Sex Ratio Imbalance Research Articles

Female sex bias in Iberian megalithic societies through bioarchaeology, aDNA and proteomics

Uncertainties regarding traditional osteological methods in biological sex estimation can often be overcome with genomic and proteomic analyses. The combination of the three methodologies has been used for a better understanding of the gender-related funerary rituals at the Iberian megalithic cemetery of Panoría. As a result, 44 individuals have been sexed including, for the first time, non-adults. Contrary to the male bias found in many Iberian and European megalithic monuments, the Panoría population shows a clear sex ratio imbalance in favour of females, with twice as many females as males. Furthermore, this imbalance is found regardless of the criterion considered: sex ratio by tomb, chronological period, method of sex estimation, or age group. Biological relatedness was considered as possible sociocultural explanations for this female-related bias. However, the current results obtained for Panoría are indicative of a female-centred social structure potentially influencing rites and cultural traditions.

Marriage squeeze in the Loess Plateau Region, Northwestern China: A case study of two villages

The quest for spouses among rural men in China has become increasingly arduous, resulting in a growing number of older bachelors. However, the mechanisms driving the marriage squeeze in underdeveloped rural areas remain poorly understood. This study analyzes time-series data from 70 marital unions across 58 households in two geographically distinct villages in the Loess Plateau Region of China. The results indicate that marriage expenses and the subsequent financial burden on the bridegroom's household increased substantially from 1969 to 2018, particularly in the most recent decade, while the bride's household received the majority of marriage-related income. There has been an overall increasing trend in economic pressure induced by marriage expenses in both villages since 1979. A cohort of older bachelors has emerged in the hilly village, where rural males traditionally marry women from more remote, underdeveloped areas. Conversely, rural males in the tableland village can consistently find spouses from comparable geographical settings and have not yet emerged as older bachelors. This study concludes that the marriage squeeze manifests as dual pressures from economic and living conditions, and excludes economically disadvantaged males in harsh environments from the marriage market within the context of rural out-migration and the sex ratio imbalance.

Boric acid toxic sugar bait suppresses male Aedes aegypti (Diptera: Culicidae): wing beat frequency and amplitude, flight activity, fecundity, insemination, and mate-finding Allee effect.

Controlling the spread of arboviral diseases remains a considerable challenge due to the rapid development of insecticide resistance in Aedes mosquitoes. This study evaluated the effects of boric acid-containing toxic sugar bait (TSB) on field populations of resistant Aedes aegypti mosquitoes. In addition, this study examined the flight activity and wing beat frequency and amplitude of males and the flight activity, fecundity, and insemination of females after pairing with males exposed to TSB. The population dynamics of Aedes mosquitoes under imbalanced sex ratios were examined to simulate realistic field conditions for male suppression under the effect of TSB. The mortality of male mosquitoes was consistently high within 24 h after exposure. By contrast, the mortality of female mosquitoes was inconsistent, with over 70% mortality observed at 168 h. The flight activity and wing beat amplitude of treated males were significantly lower than those of controls, but no significant difference in wing beat frequency was detected. The fecundity and insemination of treated female mosquitoes were lower than those of controls. A simulation study indicated that considerably low male population densities led to mating failures, triggering a mate-finding Allee effect and resulting in persistently low population levels. Boric acid-containing TSB could effectively complement current chemical intervention approaches to control resistant mosquito populations. TSB is effective in reducing field male populations and impairing male flight activity and female-seeking behavior, resulting in decreased fecundity and insemination. Male suppression due to TSB potentially results in a small mosquito population. © 2024 Society of Chemical Industry.

The Impact of Children’s Gender on Family Housing Assets

China's household asset investment shows the characteristics of real estate concentration, which reduces the short-term risk-resistant ability of households and restricts the consumption ability of residents. This paper puts forward the theoretical hypothesis that “families whose eldest son is a boy have stronger housing investment motives”. A probit model is constructed using data from CHFS2019 for empirical testing. The results find that households whose eldest son is a boy have a stronger propensity to invest in housing than households whose eldest son is a girl. The degree of local sex ratio imbalance and the risk attitude of the head of household also influence investment behavior.

Accurate Bayesian inference of sex chromosome karyotypes and sex-linked scaffolds from low-depth sequencing data.

The identification of sex-linked scaffolds and the genetic sex of individuals, i.e. their sex karyotype, is a fundamental step in population genomic studies. If sex-linked scaffolds are known, single individuals may be sexed based on read counts of next-generation sequencing data. If both sex-linked scaffolds as well as sex karyotypes are unknown, as is often the case for non-model organisms, they have to be jointly inferred. For both cases, current methods rely on arbitrary thresholds, which limits their power for low-depth data. In addition, most current methods are limited to euploid sex karyotypes (XX and XY). Here we develop BeXY, a fully Bayesian method to jointly infer the posterior probabilities for each scaffold to be autosomal, X- or Y-linked and for each individual to be any of the sex karyotypes XX, XY, X0, XXX, XXY, XYY and XXYY. If the sex-linked scaffolds are known, it also identifies autosomal trisomies and estimates the sex karyotype posterior probabilities for single individuals. As we show with downsampling experiments, BeXY has higher power than all existing methods. It accurately infers the sex karyotype of ancient human samples with as few as 20,000 reads and accurately infers sex-linked scaffolds from data sets of just a handful of samples or with highly imbalanced sex ratios, also in the case of low-quality reference assemblies. We illustrate the power of BeXY by applying it to both whole-genome shotgun and target enrichment sequencing data of ancient and modern humans, as well as several non-model organisms.

The Research on Prisoners Dilemma in Prenatal Sex Determination

Inequality in the sex ratio is a significant issue in China. Some illegal sex determination mechanisms that give parents of young children gender information significantly contribute to the sex ratio imbalance. As a result, some parents make prejudiced decisions to abort girls. Regulation of prenatal sex determination by governmental and medical institutions will be challenging due to the high degree of information asymmetry. A few of the governments initiatives have yet to show obvious results. Medical institutions and women of childbearing age automatically cooperate in spite of information asymmetry. The prenatal sex determination regulation model is given a new interpretation in this paper using the game theory analysis method. Additionally, the paper explains the causes of the regulations difficulty and proposes ideas, countermeasures, and solutions. The idea of cooperation contained in game theory is of great significance in resolving interest conflicts and achieving social harmony under the condition of interest differentiation.

Male-biased sex ratios increase the support for a strong leader: An evolutionary threat management perspective

An evolutionary threat management approach to leadership assumes that humans have an adaptive followership psychology that responds to specific ecological threats by selecting appropriate leaders to mitigate any risks. We hypothesize that having an imbalanced sex ratio in society (with either an abundance of adult men or women) increases the support for a strong leader, because people find such imbalances threatening to themselves and to society. We tested our hypothesis with five preregistered experimental studies and one archival study. In the five online scenario studies (total N=2249), we manipulated the operational sex ratios within a fictitious country and measured both explicit leader preferences (ideal leader traits) and implicit preferences (facial cues of leaders). The results showed that a male-biased sex ratio (abundance of men) robustly increased the preference for a strong leader across all studies, but the effects of a female-biased sex ratio (abundance of women) were smaller and not consistent. Furthermore, a male-biased sex ratio in society activated the impression that society is a competitive, dangerous place. Overall, the studies enhance our understanding of the impact of an ecological factor, the sex ratio in society, on the support for political leadership.

Heat-induced female biased sex ratio during development is not mitigated after prolonged thermal selection

BackgroundThe negative impacts of climate change on biodiversity are consistently increasing. Developmental stages are particularly sensitive in many ectotherms. Moreover, sex-specific differences in how organisms cope with thermal stress can produce biased sex ratios upon emergence, with potentially major impacts on population persistence. This is an issue that needs investigation, particularly testing whether thermal selection can alleviate sex ratio distortions in the long-term is a critical but neglected issue. Here, we report an experiment analyzing the sex ratio patterns at different developmental temperatures in Drosophila subobscura populations subjected to long-term experimental evolution (~ 30 generations) under a warming environment.ResultsWe show that exposure to high developmental temperatures consistently promotes sex ratio imbalance upon emergence, with a higher number of female than male offspring. Furthermore, we found that thermal selection resulting from evolution in a warming environment did not alleviate such sex ratio distortions generated by heat stress.ConclusionsWe demonstrate that heat stress during development can lead to clear sex ratio deviations upon emergence likely because of differential survival between sexes. In face of these findings, it is likely that sex ratio deviations of this sort occur in natural populations when facing environmental perturbation. The inability of many insects to avoid thermal shifts during their (more) sessile developmental stages makes this finding particularly troublesome for population subsistence in face of climate warming events.

Imbalanced Sex Ratios and Marital Transitions in Mexico

Migration from Mexico to the United States results in numerical imbalances between men and women in the communities left behind, but little is known about how these imbalanced sex ratios in Mexican communities affect family formation behavior. Using two waves of data from the Mexican Family Life Survey (MxFLS) and 2000 Mexican census data, we examine how the sex composition of the municipality population is associated with the likelihood that Mexican women and men marry. Consistent with demographic-opportunity theory, but not sociocultural theory, results from logistic regression analyses show that men’s probability of marrying is positively associated with the numerical availability of eligible women in the municipality population. Consistent with the argument that many Mexican migrant men, but not migrant women, remain eligible partners for those who remain in Mexico, the sex composition of the municipal population is significantly associated with men’s but not women’s likelihood of marrying.

Factors affecting male-to-female ratio at birth in frozen-thawed embryo transfer cycles: a large retrospective cohort study.

ICSI (intracytoplasmic sperm injection) leads to a reduced male-to-female ratio at birth, whereas blastocyst transfer results in an increased male-to-female ratio. However, limited knowledge exists regarding the impact of these factors on the live birth rate for each gender. This study aimed to investigate the influence of patient characteristics and treatment parameters on the live birth rate for each gender, as well as the ultimate male-to-female ratio at birth in frozen-thawed embryo transfer (FET) cycles. This retrospective cohort study involved a total of 28,376 FET cycles and 9,217 subsequent deliveries, spanning from January 2003 to December 2015. The study consisted of two parts. First, logistic regression models were constructed to determine the factors influencing the male-to-female ratio among babies born after FET. Second, we aimed to investigate the mechanisms underlying this sex ratio imbalance by analyzing data from all transfer cycles. Generalized estimated equations were employed to assess the impact of risk factors on rates of male and female live births separately. ICSI resulted in a lower proportion of male offspring compared to in vitro fertilization (IVF) (50.1% vs. 53.7%, aOR: 0.87, 95% CI: 0.80-0.96). Conversely, blastocyst transfer yielded a higher proportion of male offspring than cleavage-stage embryo transfer (58.7% vs. 51.6%, aOR: 1.32, 95% CI: 1.17-1.48). Analysis of all cycles indicated that ICSI resulted in a reduced likelihood of male live birth in comparison to IVF (19.8% vs. 21.6%, aOR: 0.90, 95% CI: 0.83-0.97). However, the transfer of blastocysts rather than cleavage-stage embryos not only increased the chance of male live birth (26.9% vs. 20.2%, aOR: 1.70, 95% CI:1.56-1.85) but also facilitated female live birth (20.3% vs. 19.3%, aOR: 1.26, 95% CI: 1.15-1.39). ICSI was associated with a reduction in the male-to-female sex ratio and a lower rate of male live births, while blastocyst transfer was associated with an increased male-to-female sex ratio at birth and a higher rate of male live births.

Bride Trafficking from Vietnam to China: The Critique of Socialist Feminism

Bride trafficking is a phenomenon where women are sold for forced marriage. This phenomenon occurs in many Vietnamese women brought to China without their consent to marry. It has been claimed that there are 'supply and demand factors in encouraging the development of bride trafficking from Vietnam to China, such as an imbalanced sex ratio in China and a lack of education. This research analyses the occurrence of bride trafficking from Vietnam to China through the lens of gender and politics. Using the narrative analysis method and literature study through the perspective of socialist feminism, this research found that bride trafficking from Vietnam to China embodies double oppression towards Vietnamese women. It results from the intersection between two oppressive structures: patriarchy and capitalism.Consequently, a practice of sexual economy is developed in the form of bride trafficking. This research also found that globalization significantly affects bride trafficking from Vietnam to China. Globalization paves the way for this phenomenon to happen. Thus, this article offers a perspective favouring women in analyzing transnational phenomena in international relations.Keywords: bride trafficking; globalization; patriarchy; capitalism; sexual objectification

The more male classmates, the worse: How male peers harm academic performance of a student

This paper examines the influence of male peer proportion on a student's academic performance. The sex ratio at 10–14 was 117.16 in 2011, and it has increased to 119.1 in 2019. The sex ratio imbalance at 10–14 tends to expand. This paper uses China Education Panel Survey (CEPS) 2013–14 and 2014–15. Considering the selection bias, this paper restricts the sample to schools that satisfy randomly-assignment conditions. The results highlight that students with a high proportion of male classmates have a lower performance in Mathematics and English but not Chinese. To explain these effects, this paper uses three channels to interpret: (1) cognitive ability, (2) learning effort, and (3) the quality of the classroom environment. It provides implications for policymakers and school administrators to take precautions in advance.

Masculinizer gene controls sexual differentiation in Hyphantria cunea.

The Masculinizer gene, Masc, encodes a lepidopteran-specific novel CCCH-type zinc finger protein, which controls sex determination and dosage compensation in Bombyx mori. Considering the potential application of it in pest control, it is necessary to investigate the function of Masc gene in Hyphantria cunea, a globally invasive forest pest. In the present study, we identified and functionally characterized the Masc gene, HcMasc, in H. cunea. Sequence analysis revealed that HcMASC contained the conserved CCCH-type zinc finger domain, nuclear localization signal, and male determining domain, in which the last was confirmed to be required for its masculinization in BmN cell line. However, expression data showed that unlike male-biased expression in B. mori, HcMasc gene expresses in main all developmental stages or tissues in both sexes. Clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9-based disruption of the common exons 1 and 3 of the HcMasc gene resulted in imbalanced sex ratio and abnormal external genitalia of both sexes. Our results suggest that the HcMasc gene is required for both male and female sexual differentiation and dosage compensation in H. cunea and provide a foundation for developing better strategies to control this pest.

Migration and Skewed Subnational Sex Ratios among Young Adults

AbstractSkewed sex ratios have been found to increase crime and spread of diseases, as well as influence fertility decisions, gender roles, and economic development. I document the extent to which international and internal migration shape national and subnational sex ratios among young adults (SRYA). For this purpose, I analyze the data from the United Nations’ Urban and Rural Population by Age and Sex and World Population Prospects, focusing on the cohort born between 1975 and 1985 in 200 countries. I find that, while 33 countries have significantly skewed country‐level sex ratios, as many as 107 of the 200 investigated countries have either rural or urban skewed SRYA in 2010. To identify the sources of sex ratio imbalances, I decompose country‐level sex ratios into three factors: sex ratio at birth, relative probability of survival, and sex‐selective migration. I show that without sex‐selective international migration, country‐level SRYA would be balanced in almost all countries of the world. In the third part of the study, I use Eurostat data for European subnational regions. I find a strong log‐linear relationship between sex ratios and population density, that is, relatively more women among young adults as population density increases. Moreover, I show that skewed SRYA can be mainly attributable to sex‐selective migration, rather than to imbalanced sex ratios at birth and differential mortality.

Educational Investment for Future Marriage? Evidence of Missing Girls from China

AbstractNumerous studies have shown that a sex ratio imbalance (more boys than girls in a society) may result in a sequence of social problems. This study investigated the expected effect of a high sex ratio on educational investment. Using nationally representative data from the China Family Panel Studies and the 2010 Census, we determined the following: (i) a high sex ratio increased educational expenditure for boys relative to girls; (ii) parents who took education seriously and who cared about their children's education were more likely to invest in education to appear attractive in the future marriage market, and (iii) the profound impact of a high sex ratio on educational expenditure was more pronounced in less educated and poorer families. Our findings raised the possibility that the effect of the sex ratio may bring about more gender inequality in the future. The implicit cost of a high sex ratio may further lead to a vicious cycle of family fertility and childbearing.

Son preference and Chinese women's biological health risk in middle and older age: A life course study

Son preference is a severe form of gender discrimination and can impair women's health. Drawing on retrospective data from a nationally representative sample, this life course study examines how experience of guardians’ son preference in childhood is associated with Chinese women's health in middle and older age. Using imbalanced sex ratio at birth at the prefecture level as a proxy, this study also examines the health implications of adulthood exposure to regional son preference. Our regression estimates show that childhood experience of the male guardian's son preference is associated with higher biological risks of developing systemic inflammation at the 2015 follow-up among middle-aged and older women who were disease-free at the 2011 baseline. In contrast, childhood experience of the female guardian's son preference is associated with lower risk of developing systemic inflammation or hypertension at the follow-up, conditional on being disease-free at the baseline. Adulthood exposure to stronger regional son preference is associated with higher risk of hypertension at the follow-up, independent of childhood experience of guardians’ son preference.

Wealth or Just Job Seekers: Medieval Skeletal Series from Kutná Hora-Sedlec (Czech Republic) with a Notable Surplus of Men

Kutná Hora entered the 14th century as a rich, prosperous, and densely-populated city producing tons of silver. Such an amount of precious metal could not be mined and processed without an influx of people from other cities and rural areas and without the contribution of skilled specialists from abroad. Despite the apparent wealth of the city, its inhabitants (either settled or newly arrived) experienced and died during mortality crises. Evidence of such events was discovered in the Kutná Hora suburbs, where the medieval burial ground, including a significant component of mass burials, has been unearthed. In the data derived from pooled catastrophic and non-catastrophic burials (n=1785 individuals), a notable surplus of males has been identified with a striking imbalanced adult sex ratio of 149. After considering factors potentially influencing this value, we suggest that the figure likely mirrors the original population composition as a consequence of the inflow of men migrating to the town for labour/economic opportunities.

Concurrent Partnerships Among Black Women in United States

The imbalanced sex ratio in the Black community could contribute to sexual partner concurrency. This study examined the association between perceptions of the availability of heterosexual male partners (sex ratio) and heterosexual Black women's attitudes and experiences with concurrent sexual partnerships. We found that perceptions of a high sex ratio (more men relative to women) were positively associated with attitudes towards concurrent sexual partnerships and prevalence of sexual concurrency. Future research must account for contextual factors influencing sexual networks such as the sex ratio that affect behaviors and attitudes influencing Black women's risk for HIV infection.

Sex-biased predation and predator intraspecific competition effects in a prey mating system

<abstract><p>In this work, we propose and investigate a predator-prey model where the prey population is structured by sex and the predators (unstructured) depredate based on sex-bias. We provide conditions for the existence of equilibrium points and perform local stability analysis on them. We derive global stability conditions for the extinction state. We show the possible occurrence of Hopf and saddle-node bifurcations. Multiple Hopf bifurcations are observed as the sex-biased predation rate is varied. This variation also shows the opposite consequences in the densities of the sex-structured prey. Our results show that sex-biased predation can cause both stabilizing and destabilizing effects for certain parameter choices. It can also cause an imbalanced sex-ratio, which has ecological consequences. Furthermore when intraspecific competition among predators is minimized, it can lead to the extinction of prey. We discuss the ecological implications and application of our results to the biocontrol of invasive species susceptible to sex-biased predation.</p></abstract>

Legacy of the One-Child Policy: Marriage Dilemmas in Urban and Rural China

China’s one-child policy, the family planning policy enforced in 1980, continued for almost 36 years and created a lasting impact on both China’s declining total fertility rate (TFR) and its sex ratio imbalance. This paper discusses the marriage dilemma caused by the one-child policy and its separate outcomes in urban and rural areas. In urban areas, the expense for childbearing, the equated monthly installment (EMI) payments, and the self-consuming nature of marriage contributed to the declining marriage rate as well as the TFR. In rural settings, the surplus of single men due to the entrenched “son preference” created a demand for the bride-trafficking market, an industry of purchasing a bride as a form of property. In this paper, I conclude that the marriage crisis and its side effects are the legacies of the one-child policy, and the Chinese government needs to craft effective approaches in addressing these problems.