Effect Of Sex Ratio Research Articles

Climate change perils for dioecious plant species.

Climate change, particularly increased aridity, poses a significant threat to plants and the biotic communities they support. Dioecious species may be especially vulnerable to climate change given that they often exhibit spatial segregation of the sexes, reinforced by physiological and morphological specialization of each sex to different microhabitats. In dimorphic species, the overexpression of a trait by one gender versus the other may become suppressed in future climates. Data suggest that males will generally be less sensitive to increased aridity than co-occurring females and, consequently, extreme male-biased sex ratios are possible in a significant number of populations. The effects of male-biased sex ratios are likely to cascade to dependent community members, especially those that are specialized on one sex.

The effects of adult sex ratio on mating competition in male and female guppies (Poecilia reticulata) in two wild populations

When competing for mates, males typically exhibit higher rates of intrasexual aggression and courtship than females. Operational sex ratio, represented here by adult sex ratio (ASR) as a proxy, is likely the best predictor of this competition, which typically increases between members of one sex as members of the opposite sex become rarer. Moreover, in populations subject to high predation, males often decrease mating competitive behaviour due to predation risk. We explored the combined effects of ASR and population of origin (low vs. high ambient predation risk) on mating competition in male and female wild-caught Trinidadian guppies. Both male and female aggression rates increased with ASR, but the increase for males was only significant in the low-predation population. In regard to male mating tactics, courtship propensity was unaffected by ASR, while the propensity to sneak increased at male-biased ASRs. Guppies from a high predation population had lower aggression rates than their low predation counterpart, but male courtship and sneaking attempts did not differ between populations. Surprisingly, females were just as aggressive as males when competing for mates. These results highlight the trade-offs between antipredator and agonistic behaviour, which may affect sexual selection pressures in wild populations.

What Will You Do If I Say ‘I Do’?: The Effect of the Sex Ratio on Time Use within Taiwanese Married Couples

This paper uses the natural experiment of a large imbalance between men and women of marriageable age in Taiwan in the 1960s to test the hypothesis that higher sex ratios lead to husbands (wives) having a lower (higher) share of couple’s time in leisure and higher (lower) share of the couple’s total work time (employment, commuting, and housework). The sample includes 18,134 Taiwanese couples’ time diaries from 1987, 1990, and 1994. The OLS analysis finds evidence of the predicted effects of the county-level sex ratio on husbands’ and wives’ share of leisure and total work time. The county-level sex ratio’s impact on college-educated husbands’ time use is shown to be larger than the impact on non-college-educated husbands’ time use. A two-stage least square analysis controlling for possible endogeneity of county of residence returns similar findings.

Sex-specific plasticity and genotype × sex interactions for age and size of maturity in the sheepshead swordtail, Xiphophorus birchmanni.

Responses to sexually antagonistic selection are thought to be constrained by the shared genetic architecture of homologous male and female traits. Accordingly, adaptive sexual dimorphism depends on mechanisms such as genotype‐by‐sex interaction (G×S) and sex‐specific plasticity to alleviate this constraint. We tested these mechanisms in a population of Xiphophorus birchmanni (sheepshead swordtail), where the intensity of male competition is expected to mediate intersexual conflict over age and size at maturity. Combining quantitative genetics with density manipulations and analysis of sex ratio variation, we confirm that maturation traits are dimorphic and heritable, but also subject to large G×S. Although cross‐sex genetic correlations are close to zero, suggesting sex‐linked genes with important effects on growth and maturation are likely segregating in this population, we found less evidence of sex‐specific adaptive plasticity. At high density, there was a weak trend towards later and smaller maturation in both sexes. Effects of sex ratio were stronger and putatively adaptive in males but not in females. Males delay maturation in the presence of mature rivals, resulting in larger adult size with subsequent benefit to competitive ability. However, females also delay maturation in male‐biased groups, incurring a loss of reproductive lifespan without apparent benefit. Thus, in highly competitive environments, female fitness may be limited by the lack of sex‐specific plasticity. More generally, assuming that selection does act antagonistically on male and female maturation traits in the wild, our results demonstrate that genetic architecture of homologous traits can ease a major constraint on the evolution of adaptive dimorphism.

The Lasting Effect of Sex Ratio Imbalance on Marriage and Family: Evidence from World War II in Russia

How does a shock to sex ratios affect marriage markets and fertility? I use the drastic change in sex ratios caused by World War II to identify the effects of unbalanced sex ratios on Russian women. Using unique data from the Soviet archives, the results indicate that male scarcity led to lower rates of marriage and fertility, higher nonmarital births and reduced bargaining power within marriage for women most affected by war deaths. The impact of sex ratio imbalance on marriage and family persisted for years after the war's end, and was likely magnified by policies that promoted nonmarital births and discouraged divorce.

Effects of environmental enrichment and stereotypic behavior on maternal behavior and infant viability in a model carnivore, the American mink (Neovison vison).

In several species, stress compromises maternal behaviors that are important for infant viability (e.g. licking and grooming). Understanding how stress in captivity affects maternal behavior could therefore be beneficial, especially for carnivores in zoos and breeding centers where infant mortality is often high. We used a model carnivore--American mink--to test two hypotheses, namely that maternal investment and/or behavior is i. improved by environmental enrichment; and ii. compromised by stereotypic behavior. We observed 22 females raised in an indoor facility, 9 enriched, 13 non-enriched. At birth, and at post-natal day 20 when altricial infants were still fully dependent on their mothers, the following offspring variables were recorded: litter size, infant mortality, litter sex ratio (post-natal day 1), and weight. Maternal behavior was assessed by recording nest shape (post-natal day 1), and the frequency of licking and grooming (post-natal days 1-7). Non-enriched females stereotyped more, had female-skewed litters at birth, and tended to make poorer, flatter nests. Maternal licking and grooming showed large, stable individual differences, but appeared unaffected by enrichment. High levels of maternal stereotypic behavior predicted slower offspring growth, replicating previous findings for farmed mink. Nevertheless, enrichment did not significantly increase infant growth rates nor decrease infant mortality. Due to small sample sizes, our study now needs replicating, particularly to explore the potential benefits of enrichment on nest building, sex ratio effects, and the implications of maternal licking and grooming for offspring stress reactivity. Findings could then apply to endangered mustelids like the European mink.

Biased Sex Ratios Influence Fundamental Aspects of Human Mating.

The operational sex ratio-the ratio of men to women in a given population-affects a range of social processes. The current research demonstrates that biased sex ratios (greater numbers of one sex than the other) influence fundamental aspects of people's mating strategy. When the sex ratio was favorable (one's own sex was in the minority), both sexes adopted strong sex-typical sociosexual orientations (relatively restricted for women; relatively unrestricted for men). When the sex ratio was unfavorable (one's own sex was in the majority), both sexes shifted toward the orientation typically favored by the other sex: Women became more unrestricted and men became more restricted (Experiment 1). When the sex ratio was unfavorable (relative to favorable), participants also displayed greater aggression toward a romantically desirable (but not undesirable) same-sex partner (Experiment 2). Exploratory analyses suggested that the sex ratio effect was present for unprovoked aggression but not provoked aggression (given the exploratory nature of that analysis, the aggression effect should be considered with some caution). Findings suggest that people's mating strategies are adaptively calibrated to contingencies within the local mating ecology.

Sex Ratio Effects on Marital Formation and Dissolution, 1980–2000

Although marriage market characteristics are often used to explain in–out marriage transitions, Guttentag and Secord's sex ratio thesis provides a unique theoretical framework by which to elucidate marriage and divorce. The theory emphasizes the availability of “opposite” sex partners as an important factor, but hypothesized outcomes assume a gendered marriage market whereby males are more socioeconomically powerful than females. Using geographically standardized census tract data (N = 65,443), I examine the theory empirically across three decennial time points. After establishing that males, on average, hold a disproportionate amount of socioeconomic power, I conduct cross‐sectional regression analyses of marriage and divorce from 1980 to 2000. Results partially support the theory. While female marriage is consistently related to sex ratios as expected, sex ratios influence male marriage as expected only in some time periods and female and male divorce do not operate as expected in any time point. The findings imply that marriage entry and dissolution have distinctive causal mechanisms, suggesting the need for further theorization and research.

Effects of local extrinsic mortality rate, crime and sex ratio on preventable death in Northern Ireland.

Individual investment in health varies greatly within populations and results in significant differences in the risk of preventable death. Life history theory predicts that individuals should alter their investment in health (somatic maintenance) in response to ecological cues that shift the perceived fitness payoffs to such investments. However, previous research has failed to isolate the effects of different ecological factors on preventable death, and has often relied on macro-level data without individual controls. Here, we test some key predictions concerning the local ecology-that higher extrinsic mortality rate (EMR), crime rate and mate-scarcity (male/female-biased sex ratio) at the ward-level-will be associated with a higher risk of preventable death. We use census-based data from Northern Ireland (n = 927 150) on preventable death during an 8.7-year period from the 2001 Census and run Cox regressions for (i) accident/suicide or alcohol-related death and (ii) deaths from preventable diseases, for men and women separately, controlling for a wide range of individual variables. We find evidence of ward-level EMR and crime rate being positively associated with preventable death among men, particularly men with low socioeconomic position. There was a tentative relationship between male-biased sex ratio and preventable death among women, but not among men. Both behaviours that might lead to 'risky' death and health neglect might be adaptive responses to local ecologies. Efforts to reduce crime might be as effective as those to reduce extrinsic mortality, and both could have positive effects on various health behaviours.

Mating behaviour of the orange mud crab, Scylla olivacea: The effect of sex ratio and stocking density on mating success

Mud crabs from the genus Scylla have high commercial value and are considered as one of the highly sought luxury seafood items. Thorough understanding about their biology and mating behaviour is vital in providing important information for a sustainable exploitation and future incorporation into the aquaculture industry. The mating process of S. olivacea lasted 82.0±10.8h was divided into four phases: precopulation, molting, copulation, and postcopulation. Courtship displays and fighting were shown by mature males while they were courting females. Precopulatory position lasted for 55.2±10.8h before the pairs disengaged for the female to molt. The molting process was 4.6±0.3h. Copulation (mean duration was 6.6±0.5h) occurred while the female’s exoskeleton was still soft. Postcopulatory guarding lasted for 13.6±0.6h. Separation of the mating pairs indicates the end of postcopulation phase. Mating success percentage was unaffected by sex ratio, but inversely affected by stocking density. Cumulative mortality increased with increasing stocking density and unequal sex ratios. Postcopulatory guarding duration was significantly shorter in treatment with 1 male:2 females ratio and treatment with the lowest stocking density (2 crabs m−2). We proposed rearing of mud crab broodstocks for mating purpose using sex ratio of 1 male:2 females and stocking density of 6 crabs m−2 to maximize output (successful mating pairs) while maintaining low mortality percentage and shorter postcopulatory guarding duration.

Serum Iron, Zinc, and Copper Levels in Patients with Alzheimer's Disease: A Replication Study and Meta-Analyses.

To evaluate whether iron, zinc, and copper levels in serum are disarranged in Alzheimer's disease (AD), we performed meta-analyses of all studies on the topic published from 1984 to 2014 and contextually carried out a replication study in serum as well. Our meta-analysis results showed that serum zinc was significantly lower in AD patients. Our replication and meta-analysis results showed that serum copper was significantly higher in AD patients than in healthy controls, so our findings were consistent with the conclusions of four previously published copper meta-analyses. Even if a possible role of iron in the pathophysiology of the disease could not be ruled out, the results of our meta-analysis showed no change of serum iron levels in AD patients, but this conclusion was not robust and requires further investigation. The meta-regression analyses revealed that in some studies, differences in serum iron levels could be due to the different mean ages, while differences in zinc levels appeared to be due to the different sex ratios. However, the effect of sex ratio on serum zinc levels in our meta-analysis is subtle and needs further confirmation. Also, diverse demographic terms and methodological approaches appeared not to explain the high heterogeneity of our copper meta-analysis. Therefore, when investigating trace elements, covariants such as age and sex have to be taken into account in the analyses. In the light of these findings, we suggest that the possible alteration of serum zinc and copper levels are involved in the pathogenesis of AD.

Effect of housing system and sex ratio of quails on egg production, fertility and hatchability

A B S T R A C T The objective of this work was to evaluate the effect of housing system and sex ratio of quails on egg production, fertility and hatchability. A total number of 305 quails of five weeks old were divided into two groups, The first group (96 birds) was housed on battery cages and divided according to sex ratio into 2 equal subgroups of ratio (1: 2) male to females and 1: 3, the second one (209 birds) was housed on floor pens and divided according to sex ratio into 2 equal subgroups of ratio (1: 2) male to females and 1: 3. Eggs were collected daily for one month to estimate egg production percentage of each group. 200 eggs from each group were artificially incubated for detection the effect of housing on fertility, hatchability and embryonic mortality. The obtained results showed that the total egg production percentage was significantly higher (P<0.001) in case of battery cages (63.54±1.68%) than those in floor system (46.67±1.68%), it was higher but not significant at sex ratio 1:3 (57.01±1.68%) than those at 1:2 (53.21±1.68%). The fertility percentage was significantly higher (P<0.001) in case of floor pens (80.67±0.75%) than those in battery cages (73.67±0.75%) and significantly higher (P<0.01) at sex ratio 1:2 (79.17±0.75%) than those at 1:3 (75.17±0.75%). The hatchability percentage of total eggs set was higher but not significant in floor pens (52.00±1.89%) than those in battery cages (49.50±1.89%), it was higher but not significant at sex ratio 1:3 (52.00±1.89%) than those at 1:2 (49.50±1.89%). The hatchability percentage of fertile eggs set was significantly higher (P<0.001) in battery cages (70.40±0.90%) than those in floor pens (64.45±0.90%) and significantly higher (P<0.001) at sex ratio 1:3 (70.12±0.90%) than those at 1:2 (64.75±0.90%).

EPIZOOTIOLOGY OF CRANIAL ABSCESS DISEASE IN WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS) OF GEORGIA, USA.

Intracranial abscess disease is a cause of natural mortality for mature male white-tailed deer (Odocoileus virginianus). Most cases of abscesses are associated with bacterial infection by Trueperella (Arcanobacterium) pyogenes, but a complete understanding of the epidemiology of this disease is lacking. We quantified the effects of individual characteristics, site-specific herd demographics, land cover, and soil variables in estimating the probability of this disease. We examined 7,545 white-tailed deer from 60 sites throughout Georgia US for signs of cranial abscesses, the predecessor of intracranial abscesses, and recorded the presence or absence of cranial abscesses for each individual examined. We detected no cranial abscesses in 2,562 female deer but 91 abscesses in 4,983 male deer examined (1.8%). A generalized linear mixed model, treating site as a random effect, was used to examine several potential explanatory risk factors including site-level landscape and soil characteristics (soil and forest type), demographic factors (deer density and male to female ratio), and individual host factors (deer sex and age). Model results indicated that the probability of a male having a cranial abscess increased with age and that adult sex ratio (male:female) was positively associated with this disease. Site-specific variables for land cover and soil types were not strongly associated with observations of the disease at the scale measured and a large amount of among-site variability remained. Given the demonstrated effect of age, gender, and local sex ratios but the remaining unexplained spatial variability, additional investigation into spatiotemporal variation of the presumed bacterial causative agent of cranial abscesses appears warranted.

Vegetative propagation as a successful reproductive strategy in woody dioecious species in tropical coastal vegetation, southeast Brazil

Dioecious plant populations are composed of two distinct sexual morphs representing the female and male counterparts. Dioecy in restinga areas has been strongly associated with fleshy fruits, woodiness, generalist entomophily, and resource-poor environments. The ability of vegetative reproduction is another ecological trait commonly associated with dioecy, but not shown for the woody dioecious species in restingas. This study aimed to investigate whether the distribution of sexual morphs in populations is due to occurrence of vegetative propagation as a reproductive strategy among dioecious woody species on sandy coastal plains. We also intended to evaluate possible effects of sex ratio on sexual reproduction (female reproductive success). The study was conducted in the sandy coastal plains (restinga) of Marica, Rio de Janeiro State. We studied six woody dioecious species. During the reproductive period, all individuals of each species and your nearest neighbor were marked using GPS, along an area with approximately 5.1 ha. The sex of the individuals was recorded. This study provides evidence of the occurrence of vegetative propagation in the woody dioecious species studied and indicates that the ability to reproduce in this manner varies between sexual morphs, generating male-biased populations in most cases. Our data suggest that asexual reproduction by vegetative propagation of the male morphs can have an effect on sexual reproduction, as it increases the amount of staminate flowers, and therefore the supply of the pollen grains. Our results provide insights into vegetative reproduction as a strategy to increase male plant fitness and an alternative to populate environments under stress.

Effect of Female-Biased Sex Ratios on Female Homosexual Behavior in Japanese Macaques: Evidence for the "Bisexual Preference Hypothesis".

We aimed to explain the frequent and prevalent female homosexual behavior in the context of female-biased operational sex ratios (OSR) and qualified sex ratios (Q) in a free-ranging group of Japanese macaques (Macaca fuscata) living at Arashiyama-Kyoto, Japan. Our data included the average availability of sexually mature males during females' putative fertile period (OSR), the ratio of sexually mature males to sexually mature females (Q), as well as heterosexual and female homosexual solicitations and consortships collected during 13 mating seasons from 136 females. Our results did not support the "heterosexual deprivation hypothesis," which holds that female homosexual behavior is attributable to a shortage of male mates. Likewise, our results did not support the "lack of opposite-sex sexual competitor hypothesis," which holds that females have more access to female mates when male sexual rivals are scarce. Of the 11 predictions tested, only one yielded statistically significant results: we found that higher ratios of availability of preferred female partners to preferred male partners were associated with female homosexual consortships rather than female heterosexual consortships. This result supported the "bisexual preference hypothesis," which holds that female homosexual behavior is attributable to female preference for certain female mates relative to certain male mates. We conclude that when a female targets another female as a mate, it is an active choice for a female sexual partner over available male alternatives, rather than a by-default situation that occurs because males are not available as sexual partners, or because females are better able to access female sexual partners due to a scarcity of male sexual competitors.

What Will You Do If I Say 'I Do'?: The Effect of the Sex Ratio on Time Use within Taiwanese Married Couples

This paper uses the natural experiment of a large imbalance between men and women of marriageable age in Taiwan in the 1960s to test the hypothesis that higher sex ratios lead to husbands (wives) having a lower (higher) share of couple’s time in leisure and higher (lower) share of the couple’s total work time (employment, commuting and housework). A large sample of Taiwanese couples’ time diaries from 1987, 1990, and 1994 is used. The analysis finds evidence of the predicted effects of the county-level sex ratio on husbands’ and wives’ share of leisure and total work time. In addition, the age difference between husbands and wives is shown to be positively correlated with heightened county-level sex ratio a result which is also consistent with the theory that marriage market participants’ choices are affected by the prevailing sex ratio.

The effect of sex ratio on size-assortative mating in two explosively breeding anurans

Size-assortative mating (SAM) is a widespread phenomenon related to individual fitness. In our study, we examined: (i) the appearance of SAM, and (ii) the effect of sex ratio on intensity of SAM in wild populations of two explosively breeding anurans, common frogs,Rana temporaria, and common toads,Bufo bufo. Despite a higher male-biased operational sex ratio (OSR) in toads, the body lengths of the paired males and females were significantly correlated only in frogs. Increasing male-male competition, assessed via the OSR, resulted in a stronger correlation also in frogs only. Thus, great variability in the presence and intensity of SAM has been observed within both studied species.

Linking short-term behavior and personalities to feeding and mating rates in female water striders

In systems of strong sexual conflict, male harassment can constrain female feeding, which can limit fecundity. Female responses to harassment can depend on the social context or differ between individuals, and could be based on social or intrinsic behavioral cues at different spatio-temporal scales. Using experimental groupings of stream water striders (Aquarius remigis), we examined individual behavioral differences and effects of sex ratio on 4 aspects of female behavior: 1) habitat use and 2) activity, which lead to differences in 3) feeding rates and 4) mating rates. We compared effects of the immediate social environment, immediate female habitat use and activity, and consistent female behavioral tendencies (personalities) on feeding and mating probabilities, and asked if population sex ratio affected the relationships among these behaviors. We found that individual females did differ significantly in all 4 behaviors. Population sex ratio strongly influenced average female habitat use, feeding, and mating behaviors, and female feeding and mating behaviors were predicted by a combination of moment-to-moment female behavioral state, moment-to-moment social factors, and consistent individual female behavioral differences. Furthermore, habitat use tendencies correlated significantly with activity tendencies, and habitat use and activity tendencies predicted mating probabilities, but not feeding probabilities. Our study elucidates the specific individual-level behavioral mechanisms that lead to observed population-level patterns and emphasizes the benefits of studying behavior at multiple spatial and temporal scales.

Sex ratio effects on reproductive strategies in humans.

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

Measles may be a Risk Factor for Malignant Brain Tumors.

BackgroundA possible risk factor for brain tumor might be measles, since late neurologic sequelae are part of measles pathology. Subacute sclerosing panencephalitis, a devastating neurologic illness, is prone to develop years after measles infection.MethodsBecause measles damage to the brain might increase the risk of brain tumor, we examined the relationship of measles incidence in 1960 and brain tumor incidence in 50 US States and the District of Columbia, 2004-2007. Data on number of cases of measles by state in 1960 are from the Morbidity and Mortality Weekly Report. In 1960 measles was a childhood illness. We calculated measles incidence by obtaining the population of each state from the 1960 US Census and then age adjusting our results to the cumulative percent of the state population under age 21, since this would have been the measles-infected group. Data on the percentage white population by state are from the US Census (www.census.gov). Age-adjusted incidence (to the 2000 US standard population) of brain tumors is from the Central Brain Tumor Registry of the United States 2011 report.ResultsThere was a significant correlation between 1960 measles incidence and incidence of malignant brain tumors in persons 20 and older in 2004-2007 (r=0.321, p=0.026). Because glioblastoma is more frequent in whites and males, multivariate linear regression was performed with tumor incidence as the dependent variable, measles incidence, percent white population, and sex ratio by state as independent variables. Measles incidence was significantly correlated with malignant brain tumor incidence (β=0.361, p<0.001) and independent of the effect of race (β=0.734, p<0.001) and sex ratio m/f (β=-0.478, p<0.001). There was no correlation of measles incidence with brain tumor incidence in persons younger than 20.ConclusionInflammation is a critical component of tumor development. The inflammation of measles-induced subacute sclerosing panencephalitis, even subclinical cases, could well promote tumor formation, since many tumors arise from sites of infection, chronic irritation and inflammation.