scholarly journals Adult sex ratio and social status predict mating and parenting strategies in Northern Ireland

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160318 ◽  
Author(s):  
Caroline Uggla ◽  
Ruth Mace
Keyword(s):  
Social Class ◽  
Northern Ireland ◽  
Sex Ratio ◽  
Parental Investment ◽  
Pair Bond ◽  
Mate Value ◽  
Stable Pair ◽  
Highly Educated ◽  
Bond Stability ◽  
Adult Sex Ratio

Evidence from animal species indicates that a male-biased adult sex ratio (ASR) can lead to higher levels of male parental investment and that there is heterogeneity in behavioural responses to mate scarcity depending on mate value. In humans, however, there is little consistent evidence of the effect of the ASR on pair-bond stability and parental investment and even less of how it varies by an individual's mate value. In this paper we use detailed census data from Northern Ireland to test the association between the ASR and pair-bond stability and parental investment by social status (education and social class) as a proxy for mate value. We find evidence that female, but not male, cohabitation is associated with the ASR. In female-biased areas women with low education are less likely to be in a stable pair-bond than highly educated women, but in male-biased areas women with the lowest education are as likely to be in a stable pair-bond as their most highly educated peers. For both sexes risk of separation is greater at female-biased sex ratios. Lastly, our data show a weak relationship between parental investment and the ASR that depends on social class. We discuss these results in the light of recent reformulations of parental investment theory. 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’.

Parental Investment by the Northern Mockingbird: Male and Female Roles in Feeding Nestlings

The Auk ◽  
1986 ◽  
Vol 103 (1) ◽  
pp. 152-159 ◽  
Author(s):  
Randall Breitwisch ◽  
Peter G. Merritt ◽  
George H. Whitesides
Keyword(s):  
Sex Ratio ◽  
Parental Investment ◽  
Feeding Rate ◽  
Mimus Polyglottos ◽  
Nestling Period ◽  
Adult Sex Ratio ◽  
Males And Females ◽  
High Level ◽  
Load Size ◽  
Northern Mockingbirds

Abstract Analysis of 3,293 feeding trips to nestling Northern Mockingbirds (Mimus polyglottos) in the first 11 days of nestling life showed that males and females fed young at similar rates. Young were fed a mixed diet of animal prey and fruits, and males and females fed similar volumes of animal prey and of fruits. Females displayed a monotonic increase in feeding rate during nestling life but did not significantly increase load size. Males significantly increased both feeding rate and load size with age of nestlings, and their feeding rate peaked in the mid-nestling period, when young grow most rapidly. Males and females fed broods of two and three young at similar rates. There was a biased breeding-adult sex ratio in this population, with males outnumbering females. The unbalanced sex ratio may allow females to demand a high level of male parental care in feeding nestlings and in other behaviors included in parental investment.

Effects of phytoseiid predators on the sex ratio of the spider mite Panonychus ulmi

1991 ◽  
Vol 69 (1) ◽  
pp. 208-212 ◽  
Author(s):  
Dan L. Johnson ◽  
Heather C. Proctor
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Spider Mite ◽  
Total Population ◽  
Panonychus Ulmi ◽  
Encounter Rate ◽  
Male Mortality ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Male Activity

The effect of predator presence on the adult sex ratio of a spider mite (Panonychus ulmi) was examined in a field experiment. Phytoseiid predators (chiefly Typhlodromus occidentalis) were removed from 32 trees harboring P. ulmi populations, and allowed to remain at natural levels on 32 other trees. Both total population density and proportion of males in the prey population were significantly higher in predator-free trees. Mechanisms that could explain the increase in the proportion of males are examined. The most probable is that greater male activity results in a higher encounter rate between predator and prey, and that subsequent higher male mortality when predators are present exaggerates the female-biased sex ratio. The theoretical effects of sex-biased predation on diplo-diploid and haplo-diploid organisms are discussed.

scholarly journals Sex ratio effects on reproductive strategies in humans

2015 ◽  
Vol 2 (1) ◽  
pp. 140402 ◽  
Author(s):  
Ryan Schacht ◽  
Monique Borgerhoff Mulder
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Ethnic Group ◽  
Reproductive Strategies ◽  
Situational Factors ◽  
Male Mating ◽  
Mating Effort ◽  
Short Term ◽  
Adult Sex Ratio ◽  
Using Data

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

scholarly journals Is biasing offspring sex ratio adaptive? A test of Fisher's principle across multiple generations of a wild mammal in a fluctuating environment

2018 ◽  
Vol 285 (1891) ◽  
pp. 20181251 ◽  
Author(s):  
Andrea E. Wishart ◽  
Cory T. Williams ◽  
Andrew G. McAdam ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Adult Sex Ratio ◽  
Secondary Sex Ratio ◽  
North American Red Squirrels ◽  
Negative Frequency Dependent Selection ◽  
Fisher’S Principle

Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels ( Tamiasciurus hudsonicus ) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.

Effect of Adult Sex Ratio on Mule Deer and Elk Productivity in Colorado

2001 ◽  
Vol 65 (3) ◽  
pp. 543 ◽  
Author(s):  
Gary C. White ◽  
David J. Freddy ◽  
R. Bruce Gill ◽  
John H. Ellenberger
Keyword(s):  
Sex Ratio ◽  
Mule Deer ◽  
Adult Sex Ratio

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

scholarly journals Sexually selected females in the monogamous Western Australian seahorse

2006 ◽  
Vol 274 (1609) ◽  
pp. 521-525 ◽  
Author(s):  
Charlotta Kvarnemo ◽  
Glenn I Moore ◽  
Adam G Jones
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Mating System ◽  
Genetic Study ◽  
Mating Success ◽  
Male Preference ◽  
Monogamous Species ◽  
Adult Sex Ratio ◽  
Western Australian ◽  
Selection Differentials

Studies of sexual selection in monogamous species have hitherto focused on sexual selection among males. Here, we provide empirical documentation that sexual selection can also act strongly on females in a natural population with a monogamous mating system. In our field-based genetic study of the monogamous Western Australian seahorse, Hippocampus subelongatus , sexual selection differentials and gradients show that females are under stronger sexual selection than males: mated females are larger than unmated ones, whereas mated and unmated males do not differ in size. In addition, the opportunity for sexual selection (variance in mating success divided by its mean squared) for females is almost three times that for males. These results, which seem to be generated by a combination of a male preference for larger females and a female-biased adult sex ratio, indicate that substantial sexual selection on females is a potentially important but under-appreciated evolutionary phenomenon in monogamous species.

Contribution of adult sex ratio to trauma and reproductive output in large breeding groups of rhesus macaques (Macaca mulatta)

2021 ◽  
Vol 30 (4) ◽  
pp. 479-492
Author(s):  
J Crast ◽  
MA Bloomsmith ◽  
CM Remillard ◽  
T Meeker
Keyword(s):  
Sex Ratio ◽  
Macaca Mulatta ◽  
Social Dynamics ◽  
Rhesus Macaques ◽  
Well Being ◽  
Primate Research ◽  
Adult Males ◽  
Adult Sex Ratio ◽  
Breeding Groups ◽  
Financial Burdens

Maintaining stable breeding groups of rhesus macaques (Macaca mulatta) can be challenging due to the complex social dynamics and despotic nature of the species. Trauma from aggression is a common problem in rhesus colonies and can cause social disruption, strain veterinary and animal management resources, and potentially affect reproduction. Previous research has shown that increasing the number of non-natal adult males in a breeding group can improve group stability, reduce trauma, and increase reproduction. Here, we used mixed-effects regression models to examine the effects of sex ratio and other factors on trauma and reproduction at the Yerkes National Primate Research Center using a historical dataset made up of four large rhesus groups over an eleven-year period (2003–2013). As expected, sex ratio was a significant predictor for both trauma and reproduction. However, group age since formation was a stronger predictor of trauma frequency and the amount of space available was a slightly better predictor of reproduction than sex ratio or trauma. These results indicate that improving sex ratios can be a viable management strategy to reduce trauma and improve reproduction, particularly when it is difficult to manipulate the group compositions and/or their housing situations. Reducing trauma is a primary goal for rhesus breeding colonies, as it directly impacts the monkeys' health and psychological well-being. Such improvements are necessary for the ethical treatment and care of the animals themselves, but also to reduce financial burdens and maintain a healthy colony for research purposes.

Parental Investment and Mate Value Measure

2018 ◽  
Author(s):  
Jan Antfolk ◽  
Agneta Sjölund
Keyword(s):  
Parental Investment ◽  
Mate Value ◽  
Value Measure
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