Level Of Theory Research Articles

Assortative (online) dating: Insights into partner choice from an experimental dating app

In Western nations, the simultaneous increases in interracial relationships and the use of dating apps such as Tinder have raised questions regarding the influence of dating apps on partner choice. This study examines whether principles of assortative mating – people's tendency to select partners similar to them – apply to dating apps, or whether the reduced cue environment used on these apps leads users to choose more heterogeneous partners. Young (age <28) Dutch participants (N = 522) used a mock dating app in which potential partners were either White or non-White, relatively low or high educated, and possessed an ethnically Dutch or non-Dutch name. Results pointed to educational assortativity for higher-educated participants and indicated that profile pictures, rather than names, influenced the choice of a White target for participants with a Dutch family background.

Unrestricted gene flow between two subspecies of translocated brushtail possums (Trichosurus vulpecula) in Aotearoa New Zealand

Two lineages of brushtail possums (Trichosurus vulpecula) were historically introduced to Aotearoa New Zealand, and these two subspecies have different phenotypic forms. Despite over 100 years of potential interbreeding, they appear to retain morphological differences, which may indicate reproductive isolation. We examined this using population samples from a confined landscape and scored each specimen for phenotype using a number of fur colour traits. This resulted in a bimodal trait distribution expected for segregated grey and black lineages. We also sought evidence for genetic partitioning based on spatial and temporal effects. Genetic structure and rates of genetic mixing were determined using seven neutral, species-specific nuclear microsatellite markers and mitochondrial DNA control region sequence. Genotype analyses indicated high levels of variation and mtDNA sequences formed two major haplogroups. Pairwise tests for population differentiation of these markers found no evidence of subdivision, indicating that these brushtail possums behave as a single randomly mating unit. Despite maintenance of two main colour phenotypes with relatively few intermediates, previous inference of assortative mating and anecdotes of distinct races, our data indicate that New Zealand brushtail possums can freely interbreed, and that in some locations they have formed completely mixed populations where neutral genetic markers are unrelated to phenotype. This has implications for effective pest management towards eradication.

Mating Market and Dynamics of Union Formation

The paper investigates the relationship between structural partner market constraints and the timing and educational sorting of unions in Germany (1985–2018). We integrate the literature on the effect of the reversed gender gap in education on educational assortative mating, with a focus on mating dynamics and the measurement of the partner market over the life course. We concentrate on two particular educational groups, low-educated men and highly educated women, those with worsening mating prospects and more subject to experience hypogamous unions. Our results show that the local education-specific mating squeeze influences union formation, its timing, and educational sorting. Indeed, for the two groups, the increasing supply of highly educated women in the partner market increases the likelihood of remaining single or establishing an hypogamous union, where she is higher educated than he. In line with search theory, we find the effects of the mating squeeze to become particularly visible after people turn 30 years of age. This is true for the risk of remaining single and forming an hypogamous union. We underline the necessity to study assortative mating and union formation from a dynamic perspective, taking into account changing structural conditions during the partner search process.

Negative assortative mating and maintenance of shell colour polymorphism in Littorina (Neritrema) species

Colour polymorphism is a widespread phenomenon in natural populations of several species. In particular, it is especially common on marine gastropod species from the genus Littorina. Recently, it has been argued that intrapopulation shell colour polymorphism in Littorina fabalis could be caused by negative frequency-dependent sexual selection via a mechanism of mate choice (indirectly estimated through negative assortative mating). Here we try to determine the existence of negative assortative mating in three species of the subgenus Neritrema (L. fabalis, L. obtusata, L. saxatilis) that share a similar shell colour polymorphism, to ascertain if this mechanism could represent an ancestral character in this subgenus that could be contributing to the maintenance of the colour polymorphism observed in each species. We collected or reanalysed from previous studies a sample of mating pairs of these three species from seven locations from NW Spain and NE Russia and estimated assortative mating using the IPSI index. Our results suggest that all species and populations show a systematic tendency towards negative assortative mating when shell colour is grouped in the broad categories ‘light’ and ‘dark’. Moreover, a more detailed analysis of each colour separately suggests that shell colour may not be the main target of assortative mating, but perhaps a physically-linked trait to the real target of selection. This hypothesis opens interesting new lines of research in Littorina snails.

Population structure of North Pacific gray whales in light of trans‐Pacific movements

AbstractRecent findings that some gray whales that feed off Sakhalin Island (SI), Russia, in the western North Pacific (WNP) overwinter in the eastern North Pacific (ENP) indicate that population structure in this species is more complex than originally thought. We generated mitochondrial DNA (mtDNA) control region sequences and microsatellite genotypes (n = 12 loci) from 156 whales sampled off SI and compared them to available data from 106 ENP whales. Significant mitochondrial and nuclear genetic differentiation between the SI and ENP whales was found. Genetic cluster analysis identified two groups among the SI whales, one of which was genetically similar to ENP whales. Photographs collected from the biopsied SI whales showed that both groups comprised whales known to migrate to the ENP, suggesting that the clustering pattern was not reflective of some SI whales interbreeding while overwintering in the WNP. Instead, the genetic differentiation observed between the SI and ENP whales may be due to assortative mating of SI whales while west of eastern migratory routes. The rare but continued reports of gray whales off the coasts of Japan and China, however, confirm that some gray whales overwinter in the WNP and highlight the need to collect additional data from these whales.

Assortative mating for between-patch dispersal status in a wild bird population: Exploring the role of direct and indirect underlying mechanisms.

Previous studies have reported functional integration between dispersal and other phenotypic traits allowing individuals to alleviate dispersal costs, and such associations can affect dispersal evolution in return. In sexually reproducing species, assortative mating according to dispersal can shape the maintenance of such trait associations. Despite the potentially crucial consequences of dispersal in natural populations, assortative mating for dispersal and its underlying mechanisms remain largely unexplored. Here, we assessed assortative mating for between-patch dispersal status in a fragmented population of a small passerine bird, the collared flycatcher, and explored whether such assortative mating could result from (i) direct mate choice based on dispersal-related behavioural (aggressiveness and boldness) and morphological traits (tarsus and wing length), (ii) biased mating due to spatio-temporal heterogeneity in the distribution of dispersal phenotypes and/or (iii) post-mating adjustment of dispersal phenotype or dispersal-related traits. We found intrinsic assortative mating (i.e. positive among-pair correlation) for current dispersal status (in the year of mating) but not for natal dispersal status, even though we could not exclude it due to limited power. We also found assortative mating for boldness and age category (yearlings vs. older adults), and the probability for pair members to be assorted for current dispersal status was higher when both pair members were of similar boldness score and of the same age compared with mixed-age pairs. Mate choice based on boldness and age thus appears as a possible mechanism underlying assortative mating for dispersal status. Our analyses however remained correlative, and only an experimental manipulation of these traits could allow inferring causal links. Non-random mating for dispersal-related traits may affect the evolution of dispersal syndromes in this population. More work is nevertheless needed to fully assess the evolutionary implications of age- and behaviour-based assortative mating for dispersal.

Two new hybrid populations expand the swordtail hybridization model system.

Natural hybridization events provide unique windows into the barriers that keep species apart as well as the consequences of their breakdown. Here, we characterize hybrid populations formed between the northern swordtail fish Xiphophorus cortezi and Xiphophorus birchmanni from collection sites on two rivers. We use simulations and new genetic reference panels to develop sensitive and accurate local ancestry calling in this novel system. Strikingly, we find that hybrid populations on both rivers consist of two genetically distinct subpopulations: a cluster of pure X. birchmanni individuals and one of phenotypically intermediate hybrids that derive ∼85-90% of their genome from X. cortezi. Simulations suggest that initial hybridization occurred ∼150 generations ago at both sites, with little evidence for contemporary gene flow between subpopulations. This population structure is consistent with strong assortative mating between individuals of similar ancestry. The patterns of population structure uncovered here mirror those seen in hybridization between X. birchmanni and its sister species, Xiphophorus malinche, indicating an important role for assortative mating in the evolution of hybrid populations. Future comparisons will provide a window into the shared mechanisms driving the outcomes of hybridization not only among independent hybridization events between the same species but also across distinct species pairs.

When Do Opposites Attract? A Model Uncovering the Evolution of Disassortative Mating.

AbstractDisassortative mating is a rare form of mate preference that promotes the persistence of polymorphism. While the evolution of assortative mating and its consequences for trait variation and speciation have been extensively studied, the conditions enabling the evolution of disassortative mating are still poorly understood. Mate preferences increase the risk of missing mating opportunities, a cost that can be compensated by a greater fitness of offspring. Heterozygote advantage should therefore promote the evolution of disassortative mating, which maximizes the number of heterozygous offspring. From the analysis of a two-locus diploid model with one locus controlling the mating cue under viability selection and the other locus coding for the level of disassortative preference, we show that heterozygote advantage and negative frequency-dependent viability selection acting at the cue locus promote the evolution of disassortative preferences. We predict conditions of evolution of disassortative mating coherent with selection regimes acting on traits observed in the wild. We also show that disassortative mating generates sexual selection, which disadvantages heterozygotes at the cue locus, limiting the evolution of disassortative preferences. Altogether, our results partially explain why this behavior is rare in natural populations.

Female education, marital assortative mating, and dowry: Theory and evidence from districts of India

AbstractWe study marital assortative mating in education and its relation to dowry in India. There are four main results and contributions of this paper. First, instrumental variable estimates using Indian Human Development Survey-II data suggest existence of positive assortative mating in education levels of husband and wife. Second, this association is weaker in dowry-prominent districts suggesting that in districts with strong patriarchal norms, high dowry transfers could substitute for lower bride's education. Third, we study the independent effect of husband's and wife's education and its interaction on dowry. Estimates suggest that dowry rises with the groom's education and falls with the bride's schooling years. However, the joint effect of husband-and-wife education on dowry is negative, implying that though dowry rises with groom's education, the rate of increase is smaller the more educated the bride is. Finally, to explain the empirical results, we propose a theoretical model of assortative mating in the presence of dowry.

SPOUSAL ASSOCIATIONS OF SERUM METABOLOMIC PROFILES BY NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Phenotype-based assortative mating is well established in humans, with the potential for further convergence through a shared environment. To assess the correlation within infertile couples of physical, social, and behavioural characteristics and 155 circulating metabolic measures.

The advantage of daughters in hypogamous families: parental heterogamy and educational outcomes among children of highly educated parents

ABSTRACT Increasing female educational attainment across OECD countries is making hypogamy a widespread phenomenon. This trend provides an opportunity to re-examine the effects of educational assortative mating on children's educational outcomes. This research explores the effects of hypergamy, homogamy, and hypogamy on gender differences in children's expectation of university graduation and actual college graduation. For the first purpose, logistic regression with country fixed-effects is applied to individual-level data from PISA 2015; a similar analysis is carried out for the second purpose with data from the European Social Survey. Three characteristics make us expect higher female advantage among children of hypogamous couples: higher probability of mothers being the main family breadwinner; higher probability of gender value conflict, eventually leading to family breakup and the father's absence; and the possibility that the father's occupation discourages sons from pursuing higher education. A systematic female advantage is indeed found among children of hypogamous couples in terms of expectation of college graduation and actual college graduation. Among the possible mechanisms behind this female advantage, only the father's and the mother's occupation could be explored with the data at hand, but none of them explain this advantage.

PNPT1, MYO15A, PTPRQ, and SLC12A2-associated genetic and phenotypic heterogeneity among hearing impaired assortative mating families in Southern India.

The study was conducted between 2018 and 2020. From a cohort of 113 hearing impaired (HI), five non-DFNB12 probands identified with heterozygous CDH23 variants were subjected to exome analysis. This resolved the etiology of hearing loss (HL) in four South Indian assortative mating families. Six variants, including three novel ones, were identified in four genes: PNPT1 p.(Ala46Gly) and p.(Asn540Ser), MYO15A p.(Leu1485Pro) and p.(Tyr1891Ter), PTPRQ p.(Gln1336Ter), and SLC12A2 p.(Pro988Ser). Compound heterozygous PNPT1 variants were associated with DFNB70 causing prelingual profound sensorineural hearing loss (SNHL), vestibular dysfunction, and unilateral progressive vision loss in one family. In the second family, MYO15A variants in the myosin motor domain, including a novel variant, causing DFNB3, were found to be associated with prelingual profound SNHL. A novel PTPRQ variant was associated with postlingual progressive sensorineural/mixed HL and vestibular dysfunction in the third family with DFNB84A. In the fourth family, the SLC12A2 novel variant was found to segregate with severe-to-profound HL causing DFNA78, across three generations. Our results suggest a high level of allelic, genotypic, and phenotypic heterogeneity of HL in these families. This study is the first to report the association of PNPT1, PTPRQ, and SLC12A2 variants with HL in the Indian population.

Strong phenotypic trait correlations between mating partners do not result from assortative mating in wild great tits (Parus major)

There is considerable debate about the occurrence of assortative mating between phenotypic traits measured within natural populations. Meta-analyses have implied that assortative mating occurs generally in natural populations, but recent work indicates these conclusions largely result from biased data. Specifically, estimates of phenotypic correlations between mating partners do not solely result from nonrandom associations between individual-level traits of partners but also from other biological processes (joint phenotypic plasticity, indirect genetic effects), methodological practices (observer bias) and other unexplained residual correlations (e.g. correlated measurement error). This paper puts this critique to test. First, we estimated the overall phenotypic correlation between phenotypic traits of mating partners for a wild population of great tits. Second, we estimated various key variance components to reveal the extent to which phenotypic correlations between partners resulted from assortative mating, reversible plasticity, social partner effects and methodological practices. We performed our analyses for a range of phenotypic traits (body mass, breathing rate, exploration behaviour, wing and tarsus length) to derive general conclusions not hinging on the specifics of the traits involved. Our analyses support the conclusion that patterns of assortative mating exist at first glance but occur because of the biasing effects of correlated residuals likely caused by a combination of phenotypic responses to unknown environmental factors or measurement error-not because of intrinsic patterns of assortative mating.

Parental assortative mating and the intergenerational transmission of human capital

We study the contribution of parental educational assortative mating to the intergenerational transmission of educational attainment. We develop an empirical model for educational correlations within the family in which parental educational sorting can translate into intergenerational transmission jointly by both parents, or transmission can originate from each parent independently. Estimating the model using educational attainment from Danish population-based administrative data for over 400,000 families, we find that on average 75 percent of the intergenerational correlation in education is driven by the joint contribution of the parents. We also document a 38 percent decline of assortative mating in education for parents born between the early 1920s and the early 1950s. While the raw correlations also show decreases in father- and mother-specific intergenerational transmissions of educational attainment, our model shows that once we decompose all factors of intergenerational mobility, the share of intergenerational transmission accounted for by parent-specific factors increased from 7 to 27 percent; an increase compensated by a corresponding fall in joint intergenerational transmission from both parents, leaving total intergenerational persistence unchanged. The mechanisms of intergenerational transmission have changed, with an increased importance of one-to-one parent-child relationships.

Opportunity and change in occupational assortative mating

This article documents how opportunity and change in the U.S. occupational structure shaped patterns of occupational assortative mating between 1970 and 2015–2017. Trends in occupational assortative mating have often been cited as potentially contributing to the rise in economic inequality—the idea that doctors increasingly marry doctors instead of nurses—thereby exacerbating the concentration of resources among advantaged households. Previous estimates of trends in occupational assortative mating are now decades old and their impact on household inequality has not been quantified. Our results show large-scale change. The prevalence of dual-professional couples nearly tripled between 1970 and 2015–2017. Changes were especially large among particular occupational combinations. For instance, male doctors have become increasingly likely to be married to female doctors, and male lawyers to female lawyers. Almost all of the changes in occupational assortative mating patterns, however, are accounted for by changes in the distributions of spouses' occupations, for example, the rise of women in professional occupations. Because of this, the contribution of occupational assortative mating to the rise in economic inequality has been small. In the absence of any association between spouses’ occupations, observed increases in household earnings inequality would have been reduced by 5%. Although this is a small portion of overall changes in inequality, it is much larger than prior estimates of the effects of educational assortative mating on inequality, which recent studies have estimated to be essentially zero.

The association between personalities, alternative breeding strategies and reproductive success in dunnocks.

Although consistent between-individual differences in behaviour (i.e. animal personality) are ubiquitous in natural populations, relatively few studies have examined how personalities influence the formation of social relationships. Yet, behavioural characteristics of both sexes might be key when it comes to pair-bond formation, and cooperation with partners to successfully rear offspring. We here use a wild population of dunnocks (Prunella modularis) to first investigate whether individuals mate nonrandomly (i.e. assortative mating) with regard to four behavioural traits-flight-initiation distance (FID), provisioning, activity and vigilance-that differ in repeatability and have previously been associated with mating patterns and fitness in other species. Second, we test whether an individual's FID is associated with variability in the dunnocks' mating system (i.e. monogamous pairs vs. polygamous groups). Finally, we determine whether FID and provisioning of males and females associate with their reproductive success. We found no statistical support for assortative mating in FID between males and females. Interestingly, in polygamous groups, co-breeding males differed in their FIDs with dominant alpha males having significantly shorter FIDs compared with subordinate beta-males. Moreover, there was evidence for assortative mating in provisioning for alpha males and females in polygamous groups. We also found that male provisioning influenced reproductive success of both sexes, whereas female provisioning rates only positively correlated with her own but not their partner(s) reproductive output. Our results suggest that personality differences may have important implications for social relationships, the emergence of different mating patterns and ultimately reproductive success within populations.

Elevated temperature increases reproductive investment in less preferred mates in the invasive European corn borer moth.

Rapidly changing environments may weaken sexual selection and lead to indiscriminate mating by interfering with the reception of mating signals or by increasing the costs associated with mate choice. If temperature alters sexual selection, it may impact population response and adaptation to climate change. Here, we examine how differences in temperature of the mating environment influence reproductive investment in the European corn borer moth (Ostrinia nubilalis). Mate preference in this species is known to be related to pheromone usage, with assortative mating occurring between genetically distinct E and Z strains that differ in the composition of female and male pheromones. We compared egg production within and between corn borer lines derived from four different populations that vary in pheromone composition and other traits. Pairs of adults were placed in a mating environment that matched the pupal environment (ambient temperature) or at elevated temperature (5°C above the pupal environment). At ambient temperature, we found that within‐line pairs produced eggs sooner and produced more egg clusters than between‐line pairs. However, at elevated temperature, between‐line pairs produced the same number of egg clusters as within‐line pairs. These results suggest that elevated temperature increased investment in matings with typically less preferred, between‐line mates. This increased investment could result in changes in gene flow among corn borer populations in warming environments.

Trends in the association between educational assortative mating, infant and child mortality in Nigeria

BackgroundExisting knowledge has established the connection between maternal education and child survival, but little is known about how educational assortative mating (EAM), relates to childhood mortality. We attempt to examine this association in the context of Nigeria.MethodsData was obtained from the 2008, 2013, and 2018 waves of the Nigeria Demographic and Health Survey, which is a cross-sectional study. The sample includes the analysis of 72,527 newborns within the 5 years preceding each survey. The dependent variables include the risk of a newborn dying before 12 months of age (infant mortality), or between the age of 12–59 months (child mortality). From the perspective of the mother, the independent variable, EAM, includes four categories (high-education homogamy, low-education homogamy, hypergamy, and hypogamy). The Cox proportional hazard regression was employed for multivariate analyses, while the estimation of mortality rates across the spectrum of EAM was obtained through the synthetic cohort technique.ResultsThe risk of childhood mortality varied across the spectrum of EAM and was particularly lowest among those with high-education homogamy. Compared to children of mothers in low-education homogamy, children of mothers in high-education homogamy had 25, 31 to 19% significantly less likelihood of infant mortality, and 34, 41, and 57% significantly less likelihood of child mortality in 2008, 2013 and 2018 survey data, respectively. Also, compared to children of mothers in hypergamy, children of mothers in hypogamous unions had 20, 12, and 11% less likelihood of infant mortality, and 27, 36, and 1% less likelihood of child mortality across 2008, 2013 and 2018 surveys, respectively, although not significant at p < 0.05. Both infant and child mortality rates were highest in low-education homogamy, as expected, lowest in high-education homogamy, and lower in hypogamy than in hypergamy. Furthermore, the trends in the rate declined between 2008 and 2018, and were higher in 2018 than in 2013.ConclusionThis indicates that, beyond the absolute level of education, the similarities or dissimilarities in partners’ education may have consequences for child survival, alluding to the family system theory. Future studies could investigate how this association varies when marital status is put into consideration.

Field of study and partner choice

There is strong assortative mating by field of study. To examine to which extent this is due to self selection or to a causal effect of access to specific ”marriage markets”, we use data from participants in admission lotteries of four oversubscribed studies in the Netherlands. For each of the four studies, we find that the winning compliers of an admission lottery are significantly more likely than the losing compliers to have a partner from the lottery study, whereas losing compliers are only marginally more likely to have a partner from the lottery study than would occur under random matching. These results indicate that assortative mating by field of study is largely due to marriage market access and that self selection plays a minor role. JEL-codes: I26, J12, J13.

Marriage Market Counterfactuals Using Matching Models

We use a simple structural matching model with unobserved heterogeneity to produce counterfactual marriage patterns, and thus quantify the contribution of changes in marital patterns in rising income inequality. We propose an algorithm that allows us to fix the degree of assortative mating without changing the level of marital gains and hence isolate the intensive and extensive margins (i.e. isolate changes in assortative mating from changes in marriage rates). We apply this approach to US data from 1962 to 2017, and show that marital patterns can explain about a quarter of the rise in income inequality, the intensive margin contributing 7%, the extensive margin the remaining 93%. Our algorithm also allows us to show that the extensive margin is itself driven for three‐fifths by a change in the total number of singles and for two‐fifths by a change in the distribution of types among singles (in particular low‐educated women).