Sex‐specific responses of Populus yunnanensis exposed to elevated CO2 and salinity

Populus yunnanensis Dode., a native dioecious woody plant in southwestern China, was employed as a model species to study sex‐specific morphological, physiological and biochemical responses to elevated CO₂ and salinity. To investigate the effects of elevated CO₂, salinity and their combination, the cuttings were exposed to two CO₂ regimes (ambient CO₂ and double ambient CO₂) and two salt treatments in growth chambers. Males exhibited greater downregulation of net photosynthesis rate (A_net) and carboxylation efficiency (CE) than females at elevated CO₂, whereas these sexual differences were lessened under salt stress. On the other hand, salinity induced a higher decrease in A_net and CE, more growth inhibition and leaf Cl^? accumulation and more damage to cell organelles in females than in males, whereas the sexual differences in photosynthesis and growth were lessened at elevated CO₂. Moreover, elevated CO₂ exacerbated membrane lipid peroxidation and organelle damage in females but not in males under salt stress. Our results indicated that: (1) females are more sensitive and suffer from greater negative effects than do males under salt stress, and elevated CO₂ lessens the sexual differences in photosynthesis and growth under salt stress; (2) elevated CO₂ tends to aggravate the negative effects of salinity in females; and (3) sex‐specific reactions under the combination of elevated CO₂ and salinity are distinct from single‐stress responses. Therefore, these results provide evidence for different adaptive responses between plants of different sexes exposed to elevated CO₂ and salinity.     

Nitrogen nutrient status induces sexual differences in responses to cadmium in Populus yunnanensis

Populus yunnanensis was employed as a model species to detect sexual differences in growth, physiological, biochemical, and ultrastructural responses to cadmium (Cd) stress, nitrogen (N) deposition, and their combination. Compared with the control conditions, Cd decreased plant biomass, damaged the photosynthetic apparatus, visible as a decreased maximum efficiency of photosystem II (PSII; F(v)/F(m)) and effective quantum yield of PSII (Yield), depressed gas exchange capacity, and induced oxidative stress, visible as the disruption of antioxidative enzymes and accumulation of reactive oxygen species (ROS), in both sexes. On the other hand, Cd toxicity was mitigated by the recovery of gas exchange capacity, a decrease in ROS, and improvement of the redox imbalance in both sexes when N deposition was applied. However, males showed a higher gas exchange capacity, lower enzyme inhibition and ROS accumulation, stronger abilities to maintain cellular redox homeostasis, and a better maintenance of chloroplast ultrastructure than did females when exposed to Cd stress alone. Although males exhibited a higher Cd content in leaves than did females, males also accumulated higher levels of non-protein thiols (NP-SHs) and free amino acids (FAAs) for detoxification than did females. Sexual differences induced by Cd, visible, for example, in F(v)/F(m), Yield, net photosynthesis rate (A), and stomatal conductance (g(s)), decreased under N deposition, as no significant differences between the sexes existed in these parameters under the combined treatment. The results indicated that females are more sensitive to Cd stress and suffer more injuries than do males. Moreover, N deposition can mitigate Cd toxicity and decrease sexual differences in Cd sensitivity.     

The effects of stress and sex on selection,genetic covariance,and the evolutionary response

The capacity of a population to adapt to selection (evolvability) depends on whether the structure of genetic variation permits the evolution of fitter trait combinations. Selection, genetic variance and genetic covariance can change under environmental stress, and males and females are not genetically independent, yet the combined effects of stress and dioecy on evolvability are not well understood. Here, we estimate selection, genetic (co)variance and evolvability in both sexes of Tribolium castaneum flour beetles under stressful and benign conditions, using a half‐sib breeding design. Although stress uncovered substantial latent heritability, stress also affected genetic covariance, such that evolvability remained low under stress. Sexual selection on males and natural selection on females favoured a similar phenotype, and there was positive intersex genetic covariance. Consequently, sexual selection on males augmented adaptation in females, and intralocus sexual conflict was weak or absent. This study highlights that increased heritability does not necessarily increase evolvability, suggests that selection can deplete genetic variance for multivariate trait combinations with strong effects on fitness, and tests the recent hypothesis that sexual conflict is weaker in stressful or novel environments.     

Reciprocal grafting separates the roles of the root and shoot in sex‐related drought responses in Populus cathayana males and females

Drought stress responses and sensitivity of dioecious plants, such as Populus cathayana Rehd., are determined by different mechanisms in each sex. In general, males tend to be more resistant while females are more sensitive. Here, we used reciprocal grafting between males and females to determine the relative importance of roots and shoots when plants are exposed to drought stress. Total dry matter accumulation (DMA), photosynthetic capacity, long‐term water‐use efficiency (Δ), water potential and ultrastructure of mesophyll cells were evaluated to determine the different roles of root and shoot in sex‐related drought responses. Plants with male roots were found to be more resistant and less sensitive to water stress than those with female roots under drought conditions. On the contrary, plants with female shoots grew better than those with male shoots under well‐watered conditions. These results indicated that the sensitivity of males and females to water stress is primarily influenced by root processes, while under well‐watered conditions sexual differences in growth are primarily driven by shoot processes. Furthermore, grafting female shoot scion onto male rootstock was proved to be an effective mean to improve resistance to water stress in P. cathayana females.     

Sexual differences and sex ratios of dioecious plants under stressful environments

雌雄异株植物对环境胁迫响应的性别差异与性别比例 雌雄异株植物在性特征(繁殖器官)和次级性特征(植物的特征)均表现出性二态。形态、生理与生态特征等次级性特征的性别差异,通常在繁殖成本和其他功能性状之间存在着权衡。尽管有证据表明性二态对环境胁迫的响应不一定存在于所有植物中,但次级性特征的权衡可能受到环境胁迫的影响。当植物表现出性二态时,不同的物种与胁迫因子可以导致性别特异性的响应。因此,胁迫作用对雌雄异株植物影响的概括性研究是必须的。另外,性二态可能会影响雌雄异株植物沿着环境梯度的频率和分布,引起生态位分化与性别空间分异。目前,控制性别比例偏差的原因和机制还知之甚少。本综述旨在讨论不利环境下的性别特异性响应与性别比例偏差,有利于深入的理解性二态对环境胁迫的响应。     

Sex‐related adaptive responses to interaction of drought and salinity in Populus yunnanensis

We used Populus yunnanensis Dode., a native dioecious species in southwestern China, as a model species to study morphological, physiological, biochemical and ultrastructural responses to drought, salinity and their combination. Females exhibited more growth inhibition, gas exchange rate depression and reactive oxygen species (ROS) accumulation; higher lipid peroxide levels, lower osmotic adjustment capacity and ascorbate–glutathione cycle enzyme activities; and more damage to cell organelles than did males under drought, salinity and especially under their combination. In addition, we found sex‐specific responses in total chlorophyll content (TC), carotenoid concentration and carbon isotope composition under different osmotic stresses. Our results indicated that: (1) females are more sensitive and suffer from greater negative effects than do males under drought, salinity and especially under their combination; (2) sexual differences in adaptive responses to drought, salinity and their combination are context dependent; and (3) sex‐specific reactions under a combination of stresses are distinct from single‐stress responses. Thus, these results provide evidence for adaptive differentiation between sexes in responses to osmotic stresses and in the sensitivity to environmental change.     

Sexual competition and N supply interactively affect the dimorphism and competiveness of opposite sexes in Populus cathayana

Several important dioecious species show sexual spatial segregation (SSS) along environmental gradients that have significant ecological effect on terrestrial ecosystem. However, little attention has been paid to understanding of how males and females respond to environmental gradients and sexual competition. We compared eco‐physiological parameters of males and females of Populus cathayana under different sexual competition patterns and nitrogen (N) supply levels. We found that males and females interacting with the same or opposite sex showed significant differences in biomass partition, photosynthetic capacity, carbon (C) and N metabolism, and leaf ultrastructure, and that the sexual differences to competition were importantly driven by N supply. The intersexual competition was enhanced under high N, while the intrasexual competition among females was amplified under low N. Under high N, the intersexual competition stimulated the growth of the females and negatively affected the males. In contrast, under low N, the males exposed to intrasexual competition had the highest tolerance, whereas females exposed to intrasexual competition showed the lowest adaptation among all competition patterns. Sexual competition patterns and N supply levels significantly affected the sexual dimorphism and competitiveness, which may play an important role in spatial segregation of P. cathayana populations.     

雌雄异株植物对环境胁迫响应的性别差异研究进展

从温度、CO2、水分以及生境变化4个方面综述了雌雄异株植物的雌雄个体在环境胁迫下出现的不同生理、生态和生化差异.温度胁迫将导致雌雄个体在气孔导度、净同化作用、耐冻性形成以及ABA含量等方面出现不同的生理响应,响应大小受限于外界条件.雄株植物的净光合速率高于雌株,而且随着CO2浓度的增高,二者的光合作用受到明显的促进,生物量均显著增加.水分胁迫使雌雄个体在干物质积累、净光合速率、蒸腾速率、水分利用效率和碳同位素值等生理指标以及部分形态指标呈现显著差异.多数植物的雄株个体在干旱环境中具有较高的水分利用效率,对水分胁迫的抗性更大.不同生境中雌雄异株植物雌雄个体的适应性各不相同.在土壤干燥、养分贫瘠、海拔较高、坡度较大的生境中,雄性植株生长良好,数量较多;而在湿润、肥沃、低海拔或低洼的生境中,雌性植株生长良好.     

Environmental tracking by females

Human females are generally reserved in their sexuality, in keeping with their heavy investment in reproduction. Males tend to be less reserved. Relative to males, however, females demonstrate more variability in sexuality and are more likely to inhibit or express high levels of sexuality. The heightened variability may in part originate with genetic mechanisms that predispose females toward greater variability (the Lyon hypothesis). Menarche, menstrual cycles, menopause, food reactions, responses to living conditions, reactions to cultural factors, and responses to sexual stimuli and potential mates are unique to or are more variable among females than males. There is a correlation between the variation expressed and female reproductive potential—females tend to shift dramatically from sexual inhibition to sexual expression. Females apparently track the quality of the environment and link their sexuality to reproductive opportunities. Successful male reproduction depends less on quality environments and more on the availability of females. In short, females track the environment; males track the females.     

Sexual conflict and environmental change: trade-offs within and between the sexes during the evolution of desiccation resistance

Intralocus sexual conflict occurs when males and females experience sex-specific selection on a shared genome. With several notable exceptions, intralocus sexual conflict has been investigated in constant environments to which the study organisms have had an opportunity to adapt. However, a change in the environment can result in differential or even opposing selection pressures on males and females, creating sexual conflict. We used experimental evolution to explore the interaction between intralocus sexual conflict, sexual dimorphism and environmental variation in Drosophila melanogaster. Six populations were selected for adult desiccation resistance (D), with six matched control populations maintained in parallel (C). After 46 generations, the D populations had increased in survival time under arid conditions by 68% and in body weight by 20% compared to the C populations. The increase in size was the result of both extended development and faster growth rate of D juveniles. Adaptation to the stress came at a cost in terms of preadult viability and female fecundity. Because males are innately less tolerant of desiccation stress, very few D males survived desiccation-selection; while potentially a windfall for survivors, these conditions mean that most males’ fitness was determined posthumously. We conjectured that selection for early maturation and mating in males was in conflict with selection for survival and later reproduction in females. Consistent with this prediction, the sexes showed different patterns of age-specific desiccation resistance and resource acquisition, and there was a trend towards increasingly female-biased sexual size dimorphism. However, levels of desiccation resistance were unaffected, with D males and females increasing in parallel. Either there is a strong positive genetic correlation between the sexes that limits independent evolution of desiccation resistance, or fitness pay-offs from the strategy of riding out the stress bout are great enough to sustain concordant selection on the two sexes. We discuss the forces that mould fitness in males under a regimen where trade-offs between survival and reproduction may be considerable.     

Fluctuating asymmetry of sexual and nonsexual traits in stalk‐eyed flies: a poor indicator of developmental stress and genetic quality

It has been proposed that females use fluctuating asymmetry (FA) in sexual ornaments to assess male quality. FA of sexual traits is predicted to show greater sensitivity to stress than FA of nonsexual traits, and to be heritable. We used a half‐sib mating design and manipulation of larval food environment to test these predictions on stalk‐eyed flies, Cyrtodiopsis dalmanni, in which females prefer males with larger eyespans. We measured size and FA of eyestalks and of two nonsexually selected characters, wing length and width. We found no evidence of an increase in FA under larval food stress in any of the individual traits, although trait size decreased under stress. We combined FA across traits into a single composite index, and found that males reared in the most benign larval environment had significantly higher composite FA than males reared on other media. There was no such effect in females. Heritability of FA was not significantly different from zero in any of the traits, in any of the environments, although trait sizes showed high heritability. We conclude that FA in sexual and nonsexual traits is a poor indicator of developmental stress and genetic quality.     

Early Stress Causes Sex-Specific,Life-Long Changes in Behaviour,Levels of Gonadal Hormones,and Gene Expression in Chickens

Early stress can have long-lasting phenotypic effects. Previous research shows that male and female chickens differ in many behavioural aspects, and respond differently to chronic stress. The present experiment aimed to broadly characterize long-term sex differences in responses to brief events of stress experienced during the first weeks of life. Chicks from a commercial egg-laying hybrid were exposed to stress by inducing periods of social isolation during their first three weeks of life, followed by a broad behavioural, physiological and genomic characterization throughout life. Early stressed males, but not females, where more anxious in an open field-test, stayed shorter in tonic immobility and tended to have delayed sexual maturity, as shown by a tendency for lower levels of testosterone compared to controls. While early stressed females did not differ from non-stressed in fear and sexual maturation, they were more socially dominant than controls. The differential gene expression profile in hypothalamus was significantly correlated from 28 to 213 days of age in males, but not in females. In conclusion, early stress had a more pronounced long-term effect on male than on female chickens, as evidenced by behavioral, endocrine and genomic responses. This may either be attributed to inherent sex differences due to evolutionary causes, or possibly to different stress related selection pressures on the two sexes during commercial chicken breeding.     

Sexual jealousy as a facultative trait: Evidence from the pattern of sex differences in adults from China and the United States

Across two studies, 716 and 308 undergraduate students from the United States and mainland China, respectively, were administered a series of measures on jealousy, emotional responses to partner infidelity, family background, and personality. Across both studies for the U.S. and Chinese samples, a higher proportion of males than females reported more distress to a partner's imagined sexual infidelity than to emotional infidelity, whereas a higher proportion of females than males reported more distress to a partner's emotional infidelity than to sexual infidelity, consistent with theoretical expectations and previous empirical research. However, a much higher proportion of U.S. males and females reported more distress to sexual infidelity than their same-sex Chinese peers, suggesting that the tendency toward sexual jealousy might be facultatively influenced by sexual permissiveness in the general culture. The overall pattern of results is considered in terms of individual and contextual differences in the expression of jealousy, as well as in terms of the emotional and behavioral responses associated with jealousy reactions.     

The sexual preference of female rats is influenced by males' adolescent social stress history and social status

Ongoing development of brain systems for social behaviour renders these systems susceptible to the influence of stressors in adolescence. We previously found that adult male rats that underwent social instability stress (SS) in mid-adolescence had decreased sexual performance compared with control males (CTL). Here, we test the hypotheses that SS in adolescence decreases the “attractiveness” of male rats as sexual partners compared with CTL rats and that dominance status is a protective factor against the effects of SS. The main prediction was that females would spend more time with CTL males than SS males, and that this bias would be greater for submissive than for dominant rats. Among dominant pairs (n = 16), females preferred SS males, spending more time with and visiting more often SS than CTL males (each pair tested 5 ×), and SS males had shorter latencies to ejaculation, shorter inter-ejaculation intervals, and made more ejaculations compared with CTL males. Among submissive pairs (n = 16), females spent more time with, visited more often, and displayed more paracopulatory behaviour with CTL than with SS males, and differences in sexual performance between SS and CTL males were modest and in the opposite direction from that in dominant pairs. The heightened motivation of SS males relative to CTL males for natural rewards may have attenuated differences in sexual performance in a paced mating context. In sum, the experience of stress in adolescence leads to long-lasting changes in males that are perceptible to females, are moderated by social status, and influence sexual behaviour.     

果蝇Drosophila biarmipes翅斑二型性的生态学意义(英文)

雌性对雄性表饰的偏好性有利于性别选择。目前尚不清楚这一偏好性是否只限于雄性表饰或这一偏好性实际上是源于影响后代适合度的基因。对于雄性可直接有利于雌性或其后代适合度的交配系统而言,答案是肯定的--雌性偏好于与对气候胁迫具有更强生理抗性的雄性交配。对果蝇Drosophila biarmipes 的室内研究已经证明了求偶过程中翅斑的作用,但是其生态学意义仍然不清楚。我们检验了有翅斑与无翅斑雄性果蝇D. biarmipes 及雌性偏好的雄性所产生的后代对环境胁迫的抗性是否不同。结果表明：在干燥或冷胁迫条件下,有翅斑的雄性果蝇比无翅斑的雄性果蝇的交配成功率明显要高。相反,在高湿条件下,无翅斑雄性果蝇的交配频率更高。我们也发现在较为干旱的条件下,与有翅斑雄性交配的雌性果蝇的生殖力以及所得后代从卵至成虫的存活率更高。我们的结果与优良基因性选择假说一致,说明交配选择能给雌性带来间接好处。这是对热带物种D. biarmipes翅色二型性生态学意义的首次报道。     

Sexual differences in response to larval food stress in two nuptial feeding orthopterans – implications for sexual selection

The extent to which a trait deteriorates in response to stress can indicate its fitness importance. Food limitation is a naturally-occurring stress in the katydid Kawanaphila nartee (Orthoptera: Tettigoniidae) and should cue larvae as to the level of sexual competition expected; hunger drives adult females to compete for copulations and thus acquire spermatophore meals. This increases sexual selection on females relative to males for increased body mass. As predicted, under experimental food-stress larval female K. nartee showed little loss of mass whereas male mass decreased. In contrast, the sizes of body parts less critical to mating success showed similar decreases in males and females. For katydids such as Conocephalus nigropleurum , where reversals in mating roles do not occur, larval food stress should result in a greater preservation of male body mass, an important trait in male mating success. This prediction was supported; male mass decreased less than that of females.     

Sexual dimorphism in reactions to stress during regular and altered photoperiods

Sexual dimorphism of rats in response to physiological stress influences was discovered. The emotional stress in female animals caused a sharp intensification of synthesis and corticosterone secretion, while in males there was an increase only in hormone synthesis and not its secretion. Females are more sensitive even to short-term changes in photoperiod. Stress reaction in females under conditions of three-day light depressed sharply and increased under conditions of three-day darkness. Stress reaction in males did not change under these conditions. The reactivity of adaptation system in females shortens the period of adaptation to the altered illumination regimen, which is manifested in the restoration of typical stress reactions. In males, refractoriness to weak stress influences lengthens the period of adaptation, which is manifested in the suppression of typical stress reaction observed in males.     

Possibility of affecting the regulation of salt and water uptake in the critical periods of development in rats]

Peculiarities in water and salt (NaCl) appetite were studied in rats under various experimental influences during critical periods of development. When sexual maturation is going on, females consume more salt than males. These sex depending differences may be altered by experimental influences but only during critical periods of development, for instance by injection of androgens into neonatal females or by gonadectomy of males, by premature cessation of rearing, etc. The effects of those early interventions manifest themselves after the termination of sexual maturation.     

Good genes, oxidative stress and condition-dependent sexual signals

The immune and the detoxication systems of animals are characterized by allelic polymorphisms, which underlie individual differences in ability to combat assaults from pathogens and toxic compounds. Previous studies have shown that females may improve offspring survival by selecting mates on the basis of sexual ornaments and signals that honestly reveal health. In many cases the expression of these ornaments appears to be particularly sensitive to oxidative stress. Activated immune and detoxication systems often generate oxidative stress by an extensive production of reactive metabolites and free radicals. Given that tolerance or resistance to toxic compounds and pathogens can be inherited, female choice should promote the evolution of male ornaments that reliably reveal the status of the bearers' level of oxidative stress. Hence, oxidative stress may be one important agent linking the expression of sexual ornaments to genetic variation in fitness-related traits, thus promoting the evolution of female mate choice and male sexual ornamentation, a controversial issue in evolutionary biology ever since Darwin.