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AbstractThe strength and direction of sexual selection can vary among populations. However, spatial variability is rarely explored at the level of the social group. Here we investigate sexual selection and sex roles in the paternally mouthbrooding, socially monogamous, and site-attached pajama cardinalfish, Sphaeramia nematoptera. Females were larger and more aggressive and had a longer dorsal fin filament, indicating reversed sex roles. At the scale of social groups, we show that the Bateman gradient and reproductive variance depend on the sex ratio and size of groups. In small and medium-sized groups with balanced or male-biased sex ratios, Bateman gradients were steeper for females, whereas gradients were equally steep for both sexes in large groups or when the sex ratio was female biased. For both sexes, reproductive variance increased with group size and with a higher male-to-female sex ratio. In S. nematoptera, mating opportunities outside the socially monogamous pair appear to impact sexual selection. We conclude that strength and direction of sexual selection can be masked by social dynamics in group-living species when considering only population and large-scale demographic processes.
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Arrecifes de Coral , Perciformes , Razón de Masculinidad , Animales , Masculino , Femenino , Perciformes/fisiología , Selección Sexual , Conducta Social , Reproducción , Grupo SocialRESUMEN
The Bateman gradient is a central concept in sexual selection theory that relates reproductive success to mate number, with important consequences for sex-specific selection. The conventional expectation is that Bateman gradients are steeper in males than females, implying that males benefit more from multiple mating than females do. This claim is supported by much empirical evidence as well as mathematical modelling. However, under some reproductive systems, reversed Bateman gradients are observed, perhaps most notably in syngnathid fishes with male pregnancy. Unlike conventional Bateman gradients, the causal basis of such reversed Bateman gradients has never been modelled mathematically. Here, we present a sex-neutral mathematical model demonstrating how restrictions in capacity for carrying or incubating gametes and embryos (brooding) interact with anisogamy, generating both conventional and reversed Bateman gradients from a single mathematical model. The results clearly demonstrate how anisogamy tends to cause conventional Bateman gradients, but diminishing male brooding capacity under male pregnancy or nesting causes a gradual reversal from conventional to fully 'reversed' Bateman gradients.
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Modelos Biológicos , Animales , Femenino , Masculino , Reproducción , Selección Sexual , Preferencia en el Apareamiento AnimalRESUMEN
Males and females often differ in ecology, behaviour and lifestyle, and these differences are expected to lead to sex differences in parasite susceptibility. However, neither the sex differences in parasite prevalence, nor their ecological and evolutionary drivers have been investigated across a broad range of taxa using phylogenetically corrected analyses. Using the most extensive dataset yet that includes 755 prevalence estimates from 151 wild bird species in a meta-analytic framework, here we compare sex differences in blood and gastrointestinal parasites. We show that despite sex differences in parasite infection being frequently reported in the literature, only Haemoproteus infections were more prevalent in females than in males. Notably, only seasonality was strongly associated with the sex-specific parasite prevalence of both Leucocytozoon and Haemoproteus, where birds showed greater female bias in prevalence during breeding periods compared to the non-breeding period. No other ecological or sexual selection variables were associated with sex-specific prevalence of parasite prevalence. We suggest that much of the variation in sex-biased prevalence could be idiosyncratic, and driven by local ecology and behavioural differences of the parasite and the host. Therefore, breeding ecology and sexual selection may only have a modest influence on sex-different parasite prevalence across wild birds.
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Evolución Biológica , Enfermedades de las Aves , Aves , Animales , Aves/parasitología , Femenino , Enfermedades de las Aves/parasitología , Enfermedades de las Aves/epidemiología , Masculino , Prevalencia , Haemosporida/fisiología , Factores Sexuales , Caracteres Sexuales , Animales Salvajes/parasitología , Estaciones del Año , Infecciones Protozoarias en Animales/epidemiología , Infecciones Protozoarias en Animales/parasitologíaRESUMEN
Parenting is considered a key evolutionary innovation that contributed to the diversification and expansion of vertebrates. However, we know little about how such diversity evolved. Amphibians are an ideal group in which to identify the ecological factors that have facilitated or constrained the evolution of different forms of parental care. Among, but also within, the three amphibian orders-Anura, Caudata, and Gymnophiona-there is a high level of variation in habitat use, fertilization mode, mating systems, and parental sex roles. Recent work using broad phylogenetic, experimental, and physiological approaches has helped to uncover the factors that have selected for the evolution of care and transitions between different forms of parenting. Here, we highlight the exceptional diversity of amphibian parental care, emphasize the unique opportunities this group offers for addressing key questions about the evolution of parenting, and give insights into promising novel directions of research.
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This linkage study examined the prevalence of traditional gender expressions in the textual and visual profile cues on mobile dating applications (MDA) (nbiographies = 396, npictures = 1352) of 396 young adults' (Mage = 22.39 years, SD = 2.86, 73% women) with attention to users' gender, sexual orientation, and platform type. For 184 users (Mage = 22.10 years, SD = 2.91, 75% women) media content data were linked to self-report survey data. Results showed that individuals aligned their self-presentations with traditional gender roles and expectations, and this link depended on their gender. No significant differences according to individuals' sexual orientation or platform type were found. Individuals' (hyper-) gender orientation also related to engagement in traditional gender expressions. Specifically, women with a stronger feminine gender orientation expressed more traditional femininity in their MDA profiles. For men, no significant associations between (aspects of) a masculine gender orientation and expressing traditional masculinity in their MDA profiles were found. Future research should further disentangle selective gendered self-presentations.
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Rol de Género , Aplicaciones Móviles , Humanos , Femenino , Masculino , Adulto Joven , Adulto , Conducta Sexual/psicología , Conducta Sexual/estadística & datos numéricos , Masculinidad , Feminidad , Identidad de Género , Relaciones Interpersonales , Cortejo/psicologíaRESUMEN
In some species, sexual selection is stronger in females than males. In classically polyandrous birds, for instance, females compete for mating opportunities and males care for offspring. Sex steroids such as testosterone have been suggested to regulate the behaviours of 'role-reversed' females and males, but comparative studies did not find evidence for a role of testosterone in relation to sex roles. However, the large variability of hormone measurements across laboratories may prevent detecting subtle differences in hormone levels. To circumvent this caveat, I compared sex steroid concentrations of females and males of two closely related and cohabiting species with different mating systems: the classically polyandrous black coucal (Centropus grillii) and the monogamous white-browed coucal (C. superciliosus). Baseline and gonadotropin-releasing hormone (GnRH)-induced testosterone concentrations were twice as high in female black coucals than female white-browed coucals, and the low pre-breeding progesterone concentrations of female black coucals were consistent with progesterone's modulatory role during agonistic interactions in this species. Baseline and GnRH-induced testosterone and progesterone concentrations did not differ between males of both species. This study provides first evidence that elevated testosterone is associated with sex-role-reversed traits in females, whereas low levels of testosterone may not be necessary to facilitate sex-role reversal in males.
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Andrógenos , Testosterona , Animales , Femenino , Rol de Género , Progesterona , Conducta Sexual Animal/fisiología , Aves/fisiología , Hormona Liberadora de Gonadotropina , Caracteres SexualesRESUMEN
Parental care patterns differ enormously among and even within species. This is exemplified by Chinese penduline tits Remiz consobrinus, where biparental care, female-only care, male-only care and biparental desertion all occur in the same population; moreover, the distribution of these care patterns differs systematically between populations. The eco-evolutionary determinants of this diversity are largely unknown. We developed an individual-based model that allows us to investigate the effects of season length and offspring needs (expressed by the efficacy with which a clutch can be raised by a single parent) on the evolution of parental care patterns. The model is largely conceptual, aiming at general conclusions. However, to keep the model realistic, its set-up and the choice of parameters are motivated by field studies on Chinese penduline tits. Exploring a wide range of parameters, we investigate how parental care patterns are affected by season length and offspring needs and whether and under what conditions diverse parental care patterns can stably coexist. We report five main findings. First, under a broad range of conditions, different care patterns (e.g. male care and biparental care) coexist at equilibrium. Second, for the same parameters, alternative evolutionary equilibria are possible; this can explain differences in care patterns across populations. Third, rapid evolutionary transitions can occur between alternative equilibria; this can explain the often-reported evolutionary lability of parental care patterns. Fourth, season length has a strong but nonmonotonic effect on the evolved care patterns. Fifth, when uniparental care efficacy is low, biparental care tends to evolve; however, in many scenarios uniparental care is still common at equilibrium. In addition, our study sheds new light on Trivers' hypothesis that the sex with the highest prezygotic investment is predestined to invest more postzygotically as well. Our study highlights that diversity in parental care can readily evolve and it shows that even in the absence of environmental change parental care patterns can be evolutionary labile. In the presence of directional environmental change, systematic shifts in care patterns are to be expected.
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Passeriformes , Conducta Sexual Animal , Masculino , Femenino , Animales , Estaciones del Año , Evolución BiológicaRESUMEN
People assign attributes to a different degree to other persons depending on whether these are male or female (sex role stereotypes). Such stereotypes continue to exist even in countries with lower gender inequality. The present research tested the idea that parents develop sex role consistent expectations of their babies' attributes based on fetal sex (by ultrasound diagnostic), as well as gendered perceptions of their recently newborn babies. A total of 304 dyads of predominantly White expecting parents from Germany were followed over the course of pregnancy until after the birth and completed a sex role inventory on their babies' expected (before birth) as well as perceived traits (after birth). Specifically, they rated to what extent they expected their babies to have normatively feminine traits (e.g., soft-spoken and warm) and normatively masculine traits (e.g., independent and assertive) twice before birth (first half of pregnancy, six weeks before due date) and to what extent they perceived their baby to have these traits eight weeks after birth. The results suggested that fathers held gendered expectations and perceptions, whereas mothers did not. These results suggest that male and female babies are likely to encounter sex role stereotypes about their alleged attributes as soon as their birth.
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Rol de Género , Motivación , Embarazo , Recién Nacido , Humanos , Masculino , Femenino , Identidad de Género , Madres , PadresRESUMEN
Individual differences in intelligence are apparent and likely to come with important interpersonal consequences. We examined (N = 476) how (manipulated) individual differences in intelligence affect likability ratings of men and women. We found that (1) ratings were generally more favorable than unfavorable, (2) the difference between favorable and unfavorable ratings of the female target differed more than those same evaluations of the male target, (3) the favorable evaluation tendency was present across relative intelligence but weakest when the target was smarter than the participant, (4) the smarter target was rated more unfavorably, and (5) the equally smart target was rated more favorably than the less intelligent target. Results suggest that people are somewhat conflicted in their evaluations of those smarter than they are whereas similarly and less intelligent people presented less of an apparent conflict in evaluations.
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Why do some heterosexual people react in a negative manner when pondering or experiencing romantic or sexual overtures from persons of their same-sex, whereas other heterosexual people react more positively? To answer this question, this cross-sectional, correlational study examined individual difference predictors of heterosexual people's responses to romantic or sexual overtures from same-sex persons. Our sample comprised 306 men and 307 women, ages 18-35 years, who were recruited from Mechanical Turk and identified as cisgender and heterosexual. Our hypotheses were premised on the theoretical construct of reactive group distinctiveness. Specifically, we explored predictors of heterosexual individuals' negative perceptions of same-sex overtures. We found that more negative reactions to same-sex overtures were uniquely predicted by old-fashioned sexual prejudice, modern sexual prejudice, and desire to be perceived as gender conforming, via the mediators of social distance from same-sex sexual minority individuals and desire to be perceived as heterosexual. Gender moderated these relationships inconsistently. These findings indicate that two classes of individual differences-sexual prejudice and gender conforming reputation desire-are uniquely associated with heterosexual persons' reactions to overtures from same-sex persons. We explain how these findings evidence the process of reactive group distinctiveness.
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Identidad de Género , Heterosexualidad/psicología , Conducta Sexual/psicología , Adolescente , Adulto , Actitud , Estudios Transversales , Femenino , Humanos , Masculino , Adulto JovenRESUMEN
Providing parental care often reduces additional mating opportunities. Paternal care becomes easier to understand if trade-offs between mating and caring remain mild. The black coucal Centropus grillii combines male-only parental care with 50% of all broods containing young sired by another male. To understand how much caring for offspring reduces a male's chance to sire additional young in other males' nests, we matched the production of extra-pair young in each nest with the periods during which potential extra-pair sires were either caring for offspring themselves or when they had no own offspring to care for. We found that males which cared for a clutch were not fully excluded from the pool of competitors for siring young in other males' nests. Instead, the relative siring success showed a temporary dip. Males were approximately 17% less likely to sire young in other males' nests while they were incubating, about 48% less likely to do so while feeding nestlings, followed by 26% when feeding fledglings, compared to the success of males that currently did not care for offspring. These results suggest that real-life care situations by males may involve trade-off structures that differ from, and are less strict than those frequently employed in theoretical considerations of operational sex ratios, sex roles and parenting decisions.
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Aves/fisiología , Conducta Paterna , Conducta Sexual Animal , Animales , TanzaníaRESUMEN
Age-related improvement in reproductive performance is widespread in vertebrates and constraints at young ages are a common cause. The sex that invests energetically more in reproduction, typically the female, is predicted to show stronger age-related performance but the effect of the male's age on reproduction has often been ignored. I studied age-related reproduction of both sexes in northern flickers, in which males invest more parental care than females, predicting that the effect of age would be stronger in males than in females. Longitudinal data on individuals collected during an 18-year field study confirmed this prediction. Laying dates for females improved only between the first 2 years of her life and no other reproductive parameter changed over her lifetime when the male's age was statistically controlled. In contrast, males improved up to age five for laying date, clutch size, hatching success and fledging success. Partner familiarity (fidelity) was further associated with earlier laying, larger clutches, improved fledging success and more fledglings. There was significant assortative pairing by age but there is apparently little benefit for males to choose older females, but a benefit to females with older males. Females appear to strategically lay larger clutches when paired to old males which invest more in paternal care than younger males. This is the first example of clutch size being influenced by only male age and not female age in any bird and suggests that sex roles in parental care are important determinants of aging patterns in vertebrates with diverse life histories.
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Aves , Identidad de Género , Animales , Tamaño de la Nidada , Femenino , Fertilidad , Masculino , ReproducciónRESUMEN
We study the evolution of male and female mating strategies and mate choice for female fecundity and male fertilization ability in a system where both sexes can mate with multiple partners, and where there is variation in individual quality (i.e. in the availability of resources individuals can allocate to matings, mate choice and production of gametes). We find that when the cost of mating differs between sexes, the sex with higher cost of mating is reluctant to accept matings and is often also choosy, while the other sex accepts all matings. With equal mating costs, the evolution of mating strategies depends on the strength of female sperm limitation, so that when sperm limitation is strong, males are often reluctant and choosy, whereas females tend to accept available matings. Male reluctance evolves because a male's benefit per mating diminishes rapidly as he mates too often, hence losing out in the process of sperm competition as he spends much of his resources on mating costs rather than ejaculate production. When sperm limitation is weaker, females become more reluctant and males are more eager to mate. The model thus suggests that reversed sex roles are plausible outcomes of polyandry and limited sperm production. Implications for empirical studies of mate choice are discussed.
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Evolución Biológica , Conducta de Elección , Conducta Sexual Animal , Animales , Femenino , Masculino , Modelos Biológicos , Reproducción , Espermatozoides/fisiologíaRESUMEN
In nature, the intensity of mate choice (i.e., choosiness) is highly variable within and between sexes. Despite growing empirical evidence of male and/or mutual mate choice, theoretical investigations of the joint evolution of female and male choosiness are few. In addition, previous approaches have often assumed an absence of trade-off between the direct benefits per mating and the lower mating rate that results from being choosy. Here we model the joint evolution of female and male choosiness when it is solely ruled by this fundamental trade-off. We show that this trade-off can generate a diversity of stable combinations of choosiness. Mutual mate choice can evolve only if both females and males exhibit long latency after mating. Furthermore, we show that an increase in choosiness in one sex does not necessarily prevent the evolution of mutual mate choice; the outcome depends on details shaping the trade-off: the life history, the decision rule for mate choice, and how the fecundity of a pair is shaped by the quality of both individuals. Last, we discuss the power of the sensitivity of the relative searching time (i.e., of the proportion of a lifetime spent searching for mates) as a predictor of the joint evolution of choosiness.
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Apareamiento , Conducta Sexual Animal , Animales , Conducta de Elección , Femenino , Masculino , Caracteres Sexuales , Razón de MasculinidadRESUMEN
This study analyzed event-level partnership data from a computer-assisted survey of 719 gay and bisexual men (GBM) enrolled in the Momentum Health Study to delineate potential linkages between anal sex roles and the so-called "sex drugs," i.e., erectile dysfunction drugs (EDD), poppers, and crystal methamphetamine. Univariable and multivariable analyses using generalized linear mixed models with logit link function with sexual encounters (n = 2514) as the unit of analysis tested four hypotheses: (1) EDD are significantly associated with insertive anal sex roles, (2) poppers are significantly associated with receptive anal sex, (3) both poppers and EDD are significantly associated with anal sexual versatility, and (4) crystal methamphetamine is significantly associated with all anal sex roles. Data for survey respondents and their sexual partners allowed testing these hypotheses for both anal sex partners in the same encounter. Multivariable results supported the first three hypotheses. Crystal methamphetamine was significantly associated with all anal sex roles in the univariable models, but not significant in any multivariable ones. Other multivariable significant variables included attending group sex events, venue where first met, and self-described sexual orientation. Results indicate that GBM sex-drug use behavior features rational decision-making strategies linked to anal sex roles. They also suggest that more research on anal sex roles, particularly versatility, is needed, and that sexual behavior research can benefit from partnership analysis.
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Bisexualidad/estadística & datos numéricos , Homosexualidad Masculina/estadística & datos numéricos , Conducta Sexual/estadística & datos numéricos , Trastornos Relacionados con Sustancias/epidemiología , Adulto , Colombia Británica/epidemiología , Humanos , Masculino , Metanfetamina , Persona de Mediana EdadRESUMEN
We examined the association between scores on the Bem Sex Roles Inventory (BSRI), Klein Sexual Orientation Grid, and utilization of hospital inpatient services, emergency departments, and outpatient clinic visits in the past 12 months among 53 men (mean age 39 years). The femininity subscale score on the BSRI, ever having had gonorrhea and age were the three variables identified in a multivariate linear regression significantly predicting use of total health services. This supports the hypothesis that sex roles can assist our understanding of men's use of health services.
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Identidad de Género , Servicios de Salud/estadística & datos numéricos , Masculinidad , Hombres , Sexualidad , Adulto , Humanos , Masculino , Persona de Mediana Edad , Psicometría , Estados UnidosRESUMEN
Gender role beliefs of African American women differ from those of women in other ethnic/racial groups and a culturally valid measure of their gender role beliefs is needed. Three studies were conducted to develop a preliminary measure. In Study 1, focus groups were conducted with a community and college sample of 44 African American women. Transcripts reviewed resulted in an initial pool of 40 items. These items were reviewed by an expert panel and 18 items were retained. In Study 2, an exploratory factor analysis was computed with data from 94 African American female college students. The 18 items were included along with measures to assess convergent and discriminant validity. Nine items were retained. These nine items comprised two subscales labeled Agency and Caretaking. The scales demonstrated good internal consistency and convergent and discriminant validity. In Study 3, a confirmatory factor analysis was computed with a different sample of 184 African American female college students. The confirmatory factor analysis showed acceptable fit for the two-factor structure of Agency and Caretaking.
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Bateman's principles explain sex roles and sexual dimorphism through sex-specific variance in mating success, reproductive success and their relationships within sexes (Bateman gradients). Empirical tests of these principles, however, have come under intense scrutiny. Here, we experimentally show that in replicate groups of red junglefowl, Gallus gallus, mating and reproductive successes were more variable in males than in females, resulting in a steeper male Bateman gradient, consistent with Bateman's principles. However, we use novel quantitative techniques to reveal that current methods typically overestimate Bateman's principles because they (i) infer mating success indirectly from offspring parentage, and thus miss matings that fail to result in fertilization, and (ii) measure Bateman gradients through the univariate regression of reproductive over mating success, without considering the substantial influence of other components of male reproductive success, namely female fecundity and paternity share. We also find a significant female Bateman gradient but show that this likely emerges as spurious consequences of male preference for fecund females, emphasizing the need for experimental approaches to establish the causal relationship between reproductive and mating success. While providing qualitative support for Bateman's principles, our study demonstrates how current approaches can generate a misleading view of sex differences and roles.
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Pollos/genética , Pollos/fisiología , Preferencia en el Apareamiento Animal , Reproducción/genética , Reproducción/fisiología , Conducta Sexual Animal , Animales , Femenino , Fertilidad , Masculino , Modelos Biológicos , Caracteres SexualesRESUMEN
Founded in accordance with 19th century sex roles and public health concerns, nursing evolved as other-directed, dependent on physician-focused diagnosis, prescription decisions, and public health advancements. The result of this other direction is that public health nurse practitioners have endured significant workplace stress resulting in burnout, especially during COVID-19. To help decrease their burnout, nurses require development of self-direction. The Health Narratives Research Group (HeNReG) has the potential to reduce burnout in nurse practitioners by encouraging the development of self-direction. The HeNReG process is presented through historically analyzed documents regarding reducing burnout in health researchers by developing self-direction including: (1) three years of archived year-end feedback results provided by participants, (2) archived participant responses to specific HeNReG-related writing prompts, and (3) a comparison of HeNReG results with the outcomes of resilience programs. The conclusion-the HeNReG offers an effective option for reducing burnout in health researchers that has the potential to decrease nurse practitioner burnout in a way that resilience programs do not. Tailoring the HeNReG process to public health nurses is discussed, inviting future research for reducing burnout in public health nurses.
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The prevalence and diversity of female ornaments poses a challenge to evolutionary theory because males should prefer mates that spend resources on offspring rather than ornaments. Among dance flies, there is extraordinary variation in sexual dimorphism. Females of many species have conspicuous ornaments (leg scales and inflatable abdominal sacs). Meanwhile males of some species have exaggerated regions of their eyes with larger ommatidial facets that allow for regionally elevated photosensitivity and/or acuity. Here, we conduct a comparative study of these traits using both species descriptions available from the literature, as well as quantitative measures of eyes and ornaments from wild-caught flies. We show a conspicuous covariance across species between exaggerated male dorsal eye regions and the extent of female ornaments: species with highly ornamented females have males with more exaggerated eyes. We discuss this pattern in the context of competing hypotheses for the evolution of these traits and propose a plausible role for sexually antagonistic coevolution.