Search

The emergence and persistence of polymorphism within populations generally requires specific regimes of natural or sexual selection. Here, we develop a unified theoretical framework to explore how polymorphism at targeted loci can be generated and maintained by either disassortative mating choice or balancing selection due to, for example, heterozygote advantage. To this aim, we model the dynamics of alleles at a single locus A in a population of haploid individuals, where reproductive success depends on the combination of alleles carried by the parents at locus A. Our theoretical study of the model confirms that the conditions for the persistence of a given level of allelic polymorphism depend on the relative reproductive advantages among pairs of individuals. Interestingly, equilibria with unbalanced allelic frequencies were shown to emerge from successive introduction of mutants. We then investigate the role of the function linking allelic divergence to reproductive advantage on the evolutionary fate of alleles within the population. Our results highlight the significance of the shape of this function for both the number of alleles maintained and their level of genetic divergence. Large number of alleles are maintained with substantial replacement of alleles, when disassortative advantage slowly increases with allelic differentiation . In contrast, few highly differentiated alleles are predicted to be maintained when genetic differentiation has a strong effect on disassortative advantage. These opposite effects predicted by our model explain how disassortative mate choice may lead to various levels of allelic differentiation and polymorphism, and shed light on the effect of mate preferences on the persistence of balanced and unbalanced polymorphism in natural population., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Decisions about which contraceptives to use are a key component of a couple's "fertility work," and these decisions can be made in homogamous or heterogamous couple contexts. Relative resource theory and the strain perspective suggest that heterogamy may lead to differences in bargaining power or higher levels of discordance within couples, thereby affecting the distribution of fertility work and decisions about which contraceptives a couple will use. While heterogamy has been linked to less effective contraceptive use amongst teenagers, its role in the contraceptive behavior of married and cohabiting women has been less widely studied. This study examines the association between relationship context in terms of education, age, and race/ethnicity heterogamy and partnered women's use of contraceptives. We used data on partnered women aged 20-45 who were trying to avoid pregnancy from the 2006-2015 National Survey of Family Growth (n = 8097). We used multinomial logistic regressions to determine whether education, age, or race/ethnicity heterogamy was associated with the use of male or female sterilization, long-acting reversible contraceptives (LARCs), other hormonal contraceptives, or other non-hormonal methods. We did not find consistent evidence that relative bargaining power due to higher education, more advanced age, or racial/ethnic privilege resulted in the use of methods requiring lower levels of fertility work. We found some evidence supporting the strain perspective. Younger women (20-34) who differed from their partners along two or more dimensions were less likely to use contraceptive methods requiring ongoing effort and coordination (i.e., LARCs, other hormonal methods, and non-hormonal methods). This association was not observed among women aged 35-45. Despite the more permanent nature of marriage/cohabitation, differences between partners in heterogamous relationships may factor into the contraceptive decision-making process, especially among younger adults at earlier stages of their relationships., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The tempo of sex chromosome evolution-how quickly, in what order, why and how their particular characteristics emerge during evolution-remains poorly understood. To understand this further, we studied three closely related species of African clawed frog (genus Xenopus ), that each has independently evolved sex chromosomes. We identified population polymorphism in the extent of sex chromosome differentiation in wild-caught Xenopus borealis that corresponds to a large, previously identified region of recombination suppression. This large sex-linked region of X. borealis has an extreme concentration of genes that encode transcripts with sex-biased expression, and we recovered similar findings in the smaller sex-linked regions of Xenopus laevis and Xenopus tropicalis . In two of these species, strong skews in expression (mostly female-biased in X. borealis , mostly male-biased in X. tropicalis ) are consistent with expectations associated with recombination suppression, and in X. borealis , we hypothesize that a degenerate ancestral Y-chromosome transitioned into its contemporary Z-chromosome. These findings indicate that Xenopus species are tolerant of differences between the sexes in dosage of the products of multiple genes, and offer insights into how evolutionary transformations of ancestral sex chromosomes carry forward to affect the function of new sex chromosomes. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)'.

Objectives: Prior research points to the importance of couple-level religious similarity for multiple dimensions of partnership quality and stability but few studies have investigated whether this association holds for older couples., Method: The current article uses dyadic data from the National Social Life, Health, and Aging Project (NSHAP), a representative sample of 953 individuals age 62-91 plus their marital or cohabiting partners. We use modified actor-partner interdependence models., Results: Religious service heterogamy predicted lower relationship happiness and satisfaction. Both associations were partially explained by the fact that religiously dissimilar partners report relatively little free time in joint activity. Further, religiously heterogamous couples had less frequent sex and engaged in less nonsexual touch than their more similar counterparts., Conclusions: Taken together, results attest to the ongoing importance of religious similarity-service attendance, in particular-for partnership quality in late life. Future research is needed to more fully examine which mechanisms account for these patterns., (© The Author(s) 2017. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Heterogamous marriages, in which partners have dissimilar attributes (e.g. by socio-economic status or ethnicity), are often at elevated risk of dissolution. We investigated the influences of heterogamy by religion and area of residence on risk of marital dissolution in Northern Ireland, a country with a history of conflict and residential segregation along Catholic-Protestant lines. We expected Catholic-Protestant marriages to have elevated risks of dissolution, especially in areas with high concentrations of a single religious group where opposition to intermarriage was expected to be high. We estimated risks of marital dissolution from 2001 to 2011 for 19,791 couples drawn from the Northern Ireland Longitudinal Study (a record linkage study), adjusting for a range of compositional and contextual factors using multilevel logistic regression. Dissolution risk decreased with increasing age and higher socio-economic status. Catholic-Protestant marriages were rare (5.9 % of the sample) and were at increased risk of dissolution relative to homogamous marriages. We found no association between local population composition and dissolution risk for Catholic-Protestant couples, indicating that partner and household characteristics may have a greater influence on dissolution risk than the wider community.