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Adult sex ratios and reproductive strategies: a critical re-examination of sex differences in human and animal societies.

ABSTRACT: It is increasingly recognized that the relative proportion of potential mates to competitors in a population impacts a range of sex-specific behaviours and in particular mating and reproduction. However, while the adult sex ratio (ASR) has long been recognized as an important link between demography and behaviour, this relationship remains understudied. Here, we introduce the first inter-disciplinary collection of research on the causes and consequences of variation in the ASR in human and animal societies. This important topic is relevant to a wide audience of both social and biological scientists due to the central role that the relative number of males to females in a population plays for the evolution of, and contemporary variation in, sex roles across groups, species and higher taxa. The articles in this theme issue cover research on ASR across a variety of taxa and topics. They offer critical re-evaluations of theoretical foundations within both evolutionary and non-evolutionary fields, and propose innovative methodological approaches, present new empirical examples of behavioural consequences of ASR variation and reveal that the ASR plays a major role in determining population viability, especially in small populations and species with labile sex determination. This introductory paper puts the contributions of the theme issue into a broader context, identifies general trends across the literature and formulates directions for future research.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'.

SUBMITTER: Schacht R

PROVIDER: S-EPMC5540852 | biostudies-other | 2017 Sep

REPOSITORIES: biostudies-other

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Project description:BackgroundThe sex differences in memory impairment were inconclusive, and the effect of female reproductive factors (age at menarche, age at menopause, and reproductive period) on the differences was not clear. We aimed to examine the sex differences in objective and subjective memory impairment in postmenopausal women and age- and education-matched men and explore whether the differences were differed by female reproductive factors.MethodsData were obtained from the China Health and Retirement Longitudinal Study. Using the case-control matching method, 3,218 paired postmenopausal women and men matched for age and education were selected. Memory was assessed using the three-word recall task and a self-rated question. Poisson regression models with a robust error variance were used.ResultsThe relative risk was 1.22 (95% confidence interval 1.08-1.38) for objective memory impairment in women compared with men (23.87% vs. 27.36%), and 1.51 (1.36-1.67) for subjective memory impairment (39.34% vs. 28.25%) after adjusting the confounders. The higher risk of objective memory impairment in women was different among groups of age at menarche in a linear pattern, with younger age at menarche associated with higher risks of objective memory impairment (p < 0.001 for trend). It was also different among groups of menopausal age and reproductive period in an approximate U-shaped pattern, with a similar risk of objective memory with men in women menopause at 52-53 years and having a reproductive period of 31-33 years and higher risks in women with earlier or later menopause (RRs raging form 1.17 to1.41) and a shorter or longer period of reproduction (RR, 1.23-1.29). The higher risks of subjective memory impairment in women were not different among different groups of reproductive factors.ConclusionsPostmenopausal women were at an increased risk of objective and subjective memory impairment than men. The higher risks in objective memory, but not subjective memory, were varied by age at menarche, age at menopause, and reproductive periods, which may help understand the underlying mechanisms of sex differences in cognitive ageing and guide precise intervention to preventing dementia among older women and men.

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Adult sex ratios and reproductive strategies: a critical re-examination of sex differences in human and animal societies.

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