Skewed Sex Ratios Research Articles

Changing sex for selfish gain: B chromosomes of Lake Malawi cichlid fish

B chromosomes are extra, non-essential chromosomes present in addition to the normal complement of A chromosomes. Many species of cichlid fish in Lake Malawi carry a haploid, female-restricted B chromosome. Here we show that this B chromosome exhibits drive, with an average transmission rate of 70%. The offspring of B-transmitting females exhibit a strongly female-biased sex ratio. Genotyping of these offspring reveals the B chromosome carries a female sex determiner that is epistatically dominant to an XY system on linkage group 7. We suggest that this sex determiner evolved to enhance the meiotic drive of the B chromosome. This is some of the first evidence that female meiotic drive can lead to the invasion of new sex chromosomes solely to benefit the driver, and not to compensate for skewed sex ratios.

Skewed adult sex ratios observed early in the North American invasion of Lycorma delicatula (Hemiptera: Fulgoridae)

Abstract The spotted lanternfly, Lycorma delicatula, (Hemiptera Fulgoridae) is an invasive pest in Korea and the United States, but originating from mainland Asia. Both tree of heaven, Ailanthus altissima, and grapevine (Vitis) are known to be preferred hosts of adults. However, much is unknown about its adult behavior with respect to mating or dispersal patterns. In 2015, just after it was discovered in the United States, we performed an observational study to elucidate movement by adults in relation to host plants. We noted weekly changes in their presence and sex ratio on host plants at four sites in a quarantine zone in Berks County, PA. Just after adult emergence, the trunks of large (>15 cm diameter at breast height) A. altissima hosted nearly exclusively females, while smaller A. altissima, Vitis, Salix nigra, and other less commonly inhabited tree species, had high proportions of males. By October 1st, greater proportions of males were observed on the trunks of the larger A. altissima trees. Pairings of males and females were observed most frequently on the smaller A. altissima and Vitis. At the very end of the season, a large mixed-sex population was found on Salix nigra, which was the only deciduous tree species in the area still bearing green leaves.

Women’s “Gender Capital” Experiences in Conjugal Housing Consumption: Understanding a New Pattern of Gender Inequality in China

This article looks into the phenomenon that many women request men to provide a house for marriage in contemporary Chinese society. Going beyond explanations such as that the skewed sex ratio motivates men to engage in a Darwinian race and that some women have materialistic mating ideology, through a feminist engagement of Bourdieu’s concept of capital, I explicate how women wield their gender capital (in particular, the female capital) in the negotiation of conjugal housing consumption. I argue that women’s re-inscription of the “less-capable” female role should be differentiated from a simple return to tradition; it is more likely to be their protection-seeking strategy to counteract the increased uncertainty in relationships and the perceived gender inequality in marital life. The intergenerational dynamics in such negotiation process are also discussed. The study asserts that the gendered advantage enjoyed by some women in conjugal property negotiation has its root in the ongoing structural and gender constraints towards women. Such operation of gender capital therefore does not embody the liberation of women; it ironically traps both genders in a vicious circle of inequality.

Exploring the ‘True Value’ of Replacement Rate Fertility

The concept of ‘replacement rate fertility’ [RRF] is widely known and referred to regularly in the popular, policy and academic literature. Sometimes presented as a ‘target’ or an ‘ideal’ fertility rate, it is usually specified as being a period total fertility rate [TFR] of ‘around 2.1’. This paper has two goals—firstly to explore the extent to which global contemporary RRF is, indeed, ‘around 2.1’; and secondly to evaluate this status a ‘target’ for national and international policymakers. We find that, in the first instance, global RRF is not 2.1; but the UN projection model suggests it will converge to this in the future. Skewed sex ratios at birth and high levels of maternal and adult mortality mean that RRF was significantly greater than 2.1 in the past, and is still the case for many countries today. We suggest that the real value of understanding and determining the value of TFR in any given territory is an indicator of human development. Rather than the popular notion of a ‘target’ TFR of ‘around 2.1’ as being an arbitrary (and ill-defined) aim for territorial population replacement, governments should aim to achieve a RRF of around 2.1, which indicated negligible mortality and a biologically normal sex ratio at birth.

Common Eland (Tragelaphus oryx) Population Trends in the Ukhahlamba-Drakensberg Park and Surrounds, South Africa, between 1942 and 2018

Management of protected areas requires an understanding of the long-term population trends of large mammal species that may influence ecosystem functioning. Common eland (Tragelaphus oryx) are the most abundant large mammal species in the uKhahlamba-Drakensberg Park. Aerial and ground surveys have been conducted over the years to monitor the common eland population. This study addressed long-term trends in population size, structure, distribution and mortality of the common eland between 1942 and 2018, examining changes in relation to climate, natural impacts, management, and efficacy of surveys. The common eland population in the Drakensberg remained relatively stable from 1942 to 1982, then increased between 1983 and 1990. However, a continuous decline was observed between 2003 and 2018 concomitant with a 37% reduction in distribution range within the Park. Adults constituted 59.4% of the population over the entire period, while subadults and calves accounted for 19.1% and 18.8%, respectively, with the remaining 2.7% of unknown ages. The ratio of adults: subadults: calves was 1: 0.32: 0.32 and males: females was 1: 3.63, indicating a skewed sex ratio and a low number of juveniles in the population. Human activities had a substantial impact on the population, with 30.3% of mortalities attributed to poaching. However, permitted offtakes of an unknown number may be the most important cause of mortality. Increased movement of eland onto farmlands outside of the protected area appears to have contributed to a decline in their distribution within the Park in recent years; however, this does not affect population trend since those on farmland are still included in counts. There is no cause for concern regarding the population trend at present; however, if the observed population decline continues well beyond the population numbers recorded in 1942, then there is cause for a management response by Ezemvelo KwaZulu-Natal Wildlife for the common eland population in the Drakensberg.

Girls for Sale? Child Sex Ratio and Girl Trafficking in India

ABSTRACTIllegal trafficking of girls results from their disadvantageous position in society, often reflected by preference for sons and neglect of daughters. India has both higher levels of illegal trafficking of girls and abnormal child sex ratios in favor of boys. This paper examines if the skewed sex ratio in India is associated with trafficking of girls. Using panel data from twenty-nine Indian states from 1980 to 2011, the study finds that a 100-unit increase in the child sex ratio is associated with a 0.635 percent increase in girl trafficking. Further, the association is heterogeneous by women’s empowerment, crime against women, and party rule in the state, and the association between the child sex ratio and trafficking of girls is stronger and larger in magnitude in states with greater women’s empowerment. Overall, it appears the results are driven both by greater reporting and a greater incidence of illegal girl trafficking.

Oil dispersant Corexit 9500 is weakly estrogenic, but does not skew the sex ratio in Alligator mississippiensis.

During the Deepwater Horizon oil spill, vast quantities of a chemical dispersant Corexit 9500 were applied in remediation efforts. In addition to the acute toxicity, it is essential to evaluate Corexit further with a broader scope of long-term sublethal endocrine endpoints. The American alligator (Alligator mississippiensis) is an excellent organism for such an endeavor. It exhibits temperature-dependent sex determination, in which egg incubation temperatures during a thermosensitive period (TSP) in embryonic development determine the sex of embryos. Estrogen signals play a critical role in this process. For example, a single exposure to exogenous estrogen during the TSP overrides the effects of temperature and leads to skewed sex ratios. At a concentration of 100ppm, Corexit significantly induced transcriptional activity of both alligator nuclear estrogen receptors 1 and 2 in vitro in reporter gene assays. To investigate the estrogenic effects of Corexit on gonadal development, alligator eggs were exposed to Corexit at environmentally relevant concentrations (0.25, 2.5 and 25ppm) before the TSP in ovo. Exposure to Corexit at 0.25 and 25ppm significantly delayed hatching and growth. Corexit exposure at any treatment level did not affect sex ratios or testicular mRNA abundance as measured at 1-week post-hatching, suggesting that the combination of Corexit components did not synergize enough to induce ovarian development in ovo. These results point to a need for further investigations on individual and combined components of Corexit to understand better their long-term effects on the development and reproductive health of alligators and other coastal aquatic wildlife.

A Study on Gender Preferences and its Sociocultural aspects among Married Women (18-45years) in Rural Gurugram

INTRODUCTION: Declining sex ratio is a major concern worldwide, especially in a developing country like India. The role of sociocultural factors in gender preference is known since ages. The skewed sex ratio in India is attributed to selective female feticides and misuse of technological advancements. This also has a strong influence on contraceptive acceptance among couples.
 OBJECTIVES: The present study was conducted to explore the contraceptive use, gender preferences and its determinants among married women in rural Gurgaon.
 MATERIALS AND METHODS: A cross-sectional study was conducted among married women (18-45years) residing in the rural field practice area of SGT medical college and hospital, Gurugram. The sample size was found to be 400. Systematic random sampling technique was used to recruit the study participants. Pre- tested, pre-designed questionnaire was used for data collection.
 RESULTS AND DISCUSSION: Among 400 married women, current contraceptive usage among study population was found to be 58.25%. The most common method of contraception used by the study subjects was intrauterine contraceptive device. The preference for male child was found among 49.5% women. The reasons cited for such preference were propagation of family name (48.2%), financial dependability in the old age (34%), social responsibilities are carried out by males (25.3%) and males are lesser economic liability (31%). Lower age group of mother, nulliparity, Hindu religion, lower educational status and lower socioeconomic status were found to be the determinants of male child preference in the present study.
 CONCLUSION: There is need of awareness and education amongst women and both the genders deserve equal respect without any preferences.

A battle of the sexes? Sex ratio and performance at small scales in dioecious Mercurialis perennis

Mercurialis perennis is a dioecious clonal woodland herb. Its male-biased shoot sex ratio may result from differential selection (with skewed genet sex ratio) and/or differential performance (fairly even genet sex ratio but skewed shoot sex ratio since male clones grow more vigorously or have a higher flowering propensity). To test both scenarios, a total of 1024 shoots were mapped and excavated in five 1 m2 plots in an old-growth forest in northeastern Germany. SSR genotyping revealed a less skewed intrinsic male:female shoot sex ratio (1.6) and a nearly even genet sex ratio. The sexes showed intermingling rather than sexual niche segregation. Most of the 36 genets found split into numerous independent units (merigenets). A slight sexual size dimorphism (SSD) was found: male clones possess on average more shoots, have longer stolons and a higher proportion of flowering shoots. Analyses of resource allocation patterns showed 1.5–2.8 times higher costs for sexual reproduction (dry mass, nitrogen) for females. Males invest surplus resources into leaves and stolons, accentuating the SSD; although for genets the difference may be smaller due to the higher flowering rate of males (53% vs. 34%). Photosynthetic performance, deduced from rapid light curves measured with a portable fluorometer, was similar for both sexes, especially in spring; the main challenge being the transformation from light to shade plant with tree foliation. Our data indicate that differential performance accounts for the male bias in shoot sex ratio; competition between sexes is unlikely given the strongly intermingled clones.

Sizes, condition factors and sex ratios of the scattered populations of the small cichlid fish, Alcolapia grahami, that inhabits the lagoons and sites of Lake Magadi (Kenya), one of the most extreme aquatic habitat on Earth

Alcolapia grahami is a small cichlid fish that inhabits the scattered lagoons and sites of Lake Magadi (Kenya). Exceptional physiological, morphological, biochemical and behavioural adaptations allow the fish to tolerate the harsh environmental conditions that exist in the locations, the most extreme milieus occupied by a species of fish on Earth. The temperature of the water is inordinately high for a fish; large diurnal fluctuations in the levels of the partial pressure of oxygen occur, with acute hypoxia happening during the night and hyperoxia during the day; the salinity of the water is ~60% of that of seawater and; the pH may be as high as 11. Having an average adult body length of less than 6 cm and a body mass of ~5 g, the fish is very small in size. Here, body mass, body length, condition factors (CFs) and sex ratios (SRs) were determined on fish sampled from nine accessible isolated populations. Except for the Cement Water Holding Tanks (CWHT) population, where the female-to-male SR was 4:1, overall, the number of male fish surpassed the female ones by a ratio of ~2:1. The male fish were heavier and longer compared to the female ones. The relatively lower ambient temperature in the CWHT (32 °C) may explain the female dominated population and the effect future increase in temperature may have on sex distribution in the various populations of A. grahami. In fish from the Fish Spring Lagoons B and D, the CFs were greater in the male fish relative to the female ones. Exhibiting poor-to-fair body states, the CFs of the different populations of A. grahami, that ranged from 1.1. to 1.8, were among the lowest that have been reported in fish living under natural setting. The skewed SRs and the markedly low CFs of A. grahami reported here may be ascribed to the harsh (stressful) environmental conditions the fish contends with. The values may signal prospective demise of the fish. Conservation measures are urgently needed to protect a very rare fish.

A Review of the Effects of Climate Change on Chelonians

Climate change is occurring at an unprecedented rate and has begun to modify the distribution and phenology of organisms worldwide. Chelonians are expected to be particularly vulnerable due to limited dispersal capabilities as well as widespread temperature-dependent sex determination. The number of papers published about the effects of climate change on turtles has increased exponentially over the last decade; here, I review the data from peer-reviewed publications to assess the likely impacts of climate change on individuals, populations, and communities. Based upon these studies future research should focus on: (1) Individual responses to climate change, particularly with respect to thermal biology, phenology, and microhabitat selection; (2) improving species distribution models by incorporating fine-scale environmental variables as well as physiological processes; (3) identifying the consequences of skewed sex ratios; and (4) assessments of community resilience and the development of methods to mitigate climate change impacts. Although detailed management recommendations are not possible at this point, careful consideration should be given regarding how to manage low vagility species as habitats shift poleward. In the worst-case scenario, proactive management may be required in order to ensure that widespread losses do not occur.

Missing Women, Gender Imbalance and Sex Ratio at Birth: Why the One-Child Policy Matters

In this paper, we show that the one-child policy has played a significant role in the decline of China’s fertility. The one-child policy had reduced China’s fertility rate by an additional 11.5%, based on a year-on-year comparison with the case if China had not implemented the policy. The methodology we introduced in estimating the number of “missing women” improves on the method employed in Anderson and Ray (2010). Our findings suggest that the one-child policy resulted in a total of approximately 11 million missing women in China, and contributed to more than 50% of its outstanding gender imbalance. The adoption of the one-child policy has prevented around 50 million births, and is confirmed to be the major cause of China’s highly skewed sex ratio at birth.

Effects of the interaction between temperature and steroid hormones on gametogenesis and sex ratio in the European flat oyster (Ostrea edulis)

Throughout Europe, populations of Ostrea edulis have been in decline since the 1970s. Temperature has an important influence on physiological, biochemical and reproductive attributes of oysters. It is also the most easily modulated environmental factor in hatcheries, so it is useful to understand the implications of temperature variation in driving gametogenesis and sex development in a protandrous sequential hermaphrodites such as O. edulis. To understand the effect of temperature on gametogenesis and sex ratio, as well as the potential mechanism of sex determination through the role of steroid hormone homologues, oysters were exposed to three temperatures (10, 14, and 18 °C) for four months. Gametogenic stage and sex ratio were assessed histologically for each treatment. In parallel, concentrations of estradiol (E2)- and testosterone (T)- were determined in developing gonads. Our data show that by some biometric parameters, gametogenesis and sex ratio were significantly influenced by temperature during the experiment. There was a weak but significant correlation between E2 and T concentration during the treatments. However, and importantly, a direct relation between gonadal maturation, sex determination and hormones concentration was not found. These results suggest that gametogenesis and sex determination are predominantly affected by temperature in this species, and that steroids may not be actively involved as endogenous modulators in sex determination. Rising sea water temperatures and warmer condition through the year could cause an accelerated gametogenesis and skewed sex ratios in natural populations of O. edulis.

Skewed sex ratios in a newly established osprey population

With recent increases in the numbers of reintroduction projects, it has become crucial to know the main factors that allow colonization of new areas and prevent the extinction of small and reintroduced populations. Dispersal is one of the most important phenomena in population biology with consequences to the proportion of individuals that keep breeding in the natal population and the number of individuals that move to other populations to breed. We studied changes in offspring sex ratio and differences in dispersal patterns between the sexes in a reintroduced population of osprey (Pandion haliaetus). Results showed that at the beginning of the colonization process breeding pairs produced more males, which dispersed shorter distances and were more philopatric than females. However, with increasing breeding population size over the years, the offspring production was skewed to females, which dispersed longer distances from their natal area and tended to breed in different areas. Here we suggest that changes in offspring sex ratio during colonization processes, together with differences in dispersal pattern between sexes, could influence colonization rate and the probability of success of future reintroduction projects.

The Right to Work and to Live: The Implications of India’s NREGS Program for Missing Women

Limited economic opportunity for women reduces their household bargaining power and the economic value of daughters, amplifying son preference. This paper studies India’s National Rural Employment Guarantee Scheme, the largest workfare program in the world, which paid men and women equal salary and mandated at least one-third of workers be women. In a setting where the gender gap in employment and wages are sizeable, NREGS represented both an income shock and a large relative improvement in the labor market for women. We use the staggered roll-out of NREGS to show that districts which implemented the program earlier experienced an improvement in child sex ratios in favor of girls. Although program implementation was nonrandom, we find impacts exist only in rural areas, not in the urban counterparts of the same district, where NREGS did not operate. Furthermore, effects are larger in middle and upper income districts and districts with the most skewed initial sex ratios, results which are inconsistent with an alternative selection story. Finally, the effects appear only for rural youth sex ratios, not for adult sex ratios, suggesting endogenous migration is not driving the results.

Inflammation induced by faulty replication during embryonic development causes skewed sex ratio.

Inflammation induced by faulty replication during embryonic development causes skewed sex ratio.

Preconception Vitamin D Status and Offspring Sex Ratio Among Women with Prior Pregnancy Loss (OR17-05-19)

ObjectivesExperimental data indicate that maternal exposure to factors known to alter inflammatory milieu may be specifically harmful to the conception or survival of male fetuses. Indeed, in a recent clinical trial, preconception administration of low dose aspirin versus placebo restored the skewed sex ratio at birth among women with elevated inflammation, providing direct evidence of this phenomenon in humans. However, it is unknown whether other factors associated with inflammation, such as vitamin D status, are associated with offspring sex ratio at birth. Our objective was thus to evaluate the association of preconception serum 25-hydroxyvitamin D levels [25(OH)D] and male live birth among 1228 reproductive-age women with a history of 1–2 prior losses who were enrolled in the Effects of Aspirin in Gestation and Reproduction trial between 2007–2011. MethodsWe estimated RRs and 95% CIs for male live birth according to 25(OH)D sufficiency (≥75 vs. <75 nmol/L) using generalized estimating equations of log-binomial regression with robust standard errors. ResultsAmong the 1086 women who completed follow-up, the proportion of live-born males was 24% (n = 136) and 30% (n = 156) in the 25(OH)D insufficient and sufficient groups, respectively. After adjustment for age, race/ethnicity, and other factors, women in the 25(OH)D sufficient group were 23% (95% CI: 1.01, 1.49) more likely to have a live-born male infant compared to the insufficient group. Associations were stronger among women with elevated versus low levels of high sensitivity C-reactive protein (>1.95 ng/mL: RR: 1.41; 95% CI: 0.99, 2.00 versus ≤1.95 ng/mL RR: 1.11; 95% CI: 0.88, 1.41), a marker of systemic low-grade inflammation. ConclusionsPreconception vitamin D status was associated with male live birth, particularly among women with low-grade inflammation. These data suggest that maternal vitamin D sufficiency may mitigate maternal inflammation that would otherwise be detrimental to male fetal survival. Funding SourcesIntramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD.

“Doing Men’s Jobs”: A Commentary on Work–Life Balance Issues Among Women in Engineering and Technology

Despite a steep increase in female representation in the workforce in the last decade, the gendered division of labour in the family remains broadly unaltered. Women, even who work for the same duration as their husbands in the office and contribute equally or more to the financial status of the family, often take most of the shares of childcare responsibility and domestic work. Work–family conflict is a global problem for working men and women; the struggle is even more prominent among working women, especially those who work in male-dominated sectors such as engineering and technology. Working in gender-atypical professions, females in engineering and technology face solo status and experience perceived discrimination and social identity threat. They require to put additional efforts to adjust to the work environment which, in turn, impacts their work–life balance status. The gendered work culture in engineering and technology sectors is reported to be masculine and patrifocal as a result of the skewed sex-ratio. Moreover, the study attempted to find out how the gender-role perception and identification of them, gender stigma consciousness, and role conflict may further aggravate the work–family conflicts among women engineers. In addition, the added responsibilities and conflicts that come with motherhood and their impacts on the work–life balance are discussed.

Quantifying reproductive state and predator effects on copepod motility in ephemeral ecosystems

Ephemeral wetlands in arid environments are unique ecosystems with atypical trophic structuring, often dominated by invertebrate predation. Copepod behavioural traits and vulnerabilities to predation can vary substantially according to reproductive status. Gravid female copepods may be more vulnerable to predation due to reduced escape speeds or higher visibility to predators. Here, we quantify how reproductive status modulates horizontal motility rates of the predatory ephemeral pond specialist copepod Lovenula raynerae, and the responsiveness of the copepod to predator cues of the notonectid Anisops debilis. Males exhibited significantly higher motility rates than gravid female copepods, however chemical predator cues did not significantly influence activity rates in either sex. The lack of responsiveness to predator cues by specialist copepods in ephemeral wetlands may result from a lack of predation pressure in these systems, or due to time stress to reproduce during short hydroperiods. In turn, this could increase predation risk to copepods from externally-recruited top predators in ephemeral wetlands, and potentially contribute to the development of skewed sex ratios in favour of females.

Size Sorting in Bonytail Skews the Sex Ratio of Stocked Fish

AbstractFor sexually dimorphic species, size‐based management can cause changes in the sex ratio of the target population. Bonytail Gila elegans populations in the Colorado River basin are augmented annually in an effort to re‐establish wild populations. To increase survival rates of stocked individuals, the Lower Colorado River Multi‐Species Conservation Program's Habitat Conservation Plan implemented a minimum stocking size. Anecdotal reports on hatchery populations suggest that females grow at a faster rate and reach larger sizes than males. If this observation is correct, a minimum stocking size may cause skewed sex ratios of stocked populations. To test this prediction, we compared average male and female lengths in 3‐year‐old fish from two cohorts before and after they were sorted by size. Our data support the observation that size in Bonytail is sexually dimorphic by age 3, with females being the larger sex. This is also the age at which fish begin to reach the minimum size to meet stocking requirements. As predicted, size‐grading produced a significantly skewed sex ratio in the animals slated for release. The consequences of augmenting wild populations with groups of animals having skewed sex ratios are largely unknown but could include increased mate competition, inadvertent artificial selection, or a reduction in genetic diversity.