of low quality. If mate choice is too stringent, partners will be of high quality but reproductive rate will be low because such partners will be rare. Stringency of mate choice is, therefore, a facet of OSR theory. Indeed, our model shows that OSR theory can be used to integrate the effect of sex differences in both mating rate and variation in mate quality to predict the direction of mate choice. Our model suggests that: (i) mate choice is only selected when individuals of the opposite sex vary in their quality as mates; (ii) if the extent of variation in mate quality is equal within each sex, the sex with the lower potential mating rate will be the more choosy sex; but (iii) if there is sufficiently greater variation in mate quality among the sex with the lower potential reproductive rate, the sex with the higher potential mating rate will be the more choosy sex.(ABSTRACT TRUNCATED AT 250 WORDS)

Game Theory↗

PubMed1997

Gene-culture coevolution and sex ratios: II. Sex-chromosomal distorters and cultural preferences for offspring sex.

Cultural preferences for the sex of offspring may produce behavior, such as female infanticide, sex-selective abortion and sex-selective parental investment, which alter the sex ratio in a population. Empirical evidence suggests that some genetic sex-ratio distorters are located on the sex chromosomes. Interactions between cultural preferences and sex-linked sex-ratio distorters are examined. Criteria for the spread of cultural preferences and sex-chromosomal distorter alleles are derived analytically, and the coevolution of preferences and distorters is examined through numerical iteration. Evolutionary equilibria and trajectories of gene-culture interactions involving sex-chromosomal distorter alleles may produce severely male- or female-biased primary sex ratios and adult sex ratios in populations. Adult sex ratios, primary sex ratios, allele frequencies and the prevalence of cultural preferences in the population are sensitive to initial conditions and cultural transmission parameters. During the coevolutionary process phenoallelic association is observed in many cases and is associated with unusual dynamics.

Adult↗

PubMed1997

Gene-Culture Coevolution and Sex Ratios: II. Sex-Chromosomal Distorters and Cultural Preferences for Offspring Sex

Journal Article↗

PubMed2001

Sex from W to Z: evolution of vertebrate sex chromosomes and sex determining genes.

Sex determination in major vertebrate groups appears to be very variable, including systems of male heterogamety, female heterogamety and a variety of genetic and environmental sex determining systems. Yet comparative studies of sex chromosomes and sex determining genes now suggest that these differences are more apparent than real. The sex chromosomes of even widely divergent groups now appear to have changed very little over the last 300+ million years, and even independently derived sex chromosomes seem to have followed the same set of evolutionary rules. The sex determining pathway seems to be extremely conserved, although the control of the genes in this pathway is vested in different elements. We present a scenario for the independent evolution of XY male heterogamety in mammals and ZW female heterogamety in birds and some reptiles. We suggest that sex determining genes can be made redundant, and replaced by control at another step of a conserved sex determining pathway, and how choice of a gene as a sex switch has led to the evolution of new sex chromosome systems. J. Exp. Zool. 290:449-462, 2001.

Animals↗

PubMed1988

Sexing of half-embryos produced by microsurgical bisection of mouse morulae and production of chimeric mouse of defined sex composition by aggregating two sexed half-embryos.

Using the halved morulae of mice obtained with microsurgical technique, the following two experiments were performed. 1) Sexing of half-embryos by chromosomal analysis and transfer of the half-embryos after determining the sex of the other monozygotic half. One half of the bisected embryo was cultured in Colcemid solution (0.04 micrograms/ml) to be ensured for chromosomal preparation. More than 50% (152/270) of the blastulated embryos from the halves could be sexed by direct sex chromosome analysis. Thirty-nine of the half-embryos of which the co-twin halves were sexed, were transplanted in to the uterine horns of 18 pseudopregnant mice, and twelve became pregnant. The autopsies of them on Day 18 to 20 of pregnancy, revealed the presence of 16 fetuses. The morphological sex of these fetuses thus obtained coincided completely with the previous judgement based on the chromosomal sexing. 2) Production of chimeras of defined sex composition by aggregating two half-morulae of defined sex. Out of 147 pairs of half-morulae of two different strains (ICR and C3H/He), which were replaced in pairs into empty zona pellucidae, 107 (72.8%) were aggregated successfully and developed in vitro into full expanding blastocysts of typical form. Among the 107 aggregate blastocysts, 31 were sexed for both component embryos by chromosomal analysis on the co-twin half-embryos. When these 31 blastocysts were transferred, 11 living offspring including 4 chimeras were obtained. Transfer of 12 male-male and 5 female-female aggregate blastocysts resulted in 8 males and 1 female, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Sex chromosomes, sex determination, and sex-linked sequences in Microtidae.

The Arvicolidae is a widely distributed rodent group with several interesting characteristics in their sex chromosomes. Here, we summarize the actual knowledge of some of these characteristics. This mammalian group has species with abnormal sex determination systems. In fact, some species present the same karyotype in both males and females, with total absence of a Y chromosome, and hence of SRY and ZFY genes. Other species present fertile, sex-reversed XY females, generally due to mutations affecting X chromosomes. Furthermore, in Microtus oregoni males and females are gonosomic mosaic (the females are XO in the soma and XX in the germ cells, while the males are XY in the soma and OY in the germ cells). Regarding sex chromosomes, some species present enlarged (giant) sex chromosomes because of the presence of large blocks of constitutive heterochromatin, which have been demonstrated to be highly heterogeneous. Furthermore, we also consider the alterations affecting composition and localization of sex-linked genes or repeated sequences. Finally, this rodent group includes species with synaptic and asynaptic sex chromosomes. In fact, several species with asynaptic sex chromosomes have been described. It is interesting to note that within the genus Microtus both types of sex chromosomes are present.

Animals↗

PubMed2003

Correlates of recent unprotected anal sex among men having sex with men attending a large sex resort in the South.

BACKGROUND: Published studies have not investigated sexually transmitted disease-associated risk behaviors among men who have sex with men (MSM) attending U.S. sex resorts. GOAL: We conducted an exploratory study to identify demographic and behavioral correlates of recently engaging in unprotected anal sex (UAS) among MSM attending a sex resort in the southern United States. STUDY DESIGN: A cross-sectional survey of 150 men. RESULTS: In multivariate analyses, men were more likely to practice risky sex if they also recently engaged in the practices of having group sex (adjusted odds ratio [AOR], 3.0), rimming (AOR, 2.0), or if they used public restrooms to meet potential sex partners (AOR, 2.6). UAS was also more likely among men vaccinated against hepatitis B (AOR, 1.9). Men who reported having primary partners and men who reported being HIV-positive were no less likely than other men in the sample to report recent UAS. CONCLUSION: Sex resorts can be an important venue for sexually transmitted disease and HIV prevention among MSM. Tailored prevention messages could be warranted for men who report group sex, rimming, meeting partners in public restrooms, or being vaccinated against hepatitis B.

Adult↗

PubMed1983

Sex-stereotyping and sex-congruency: components in the sex role definition of medical specialties in India.

This paper draws a distinction between sex-stereotyping and sex-congruency by analyzing medical students' specialty preferences and choices and faculty views on the sex-suitability of various specialties at a medical college in India. Sex-stereotyping is seen as being rooted in and stemming from the nature of a society, particularly its normative structure. Thus the female stereotyping of obstetrics and gynecology in India is rooted in the widely accepted norm of sex segregation. Sex-congruency refers to the perceived compatibility between sex role expectations and the demands of a specialty. In addition, there was a growing realization among S.M.S. female medical students and among most of the faculty at the college that specialties such as ophthalmology, pathology and anesthesiology involving delicate surgery, less competition, infrequent emergencies and regular hours are better suited for females than are the more demanding specialties. The rationalization of sex-congruency seems to be much more logically consistent than stereotyping. Yet it is the latter that constitutes the most widely shared, and highly consensual rationalization within a given cultural context. These two forms of rationalization may overlap, but they basically differ from each other in many ways: stereotyping has a much longer past, is passed on from generation to generation, is culturally specific, highly crystallized, rigid, and resistant to change. Congruency, by contrast, is based on cross-culturally accepted standards, yet is less structured, more flexible and subject to local variations and finally to individual interpretation.

Attitude↗

PubMed2002

Is there a "bladder sex"? The relation of different sex hormones and sex hormone receptors in bladder in childhood.

The aim of this study was to review the classical concept of bladder physiology in regard to sex hormone effects and to focus on a new concept. Sex hormones affect bladder functions and the classical concept tries to explain these effects via alpha and beta adrenoreceptors. The effects of hormones had been investigated in this understanding. To obtain a biological response to steroids in target tissues, specific proteins--so-called receptors--are warranted. After the demonstration of the sex hormone receptors in bladder first in adults and in children urge questioning the effects of hormones in this regard. The hypothesis is based on the fact that, if a special receptor is present, the direct (via sex hormone receptors) effect is more likely to occur as an indirect effect (via alpha and beta adrenoreceptors). There is evidence that there is a sex difference and the sex receptors and hormones play an important role in some bladder disorders. Therefore we stress the importance of investigating especially the pediatric patients with bladder problems in regard to sex hormone receptors and hormonal status.

Child↗

PubMed1985

The influence of sex-specific brain differentiation and of postpuberal sex hormone levels on the development of sex-specific differences of body weights as well as triglyceride, high-density-lipoprotein-cholesterol and total cholesterol serum levels in rats.

The effects of perinatal sexual differentiation of the brain and of postpuberal sex hormone levels on the development of sex-specific differences in body weight as well as triglyceride (TG), high-density-lipoprotein-cholesterol (HDL-CHOL) and total cholesterol were investigated. Significant differences in body weight of male and female rats are attributed to the influence of different androgen levels during the perinatal period as well as to the influence of different postpuberal estrogen (E) and androgen (A) levels. Sex-specific differences in TG serum levels are essentially caused by varying influence of androgens during the perinatal period, possibly in part after conversion to estrogens. Different postpuberal sex hormone concentrations seem to have only little effect on the TG levels. Sex-specific differences in HDL-CHOL serum levels appear to be independent of androgens during the perinatal period as well as of physiological postpuberal estrogen levels. These differences are mainly the result of the current postpuberal androgen levels. Total CHOL did not show any sex-specific differences under the conditions of the experiment.

Aging↗

PubMed1998

Sex-lethal, the master sex-determining gene in Drosophila, is not sex-specifically regulated in Musca domestica.

Sex-lethal (Sxl) is the master switch gene for somatic sex determination in Drosophila melanogaster. In XX animals, Sxl becomes activated and imposes female development; in X(Y) animals, Sxl remains inactive and male development ensues. A switch gene for sex determination, called F, has also been identified in the housefly, Musca domestica. An active F dictates female development, while male development ensues when F is inactive. To test if the switch functions of Sxl and F are founded on a common molecular basis, we isolated the homologous Sxl gene in the housefly. Though highly conserved in sequence, Musca-Sxl is not sex-specifically regulated: the same transcripts and protein isoforms are expressed in both male and female animals throughout development. Musca-Sxl is apparently not controlled by the primary sex-determining signal and, thus, is unlikely to correspond to the F gene. Ectopic expression of Musca-SXL protein in Drosophila does not exert any noticeable effects on the known target genes of endogenous Sxl. Instead, forced overexpression of the transgene eventually results in lethality of both XY and XX animals and in developmental abnormalities in some escaper XY animals. Similar results were obtained with the Sxl homologue of Ceratitis capitata (Saccone, G., Peluso, I., Artiaco, D. , Giodano, E., Bopp, D. and Polito, L. C. (1998) Development 125, 1495-1500) suggesting that, in these non-drosophilid species, Sxl performs a function different from that in sex determination.

Amino Acid Sequence↗

PubMed1996

Sex-specific control of Sex-lethal is a conserved mechanism for sex determination in the genus Drosophila.

In D. melanogaster the binary switch gene Sex-lethal (Sxl) plays a pivotal role in somatic sex determination -- when the Sxl gene is on the female pathway is followed, while the male pathway is followed when the gene is off. In the present study we have asked whether the Sxl gene is present in other species of the genus Drosophila and whether it is subject to a similar sex-specific on-off regulation. Sxl proteins were found in all of the drosophilids examined, and they display a sex-specific pattern of expression. Furthermore, characterization of the Sxl gene in the distant drosophilan relative, D. virilis, reveals that the structure and sequence organization of the gene has been well conserved and that, like melanogaster, alternative RNA processing is responsible for its sex-specific expression. Hence, this posttranscriptional on-off regulatory mechanism probably existed before the separation of the drosophilan and sophophoran subgenera and it seems likely that Sxl functions as a sex determination switch gene in most species in the Drosophila genus. Although alternative splicing appears to be responsible for the on-off regulation of the Sxl gene in D. virilis, this species is unusual in that Sxl proteins are present not only in females but also in males. The D. virilis female and male proteins appear to be identical over most of the length except for the amino-terminal approx. 25 aa which are encoded by the differentially spliced exons. In transcriptionally active polytene chromosomes, the male and female proteins bind to the same cytogenetic loci, including the sites corresponding to the D. virilis Sxl and tra genes. Hence, though the male proteins are able to interact with appropriate target pre-mRNAs, they are apparently incapable of altering the splicing pattern of these pre-mRNAs.

Alternative Splicing↗

PubMed1982

Bulimia nervosa: sex role attitude, sex role behavior, and sex role related locus of control in bulimarexic women.

Thirty-four women with bulimia nervosa and 34 women without bulimarexic symptoms (but matched for age, weight, deviance from ideal weight, and educational status) were compared as to how liberated their attitude towards the woman's role in society (= their sex role attitude, SRA) and their actual own behavior as females (= their sex role behavior, SRB) were. The degree to which their general attitude towards sex role and their own sex role behavior differed from each other was also investigated. Experimental and control group were also compared concerning their sex role related locus of control (SRLC). SRA and SRB were significantly less liberated in the bulimarexic group than in the control group. In addition, the bulimarexic group showed a wide gap between their general attitude (SRA) and actual behavior (SRB) as to the degree of liberation. No such discrepancy was found in the control subjects. The sex related locus of control data showed that bulimarexic women had significantly higher external and fatalistic control, and lower internal control than the comparison subjects.

Adult↗

PubMed1979

Interpersonal aggression as a function of subject's sex, subject's sex role identification, opponent's sex, and degree of provocation.

Ninety-five undergraduates served as subjects in an experiment where they could administer electric shock to an opponent and receive the same from an opponent. The independent variables were subject's sex, subject's sex role identification (as measured by the Bem Sex Role Inventory), opponent's sex, as well as degree of provocation from the opponent. Aggression was defined as level of shock chosen by the subject for the opponent. The results indicated that masculine subjects facing a male opponent were more aggressive than individuals of other sex role identifications whether or not they were provoked. It was also found that masculine males were more aggressive than other males or anyof the females. Furthermore, opponent's sex influenced the males' aggressiveness but had no effect on the degree of aggression in females. Finally, aggression increased in all subjects following increases in provocation. The results are discussed in terms of their implications for pyschological androgyny.

Aggression↗

PubMed1989

Field independence as a function of sex, sex-roles, and the sex-role appropriateness of the task.

Two experiments were conducted to explain the sex difference in field independence by reference to socialization factors. It was hypothesized that the sex-role appropriateness of the task as masculine or feminine-typed would influence the performance of masculine and feminine women in a manner congruent with their sex-role orientation. 28 pilot subjects and 100 subjects in Study 2 were equally divided between the sexes. Both studies used the Bem Sex-role Inventory, but different versions of the Embedded Figures Test. The over-all results suggested that feminine women varied their performance according to task appropriateness, although not always in a manner congruent with their sex-role orientation. Androgynous individuals and masculine men did not alter their performance.

Adult↗