Sex differences in nutrient-dependent reproductive ageing

Evolutionary theories of aging predict that fitness-related traits, including reproductive performance, will senesce because the strength of selection declines with age. Sexual selection theory predicts, however, that male reproductive performance (especially sexual advertisement) will increase with age. In both bodies of theory, diet should mediate age-dependent changes in reproductive performance. In this study, we show that the sexes exhibit dramatic, qualitative differences in age-dependent reproductive performance trajectories and patterns of reproductive ageing in the cricket Teleogryllus commodus. In females, fecundity peaked early in adulthood and then declined. In contrast, male sexual advertisement increased across the natural lifespan and only declined well beyond the maximum field lifespan. These sex differences were robust to deviations from sex-specific dietary requirements. Our results demonstrate that sexual selection can be at least as important as sex-dependent mortality in shaping the signal of reproductive ageing.     

Sex differences in the onset of seasonal reproductive quiescence in hamsters

Day length is the primary cue used by many mammals to restrict reproduction to favourable spring and summer months, but it is unknown for any mammal whether the seasonal loss of fertility begins at the same time and occurs at the same rate in females and males; nor it established whether the termination of mating behaviour in males and females coincides with the loss of fertility. We speculated that females, owing to their greater energetic investment in reproduction, are the limiting sex in terminating offspring production in short days (SDs). Oestrous cycles and production of young were monitored in Syrian hamsters (Mesocricetus auratus) transferred from long days (LDs) to SDs. Females were mated to LD males after three to eight weeks of SD treatment; in a parallel experiment, males housed in SDs were mated to LD females. After five and eight weeks in SDs, at least twice as many males as females were fertile. Both males and females continued to copulate for several weeks after becoming infertile. The onset of seasonal infertility occurs earlier in females than males and the decline in fertility precedes the seasonal loss of mating behaviour in both sexes.     

Sex differences in the drivers of reproductive skew in a cooperative breeder

Many cooperatively breeding societies are characterized by high reproductive skew, such that some socially dominant individuals breed, while socially subordinate individuals provide help. Inbreeding avoidance serves as a source of reproductive skew in many high‐skew societies, but few empirical studies have examined sources of skew operating alongside inbreeding avoidance or compared individual attempts to reproduce (reproductive competition) with individual reproductive success. Here, we use long‐term genetic and observational data to examine factors affecting reproductive skew in the high‐skew cooperatively breeding southern pied babbler (Turdoides bicolor). When subordinates can breed, skew remains high, suggesting factors additional to inbreeding avoidance drive skew. Subordinate females are more likely to compete to breed when older or when ecological constraints on dispersal are high, but heavy subordinate females are more likely to successfully breed. Subordinate males are more likely to compete when they are older, during high ecological constraints, or when they are related to the dominant male, but only the presence of within‐group unrelated subordinate females predicts subordinate male breeding success. Reproductive skew is not driven by reproductive effort, but by forces such as intrinsic physical limitations and intrasexual conflict (for females) or female mate choice, male mate‐guarding and potentially reproductive restraint (for males). Ecological conditions or “outside options” affect the occurrence of reproductive conflict, supporting predictions of recent synthetic skew models. Inbreeding avoidance together with competition for access to reproduction may generate high skew in animal societies, and disparate processes may be operating to maintain male vs. female reproductive skew in the same species.     

Sex differences in plasma corticosterone in desert tortoises, Gopherus agassizii, during the reproductive cycle

Blood samples from 30 female and 20 male adult desert tortoises, Gopherus agassizii, were collected at monthly intervals during the annual reproductive cycle (April to October). Plasma corticosterone and the sex steroids in each of the samples were analyzed by radioimmunoassay. Mean corticosterone levels in males were significantly higher than in females (P < 0.001) in every month. Male tortoises showed a marked seasonal pattern in plasma corticosterone with a highly significant peak in July, August, September, and October that corresponded with a similar peak in plasma testosterone. Testosterone and corticosterone in the male showed a highly significant correlation (P < 0.0001). The pattern of corticosterone in the female was less marked, with a significant peak in May during the mating and nesting season, but no association with the peak in estradiol in late summer was apparent. The highest levels of corticosterone in the males were associated with the peak in spermatogenesis and intense male-male combat. These results support similar data from other reptiles that suggest increased glucocorticoid secretion during periods of increased activity and metabolism.     

Sex differences in human adipose tissues - the biology of pear shape

ABSTRACT: Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology.     

Evidence of a Male Sex Pheromone in the Round Goby (Neogobius melanostomus)

The reproductive success of the round goby (Neogobius melanostomus), an invasive fish, may be mediated by the use of pheromones. We hypothesized that reproductive male (RM) round gobies release sex pheromone to which reproductive females (RF) respond. In this study, we compared behavioural and electrophysiological responses of reproductive and non-reproductive female round gobies to conspeci fic males. Results of behavioural experiments in the laboratory showed that RF spent significantly more time near the source of the male odour compared with odours from control water. However, RF did not distinguish between odours from non-reproductive male (non-RM) water and control water. Non-reproductive females (non-RF) were not attracted to odours released from RM or non-RM water. Results of electro-olfactogram (EOG) responses showed that both RF and non-RF discriminated between HPLC fractionated RM and non-RM odours. However, the EOG responses of RF were about eight-fold higher than non-RF exposed to RM odours. These findings confirm that RM round gobies release a pheromone signal that attracts RF. The results of this research may be useful in developing control strategy using natural pheromones to disrupt the reproductive behaviour of the invasive round goby and to curtail its effects on native species. An erratum to this article is available at .     

Sex differences, dominance, and personality in the chimpanzee

This study demonstrates a useful methodology for judging the personality of chimpanzees (Pan troglodytes schweinfurthi). Observers rated the chimpanzees on a forced-choice rating scale which yielded measures on eight emotion dimensions. The rating scale, Emotions Profile Index, is derived from a theory of personality which stresses the adaptive significance of emotions at all evolutionary levels. This method has theoretical generality, having been successfully applied previously to humans, baboons and dolphins. Observers were able to rate chimpanzees with reasonable reliability. Sex differences in personality were evident in this chimpanzee sample. In addition, dominance rank was found to correlate with certain emotion dimensions.     

Sex differences in haem biosynthesis and porphyrin content in the Harderian gland of the golden hamster

Methods are described for the measurement of seven haem biosynthetic enzymes in Harderian gland tissue from male and female golden hamsters. Sex differences were found in five of the seven enzymes. In each case, female tissue exhibited higher activity than male tissue. These differences in enzyme activity are sufficient to account for the major sex difference in porphyrin content in the Harderian gland of this species.     

长爪沙鼠对植物血凝素的反应及能量学代价的性别和季节差异

以野生长爪沙鼠为对象,通过外源注射植物血凝素(Phytohemagglutinin,PHA)和磷酸盐缓冲液,分别测定了夏季和冬季沙鼠注射前、注射24 h 和48 h 后体重和静止代谢率(Resting metabolic rate,RMR)的变化,以及48 h 后沙鼠足增重量和白细胞总数(White blood cell counts,WBCs)的变化,以检测沙鼠的免疫功能和能量代价的性别和季节差异。结果显示:1)注射PHA 能显著增加沙鼠足重和白细胞的总数,夏季白细胞的总数高
于冬季;2)冬季沙鼠体重高于夏季,雄鼠大于雌鼠,但PHA 处理对注射前后沙鼠的体重无影响;3)冬季RMR高于夏季,雄鼠大于雌鼠,但PHA 处理对沙鼠的RMR 无影响,PHA 处理对注射前后沙鼠的RMR 也无影响。这些结果表明,长爪沙鼠对PHA 的反应具有季节差异,但无性别差异,也没有发现明显的能量学代价,这可能与野外环境条件的大幅度波动(如环境温度和食物条件等)和沙鼠的繁殖状态有关。     

Sex differences in the effects of juvenile and adult diet on age‐dependent reproductive effort

Sexual selection should cause sex differences in patterns of resource allocation. When current and future reproductive effort trade off, variation in resource acquisition might further cause sex differences in age‐dependent investment, or in sensitivity to changes in resource availability over time. However, the nature and prevalence of sex differences in age‐dependent investment remain unclear. We manipulated resource acquisition at juvenile and adult stages in decorated crickets, Gryllodes sigillatus, and assessed effects on sex‐specific allocation to age‐dependent reproductive effort (calling in males, fecundity in females) and longevity. We predicted that the resource and time demands of egg production would result in relatively consistent female strategies across treatments, whereas male investment should depend sharply on diet. Contrary to expectations, female age‐dependent reproductive effort diverged substantially across treatments, with resource‐limited females showing much lower and later investment in reproduction; the highest fecundity was associated with intermediate lifespans. In contrast, long‐lived males always signalled more than short‐lived males, and male age‐dependent reproductive effort did not depend on diet. We found consistently positive covariance between male reproductive effort and lifespan, whereas diet altered this covariance in females, revealing sex differences in the benefits of allocation to longevity. Our results support sex‐specific selection on allocation patterns, but also suggest a simpler alternative: males may use social feedback to make allocation decisions and preferentially store resources as energetic reserves in its absence. Increased calling effort with age therefore could be caused by gradual resource accumulation, heightened mortality risk over time, and a lack of feedback from available mates.     

Sex,status, and reproductive success in the contemporary United States

This paper reexamines the relationship between status and reproductive success (at the ultimate and proximate levels) using data on sex frequency and number of biological children from representative samples of the U.S. population. An ordered probit analysis of data from the 1989–2000 General Social Survey (GSS) shows that high-income men report greater frequency of sex than all others do. An OLS regression of data from the 1994 GSS shows that high-income men have more biological children than do low-income men and high-income women. Furthermore, more educated men have more biological children than do more educated women. Results also show that intelligence decreases the number of offspring and frequency of sex for both men and women.     

Seasonal variations in the physiological status and energy content of somatic and reproductive tissues of chub

The seasonal fluctuations in condition, nutrition and somatic energy content, and gonad development cycle were investigated in chub Leuciscus pyrenaicus from the headwaters of the Guadalete River, a freshwater ecosystem characterized by strong seasonal fluctuations in discharge and water level, temperature and food supply. The relationship between somatic stage and gonad cycle was also investigated and discussed. Condition, nutrition and somatic energy cycles could be divided into two distinct periods: from April to January with summer decreases and autumn increments, which is common for juveniles and mature fish; and from January to March, when juveniles and mature fish displayed different temporal variations related to the reproductive cycle. Gonad development took place from the end of the winter into the summer, the testes developing before the ovaries. Spawning started in late spring (May) and continued into summer (June and July), with fish quiescent by autumn (September). The results suggest that, for L. pyrenaicus , both environmental factors (e.g. food supply, water temperature) and reproduction needs affect the condition, nutrition and somatic energy storage of fish, which have been used as indicators of the physiological status of the population.     

Sex differences in recombination

One of the stronger empirical generalizations to emerge from the study of genetic systems is that achiasmate meiosis, which has evolved 25–30 times, is always restricted to the heterogametic sex in dioecious species, usually the male. Here we collate data on quantitative sex differences in chiasma frequency from 54 species (4 hermaphroditic flatworms, 18 dioecious insects and vertebrates and 32 hermaphroditic plants) to test whether similar trends hold. Though significant sex differences have been observed within many species, only the Liliaceae show a significant sexual dimorphism in chiasma frequency across species, with more crossing over in embryo mother cells than in pollen mother cells; chiasma frequencies are unrelated to sex and gamety in all other higher taxa studied. Further, the magnitude of sexual dimorphism, independent of sign, does not differ among the three main ecological groups (dioecious animals, plants, and hermaphroditic animals), contrary to what would be expected if it reflected sex-specific selection on recombination. These results indicate that the strong trends for achiasmate meiosis do not apply to quantitative sex differences in recombination, and contradict theories of sex-specific costs and benefits. An alternative hypothesis suggests that sex differences may be more-or-less neutral, selection determining only the mean rate of recombination. While male and female chiasma frequencies are more similar than would be expected under complete neutrality, a less absolute form of the hypothesis is more difficult to falsify. In female mice the sex bivalent has more chiasmata for its length than the autosomes, perhaps compensating for the absence of recombination in males. Finally, we observe that chiasma frequencies in males and females are positively correlated across species, validating the use of only one sex in comparative studies of recombination.     

Sex differences in bedbug nymphs,Cimex lectularius

Bedbugs, Cimex lectularius, have re-gained their status as economically important insects in many parts of the world and, consequently, re-attracted research into their biology. Standardizing age, feeding and mating status of experimental animals requires easy and reliable identification of the nymphal sex. Here, we show the angle of the pointedness of the abdomen to be a reliable sex marker in nymphal stage 5, as well as the shape of the 9th sternite, allowing rapid nymph sorting by sex. The sexual dimorphism was driven by males, not females, departing from the larval growth trajectory.