Level Of Theory Research Articles

Racial and ethnic variation in the relationship between parental educational similarity and infant health

Evidence suggests benefits of parental educational homogamy for infant and child well-being but ignores potential racial and ethnic variation in these benefits. Increasing disparities in infant health by maternal education and race, along with increasing educational sorting, raise questions about whether educational homogamy could contribute to these disparities. Drawing on a random sample of over 4 million live births in NVSS data from 2011 to 2020 and ordinary least squares regression, this study examines the relationship between infant health, parental educational similarity, and race and ethnicity. Our findings indicate a weak overall relationship between educational sorting and infant health at birth, with significant variation by race and ethnicity. In addition, absolute education levels and marital status more strongly predict infant health than educational assortative mating. Sensitivity analyses confirm the robustness of these findings across different modeling approaches and sample sizes. Our results indicate that parental educational sorting is only weakly related to infant health and cannot explain widening infant health gaps by race.

Ecological speciation in sympatric palms: 5. Evidence for pleiotropic speciation genes using gene knockout and high-throughput phenotyping

Abstract Theoretical models predict that sympatric, ecological speciation may be facilitated more readily when so-called ‘magic traits’ are present, linking traits under divergent selection with assortative mating. Such traits might be encoded by pleiotropic genes, that is, genes that affect multiple, apparently unrelated, phenotypes. However, few convincing examples of sympatric speciation exist, and empirical evidence for the role of magic traits in driving such speciation is rare. One of the strongest cases of sympatric speciation is the Howea palms of Lord Howe Island, Australia, comprising the sister species Howea belmoreana and Howea forsteriana, which have diverged due to soil substrate preferences and flowering time displacement. Here we investigate the role that pleiotropy may have played in the speciation process by carrying out high-throughput phenotyping experiments using 1830 Arabidopsis thaliana plants with knockouts of candidate Howea ‘speciation genes’. We identify several genes that show signatures of adaptive divergence between the Howea species and demonstrate pleiotropic roles in soil stress tolerance and flowering time, consistent with the Howea speciation scenario—notably, Howea orthologues of the A. thaliana loci At2-MMP, DCL1, RCD1, SAL1, and SIZ1. Empirical evidence is provided, therefore, for a range of pleiotropic genes with the potential to have driven sympatric speciation by generating magic traits which link divergent selection to non-random mating.

An experimental field study of inbreeding depression in an outcrossing invasive plant.

Inbreeding depression is likely to play an important role during biological invasion. But relatively few studies have investigated the fitness of selfed and outcrossed offspring in self-incompatible invasive plants in natural environments in their introduced range. Moreover, the majority of studies on inbreeding depression have investigated self-compatible species with mixed mating, and less is known about the intensity of inbreeding depression in outcrossing self-incompatible species. Here, we address these questions experimentally by comparing selfed and outcrossed progeny of purple loosestrife (Lythrum salicaria) over four growing seasons, including three under field conditions in a freshwater marsh in southern Ontario, Canada, a region where L. salicaria is highly invasive. The tristylous mating system of L. salicaria involves disassortative mating among floral morphs enforced by trimorphic incompatibility. However, owing to partial incompatibility, self-fertilized seed can be obtained by manual self-pollination thus facilitating comparisons of selfed and outcrossed progeny. We compared progeny with and without intraspecific competition from selfed or outcrossed neighbours and examined the influence of breeding treatment and competition on fitness correlates by measuring a range of life-history traits including: proportion of seeds germinating, days to germination, survival, proportion of plants flowering, time to flowering, vegetative mass, and inflorescence number and mass. We analysed data for each trait using functions from time series estimates of growth and two multiplicative estimates of fitness. We detected varying intensities of inbreeding depression for several traits in three of the four years of the experiment, including inflorescence mass and reproductive output. Cumulative inbreeding depression over four years averaged δ = 0.48 and 0.68, depending on the method used to estimate multiplicative fitness. The competition treatments did not significantly affect plant performance and the magnitude of inbreeding depression. Given the primarily outcrossing mating system of L. salicaria populations, the detection of inbreeding depression for several key life-history traits was as predicted by theory. Our results suggests that biparental inbreeding and low selfing in colonizing populations may have significant effects on demographic parameters such as population growth.

Social exchange or reinforcement of women’s educational advantage? The influence of educational assortative mating on occupational assortative mating for couples in Spain

The reversal of the gender gap in education has transformed traditional patterns of assortative mating, increasing the number of hypogamous couples. This change has been particularly intense in the case of Spain, a country of great interest due to the ambivalence of strong support for egalitarian attitudes and high proportion of traditional couples. Using quarterly microdata from the Spanish Labour Force Survey, applying generalised ordered-logit models, this research reveals that educational hypogamy increases the probability of occupational hypogamy. This association is consistent with the use of different occupational classifications and levels of disaggregation. But there are some factors that limit the transmission of women’s educational advantages to their occupational levels, mainly gender differences in access to the labour market and an uneven distribution of professional achievements by sex. The findings obtained underline the relevance of using different measures as well as different theoretical approaches to explain seemingly contradictory couple equilibria.

Effects of Recurrent Selection on Population Structure and Allele Frequencies in the M3S Maize Population

The effects of four cycles of recurrent selection on the allele frequencies of simple sequence repeat (SSR) markers and population structure were examined in the Maksimir 3 Synthetic (M3S) maize population (Zea mays L.). Genotyping of 32 plants from each selection cycle at 38 SSR loci revealed that the mean number of alleles per locus and the mean expected heterozygosity were preserved across selection cycles, indicating the maintenance of sufficient genetic variability in the population required for future genetic gain. The Waples test of selective neutrality revealed that genetic drift was the main force in changing allele frequencies in the population. The proportion of selectively non-neutral loci in single cycles of selection varied between 16% and 37%. Some non-neutral loci shared the same genomic locations with previously published QTLs controlling important agronomic traits. An analysis of molecular variance revealed that 5.6% of the genetic variation occurred among and 94.4% within cycle populations. Between 5% and 29% of loci were found to be in a significant Hardy–Weinberg (HW) disequilibrium, with the majority showing an excess of homozygosity. The excess of homozygosity at several loci was highly consistent across cycle populations, suggesting positive assortative mating as a possible cause of the observed HW disequilibrium. Linkage disequilibrium (LD) tests revealed that the M3S population was essentially in linkage equilibrium. The proportion of pairs of loci in significant LD varied from 0.1% to 1.8% across selection cycles, probably due to the effects of genetic drift and epistatic selection.

Geographically variable mate preferences shed light on the processes maintaining inversion polymorphism

Abstract An important question in evolution is to understand the mechanisms that maintain phenotypic diversity, despite selection that should drive homogeneity. For example, selection by predators may promote the convergence of colour patterns among defended prey, resulting in the formation of mimetic communities. However, certain aposematic species, such as the Neotropical butterfly Heliconius numata, are polymorphic. In H. numata, wing pattern polymorphism, which is associated with chromosomal inversions, may be maintained via disassortative mating preferences, thought to favour the co-occurrence of individuals with different mimicry phenotypes in Peru. To test whether environmental variation due to geography influences mate choice, here we investigate the occurrence of disassortative mating among the two coexisting forms of H. numata in French Guiana, and its potential role in the maintenance of this polymorphism. Our experimental approach demonstrates that the two forms display weak and slightly asymmetrical disassortative mate preferences. Modelling and simulations suggest that this pattern of mate preference alone is not sufficient to maintain polymorphism, and predict the loss of the choosiest form, unless this form enjoys a survival advantage. In this aposematic species, such an advantage could arise from mimicry, but further studies into the benefits of mimicry and predator generalization are needed to test this hypothesis. More importantly, our results suggest that the balance between selective forces influencing polymorphism may vary across geographical and ecological contexts, and this warrants further study.

Educational assortative mating and motherhood penalty in China

Mothers earn less than comparable childless women, and such motherhood penalty differs in magnitude by women’s socioeconomic and demographic characteristics. Prior research, however, has rarely considered how the effect of parenthood on women’s income may also depend on the characteristics of their partners. Using data from the China Family Panel Studies 2010–2018, we examine how the effects of motherhood on women’s earnings and within-couple income inequality vary by couples’ educational pairings in China. A large educational gap between spouses–hypergamy or hypogamy–exacerbates the motherhood penalty on a woman’s individual income and her share of the couple’s combined income. However, when the educational gap between spouses is moderate, hypergamy lessens the motherhood penalty on women’s individual income, whereas hypogamy mitigates the penalty on their share of couples’ combined earnings. In the context of China’s declining fertility, narrowing gender gap in education, and widening gender pay gap, these findings provide descriptive empirical evidence on how the motherhood penalty varies by educational assortative mating and underscore the significance of considering couple dynamics in understanding the motherhood penalty.

Genomic insights into the Montseny brook newt (Calotriton arnoldi), a Critically Endangered glacial relict

The Montseny brook newt (Calotriton arnoldi), considered the most endangered amphibian in Europe, is a relict salamandrid species endemic to a small massif located in northeastern Spain. Although conservation efforts should always be guided by genomic studies, those are yet scarce among urodeles, hampered by the extreme sizes of their genomes. Here, we present the third available genome assembly for the order Caudata, and the first genomic study of the species and its sister taxon, the Pyrenean brook newt (Calotriton asper), combining whole-genome and ddRADseq data. Our results reveal significant demographic oscillations which accurately mirrored Europe's climatic history. Although severe bottlenecks have led to depauperate genomic diversity and long runs of homozygosity along a gigantic genome, inbreeding might have been avoided by assortative mating strategies. Other life history traits, however, seem to have been less advantageous, and the lack of land dispersal has driven to exceptional levels of population fragmentation.

Combining Mendelian randomization with the sibling comparison design.

Mendelian randomization (MR) is a popular epidemiologic study design that uses genetic variants as instrumental variables (IVs) to estimate causal effects, while accounting for unmeasured confounding. The validity of the MR design hinges on certain IV assumptions, which may sometimes be violated due to dynastic effects, population stratification, or assortative mating. Since these mechanisms act through parental factors it was recently suggested that the bias resulting from violations of the IV assumptions can be reduced by combing the MR design with the sibling comparison design, which implicitly controls for all factors that are constant within families. In this article, we provide a formal discussion of this combined MR-sibling design. We derive conditions under which the MR-sibling design is unbiased, and we relate these to the corresponding conditions for the standard MR and sibling comparison designs. We proceed by considering scenarios where all three designs are biased to some extent, and discuss under which conditions the MR-sibling design can be expected to have less bias than the other two designs. We finally illustrate the theoretical results and conclusions with an application to real data, in a study of low-density lipoprotein and diastolic blood pressure using data from the Swedish Twin Registry.

Sympatry and parapatry among rocky reef cichlids of Lake Victoria explained by female mating preferences.

Work on the Lake Victoria cichlids Pundamilia nyererei (red dorsum males, deeper water), Pundamilia pundamilia (blue males, shallower water) and related species pairs has provided insights into processes of speciation. Here, we investigate the female mating behaviour of 5 Pundamilia species and 4 of their F1 hybrids through mate choice trials and paternity testing. Complete assortative mating was observed among all sympatric species. Parapatric species with similar depth habitat distributions interbred whereas other parapatric and allopatric species showed complete assortative mating. F1 hybrids mated exclusively with species accepted by females of the parental species. The existence of complete assortative mating among some currently allopatric species suggests that pre-existing mating barriers could be sufficient to explain current patterns of co-existence, although, of course, many other factors may be involved. Regardless of the mechanism, mating preferences may influence species distribution in potentially hybridizing taxa, such as in the adaptive radiation of cichlid fish. We suggest that this at least partly explains why some species fail to establish breeding populations in locations where they are occasionally recorded. Our results support the notion that the mating preferences of potentially cross-breeding species ought to be included in coexistence theory.

The two faces of secondary contact on islands: Introgressive hybridization between endemics and reproductive interference between endemics and introduced species

AbstractAimHybridization is thought to have played an important role in shaping the evolutionary history of diverse island taxa. Here, we propose an ecological and evolutionary framework for understanding the causes and consequences of heterospecific mating on islands—with and without introgressive hybridization. We use this framework to support our main contention that cases of secondary contact among endemic species should commonly result in introgressive hybridization whereas cases of contact between endemic and introduced species should commonly result in reproductive interference (RIN)—resulting in two qualitatively different faces of secondary contact on islands.LocationCanary Islands, Galapagos, New Zealand, Caribbean and Hawaii.Taxa705 vertebrate, invertebrate and plant species spanning 167 genera and 99 families.MethodsUsing a quantitative analysis of empirical research on secondary contact on islands, we weigh evidence for the causes and consequences of secondary contact and heterospecific mating on islands. In particular, we compare cases of secondary contact between endemic species versus secondary contact between endemic and introduced species.ResultsWe find that the drivers of secondary contact and heterospecific mating on islands most frequently reported in the literature are disturbance, long‐distance (e.g. inter‐island) dispersal and compromised assortative mating. We find support for the hypothesis that extensive introgression is a more common outcome between endemic species while RIN is a more common outcome between endemic and introduced species.Main ConclusionsWe conclude that there are biological reasons to predict secondary contact and heterospecific mating to be common on islands for all taxa, but that the consequence of secondary contact is categorically different for contact between endemic species and contact between endemic and introduced species. We conclude that the former likely explains the apparent frequency of hybridization on islands, while the latter presents a cryptic and underappreciated conservation threat.

Threshold‐dependent gene regulation and partial assortative mating determine wing dimorphism of an insect

Wing dimorphism is a life‐historical trait of insects which indicates the developmental trend of populations, going as migrants or staying as residents. The alternative wing morph enhances adaptability of insects to changing environments. However, the underlying mechanism for maintaining wing dimorphism remains vague. The brown planthoppers Nilaparvata lugens, a serious pest of rice, are either short‐winged or long‐winged. The shift between two wing morphs is determined by two insulin receptors. So, this pest is a better model organism to explore the mechanism of wing dimorphism. Here, the short‐ and long‐winged strains of N. lugens were selected. Rates of a selected wing morph were linearly increased in populations, and the selection response of the short‐winged morph was stronger than that of the long‐winged. Selection enhanced the migratory or resident propensity. Directional selection for the long‐winged morph resulted in longer and lighter forewings, while selection for the short‐winged morph generated shorter and thicker wings and higher fecundity. Relative expression levels of wing development genes InR1, InR2 and Foxo were positively correlated with the short‐winged rate in the short‐winged strain, while they were negatively correlated with the long‐winged rate in the long‐winged strain at specific stages. The change rate of expression levels was approximately two times as high as that of the wing morph rates in populations, indicating a high threshold‐dependent gene expressed regulation of wing morph. A partial assortative mating behavior occurred between the nearly pure‐bred lineages of short‐ and long‐winged strains. The short‐winged males preferred to mate with short‐winged females while the long‐winged males mated with the short‐ and long‐winged females equally. The threshold‐dependent mode may be more flexible to adjust wing morphs according to environmental conditions and the partial assortative mating promotes the genetic exchange between two wing morphs which drive the maintenance of wing dimorphism.

The genomic footprint of social stratification in admixing American populations.

Cultural and socioeconomic differences stratify human societies and shape their genetic structure beyond the sole effect of geography. Despite mating being limited by sociocultural stratification, most demographic models in population genetics often assume random mating. Taking advantage of the correlation between sociocultural stratification and the proportion of genetic ancestry in admixed populations, we sought to infer the former process in the Americas. To this aim, we define a mating model where the individual proportions of the genome inherited from Native American, European, and sub-Saharan African ancestral populations constrain the mating probabilities through ancestry-related assortative mating and sex bias parameters. We simulate a wide range of admixture scenarios under this model. Then, we train a deep neural network and retrieve good performance in predicting mating parameters from genomic data. Our results show how population stratification, shaped by socially constructed racial and gender hierarchies, has constrained the admixture processes in the Americas since the European colonization and the subsequent Atlantic slave trade.

Assortative mating and parental genetic relatedness contribute to the pathogenicity of variably expressive variants

We examined more than 97,000 families from four neurodevelopmental disease cohorts and the UK Biobank to identify phenotypic and genetic patterns in parents contributing to neurodevelopmental disease risk in children. We identified within- and cross-disorder correlations between six phenotypes in parents and children, such as obsessive-compulsive disorder (R= 0.32-0.38, p<10-126). We also found that measures of sub-clinical autism features in parents are associated with several autism severity measures in children, including biparental mean Social Responsiveness Scale scores and proband Repetitive Behaviors Scale scores (regression coefficient= 0.14, p=3.38×10-4). We further describe patterns of phenotypic similarity between spouses, where spouses show correlations for six neurological and psychiatric phenotypes, including a within-disorder correlation for depression (R= 0.24-0.68, p<0.001) and a cross-disorder correlation between anxiety and bipolar disorder (R= 0.09-0.22, p<10-92). Using a simulated population, we also found that assortative mating can lead to increases in disease liability over generations and the appearance of "genetic anticipation" in families carrying rare variants. We identified several families in a neurodevelopmental disease cohort where the proband inherited multiple rare variants in disease-associated genes from each of their affected parents. We further identified parental relatedness as a risk factor for neurodevelopmental disorders through its inverse relationship with variant pathogenicity and propose that parental relatedness modulates disease risk by increasing genome-wide homozygosity in children (R= 0.05-0.26, p<0.05). Our results highlight the utility of assessing parent phenotypes and genotypes toward predicting features in children who carry rare variably expressive variants and implicate assortative mating as a risk factor for increased disease severity in these families.

Genetic divergences and hybridization within the Sebastes inermis complex.

The Sebastes inermis complex includes three sympatric species (Sebastes cheni, viz Sebastes inermis, and Sebastes ventricosus) with clear ecomorphological differences, albeit incomplete reproductive isolation. The presence of putative morphological hybrids (PMH) with plausibly higher fitness than the parent species indicates the need to confirm whether hybridization occurs within the complex. In this sense, we assessed the dynamics of genetic divergence and hybridization within the species complex using a panel of 10 microsatellite loci, and sequences of the mitochondrial control region (D-loop) and the intron-free rhodopsin (RH1) gene. The analyses revealed the presence of three distinct genetic clusters, large genetic distances using D-loop sequences, and distinctive mutations within the RH1 gene. These results are consistent with the descriptions of the three species. Two microsatellite loci had signatures of divergent selection, indicating that they are linked to genomic regions that are crucial for speciation. Furthermore, nonsynonymous mutations within the RH1 gene detected in S. cheni and "Kumano" (a PMH) suggest dissimilar adaptations related to visual perception in dim-light environments. The presence of individuals with admixed ancestry between two species confirmed hybridization. The presence of nonsynonymous mutations within the RH1 gene and the admixed ancestry of the "Kumano" morphotype highlight the potential role of hybridization in generating novelties within the species complex. We discuss possible outcomes of hybridization within the species complex, considering hybrid fitness and assortative mating. Overall, our findings indicate that the genetic divergence of each species is maintained in the presence of hybridization, as expected in a scenario of speciation-with-gene-flow.

Experimental evidence of mate choice as the driving mechanism behind negative assortative mating for shell colour in a marine snail

Abstract How colour polymorphisms are maintained in natural populations constitutes a key subject of study for evolutionary ecologists. One of the mechanisms that has been put forward to explain this phenomenon is negative frequency-dependent selection, which can be caused by different mechanisms. Among these mechanisms is mate choice, or the selection as a potential mate of the rare or dissimilar colour morph by the choosy sex of a given species. In the context of colour polymorphism, mate choice predicts the occurrence of a negative assortative mating pattern, whereby different colour morphs mate more often than expected by chance alone. However, negative assortative mating can also result from other mechanisms, making it, at best, a fallible indicator of a mate choice-driven negative frequency-dependent selection. For this reason, experimental evidence explicitly connecting such a mating pattern to mate choice is necessary to claim that a particular colour polymorphism is being maintained by negative frequency-dependent selection. Here we present experimental evidence backing this relationship for the colour polymorphic marine gastropod Littorina saxatilis from the Ría de Vigo (NW Iberian Peninsula), although how specifically these organisms choose their mates remains unclear. This calls for further experimental efforts to clarify this issue and its relationship to the maintenance of colour polymorphism in L. saxatilis.

Supplemental Material for Why Intimate Partners Are Similar to Each Other: Four Pathways to Assortative Mating

Supplemental Material for Why Intimate Partners Are Similar to Each Other: Four Pathways to Assortative Mating

Why intimate partners are similar to each other: Four pathways to assortative mating.

Why intimate partners are similar to each other: Four pathways to assortative mating.

Social Plasticity Enhances Signal-Preference Codivergence.

AbstractThe social environment is often the most dynamic and fitness-relevant environment animals experience. Here we tested whether plasticity arising from variation in social environments can promote signal-preference divergence-a key prediction of recent speciation theory but one that has proven difficult to test in natural systems. Interactions in mixed social aggregations could reduce, create, or enhance signal-preference differences. In the latter case, social plasticity could establish or increase assortative mating. We tested this by rearing two recently diverged species of Enchenopa treehoppers-sap-feeding insects that communicate with plant-borne vibrational signals-in treatments consisting of mixed-species versus own-species aggregations. Social experience with heterospecifics (in the mixed-species treatment) resulted in enhanced signal-preference species differences. For one of the two species, we tested but found no differences in the plastic response between sympatric and allopatric sites, suggesting the absence of reinforcement in the signals and preferences and their plastic response. Our results support the hypothesis that social plasticity can create or enhance signal-preference differences and that this might occur in the absence of long-term selection against hybridization on plastic responses themselves. Such social plasticity may facilitate rapid bursts of diversification.

Effect of charge transfer on the first hyper-polarizability of N,N-dimethylaniline and julolidine: a DFT based comparative study.

Quantum mechanical calculations involving electron correlation, frequency dispersion, and solvent effects were carried out to examine the second-order nonlinear optical response ofvarious acceptor, X (-CF3, -CN, -NO2) substituted in N,N-dimethylaniline (DMA) and julolidine(JLD). Here, both DMA and JLD acts as donor and the three substituted groups, X (-CF3, -CNand -NO2) at the para position of both the ring systems as acceptor. The NLO response (βHRS) of -CF3 and -CN substituted DMA and JLD is relatively lower compared to DMA-NO2 andJLD-NO2. The charge distribution is found higher in case of -NO2substituted DMA and JLD (±443 and ±449) compared to their -CF3 or -CN substitution. Electronic characteristics such asUV-Vis absorption spectra, crucial excited state parameters and charge transfer contribution to βHRS have been used to explain the NLO parameter of DMA-X and JLD-X. Variation of theincident optical frequency of light shows fluctuation of βHRS value and highest values of βHRS are obtain at the λmax frequency of each compound. Solvent polarity variation study on βHRSshows that βHRS varies linearly with the Kirkwood-Onsagar dielectric factor (D). All computational studies have been carried out using density functional theory (DFT) based method. Since CAM-B3LYP based hybrid functional improves the asymptotic behavior of theexchange interaction by dividing into short-range and long-range components, first hyperpolarizability values in the present study were computed using DFT/ CAM-B3LYP/ 6-31G+(d,p) level oftheory.