Does perceived sex ratio influence intrasexual competitiveness in women?

2020 ◽  
Author(s):  
Thomas Richardson
Keyword(s):  
Sex Ratio ◽  
Statistical Power ◽  
Sex Ratios ◽  
Facial Attractiveness ◽  
Single Women ◽  
Operational Sex Ratio ◽  
Type I ◽  
Double Blind ◽  
Future Career ◽  
Biased Sex Ratio

The operational sex ratio has been shown to influence a variety of behaviours in humans and non-human animals, particularly relating to intrasexual competition. One way females compete for mates is by derogating other women’s attractiveness. Recent studies have shown that priming participants with different sex ratios can induce sex ratio effects on behaviour. In a pre-registered, double blind experiment, 71 single women came to the lab twice and were primed with either a favourable (many men) or unfavourable (few men) sex ratio. I assessed whether unfavourable sex ratios increased self reported intrasexual competitiveness, as well as competitor derogation in the form of decreased ratings of female facial attractiveness and kindness. I also assessed whether they expressed less choosiness by rating male faces as more attractive. I tested whether any sex ratio effects are weaker for more attractive women. Finally, I attempted to replicate previous work suggesting that a male biased sex ratio increases women's preference for their future career over their future family. Despite having higher statistical power than most previous studies of this type, I did not find evidence for any of the hypothesised effects and failed to replicate 2 previous findings. The data indicated that the sex ratio manipulation likely did not work.

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.

The effects of body size, ownership and sex-ratio on the precopulatory mate guarding of Caprella penantis (Crustacea: Amphipoda)

2009 ◽  
Vol 90 (2) ◽  
pp. 275-279 ◽  
Author(s):  
Fumio Takeshita ◽  
Yasuhisa Henmi
Keyword(s):  
Body Size ◽  
Sex Ratio ◽  
Laboratory Experiments ◽  
Mate Guarding ◽  
Operational Sex Ratio ◽  
Receptive Female ◽  
Type I ◽  
Male Body ◽  
Precopulatory Mate Guarding ◽  
Secondary Factor

Precopulatory mate guarding behaviour of the skeleton shrimp Caprella penantis is described. Moreover, the effects of body size, ownership and sex-ratio on mate guarding were examined experimentally in the laboratory. In the field population, the operational sex-ratio was male-biased. Guarding pairs, which were collected from the field, continued guarding for an average of 350 minutes in the laboratory, indicating that the normal guarding duration is approximately 10 hours. In this species, two guarding types were found: Type O and Type I-like. In Type O guarding, the male would fold the female into a horseshoe shape, whilst the male held the female parallel to him in Type I-like guarding. In the laboratory experiments, male body size was the most important factor affecting competition for a receptive female; ownership was the secondary factor. Guarding duration was prolonged when the sex-ratio was male-biased. Thus, the precopulatory mate guarding behaviour of C. penantis is influenced by several factors, such as body size, ownership and sex-ratio.

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.

Estimating sex ratios of loggerhead turtles in Brazil from pivotal incubation durations

1997 ◽  
Vol 75 (5) ◽  
pp. 755-770 ◽  
Author(s):  
Maria Ângela Marcovaldi ◽  
Matthew H. Godfrey ◽  
N. Mrosovsky
Keyword(s):  
Sex Ratio ◽  
Sexual Differentiation ◽  
Sex Ratios ◽  
Caretta Caretta ◽  
Temperature Dependent ◽  
Loggerhead Turtles ◽  
Biased Sex Ratio ◽  
Nesting Beaches

A method of estimating natural sex ratios of hatchlings of species with temperature-dependent sexual differentiation from data on incubation durations is described. The method was applied to loggerhead turtles (Caretta caretta) nesting in Brazil. Data on incubation durations were collected from 11 nesting beaches monitored for up to six seasons. It was estimated that 82.5% of the loggerhead hatchlings produced were female. The strongly female-biased sex ratio in Brazil is similar to that found previously for loggerheads using beaches in the eastern U.S.A. This suggests that a female-biased hatchling sex ratio may be a feature of loggerhead populations.

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’.

scholarly journals Cooperative interactions among females and even more extraordinary sex ratios

2020 ◽  
Author(s):  
Ryosuke Iritani ◽  
Stuart A West ◽  
Jun Abe
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Structured Populations ◽  
Local Mate Competition ◽  
Mate Competition ◽  
Wasp Species ◽  
Cooperative Interactions ◽  
Competition Theory ◽  
Local Mate ◽  
Biased Sex Ratio

AbstractHamilton’s local mate competition theory provided an explanation for extraordinary female biased sex ratios in a range of organisms. When mating takes place locally, in structured populations, a female biased sex ratio is favoured to reduce competition between related males, and to provide more mates for males. However, there are a number of wasp species where the sex ratios appear to more female biased than predicted by Hamilton’s theory. We investigated theoretically the extent to which cooperative interactions between related females can interact with local mate competition to favour even more female biased sex ratios. We found that: (i) cooperative interactions between females can lead to sex ratios that are more female biased than predicted by local competition theory alone; (ii) sex ratios can be more female biased when the cooperative interactions are offspring helping parents before dispersal, rather than cooperation between siblings after dispersal. Our results can be applied to a range of organisms, and provide an explanation for the extreme sex ratio biases that have been observed in Sclerodermus and Melittobia wasps.

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.

Increased secondary sex ratios in golden hamster litters sired by males without coagulating glands and seminal vesicles

1996 ◽  
Vol 8 (2) ◽  
pp. 297 ◽  
Author(s):  
PH Chow ◽  
MP Cheung ◽  
WS O
Keyword(s):  
Sex Ratio ◽  
Y Chromosome ◽  
Sex Ratios ◽  
Seminal Vesicles ◽  
Differential Survival ◽  
Bilateral Ablation ◽  
Primary Sex Ratio ◽  
Sh Group ◽  
Biased Sex Ratio ◽  
Coagulating Gland

In golden hamsters, although bilateral ablation of paternal coagulating glands (CGX) and seminal vesicles (SVX) did not affect fertility, a higher number of male pups were born. The present study aimed at determining whether this male-biased sex ratio was due to an imbalance of fertilization by X and Y chromosome-bearing sperms or whether it was the consequence of a sex-related differential survival of embryos. The sex of embryos sired by sham-operated (SH) controls or males subjected to bilateral ablation of ampullary glands (AGX), CGX and SVX was determined from chromosomal spreads at 10 h post coitum and 10 days post coitum. The primary sex ratio of of the SH group did not deviate from the hypothetical sex ratio of 1:1. The sex ratios of zygotes from the three experimental groups did not differ from that of the controls. However, by mid gestation, the sex ratio was significantly higher in the SVX group (P < 0.05) and the CGX group (P < 0.005). The absence of secretions from the ampullary gland, coagulating gland and seminal vesicle had no effect on the primary sex ratio, thus these glands did not appear to affect fertilization by the X and Y chromosome-bearing sperm. The increased secondary sex ratios observed in the SVX and CGX groups were due to the preferential survival of males.

Experimental observations on the sex ratio of adult Schistosoma mansoni, with comments on the natural male bias

Parasitology ◽  
2000 ◽  
Vol 121 (4) ◽  
pp. 379-383 ◽  
Author(s):  
J. BOISSIER ◽  
H. MONÉ
Keyword(s):  
Sex Ratio ◽  
Schistosoma Mansoni ◽  
Sex Ratios ◽  
Vertebrate Host ◽  
Natural Conditions ◽  
Male And Female ◽  
Male Bias ◽  
Biased Sex Ratio ◽  
And Bisexual

The sex ratio of adult worms has been observed biased towards males in Schistosoma mansoni under natural conditions. The origin of this bias is unknown. This paper determines whether males are more infective than females under controlled experimental bisexual conditions, and hence if the sex ratio is male-biased as a consequence of this. The male and female cercarial infectivities in uni- and bisexual vertebrate host infections using a range of controlled cercarial sex ratios were studied. The results showed that, in experimental unisexual infections, male cercariae were more infective than females, and that in experimental bisexual infections, male cercarial infectivity was similar to that of female, irrespective of cercarial sex ratio. Furthermore, cumulative male and female cercarial infectivity was maximal when sex ratio was equilibrated. The unbiased sex ratios obtained in our experimental bisexual infections are discussed in terms of behavioural and/or biochemical male–female interaction. Alternative explanations of the natural biased sex ratio are proposed.

The genetic basis of sex ratio in Silene alba (= S. latifolia).

Genetics ◽  
1994 ◽  
Vol 136 (2) ◽  
pp. 641-651
Author(s):  
D R Taylor
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Natural Populations ◽  
Sex Ratio Bias ◽  
Deleterious Alleles ◽  
Silene Alba ◽  
Biased Sex Ratio ◽  
Paternal Parent ◽  
Reciprocal Crossing ◽  
Female Bias

Abstract A survey of maternal families collected from natural populations showed that the sex ratio in Silene alba was slightly female biased. Sex ratio varied among populations and among families within a female biased population. Crosses among plants from the most female biased population and the most male biased population showed that the sex ratio polymorphism was inherited through or expressed in the male parent. Males from one family in particular exhibited a severe female bias, characterized by less than 20% male progeny. The inheritance of sex ratio was investigated using a reciprocal crossing design. Sex ratios from reciprocal crosses were significantly different, indicating either sex-linkage or cytoplasmic inheritance of sex ratio. The sex ratios produced by males generally resembled the sex ratios produced by their male parents, indicating that the sex ratio modifier was Y linked. The maternal parent also significantly influenced sex ratio through an interaction with the genotype of the paternal parent. Sex ratio, therefore, is apparently controlled by several loci. Although sex ratio bias in this species may be due to deleterious alleles on the Y chromosome, it is more likely to involve an interaction between loci that cause the female bias and a Y-linked locus that enhances the proportion of males in the progeny.

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