Operational Sex Ratio and Female Competition

2014 ◽  
Author(s):  
Haley M. Dillon ◽  
Lora E. Adair ◽  
Gary L. Brase
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Intrasexual Competition ◽  
Operational Sex Ratio ◽  
Female Competition ◽  
Future Directions ◽  
Adaptive Changes ◽  
Mating Market ◽  
Mating Behaviors ◽  
Theoretical Foundations

When there is a surplus of one sex in a population, members of that sex often compete against each other for access to the scarcer sex. This chapter reviews the theoretical foundations for this phenomenon, focusing on the concept of operational sex ratio (OSR; the ratio of viable and available males to females in a given mating market) versus overall sex ratio, as well as the phylogenetic evidence of sex ratios as an important factor influencing mating behaviors. Research on human OSR and its effects is a fairly recent development but has already led to findings that are generally coherent and consistent with the nonhuman evidence. The evidence to date indicates that people who find themselves in female-disadvantaged mating markets show systematic and adaptive changes in their behaviors, including increased female intrasexual competition. The chapter concludes with discussions of additional issues and future directions for research on OSR.

scholarly journals Sex Chromosome Meiotic Drive in Stalk-Eyed Flies

Genetics ◽  
1997 ◽  
Vol 147 (3) ◽  
pp. 1169-1180 ◽  
Author(s):  
Daven C Presgraves ◽  
Emily Severance ◽  
Gerald S Willrinson
Keyword(s):  
Sex Ratio ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Meiotic Drive ◽  
Operational Sex Ratio ◽  
Genetic Modifiers ◽  
Ratio Distortion ◽  
The Impact ◽  
Sex Ratio Distortion

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13–17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

Conclusion

2017 ◽  
Author(s):  
Gregory L. Carter ◽  
Maryanne L. Fisher
Keyword(s):  
Sex Ratio ◽  
Operational Sex Ratio ◽  
Future Research ◽  
Female Competition ◽  
Mate Poaching ◽  
Attitudes And Behaviors ◽  
Theoretical Perspectives ◽  
Wide Range ◽  
Mate Copying

This handbook has presented a wide range of theoretical perspectives on the motivations, attitudes, and behaviors involved in female competition. Using a metatheoretical framework, the contributors have examined how, when, and why women compete. This conclusion articulates the book’s main themes, beginning with evidence regarding women as active, competitive individuals and the value of mating information, addressing topics such as women’s competitive choices regarding mate copying, mate poaching, and mate retention. It then considers the role of intrasexual aggression in adolescence in relation to dating and reproduction, the importance of Operational Sex Ratio (OSR) to female competition, the concept of cooperative mothering or allomothering, and infanticide. It also discusses women as competitors in both traditional and novel social arenas as well as the role of women’s physiology in their competitive behaviors. Finally, it suggests directions for future research on topics that warrant further scrutiny.

scholarly journals Female Chemical Warfare Drives Fitness Effects of Group Sex Ratio

2017 ◽  
Author(s):  
Imroze Khan ◽  
Arun Prakash ◽  
Swastika Issar ◽  
Mihir Umarani ◽  
Rohit Sasidharan ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Interference Competition ◽  
Female Competition ◽  
Female Fitness ◽  
Female Fecundity ◽  
Individual Fitness ◽  
Flour Beetles ◽  
Group Sex

SUMMARYIn animals, skewed sex ratios can affect individual fitness either via sexual interactions (e.g. intersexual conflict or intrasexual mate competition) or non-sexual interactions (e.g. sex-specific resource competition). Because most analyses of sex ratio focus on sexual interactions, the relative importance of these mechanisms remains unclear. We addressed this problem using the flour beetle Tribolium castaneum, where male-biased sex ratios increase female fitness relative to unbiased or female-biased groups. Although flour beetles show both sexual and non-sexual (resource) competition, we found that sexual interactions did not explain female fitness. Instead, female fecundity was dramatically reduced even after a brief exposure to flour conditioned by other females. Earlier studies suggested that quinones (secreted toxins) might mediate density-dependent population growth in flour beetles. We identified ethyl- and methyl-benzoquinone (EBQ and MBQ) as the primary components of adult stink glands that regulate female fecundity. In female-biased groups (i.e. at high female density), females upregulated quinones and suppressed each other’s reproduction. In male-biased groups, low female density lead to low quinone levels, allowing higher fecundity. Thus, quinones serve both as indicators and mediators of female competition, resulting in the observed fitness decline in female-biased groups. Our results underscore the importance of non-sexual interference competition that may often underlie the fitness consequences of skewed sex ratios.

Sexual selection, the division of labor, and the evolution of sex differences

1998 ◽  
Vol 21 (3) ◽  
pp. 444-447 ◽  
Author(s):  
David C. Geary
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Sex Ratio ◽  
Division Of Labor ◽  
Operational Sex Ratio ◽  
Female Competition ◽  
Human Populations ◽  
Human Sex Differences ◽  
Male Choice ◽  
Relative Contribution

Sexual selection traditionally involves male-male competition and female choice, but in some species, including humans, sexual selection can also involve female-female competition and male choice. The degree to which one aspect of sexual selection or another is manifest in human populations will be influenced by a host of social and ecological variables, including the operational sex ratio. These variables are discussed in connection with the relative contribution of sexual selection and the division of labor to the evolution of human sex differences.

The Behavioral Ecology of Sex Tourism: The Consequences of Skewed Sex Ratios

2020 ◽  
pp. 004728752094610
Author(s):  
Florian Kock
Keyword(s):  
Sex Ratio ◽  
Behavioral Ecology ◽  
Sex Ratios ◽  
Reproductive Age ◽  
Operational Sex Ratio ◽  
Future Research ◽  
Sex Tourism ◽  
Same Sex ◽  
Biological Perspective ◽  
Attitudes Toward Sex

The operational sex ratio (i.e., the ratio of reproductive-age females to males in a population) shapes both animal and human behavior in important ways. Drawing on research in evolution and ecology, the author proposes that a local male-skewed sex ratio (i.e., a surplus of males) influences local men’s attitudes toward sex tourism. Analyzing historical field (study 1) and experimental data (study 2), the author demonstrates that male-skewed sex ratios increase men’s sex tourism rationalization and intent, while women’s predispositions are not sensitive to sex ratios. Sex tourism is explained as a subconscious ecological plasticity in response to perceived increased intensities of same-sex competition for mates, signaled by male-skewed sex ratios. The findings demonstrate a link between mating ecologies and sex tourism, with the latter serving as a compensatory behavior of same-sex mating competition. This research contributes a novel, biological perspective on sex tourism with implications for future research and practice.

Competitive Motherhood from a Comparative Perspective

2016 ◽  
Author(s):  
Katherine A. Valentine ◽  
Norman P. Li ◽  
Jose C. Yong
Keyword(s):  
Reproductive Success ◽  
Sex Ratio ◽  
Nonhuman Primates ◽  
Resource Competition ◽  
Sex Ratios ◽  
Comparative Perspective ◽  
Future Directions ◽  
Competition Hypothesis ◽  
Resource Enhancement

Mothers play an important role in helping their children achieve maximal reproductive success. We explore how mothers across species manipulate birth sex ratios favoring the sex that will be best suited to their environments and how maternal competition affects offspring reproductive success in nonhuman mammals as well as humans. The Trivers-Willard hypothesis, resource competition hypothesis, resource enhancement hypothesis, and maternal dominance hypothesis are considered with respect to maternal birth sex ratio manipulation. Next, the primate literature is reviewed as inspiration for hypotheses on maternal competition for positive offspring outcomes. Nonhuman primates as well as humans are argued to compete for status, breeding opportunities, and allomothers (i.e., caregivers apart from the mother), and these factors have an impact on their reproductive success. Status is passed on from mother to offspring, amplifying the effects of competition for status. Future directions are delineated to fill in gaps in the existing literature.

scholarly journals Sex roles and adult sex ratios: insights from mammalian biology and consequences for primate behaviour

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160321 ◽  
Author(s):  
Peter M. Kappeler
Keyword(s):  
Life History ◽  
Sex Ratio ◽  
Social Organization ◽  
Sex Roles ◽  
Paternal Care ◽  
Sex Role ◽  
Sex Ratios ◽  
Theoretical Models ◽  
Operational Sex Ratio ◽  
Minimum Length

Theoretical models and empirical studies in various taxa have identified important links between variation in sex roles and the number of adult males and females (adult sex ratio (ASR)) in a population. In this review, I examine these relationships in non-human primates. Because most existing theoretical models of the evolution of sex roles focus on the evolutionary origins of sex-biased behaviour, they offer only a general scaffold for predicting variation in sex roles among and within species. I argue that studies examining sex role variation at these more specific levels need to take social organization into account to identify meaningful levels for the measurement of ASR and to account for the fact that ASR and sex roles mutually influence each other. Moreover, taxon-specific life-history traits can constrain sex role flexibility and impact the operational sex ratio (OSR) by specifying the minimum length of female time outs from reproduction. Using examples from the primate literature, I highlight practical problems in estimating ASR and OSR. I then argue that interspecific variation in the occurrence of indirect forms of paternal care might indeed be linked to variation in ASR. Some studies also indicate that female aggression and bonding, as well as components of inter-sexual relationships, are sensitive to variation in ASR. Thus, links between primate sex roles and sex ratios merit further study, and such studies could prompt the development of more specific theoretical models that make realistic assumptions about taxon-specific life history and social organization. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

Sociosexuality and sex ratio: Sex differences and local markets

2005 ◽  
Vol 28 (2) ◽  
pp. 288-288
Author(s):  
John Lazarus
Keyword(s):  
Sex Differences ◽  
Sex Ratio ◽  
Local Level ◽  
Psychological Effects ◽  
Operational Sex Ratio ◽  
Know How ◽  
Males And Females ◽  
Mating Market ◽  
The Relationship ◽  
Ratio Measure

Operational sex ratio (OSR) is the correct sex ratio measure for predicting sociosexuality, but it is unclear whether this is the measure used. It would be valuable to know how OSR and sociosexuality correlate separately for males and females. The relationship between sociosexuality and OSR should also be examined with OSR measured at the local level of the mating market, where sex ratio must be having its psychological effects.

Women’s Intrasexual Competition Results in Beautification

2020 ◽  
pp. 194855062093340
Author(s):  
Xijing Wang ◽  
Hao Chen ◽  
Zhansheng Chen ◽  
Ying Yang
Keyword(s):  
Cosmetic Surgery ◽  
Intrasexual Competition ◽  
Operational Sex Ratio ◽  
Female College Students ◽  
Psychology Research ◽  
Search Query ◽  
Mating Market ◽  
Self Objectification ◽  
Google Search ◽  
The Ideal

Psychology research focuses primarily on male competition. This research, however, investigates women’s competition for love and the ideal partner in the mating market and reveals one psychological consequence for women, that is, beautification. This is demonstrated with ecologically valid, real-world archive and online search query data, a quasi-experiment, and a series of controlled experiments with random assignments. Intrasexual competition, indexed by the operational sex ratio (OSR) and income inequality (GINI), predicts women’s beautification reflected by Google search queries for cosmetic surgery terms (Study 1) and the density of certificated plastic surgeons (Study 2). Female college students from faculties with female-biased OSRs exhibit greater appearance focus than women from male-biased faculties (Study 3). A causal relationship, between women’s intrasexual competition and beautification (and even self-objectification), is subsequently demonstrated in experiments (Studies 4–6). Additionally, self-objectification due to intrasexual competition leads to women’s preference for appearance-oriented products (Study 6). Implications are discussed.

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