Men's facial masculinity predicts changes in their female partners' sexual interests across the ovulatory cycle,whereas men's intelligence does not

A substantial body of work demonstrates that women's mate preferences change across the ovulatory cycle. When fertile in their cycles, women are especially attracted to masculine features (e.g., faces, voices, bodies), socially dominant behavior, and male scents associated with body symmetry and social dominance. Women may also find intelligent men particularly attractive when fertile, though findings are mixed. Related research shows that, on average, romantically-involved women report stronger sexual attraction to men other than their pair-bond partners, but not partners, when fertile, and especially when their partners lack features fertile women prefer (e.g., symmetry). In the current study, we examined whether women's patterns of sexual interests across the cycle are similarly moderated by partners' facial masculinity, facial attractiveness, and intelligence. Results revealed predicted effects of male partners’ facial masculinity but none for partners’ intelligence. Facial attractiveness may have effects, but we find no evidence that it does so independently of facial masculinity.     

A primary role of developmental instability in sexual selection

In evolutionary biology, fluctuating asymmetry (FA) is thought to reveal developmental instability (DI, inability to buffer development against perturbations), but its adaptive and genetic bases are being debated. In other fields, such as human clinical genetics, DI is being assessed as incidence of minor morphological abnormalities (MMAs) and used to predict certain fitness outcomes. Here, for the first time, we combine these complementary measures of DI in sexual selection and quantitative genetic studies of a natural population. Comprehensive multivariate analyses demonstrate that FA and MMAs in a condition-dependent sexual ornament, the male Drosophila bipectinata sex comb used in courtship, are sole significant targets of selection favouring their reduced expression in New Caledonia. Comb FA and MMAs are positively correlated, confirming that each are linked to a common buffering system. Ornament size and DI (as FA and MMAs) are positively correlated, genetically and phenotypically, contrary to theoretical expectation of negative size-FA scaling under the assumption that FA reveals overall genetic quality. There exists significant additive genetic variance for MMAs, demonstrating their evolutionary potential. Ornament DI in New Caledonia is markedly elevated compared with populations where such selection was not detected, suggesting that the increased population-level DI is capacitating adaptive evolution.     

Intersexual conflict across women's ovulatory cycle

A growing literature shows that the features women find particularly attractive in men vary across the ovulatory cycle. Women furthermore appear to more frequently report attraction to men other than primary partners when they are fertile in their cycle than in the infertile luteal phase. Previous studies have shown that men are more vigilant of or attentive to their primary partners during the fertile phase compared to the luteal phase. This study had several aims: First, to replicate and extend previous findings concerning men's vigilance of partners using male as well as female reports of men's behavior; second, to examine changes in women's behavior toward partners across the cycle; third, to examine ways in which women resist men's attempts to mate-guard across the cycle. Results indicate that (a) men are particularly self-assertive toward partners when their partners are fertile; (b) similarly, women are especially self-assertive toward partners when they are fertile; (c) women report engaging in more behaviors that resist male vigilance and mate guarding when they are fertile, especially in ways that are unobservable to male partners; and (d) these effects are especially strong when women themselves report greater attraction to men other than partners when they are fertile, compared to the luteal phase.     

Women's preferences for men's scents associated with testosterone and cortisol levels: Patterns across the ovulatory cycle

Women in the fertile phase of their menstrual cycle show an enhanced sexual preference for masculine expressions in behavioral, morphological and scent traits. These masculinity preferences may be associated with testosterone (T) levels in males and hence connote male quality as a sire. Thus, a scent preference of fertile-phase women for T is predicted. A recent study, however, found no evidence for this, but reported that women prefer the scent of men with high cortisol (C). That study had low power to detect the predicted effect, as well as other methodological limitations. We tested women's preferences across their ovulatory cycle for the body scent of men who varied in T and C, using a larger sample of men and methods used in research on cycle preferences for symmetry-related male body scent. Conception risk in the cycle positively predicted women's scent ratings of men's T; scent ratings of C or T × C interaction were not robustly related to conception risk. Conception risk is related positively to a preference for scent of men's symmetry. This preference is distinct from that arising from a preference for the scent of T. The male-emitted chemical(s) responsible for these preferences shifts across women's cycle remain unknown.     

Early maternal effects mediated by immunity depend on sexual ornamentation of the male partner

Vertebrates have an immature immune system soon after birth, and parasites can therefore be particularly virulent to young hosts. Transfer of immune factors via the egg can give rise to early maternal effects with important consequences for offspring fitness, as maternally derived immunity confers anti-parasite protection. Mothers are expected to allocate immunity differentially to the eggs according to the reproductive value of their offspring as influenced by the quality of their father. In this study, we analysed transmission to the yolk of antibodies specific to an antigen (Newcastle disease virus vaccine, NDV) by vaccinated female barn swallows (Hirundo rustica) mated to males whose secondary sexual characteristics had been manipulated. Concentration of anti-NDV antibodies in the yolk positively covaried with that in maternal plasma. Anti-NDV antibodies were more concentrated in the first but not the fourth eggs laid by females mated with tail-elongated males compared with those mated with tail-shortened and control males. This experiment shows that allocation of maternal immune factors to the eggs is affected by quality of the male, as signalled by its secondary sexual characteristic. Thus, early maternal effects are influenced by sexual attractiveness of male mates and are mediated by immunity.     

Conditional expression of women's desires and men's mate guarding across the ovulatory cycle

Thirty-eight normally cycling women provided daily reports of sexual interests and feelings for 35 days. Near ovulation, both pair-bonded and single women reported feeling more physically attractive and having greater interest in attending social gatherings where they might meet men. Pair-bonded women who were near ovulation reported greater extra-pair flirtation and greater mate guarding by their primary partner. As predicted, however, these effects were exhibited primarily by women who perceived their partners to be low on hypothesized good genes indicators (low in sexual attractiveness relative to investment attractiveness). Ovulation-contingent increases in partner mate guarding were also moderated by female physical attractiveness; midcycle increases in mate guarding were experienced primarily by less attractive women, whereas more attractive women experienced relatively high levels of mate guarding throughout their cycle. These findings demonstrate ovulation-contingent shifts in desires and behaviors that are sensitive to varying fitness payoffs, and they provide support for the good genes hypothesis of human female extra-pair mating. The daily assessment method provides an important supplement to existing studies using scheduled laboratory visits as the purpose of the study (examining cycle-related variation) is not known by participants.     

Changes in women's sexual interests and their partners' mate-retention tactics across the menstrual cycle: evidence for shifting conflicts of interest

Because ancestral women could have obtained genetic benefits through extra-pair sex only near ovulation, but paid costs of extra-pair sex throughout the cycle, one might expect selection to have shaped female interest in partners, other than primary partners, to be greater near ovulation than during the luteal phase. Because men would have paid heavier costs if their partners had extra-pair sex near ovulation, one might also expect selection to have shaped males' efforts to track their primary partners' whereabouts to be increased near ovulation, relative to the luteal phase. Women filled out questionnaires about their sexual interests and their partners' mate-retention tactics twice: once within 5 days before a lutenizing hormone surge and once during the luteal phase. Results showed that: (i) women reported greater sexual interest in, and fantasy about, non-primary partners near ovulation than during the luteal phase; (ii) women did not report significantly greater sexual interest in, and fantasy about, primary partners near ovulation; (iii) women reported that their primary partners were both more attentive and more proprietary near ovulation.     

Women's attractiveness judgments of self-resembling faces change across the menstrual cycle

Two lines of reasoning predict that women's preferences for people exhibiting cues to kinship will be lower in the follicular phase than in the luteal phase of the menstrual cycle. Women may avoid kinship cues during the follicular phase when they are most fertile due to the costs of inbreeding. Alternatively, women may seek kinship cues during the luteal phase as a byproduct of the benefits of associating with kin during pregnancy, which is also characterized by high progesterone. We find that preferences for facial resemblance, a putative kinship cue, follow this predicted pattern and are positively correlated with estimated progesterone levels based on cycle day. Neither estimated estrogen levels nor conception risk predicted preferences for self-resemblance, and the cyclic shift was stronger for preferences for female faces than male faces. These findings lead to the possibility that this cyclic change in preference for self-resemblance may be a byproduct of a hormonal mechanism for increasing affiliative behavior toward kin during pregnancy rather than a mechanism for preventing inbreeding during fertile periods.     

Gender-Related developmental instability and herbivory ofPistacia atlantica across a steep environmental gradient

To examine gender-related developmental instability and herbivory of a plant across a steep climatic gradient, we studiedPistacia atlantica DESF., a dioecious tree of the Irano-Turanian zone in the Middle East. Leaves were sampled from five populations along a climatic gradient in Israel from mesic Mediterranean to xeric (and geographically peripheral) sites. Leaves of the xeric populations were ca. 25% smaller in size (length) than leaves of other populations. Leaf developmental instability (an indicator of stress) was examined using the measurement of leaf asymmetry (LA), estimated by the deviation from the origin of paired lateral leaflets and by the presence vs. absence of the terminal leaflet. LA was not correlated with the climatic (site) gradient and had the highest, though not significantly, levels in the intermediate ecotonal zone between the Mediterranean and the arid ecosystems. Male trees were 13% higher in LA than females. Density of two specialist gall-forming aphids varied with site but was not affected by plant gender. Gender-related developmental instability is discussed in relation to resource allocation in early spring. Because the study was limited to five populations further research is clearly needed.     

A latent variable model of developmental instability in relation to men's sexual behaviour

A single trait's fluctuating asymmetry (FA) is expected to be a poor measure of developmental instability. Hence, studies that examine associations between FA and outcomes expected to covary with developmental instability often have little power in detecting meaningful relationships. One way of increasing the power of detecting relationships between developmental instability and outcomes is through the use of multiple traits' FA. The way multiple traits have typically been used is in trait aggregates. Here, we illustrate another way of examining relationships with developmental instability using multiple traits' FA: through structural equation modelling. Covariances between measures of FA and an outcome variable are interpreted within the context of an explicit model of associations between variables, which is tested for fit and the parameters specified within the model are estimated. We used nine traits' FA as markers of a latent variable of men's developmental instability, which was associated with the number of sexual partners. The results indicate a sizeable correlation between developmental instability and men's sexual history, despite small correlations between individual traits' FA and sexual history.     

Effect of the ovulatory cycle on oviductal sperm storage in the domestic fowl

Anovulatory domestic hens (pregnant mare serum-treated) and normally cyclic domestic hens were artificially inseminated with 0.034 ml of pooled semen. A subsequent microscopic assessment of the uterovaginal sperm storage glands on days 1, 3, 6, 9 and 12 post-insemination indicated that the sperm glands emptied over time in the normally cyclic hens, but not in the anovulatory hens. The data suggest that events associated with ovulation and/or oviposition are important to the sperm gland emptying process.     

Directional asymmetry and the measurement of developmental instability

Three widely used methods of estimating fluctuating asymmetry may yield serious overestimates if directional asymmetry is present. When two sides of a bilateral trait grow at different rates, then the asymmetry variance (Var[l-r]) increases with size, even when developmental noise is nil. But the residual variance around a population's mean developmental trajectory is invariant with respect to size. Thus, it can be used as a measure of developmental instability. We introduce a measure of developmental instability, the residual variance (s²δ), obtainable from either a major axis regression, which is equivalent to a principal component analysis on l and r, or a general structural model. This residual variance can be estimated from directionally asymmetric or even antisymmetric traits. We present examples of developmental instability estimated from directionally asymmetric mandibles (house mouse) and leaves (soybean), and antisymmetric claws (fiddler crab).     

Fear recognition across the menstrual cycle

This study assesses the mediating role of stage of menstrual cycle in the recognition of emotional expressions. It was hypothesised that fear recognition ability would be stronger at high-oestrogen stages of the menstrual cycle. The accuracy of recognising emotional expressions was compared across 50 women who were at different stages of their menstrual cycle. It was found that accuracy to recognise emotions was significantly affected by the interaction between stages of the menstrual cycle and the emotion being displayed. Further analysis revealed that for the emotion expression of fear alone, participants were significantly more accurate at the preovulatory surge (highest oestrogen levels) than at menstruation (oestrogen levels at lowest point). The results have implications for the processes that underlie fear processing and a possible insight into the sexual dimorphism of this ability and conditions that show variations in fear recognition (e.g., autism, Turner syndrome).     

Cell cycle effects by C-FADD depend on its C-terminal phosphorylation site

Expression of a truncated form of the death receptor adaptor FADD (C-FADD) as a transgene in mice blocks T cell proliferation. Here we provide evidence that the C-terminal phosphorylation site Ser194 in C-FADD affects the cell cycle in nonlymphoid cells as well. High expression of wild type C-FADD but not C-FADD with a S194A point mutation arrested the nontumor cell line MCF10A in G2/M but not the tumor cell line MCF7. BJAB as well as MCF10A cells expressing moderate levels of C-FADD with a S194E mutation mimicking phosphorylated C-FADD were more susceptible to a Taxol-induced G2/M arrest than cells expressing C-FADD S194A suggesting that C-FADD S194E lowers the threshold for G2/M arrest. Our data suggest that C-FADD may affect apoptosis sensitivity of cells by interfering with cell cycle progression and not only by binding to death receptors.     

Women's genital sexual arousal to oral versus penetrative heterosexual sex varies with menstrual cycle phase at first exposure

Reproductive-aged women show increased interest in sexual activity during the fertile phase of the menstrual cycle that can motivate sexual behavior and thereby increase the likelihood of conception. We examined whether women demonstrated greater sexual responses (subjective and genital sexual arousal) to penetrative versus oral sexual activities during the fertile versus non-fertile phases of their cycles, and whether women's arousal responses were influenced by the phase during which they were first exposed to these sexual stimuli (e.g., Slob et al., 1991; Wallen and Rupp, 2010). Twenty-two androphilic women completed two identical sexual arousal assessments in which genital responses were measured with a vaginal photoplethysmograph and their feelings of sexual arousal were recorded. Women viewed an array of 90 s films varying by couple type (female–female, male–male, female–male) and sexual activity type (oral or penetrative), during the fertile (follicular) and non-fertile (luteal) phases of their menstrual cycle, with the order of cycle phase at the first testing session counter-balanced. Women tested first in the fertile phase showed significantly greater genital arousal to female–male penetrative versus oral sex in both testing sessions, whereas self-reports of sexual arousal were not affected by cycle phase or testing order. These results contribute to a growing body of research suggesting that fertility status at first exposure to sexual stimuli has a significant effect on subsequent sexual responses to sexual stimuli, and that this effect may differ for subjective versus genital sexual arousal.     

Women's interest in visual sexual stimuli varies with menstrual cycle phase at first exposure and predicts later interest

This study investigated whether women's interest in visual sexual stimuli varied with their hormonal state. Viewing times of 30 women, 15 normal cycling (NC) and 15 oral contracepting (OC), to sexually explicit photos were measured at three different times. NC women were tested during their menstrual, periovulatory, and luteal phases, and OC women were tested at equivalent temporal intervals. Subjects viewed stimuli as long as desired, thus viewing time measured subject interest. Subjective ratings of stimulus sexual attractiveness were obtained on each test. There was no overall relationship between menstrual cycle phase and viewing time. However the participant's menstrual cycle phase during first exposure to sexual stimuli predicted subsequent interest in sexual stimuli during the next two tests. NC women who first viewed stimuli during their periovulatory phase looked longer at the sexual stimuli across all sessions than did women first tested in their luteal phase. OC women first exposed to the sexual stimuli during menstruation looked longer at the stimuli across all sessions than did OC women first exposed at other test phases. Neither current test phase nor initial cycle phase influenced subjective ratings. Women had increased interest in sexual stimuli across all sessions if first exposed to sexual stimuli when endogenous estrogens were most likely highest. These data suggest that women's interest in visual sexual stimuli is modulated by hormones such that the hormonal condition at first exposure possibly determines the stimuli's emotional valence, markedly affecting subsequent interest in sexual stimuli.