Head and neck anthropometry, vertebral geometry and neck strength in height-matched men and women

Women have an increased incidence of whiplash injury and neck pain compared to men. Physical and numerical models represent one avenue to explore and potentially explain these gender differences, but a valid model of the female neck does not yet exist. A fundamental question in the development of a female neck model is whether female necks are simply scaled versions of male necks, or whether there are significant inter-gender geometrical differences. The goal of this study was to quantify differences in head and neck geometry and neck strength in pairs of male and female subjects matched for standing height and neck length. Based on 14 matched pairs of men and women, we found that most head and neck anthropometric parameters were significantly smaller in females compared to males. Moreover, gender differences in a number of neck anthropometry parameters (an average of 9-16% smaller in females) were larger than differences in head anthropometry parameters (an average of 3-6% smaller in females). Female vertebrae between C3 and C7 were significantly smaller than male vertebrae in the anterior-posterior dimension (p < 0.012) but not in the medial-lateral dimension (p > 0.07). Female necks were also significantly weaker than male necks (32% weaker in flexion and 20% weaker in extension; p < 0.001), and these strength differences corresponded well to those predicted solely from the observed geometric differences. These results demonstrate that male and female necks are not geometrically similar and indicate that a female-specific model will be necessary to study gender differences in neck-related disorders.     

Geographic distribution of human skin colour: A selective compromise between natural selection and sexual selection?

Modern humans have been shaped by the cumulative action of natural selection, non-adaptive random change, and sexual selection. The last of these is not universal and has prevailed in one of two circumstances: (1) A surplus of females due to high male mortality, combined with ecological constraints on female participation in food procurement which discourage males from taking second wives; (2) A surplus of single males due to generalized polygyny with relatively low male mortality. These circumstances are most likely to occur in (1) Arctic tundra environments, specifically the vast expanse of tundra covering most of Europe up to 10,000 B.P., and in (2) regions dominated by generalized polygyny, notably sub-Saharan Africa. Sexual selection often acts on existing sex differences, including perhaps sexual dimorphism in human skin colour. Whereas women are universally fairer in complexion, men are browner and ruddier; parallel to this, most human societies see lighter skin as more feminine and darker skin as more masculine. Hence, sexual selection should favour lighter pigmented women when a surplus of single females must compete for a mate. Since skin colour is only mildly sex-linked, both sexes would lighten in pigmentation within the population in question. Similarly, when a surplus of single males must compete for a mate, both sexes would darken. Geographic variation in human skin colour may thus represent a selective compromise between two counterbalancing forces: natural selection, as determined by latitudinal variation in sunlight; and sexual selection, as determined by variations in the following: male mortality rates, incidence of polygyny, and ecological constraints on female participation in food procurement.     

Higher variability in the number of sexual partners in males can contribute to a higher prevalence of sexually transmitted diseases in females

By examining published, empirical data we show that men and women consistently differ in the shape of the distribution of the number of sexual partners. The female distribution is always relatively narrow—variance is low—with a big majority of women having a number of partners close to the average. The male distribution is much wider—variance is high—with many men having few sex partners and many others having more partners than most females.Using stochastic modelling we demonstrate that this difference in variance is, in principle, sufficient to cause a difference in the gender prevalence of sexually transmitted diseases: compared to the situation where the genders have identical sex partner distributions, men will reach a lower equilibrium value, while women will stay at the same level (meaning that female prevalence becomes higher than male). We carefully analyse model behaviour and derive approximate expressions for equilibrium prevalences in the two different scenarios. We find that the size of the difference in gender prevalence depends on the variance ratio (the ratio between the variances of the male and female sex partner distributions), on the expected number of life-time partners, and on the probability of disease transmission. We note that in addition to humans, the variance phenomenon described here is likely to play a role for sexually transmitted diseases in other species also.We also show, again by examining published, empirical data, that the female to male prevalence ratio increases with the overall prevalence of a sexually transmitted disease (i.e., the more widespread the disease, the more women are affected). We suggest that this pattern may be caused by the effect described above in highly prevalent sexually transmitted diseases, while its impact in low-prevalence epidemics is surpassed by the action of high-risk individuals (mostly males).     

Albumin obscures sex differences in blood protein patterns of rats and humans.

Sex related differences in the blood protein patterns of male and female rats and humans have been studied by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. In rats, a prominent band of mol.wt. 74000--78000 is seen in females in far greater quantity than in males, castrated males or ovariectomized females. A secondary band of 100000 is seen under non-reducing conditions in female rats that is absent in males. In humans, bands of 92000 and 88000 mol.wt. appear to be variable in concentration in men although relatively constant in women. The above differences are observable only if serum albumin is removed from the samples before electrophoresis. The results suggest that each sex has its own characteristic blood protein pattern.     

Male age and strain affect ejaculate quality in the Mexican fruit fly

Aging in all organisms is inevitable. Male age can have profound effects on mating success and female reproduction, yet relatively little is known on the effects of male age on different components of the ejaculate. Furthermore, in mass‐reared insects used for the Sterile Insect Technique, there are often behavioral differences between mass‐reared and wild males, while differences in the ejaculate have been less studied. The ejaculate in insects is composed mainly of sperm and accessory gland proteins. Here, we studied how male age and strain affected (i) protein quantity of testes and accessory glands, (ii) the biological activity of accessory gland products injected into females, (iii) sperm viability, and (iv) sperm quantity stored by females in wild and mass‐reared Anastrepha ludens (Diptera: Tephritidae). We found lower protein content in testes of old wild males and lower sperm viability in females mated with old wild males. Females stored more sperm when mated to young wild males than with young mass‐reared males. Accessory gland injections of old or young males did not inhibit female remating. Knowledge of how male age affects different ejaculate components will aid our understanding on investment of the ejaculate and possible postcopulatory consequences on female behavior.     

A window of opportunity: improving cardiovascular health in women

From our daily lives we know that men and women differ considerably. Men buy cars and women shoes, men ruin the white laundry and women destroy acceleration gears, and we eagerly read the books describing that men are from Mars and women from Venus. These stereotypes do reflect the constant debate on gender differences in society. Similarly, it is increasingly accepted within cardiovascular health care that male and female patients might need another approach.     

What doesn’t kill her,will make her depressed

In this paper we study the long run effects of the 1959–61 Chinese Famine on mental health outcomes. We focus on cohorts that were born during the famine and examine their mental health as adults, when they are roughly 55 years of age. We find that early-life exposure to this famine leads to a large statistically significant negative impact on women’s mental health, while there is limited effect on men. This gender differential effect is observed because male fetuses experience a stronger natural selection as compared to female fetuses, which implies that in the longer run, surviving females may exhibit larger detrimental effects of early-life famine exposure. Thus, the observed effects are a composite of two well-established factors, the survival of the fittest and the Fetal Origins hypothesis.     

Participation rates and the difference in performance of women and men in chess

The superiority of men over women in chess has been cited as evidence that there are fundamental differences in male and female intelligence (Howard, 2005a, 2006; Irwing & Lynn, 2005). An alternative interpretation of the difference is that it is due to differential male and female participation rates in chess (Charness & Gerchak, 1996; Bilali? & McLeod, 2006; Chabris & Glickman, in press). This has been dismissed by Howard (2006) on the grounds that changes in the difference in skill level between top male and female players in recent years are not correlated with changing relative participation rates. Here it is shown that Howard's analysis is misleading. The data are consistent with differential participation rates as the explanation of the gap between the performance of women and men in chess.     

How does plant sex alter microbiota assembly in dioecious plants?

Plant microbiota can greatly impact plant growth, defense, and health in different environments. Thus, it might be evolutionarily beneficial for plants to be able to control processes related to microbiota assembly. Dioecious plant species display sexual dimorphism in morphology, physiology, and immunity. These differences imply that male and female individuals might differently regulate their microbiota, but the role of sex in microbiota assembly has been largely neglected so far. Here, we introduce the mechanism of how sex controls microbiota in plants analogically to the sex regulation of gut microbiota in animals, in particular in humans. We argue that plant sex imposes selective pressure on filtering and constructing microbiota in the rhizosphere, phyllosphere, and endosphere along the soil–plant continuum. Since male plants are more resistant than female plants to environmental stresses, we suggest that a male host forms more stable and resistant plant microbiota that cooperate more effectively with the host to resist stresses. Male and female plants can distinguish whether a plant is of the same or different sex, and males can alleviate stress-caused damage in females. The impact of a male host on microbiota would protect female plants from unfavorable environments.     

Sex differences in cannabinoid pharmacology: A reflection of differences in the endocannabinoid system?

Marijuana is the most widely used illicit drug in the U.S., and marijuana use by women is on the rise. Women have been found to be more susceptible to the development of cannabinoid abuse and dependence, have more severe withdrawal symptoms, and are more likely to relapse than men. The majority of research in humans suggests that women are more likely to be affected by cannabinoids than men, with reports of enhanced and decreased performance on various tasks. In rodents, females are more sensitive than males to effects of cannabinoids on tests of antinociception, motor activity, and reinforcing efficacy. Studies on effects of cannabinoid exposure during adolescence in both humans and rodents suggest that female adolescents are more likely than male adolescents to be deleteriously affected by cannabinoids. Sex differences in response to cannabinoids appear to be due to activational and perhaps organizational effects of gonadal hormones, with estradiol identified as the hormone that contributes most to the sexually dimorphic effects of cannabinoids in adults. Many, but not all sexually dimorphic effects of exogenous cannabinoids can be attributed to a sexually dimorphic endocannabinoid system in rodents, although the same has not yet been established firmly for humans. A greater understanding of the mechanisms underlying sexually dimorphic effects of cannabinoids will facilitate development of sex-specific approaches to treat marijuana dependence and to use cannabinoid-based medications therapeutically.     

Function specific supersensitivity of m-chlorophenyl piperazine-induced serotonergic neurotransmission in female compared to male rats

Administration of various doses of m-chlorophenylpiperazine (m-CPP), a 5-hydroxytryptamine (5-HT) agonist, to rats increased plasma level sof corticosterone and decreased locomotor activity in a dose dependent manner. The increases of plasma corticosterone but not the decreases of locomotor activity were greater in female than male rats. Hypophagic effects of m-CPP not different in freely feeding male and female rats were greater in females when food deprived animals used. The findings along with our previous report show a functional supersensitivity of 5-HT neurotransmission involved in the regulation of hypothalamo-pituitary adrenocortical axis and appetite supression in female sex, and suggest a possible basis for the greater occurence of depression and anorexia in women than men.     

Women in medicine: practice patterns and attitudes.

Increasing numbers of women are entering medicine in Canada. In 1959 women accounted for 6% of the medical school graduates, but by 1989 they accounted for 44%. Although there has been little systematic investigation of the impact of this increase on Canada''s health care system, there are grounds for believing that female physicians bring with them distinctive values and interests, which may be reflected in the way they conduct their professional practices. We used data from a recent national survey of 2398 Canadian physicians to examine differences between women and men in their practices and their attitudes toward health care issues. Significant differences were found in the organization and management of the practices. Women preferred group over solo practice and were overrepresented in community health centres, health service organizations and centres locaux de services communautaires in Quebec. One-third of the women, as compared with half of the men, were in specialties. Even after adjusting for differences in workloads the incomes of the women were significantly lower than those of the men. Only minor differences were observed in the assessment of the health care system and alternative modes of organizing health care services. We believe that the differences were due to the double workload of women as professionals and family caregivers and the powerful socialization effects of medical education. As women overcome their minority status in the medical profession, differences between the sexes may become more apparent. Thus, the extent and effects of the progressive increase in the number of women in Canadian medicine should be assessed on an ongoing basis.     

Decomposing body mass index gaps between Mediterranean countries: A counterfactual quantile regression analysis

Wide cross-country variation in obesity rates has been reported between European Union member states. Although the existing cross-country differences have not been analyzed in depth, they contain important information on health production determinants. In this paper we apply a methodology for conducting standardized cross-country comparisons of body mass index (BMI). We draw on estimations of the marginal density function of BMI for Italy and Spain in 2003, two countries with similar GDP and socio-economic conditions. We produce different counterfactual distribution estimates using covariates (health production inputs) specified in a quantile regression. Our findings suggest that Spain-to-Italy BMI gaps among females are largely explained by cross-country variation in the returns to each covariate, especially for younger women. We find that adverse underlying determinants do not explain the gap observed in particular between younger Spanish females and their Italian counterfactuals; behavioural differences appear to be the key. We tentatively conclude that Spanish policy on obesity should target mainly younger females.     

云南昆明不同产地滇蛙的食物变化比较

要真正了解一种蛙的生态习性及食性,调查和分析其不同种群、不同生长阶段和不同性别的年周期食物组成是必要的。自1998年5月至2003年11月在昆明白龙寺、花红洞和西街口逐月采集滇蛙Rana pleuraglen标本进行食性分析,结果表明,滇蛙种群间和不同生长阶段、及雌雄个体间的食量百分比上有差异。Kruskal-Wallis检验结果显示,不同种群间和不同生长阶段的食物量组成无显著差异。Mann—Whitney U检验和Kolmogorov—Smirnov Z检验结果显示,各产地雌雄滇蛙食物量组成均无显著差异。滇蛙的食物类群相对丰富,反映它是捕食的多面手。昆明地区气候稳定,不同小地域农田生境的昆虫相几乎相同。这是食物成分相同的主要原因。而滇蛙不同种群的食物成分中,一些类群所占的比例不完全相同,又反映出三地气候和／或昆虫相的微小差异。幼年组食物中双翅目和膜翅的成分高于成年Ⅰ、Ⅱ组的。这可能与上述食物类群富含幼年组个体所需要的营养成分或者比例较高有关,所以它们食之较多。     

Cooperation and conflict: The behavioral ecology of the sexual division of labor

When it comes to subsistence, men and women in almost all societies do it differently. One long-standing explanation for this sexual division of labor is that men and women pair up to provision offspring and specialize in subsistence activities in order to maximize household productivity. This model of cooperative parental provisioning has generally been supported by the proposal that both male and female reproductive success is maximized by provisioning current offspring rather than deserting them in order to seek new mating opportunities. But recent analyses of bird behavior have often failed to support this premise. We now know that among many species conflicting reproductive strategies between males and females often result in less than optimal compromises with regard to mating and parenting. This new focus on the role of sexual selection in creating compromise and conflict between the sexes has the potential to illuminate many puzzling aspects of human partnerships between men and women. To demonstrate its potential, I compare the explanatory power of a cooperative provisioning model of sex difference in human foraging and food sharing with a model incorporating conflicting reproductive goals.     

Estrogen regulation of protein expression and signaling pathways in the heart

Sex differences in cardiovascular disease and cardiac physiology have been reported in humans as well as in animal models. Premenopausal women have reduced cardiovascular disease compared to men, but the incidence of cardiovascular disease in women increases following menopause. Sex differences in cardiomyocytes likely contribute to the differences in male–female physiology and response to disease. Sex differences in the heart have been noted in electrophysiology, contractility, signaling, metabolism, and cardioprotection. These differences appear to be due, at least in part, to differences in gene and protein expression as well as in posttranslational protein modifications. This review will focus primarily on estrogen-mediated male–female differences in protein expression and signaling pathways in the heart and cardiac cells. It should be emphasized that these basic differences are not intrinsically beneficial or detrimental per se; the difference can be good or bad depending on the context and circumstances.     

Female feeding priority in bonobos, Pan paniscus, and the question of female dominance

The question of whether bonobos show feeding priority and female dominance has been proposed and examined, both in the wild and in captive studies, with differing results. The relationship between female dominance and female feeding priority has been best studied in prosimian primates. These studies use established criteria of females consistently evoking submissive behavior from males in dyadic encounters for determining female dominance. Although the relationship is complex, female dominance in prosimians is associated with preferential access to food. Data from studies of wild habituated bonobos in the Lomako Forest, Democratic Republic of the Congo, are examined for evidence of both female feeding priority and female social dominance using similar criteria as used for prosimians. Bonobos showed evidence of female feeding priority in small, but not in large, food patches. Male-male competition for mating opportunities at the start of the food bout was related to some, but not all, differences in time spent feeding between the sexes. Female dominance similar to that seen in prosimians was not observed in these bonobos. Males were consistently dominant in dyadic interactions. Female feeding priority with male dyadic social dominance implies that male deference during feeding cannot be excluded as one explanation of interpretations of female dominance in bonobos. Additionally, dominance of male bonobos by females appears to require the presence of female coalition partners. As in other primates with female feeding priority, bonobo females express this trait where food is economically defendable. Unlike prosimians, however, bonobo female feeding priority may result from male deference and the importance of female coalitions in nondyadic interactions.     

Contest dynamics for food and reproductive resources are defined by health condition in a dung beetle

Male dung beetles compete to obtain food and females, and early resource recognition and appropriation increase the probability of mating. The outcome of such encounters is expected to be defined by self‐ and the opponent’s health condition. In this study, we analyzed the effect of body condition and immune defense on the contest dynamics between males that rolled a food ball with a partner female (owner males) and intruder males of dung beetle Canthon cyanellus. Body condition was measured as body size, body dry mass, lipid mass, and muscle mass; immune defense was estimated via phenoloxidase activity. Owner males with higher lipid mass contacted the food ball significantly earlier than owner males with lower lipid mass. Individuals with lower phenoloxidase activity started to roll food balls earlier than individuals with higher phenoloxidase activity. Owner males that had higher body dry mass, compared to female partners, began to roll the food ball significantly earlier than male–female pairs with lower differences in dry mass. Heavier males won significantly more contests than lighter males. Our results suggest that the health condition is a key factor related to the dynamics and outcome of male–male contests for resources and females in C. cyanellus. Consequently, differences in individual condition are main determinants of contest outcomes in dung beetles.     

The mechanical efficiency of locomotion in men and women with special emphasis on stretch-shortening cycle exercises

The mechanical efficiency of the leg extensor musculature of men and women was examined with a special "sledge ergometer". The subjects (ten males and ten females) performed pure positive work, pure negative work and a combination of negative and positive work (stretch-shortening cycle). The mechanical efficiency of pure positive work was on average 19.8 +/- 1.2% for female subjects and 17.4 +/- 1.2% for male subjects (t = 4.12, P less than 0.001), although the work intensity was equal in both groups. The mechanical efficiency of pure negative work was slightly lower in women than in men (59.3 +/- 14.4% vs 75.6 +/- 29.3%). The mechanical efficiency of positive work (eta +) in a stretch-shortening cycle exercise was 38.1 +/- 6.8% in men and 35.5 +/- 6.9% in women. The utilization of prestretch was better for female subjects at low prestretch levels, whereas males showed greater potentiation of elastic energy at higher prestretch levels. Regarding absolute Wel (work due to elasticity) values, male subjects showed greater (P less than 0.001) values than females (189 +/- 44 J vs 115 +/- 36 J, respectively). Fundamental differences in neuromuscular functions in men and women might cause the differences in the results obtained.     

Effects of reproduction on sexual dimorphisms in rat bone mechanics

Osteoporosis most commonly affects postmenopausal women. Although men are also affected, women over 65 are 6 times more likely to develop osteoporosis than men of the same age. This is largely due to accelerated bone remodeling after menopause; however, the peak bone mass attained during young adulthood also plays an important role in osteoporosis risk. Multiple studies have demonstrated sexual dimorphisms in peak bone mass, and additionally, the female skeleton is significantly altered during pregnancy/lactation. Although clinical studies suggest that a reproductive history does not increase the risk of developing postmenopausal osteoporosis, reproduction has been shown to induce long-lasting alterations in maternal bone structure and mechanics, and the effects of pregnancy and lactation on maternal peak bone quality are not well understood. This study compared the structural and mechanical properties of male, virgin female, and post-reproductive female rat bone at multiple skeletal sites and at three different ages. We found that virgin females had a larger quantity of trabecular bone with greater trabecular number and more plate-like morphology, and, relative to their body weight, had a greater cortical bone size and greater bone strength than males. Post-reproductive females had altered trabecular microarchitecture relative to virgins, which was highly similar to that of male rats, and showed similar cortical bone size and bone mechanics to virgin females. This suggests that, to compensate for future reproductive bone losses, females may start off with more trabecular bone than is mechanically necessary, which may explain the paradox that reproduction induces long-lasting changes in maternal bone without increasing postmenopausal fracture risk.