Secondary sex ratio of the cyclic parthenogen Daphnia magna (Crustacea: Cladocera) in the Canadian Arctic

1986 ◽  
Vol 64 (5) ◽  
pp. 1137-1143 ◽  
Author(s):  
David M. Barker ◽  
Paul D. N. Hebert
Keyword(s):  
Sex Ratio ◽  
Daphnia Magna ◽  
Sex Ratios ◽  
Canadian Arctic ◽  
Male Offspring ◽  
Environmental Cues ◽  
Environmental Cue ◽  
A Value ◽  
Secondary Sex Ratio ◽  
Ratio Response

Secondary sex ratios of the cyclic parthenogen Daphnia magna were studied in habitats near Churchill, Manitoba. Daphnia magna is believed to possess an environmentally mediated sex-determining system. Throughout the season females produced broods that were predominantly unisexual. The proportion of male offspring was low early in the season but rose to a value near 50% in each of four populations. It is hypothesized that after they have an initial series of female broods, individual females begin to alternate the sexes of their broods in response to an environmental cue. Such an alternation of brood sexes would explain the population sex-ratio pattern observed and would satisfy theoretical requirements for population and individual secondary sex ratios of 1:1. In studies on cladocerans, environmental cues inducing the sex-ratio response must be distinguished from cues with a sex-determining effect.

scholarly journals HIGHER PARENTAL PERCEPTIONS OF WEALTH ASSOCIATED WITH THE BIRTH OF MORE SONS IN AN AUSTRALIAN POPULATION

2017 ◽  
Vol 50 (4) ◽  
pp. 569-572
Author(s):  
A. M. Behie ◽  
M. H. O’Donnell
Keyword(s):  
Sex Ratio ◽  
Environmental Conditions ◽  
Parental Perceptions ◽  
Male Offspring ◽  
Harsh Environments ◽  
Maternal Factors ◽  
Australian Population ◽  
Industrialized Nations ◽  
Secondary Sex Ratio ◽  
Potential Factors

SummaryMany industrialized nations are currently experiencing a decline in average secondary sex ratio (SSR) resulting in fewer boys being born relative to girls. While many potential factors may explain the decline in the birth of males relative to females, it seems most studies support the idea that male offspring are produced less often when environmental conditions are poor owing to males being more susceptible to loss in harsh environments. This study investigates the maternal factors that are associated with the sex of offspring in a cohort of the Australian population. It found that greater parental perceptions of wealth were significantly associated with an increase in the number of sons produced. These results suggest that male offspring are born at increased numbers to women with higher available resources, which may reflect the fact that male offspring are more vulnerable in poor environments.

Do histocompatibility genes influence sex ratio (% males)?

1991 ◽  
Vol 3 (3) ◽  
pp. 267 ◽  
Author(s):  
WG Beamer ◽  
WK Whitten
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Strain Differences ◽  
Male Offspring ◽  
Mouse Strains ◽  
Primary Sex Ratio ◽  
Human Male ◽  
Female Survival ◽  
Mendelian Expectation

Breeding records for 15 of the 42 C57BL/10SnJ Congenic Histocompatibility Mouse Strains from the Special Mouse Stocks Resource (SMSR) showed three with a significant excess of male offspring. Strain B10.R111(71NS), hereafter R, gave the highest proportion of males (55.68 +/- 0.59% of 7129 newborn) which is significantly more than the proportion of male offspring (49.81 +/- 0.94% of 2853 newborn) from the C57BL/10SnJ progenitor strain, hereafter B. All mice in the SMSR colonies were fed Old Guildford 96 and Old Guildford 96W liberally on alternate weeks. Breeding females of B and R strains were established in a research colony at the Jackson Laboratory under conditions similar to those in SMSR except that they were fed Wayne Sterilizable Rodent Blox. More than 5000 inbred, hybrid and backcross fetuses were examined but no evidence of an excess of males was found. Also, there were no strain differences in the neonatal data. However, the sex ratio of the 4396 neonates was just significantly higher (P less than 0.05) than that of the fetuses, indicating some perinatal loss of females. An even greater loss of females was most probably the cause of the high sex ratios in the preliminary and follow-up surveys of SMSR R mice, which we ascribe to an interaction between the H-2 haplotype of the R strain, or a gene linked thereto, and the Old Guildford diet that is unfavourable to female survival. The sex ratio of fetuses agreed so closely with the Mendelian expectation as to indicate that the primary sex ratio was 50% males and that the R strain is not a model for the human male bias. There were no hermaphrodites or twins and the sex ratio of the fetuses in litters without resorptions was normal. These findings emphasize the variability of presumptive secondary sex ratios.

scholarly journals Sex-specific deaths in Norway and Sweden during the COVID-19 pandemic: Did mandates make a difference?

2021 ◽  
pp. 140349482110100
Author(s):  
Ralph Catalano
Keyword(s):  
Sex Ratio ◽  
Infection Control ◽  
Temporal Variation ◽  
Risky Behavior ◽  
Control Strategies ◽  
Sex Ratios ◽  
Female Mortality ◽  
All Cause Mortality ◽  
Societal Expectations ◽  
Male To Female

Aims: To determine whether differences between Norway’s and Sweden’s attempts to contain SARS-CoV-2 infection coincided with detectably different changes in their all-cause mortality sex ratios. Measuring temporal variation in the all-cause mortality sex ratio before and during the pandemic in populations exposed to different constraints on risky behavior would allow us to better anticipate changes in the ratio and to better understand its association with infection control strategies. Methods: I apply time Box–Jenkins modeling to 262 months of pre-pandemic mortality sex ratios to arrive at counterfactual values of 10 intra-pandemic ratios. I compare counterfactual to observed values to determine if intra-pandemic ratios differed detectably from those expected as well as whether the Norwegian and Swedish differences varied from each other. Results: The male to female mortality sex ratio in both Norway and Sweden increased during the pandemic. I, however, find no evidence that the increase differed between the two countries despite their different COVID-19 containment strategies. Conclusion: Societal expectations of who will die during the COVID-19 pandemic will likely be wrong if they assume pre-pandemic mortality sex ratios because the intra-pandemic ratios appear, at least in Norway and Sweden, detectably higher. The contribution of differences in policies to reduce risky behavior to those higher ratios appears, however, small.

scholarly journals Sex Ratios in a Warming World: Thermal Effects on Sex-Biased Survival, Sex Determination, and Sex Reversal

2021 ◽  
Vol 112 (2) ◽  
pp. 155-164
Author(s):  
Suzanne Edmands
Keyword(s):  
High Temperature ◽  
Sex Ratio ◽  
Sex Determination ◽  
Heat Tolerance ◽  
Sex Ratios ◽  
Sex Reversal ◽  
Survival Sex ◽  
Ratio Distortion ◽  
Warming World ◽  
Sex Ratio Distortion

Abstract Rising global temperatures threaten to disrupt population sex ratios, which can in turn cause mate shortages, reduce population growth and adaptive potential, and increase extinction risk, particularly when ratios are male biased. Sex ratio distortion can then have cascading effects across other species and even ecosystems. Our understanding of the problem is limited by how often studies measure temperature effects in both sexes. To address this, the current review surveyed 194 published studies of heat tolerance, finding that the majority did not even mention the sex of the individuals used, with <10% reporting results for males and females separately. Although the data are incomplete, this review assessed phylogenetic patterns of thermally induced sex ratio bias for 3 different mechanisms: sex-biased heat tolerance, temperature-dependent sex determination (TSD), and temperature-induced sex reversal. For sex-biased heat tolerance, documented examples span a large taxonomic range including arthropods, chordates, protists, and plants. Here, superior heat tolerance is more common in females than males, but the direction of tolerance appears to be phylogenetically fluid, perhaps due to the large number of contributing factors. For TSD, well-documented examples are limited to reptiles, where high temperature usually favors females, and fishes, where high temperature consistently favors males. For temperature-induced sex reversal, unambiguous cases are again limited to vertebrates, and high temperature usually favors males in fishes and amphibians, with mixed effects in reptiles. There is urgent need for further work on the full taxonomic extent of temperature-induced sex ratio distortion, including joint effects of the multiple contributing mechanisms.

scholarly journals Sex Chromosome Meiotic Drive in Stalk-Eyed Flies

Genetics ◽  
1997 ◽  
Vol 147 (3) ◽  
pp. 1169-1180 ◽  
Author(s):  
Daven C Presgraves ◽  
Emily Severance ◽  
Gerald S Willrinson
Keyword(s):  
Sex Ratio ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Meiotic Drive ◽  
Operational Sex Ratio ◽  
Genetic Modifiers ◽  
Ratio Distortion ◽  
The Impact ◽  
Sex Ratio Distortion

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13–17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

scholarly journals Fisher vs. The Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms That Produce Them

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1793
Author(s):  
Justin Van Goor ◽  
Diane C. Shakes ◽  
Eric S. Haag
Keyword(s):  
Sex Ratio ◽  
Sperm Competition ◽  
Sex Chromosomes ◽  
Sex Ratios ◽  
Environmental Sex Determination ◽  
Fitness Advantage ◽  
Selection For ◽  
Facultative Parthenogenesis ◽  
Multicellular Organisms ◽  
Inbred Populations

Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two “seminal” contributions of G. A. Parker. 

scholarly journals Maternal exposure to airborne polychlorinated biphenyls (PCBs) and risk of adverse birth outcomes

2021 ◽  
Author(s):  
Ane Bungum Kofoed ◽  
Laura Deen ◽  
Karin Sørig Hougaard ◽  
Kajsa Ugelvig Petersen ◽  
Harald William Meyer ◽  
...  
Keyword(s):  
Birth Weight ◽  
Preterm Birth ◽  
Sex Ratio ◽  
Polychlorinated Biphenyls ◽  
Birth Outcomes ◽  
Gestational Age ◽  
Small For Gestational Age ◽  
Maternal Exposure ◽  
Adverse Birth Outcomes ◽  
Secondary Sex Ratio

AbstractHuman health effects of airborne lower-chlorinated polychlorinated biphenyls (LC-PCBs) are largely unexplored. Since PCBs may cross the placenta, maternal exposure could potentially have negative consequences for fetal development. We aimed to determine if exposure to airborne PCB during pregnancy was associated with adverse birth outcomes. In this cohort study, exposed women had lived in PCB contaminated apartments at least one year during the 3.6 years before conception or the entire first trimester of pregnancy. The women and their children were followed for birth outcomes in Danish health registers. Logistic regression was performed to estimate odds ratios (OR) for changes in secondary sex ratio, preterm birth, major congenital malformations, cryptorchidism, and being born small for gestational age. We performed linear regression to estimate difference in birth weight among children of exposed and unexposed mothers. All models were adjusted for maternal age, educational level, ethnicity, and calendar time. We identified 885 exposed pregnancies and 3327 unexposed pregnancies. Relative to unexposed women, exposed women had OR 0.97 (95% CI 0.82, 1.15) for secondary sex ratio, OR 1.13 (95% CI 0.76, 1.67) for preterm birth, OR 1.28 (95% CI 0.81, 2.01) for having a child with major malformations, OR 1.73 (95% CI 1.01, 2.95) for cryptorchidism and OR 1.23 (95% CI 0.88, 1.72) for giving birth to a child born small for gestational age. The difference in birth weight for children of exposed compared to unexposed women was − 32 g (95% CI—79, 14). We observed an increased risk of cryptorchidism among boys after maternal airborne LC-PCB exposure, but due to the proxy measure of exposure, inability to perform dose–response analyses, and the lack of comparable literature, larger cohort studies with direct measures of exposure are needed to investigate the safety of airborne LC-PCB exposure during pregnancy

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