Mating Patterns Research Articles

Size, Endurance, or Parental Care Performance? Male–Male Competition, Female Choice, and Non-Random Mating Pattern in the Glassfrog Centrolene savagei

Previous work has shown that Centrolene savagei is unique among the more than 150 species in the family Centrolenidae in demonstrating large-male mating advantage. However, it is still unknown whether non-random mating in this species is mediated by intrasexual and/or intersexual selection. To disentangle the effect of these selective pressures on mating pattern in this species, we monitored the breeding behavior of individuals in a population located in the department of Quindío, Central Andes of Colombia. We conducted diurnal and nocturnal surveys each weekend between February and July of 2016 in which we documented morphological (i.e., body size) and behavioral (i.e., chorus tenure, parental-care behavior) characteristics of males to determine their relationship with mating success. We corroborated that in this population of C. savagei, larger males obtain a higher number of mates than do smaller males; male body size co-varies positively with chorus tenure and drives this mating pattern. Male body size was not related to higher fertilization efficiency of eggs laid by females, or a higher survival of embryos in clutches cared for by them. In sum, the higher mating success of larger males in the glassfrog C. savagei seems most strongly related to a mechanism of endurance rivalry competition (intrasexual selection) than female choice (intersexual selection) based on egg fertilization efficiency or parental care quality.

Fitness differences due to allelic variation at Esterase-4 locus in Drosophila ananassae.

Esterases are known to play essential role inmetabolism, reproductive physiology and behaviour of Drosophila. Esterases are highly polymorphic enzymes in Drosophila, but the polymorphism of these enzymes is not well studied in Drosophila ananassae. Recent studies on esterase polymorphism in D. ananassae revealed that Est-4 locus comprises Est-4 active and Est-4 null alleles depending on enzymatic activity. For the in vivo functional characterization of this locus, homozygous lines of genotypes Est-4 active and Est-4 null were derived from the flies collected from Gangtok, Sikkim, in 2006. Mating propensity, mating pattern, fecundity, fertility and productivity of female, life span and triglycerides level were investigated in the flies bearing either Est-4 active or Est-4 null genotypes. Results showed that mating occurred randomly with nonsignificant difference in mating propensity between Est-4 active and Est-4 null flies. However, a significant difference in fecundity and strong dependency between genotypes and the rate of fertility was found. The median values of progeny produced per female were 24 and 20 for Est-4 active and Est-4 null genotypes, respectively. The life span assay showed a significant difference in the survivorship between the two genotypes. Triglycerides level was higher in Esterase-4 active larval haemolymph as well as in mature flies' homogenate than that of Esterase-4 null. Thus, Esterase-4 locus of D. ananassae has its role in fecundity, fertility and productivity of female, life span control and lipid metabolism.

First observation on courtship behavior of short-tailed viper snake, Gloydius saxatilis (Squamata: Viperidae) in Korea

Most reptile species have their own mating patterns. Therefore, courtship behaviors are important factors in understanding taxonomic features and species-specific breeding habits in the genus. This study explores the mating behaviors of the short-tailed viper snake (Gloydius saxatilis) which has never been reported. From September 2012 to August 2013, we observed the courtship behaviors of short-tailed viper snakes in Chunma Mountain County Park, Namyangju City, Gyeonggi Province, South Korea. In this study, 10 courtship behaviors from three snake couples were considered and compared. The results showed that, in general, most courtship behaviors of G. saxatilis were similar to those of other species of the family Viperidae. However, the most remarkable behavior of female short-tailed viper snakes was “quivering,” which had not yet been reported in females from the other species of the family Viperidae. These results can provide valuable information for research in systematics of short-tailed viper snakes.

Microsatellite primers in Plantago virginica (Plantaginaceae), an invasive species with both cleistogamous and chasmogamous flowers.

Polymorphic microsatellite markers were developed in Plantago virginica, an invasive species in China with both cleistogamous and chasmogamous flowers, to investigate its genetic structure and mating patterns. Fourteen novel microsatellite primer sets were designed, and the marker loci they amplified were characterized in 96 individuals from four populations. Eleven of these markers showed polymorphism and the number of alleles per locus ranged from two to six. AMOVA and STRUCTURE indicated that there were distinct patterns of genetic differentiation among the one invasive and three native US populations. These markers provide a useful tool for investigating genetic diversity in P. virginica and studying the mechanisms of invasion success.

Mating patterns of the gum arabic tree (Acacia senegal synonym Senegalia senegal) in two different habitats

Understanding the variation of mating patterns in disturbed habitats provide insight into the evolutionary potential of plant species and how they persist over time. However, this phenomenon is poorly understood in tropical dryland tree species. In the present study, we investigated how Acacia senegal reproduces in two different environmental contexts in Kenya. Open-pollinated progeny arrays of 10 maternal trees from each environmental context were genotyped using 12 nuclear microsatellite markers. Overall, A. senegal displayed a predominantly allogamous mating pattern. However, higher multilocus outcrossing rate (tm) was found in Lake Bogoria (tm = 1.00) than in Kampi ya Moto population (tm = 0.949). Higher biparental inbreeding (t m − t s = 0.116) and correlation of outcrossed paternity (rp = 0.329) was found in Kampi ya Moto than in Lake Bogoria population (t m − t s = 0.074, rp = 0.055), showing the occurrence of mating among relatives. Coefficient of coancestry (Θ = 0.208) showed that full-sibs constitute about 21% of the offspring in Kampi ya Moto population compared to about 14% (Θ = 0.136) in Lake Bogoria population. The results demonstrate that low adult tree density of A. senegal may be promoting seed production through consanguineous mating and suggest that man-made disturbance can affect mating patterns of the species. Despite these mating differences, trees from both populations can contribute as seed source for conservational plans, and to support effective genetic conservation and artificial regeneration programs of A. senegal. We suggest collection of seeds from at least 42 and 63 trees in Lake Bogoria and Kampi ya Moto populations, respectively, to retain a progeny array with a total effective population size of 150.

Laboratory social environment biases mating outcome: a first quantitative synthesis in a butterfly

Sexual selection is by essence social selection: an individual’s fitness is partly determined by the phenotype of its social partners (i.e., the social environment). Nevertheless, most behavioral studies on mating patterns and sexual selection are conducted in laboratory standardized conditions, and it is unclear how potential laboratory-induced social biases affect mating outcome. The social environment may actually dictate which of female mate choice or male-male competition is the primary determinant of mating outcome. This matters because we expect sexually selected traits to evolve differently if mating outcome is determined by female mate choice or by male-male competition. We address this issue by performing an in-depth quantitative synthesis testing the effects of common extrinsic (population density, sex ratio), intrinsic (age), and laboratory-induced (cage volume, experimental duration) biases of the social environment of adults on mating outcome. For this, we used the butterfly Bicyclus anynana, as it provides a reasonable sampling of mating experiments in diverse laboratory conditions (i.e., 31 publications from 7 different laboratories since 2001). We found that all tested social environmental variables displayed strong variation across B. anynana mating studies, and that most variables had significant effects usually in interaction with another variable and with opposite effects between sexes. Hence, mating outcome is affected by laboratory biases on the social environment. Our quantitative synthesis offers a first case example of the effects of a pervasive and recurrent issue in animal behavioral research on sexual selection, i.e., the need to root mating experiments in ecologically relevant laboratory environments, in order to produce meaningful results about the selective force(s) driving the evolution of sexually selected traits in nature. Mating outcome is biased by the laboratory social environment in which experiments are conducted. Male and female age, density, ratio, as well as cage volume and experimental duration all affect mating proportions, and this blurs our understanding of how sexual selection shapes sexually selected traits in the wild. This first systematic review was conducted on 31 studies in a single butterfly species, but our results are likely relevant in any taxonomic group.

Differences in mating behavior between two allopatric populations of a Neotropical scorpion

Courtship and mating behavior generally evolve rapidly in diverging populations and species. The adaptation to different environments may cause behavioral divergence in characteristics involved in mate choice. Our objective in this study was to compare the sexual behavior of two distant populations of the scorpion Bothriurus bonariensis. This species has a broad distribution in South America, inhabiting Central Argentina, Uruguay and south-eastern Brazil. It is known that in this species there is a divergence in morphological patterns (body size, coloration, allometry and fluctuating asymmetry indexes) among distant populations. Considering the differences in environmental conditions between localities, we compare the sexual behavior in intra-population and inter-population matings from Central Argentina and southern Uruguay populations. We found significant differences in mating patterns, including differences in the frequency and duration of important stimulatory courtship behaviors. In addition, most inter-population matings were unsuccessful. In this framework, the differences in reproductive behavior could indicate reproductive isolation between these populations, which coincides with their already known morphological differences. This is the first study comparing the sexual behavior of allopatric populations of scorpions; it provides new data about the degree of intraspecific geographical divergence in the sexual behavior of B. bonariensis.

Detection of Imprinting Effects for Quantitative Traits on X Chromosome Using Nuclear Families with Multiple Daughters.

Genomic imprinting is an epigenetic phenomenon in which the expression of an allele copy depends on its parental origin. This mechanism has been found to play an important role in many complex diseases. Statistical tests for imprinting effects have been developed for more than 15 years, but they are only suitable for autosomes. It was not until recently that the parental-asymmetry test on the X chromosome (XPAT) was proposed to test for imprinting effects. However, this test can only be used for qualitative traits. Therefore, in this article, we propose a class of PAT-type tests to test for imprinting for quantitative traits on the X chromosome in the presence of association, namely, Q-XPAT(c), Q-1-XPAT(c) and Q-C-XPAT(c), where c is a constant. These methods can accommodate complete and incomplete nuclear families with an arbitrary number of daughters. Extensive simulation studies demonstrate that the proposed tests control the size well under the null hypothesis of no imprinting effects and are powerful under various family structures. Moreover, by setting the inbreeding coefficient in females to be nonzero and using the assortative mating pattern in simulations, the proposed tests are shown to be valid under Hardy-Weinberg disequilibrium.

Implications of mating system and pollen dispersal indices for management and conservation of the semi-arid species Prosopis flexuosa (Leguminosae)

Recruitment by fencing of semi-arid trees is a common woodland conservation strategy that may have both positive and negative implications. Domestic herbivores can act as efficient dispersal seed agents but they can also affect the survival and growth of the trees first stages. Prosopis flexuosa (algarrobo) woodlands represent the most important plant community in the Monte region in Argentina and as this resource is affected by deforestation, grazing, natural fires and replacement of natural ecosystems by croplands, in order to protect the “algarrobo” a reserve had been established. As efficient management and conservation program depends on the information on population structure and mating system, the objectives of this work were to estimate mating and pollen dispersal patterns in a wild P. flexuosa population from the Ñacuñan fenced to exclude domestic cattle for 40years. This population is mainly outcrosser (tm=0.996), sensitive to inbreeding depression at seed stage, having relative reduced pollen mediated gene dispersal distance (4.56–20.35m), which favors inbreeding as a consequence of mating between related individuals. Our results suggest that for ex situ conservation the distance that would be enough to avoid full sib sampling among harvested seed-trees is about 20m. Collecting seeds from different pods reduce the proportion of full sibs within progeny arrays. For in situ conservation it is important to take into account that forest patches separated by more than 250m are expected to be isolated, increasing the risk of genetic variability loss, inbreeding increase and population extinction. The results are discussed in reference to the “algarrobo” management program; while in some case excluding big mammals from the stands should be advisable, the interaction with long dispersal big herbivores might be considered as a strategy to promote increased outbreeding reducing the rate of mating between related individuals.

Drivers of tree fecundity in pedunculate oak (Quercus robur) refugial populations at the species' southwestern range margin.

The current low latitudinal range margins of many extra-tropical plant species consist of small and scattered populations that persist locally in microrefugia. It remains poorly understood how their refugial distribution affects mating patterns and reproductive success. Here we examine flower and acorn production and their determinants in refugial populations of the widespread European forest tree pedunculate oak (Quercus robur). We monitored male flower, female flower and acorn production in 159 adult trees from 12 oak stands over 2years. We related these and derived parameters to a series of ecological and genetic predictor variables extrinsic (stand size, density and isolation as well as elevation, topography and forest cover) or intrinsic (size, phenology and several genotypic measures) to the target tree. Tree fertility was unrelated to extrinsic factors but determined by tree size, although we detected size-independent variation in reproductive investment. Female flower number accurately predicted acorn crop size. Fruit set differed between years, evidencing the existence of pollen limitation at the landscape but not at the local scale. Fruit setalso tended to increase with the number of mates of the target tree. We detected no other evidence for genetic constraints on mating. Reproduction was triggered by a combination of small-scale and landscape-scale drivers. Although short-distance mating prevailed, limited pollen flow did not appear to significantly constrain reproductive success. The high intrinsic ability of populations to maintain their reproductive capacity may help explain their successful long-term persistence in an adverse broader environment.

The erratic and contingent progression of research on territoriality: a case study

Our understanding of animal mating systems has changed dramatically with the advent of molecular methods to determine individuals’ reproductive success. But why are older behavioral descriptions and newer genetic descriptions of mating systems often seemingly inconsistent? We argue that a potentially important reason for such inconsistencies is a research trajectory rooted in early studies that were equivocal and overreaching, followed by studies that accepted earlier conclusions at face value and assumed, rather than tested, key ideas about animal mating systems. We illustrate our argument using Anolis lizards, whose social behavior has been studied for nearly a century. A dominant view emerging from this behavioral research was that anoles display strict territorial polygyny, where females mate with just the one male in whose territory they reside. However, all genetic evidence suggests that females frequently mate with multiple males. We trace this mismatch to early studies that concluded that anoles are territorial based on limited data. Subsequent research assumed territoriality implicitly or explicitly, resulting in studies that were unlikely to uncover or consider important any evidence of anoles’ departures from strict territorial polygyny. Thus, descriptions of anole behavior were largely led away from predicting a pattern of female multiple mating. We end by considering the broader implications of such erratic trajectories for the study of animal mating systems and posit that precise definitions, renewed attention to natural history, and explicitly questioning assumptions made while collecting behavioral observations will allow us to move towards a fuller understanding of animal mating systems. Mismatches between behavioral and genetic descriptions of mating systems are widespread across animals. We argue that these discrepancies can arise from the erratic and contingent progression of research on space use behavior and social interactions. We demonstrate such a trajectory in Anolis lizards, where decades of behavioral data led not only to the conclusion that anoles are territorial but also to the erroneous expectation, disproven by genetic evidence, that each female mates with just one male. The earliest studies concluded that anoles are territorial based on flimsy evidence, leading subsequent studies to implicitly and explicitly assume territorial behavior; later studies were thus unlikely to detect, or consider important, departures from territoriality that could facilitate female multiple mating. Such research trajectories are likely not unique to anoles, and we contend that avoiding these trajectories requires renewed and continued attention to the natural history of even well-studied organisms.

Asymmetric Hybridization in Cattails (Typha spp.) and Its Implications for the Evolutionary Maintenance of Native Typha latifolia.

Cattails (Typha spp.) have become an increasingly dominant component of wetlands in eastern North America and this dominance is largely attributable to the high frequency of Typha × glauca, the hybrid of native Typha latifolia and putatively introduced Typha angustifolia. Hybridization in this group is asymmetric, with T. angustifolia nearly always the maternal parent of F1 hybrids. However, the magnitude of hybrid infertility and whether mating asymmetries extend to the formation of advanced-generation hybrids have not been examined. We used hand-crosses to measure seed set and germination success. We found that mating asymmetries extend to the formation of back-crosses, with ~0 seeds set when T. latifolia was pollinated by hybrid cattails. Seed set was unaffected by pollen source for T. × glauca or T. angustifolia. However, seed production by T. angustifolia was consistently high while that of T. × glauca was variable and when pollinated by other T. × glauca more than 75% lower than for any other intraspecific cross indicating reduced hybrid fertility. We used these results to parameterize a model of hybrid zone evolution in which mating patterns and fertility were governed by interactions between alleles at nuclear and cytoplasmic loci. The model revealed that asymmetric mating and reduced hybrid fertility should favor the maintenance of T. latifolia over T. angustifolia compared to null expectations. However, the model also indicated restrictive conditions for the long-term maintenance of T. latifolia within populations, indicating that asymmetric mating might only stall rather than prevent the displacement of native cattails by hybrids.

Mating patterns and post-mating isolation in three cryptic species of the Engystomops petersi species complex.

Determining the extent of reproductive isolation in cryptic species with dynamic geographic ranges can yield important insights into the processes that generate and maintain genetic divergence in the absence of severe geographic barriers. We studied mating patterns, propensity to hybridize in nature and subsequent fertilization rates, as well as survival and development of hybrid F1 offspring for three nominal species of the Engystomops petersi species complex in Yasuní National Park, Ecuador. We found at least two species in four out of six locations sampled, and 14.3% of the wild pairs genotyped were mixed-species (heterospecific) crosses. We also found reduced fertilization rates in hybrid crosses between E. petersi females and E. “magnus” males, and between E. “magnus” females and E. “selva” males but not in the reciprocal crosses, suggesting asymmetric reproductive isolation for these species. Larval development times decreased in F1 hybrid crosses compared to same species (conspecific) crosses, but we did not find significant reduction in larval survival or early metamorph survival. Our results show evidence of post-mating isolation for at least two hybrid crosses of the cryptic species we studied. The general decrease in fertilization rates in heterospecific crosses suggests that sexual selection and reinforcement might have not only contributed to the pattern of call variation and behavioral isolation we see between species today, but they may also contribute to further signal divergence and behavioral evolution, especially in locations where hybridization is common and fertilization success is diminished.

Mate choice based on behavioural type: do convict cichlids prefer similar partners?

In monogamous species that provide biparental care, partners with similar behavioural types generally have a better reproductive success than dissimilar ones. The pattern of assortative mating for behavioural type is thus often interpreted as resulting from a mate choice process. However, an alternative process is also possible when the partners become similar through postpairing adjustments (behavioural convergence). The disentanglement of these two nonexclusive mechanisms is an important evolutionary question. Only sexual selection based on behavioural similarity before pairing can explain the maintenance of the behavioural type variability. In a previous study, we reported the existence of behavioural convergence for aggressiveness between partners in convict cichlids Amatitlania siquia, a monogamous tropical fish. We tested herein the assumption of mate choice based on behavioural similarity for aggressiveness using either short-term binary choice or long-term group level pairing. Pairing was not based on behavioural similarity between potential partners. Choosing a behaviourally compatible partner is a complex task because it requires profiling the potential mates. Individuals would thus achieve higher fitness benefits from choosing a partner on more conspicuous criteria (such as size for instance) and then attempt to increase partner similarity by convergence after pairing. Sexual selection does not appear to drive the maintenance of aggressiveness type variability in convict cichlids.

Temporal variation in size-assortative mating and male mate choice in a spider with amphisexual care.

Males should be more selective when they have a high investment in reproduction, especially in species with biparental or paternal care. In this context, male mate choice can promote size-assortative mating (SAM) when (1) large males win intrasexual disputes, (2) large females are more fecund, and (3) males prefer larger females to smaller ones. In the spider Manogea porracea, males exhibit high reproductive investment by building their webs above those of females and exhibiting extended care of offspring in the absence of females. Under these circumstances, we expect the occurrence of SAM and male preference for large females. Herein, we performed observations and experiments in the field to evaluate the hypotheses that (1) M. porracea mates assortatively by size and (2) SAM is influenced by male mate choice. Furthermore, we measured variables that could affect mating patterns, the sex ratios, and densities of both sexes. Pairing in M. porracea was positively size-assortative in 2012, but not in 2013. Large males won most disputes for mates and preferred larger females, which produced more eggs. The inconsistency in detection of SAM was due to population dynamics, namely variations in sex ratio and population density across the breeding season. Furthermore, we found that the significance of male mate choice on sexual selection of body size in M. porracea strongly depends on the competition intensity for mating opportunities. The traditional sexual selection hypothesis of SAM needs to be reviewed and must include measures of competition intensity.

The Y chromosomes of the great apes.

The great apes (orangutans, gorillas, chimpanzees, bonobos and humans) descended from a common ancestor around 13 million years ago, and since then their sex chromosomes have followed very different evolutionary paths. While great-ape X chromosomes are highly conserved, their Y chromosomes, reflecting the general lability and degeneration of this male-specific part of the genome since its early mammalian origin, have evolved rapidly both between and within species. Understanding great-ape Y chromosome structure, gene content and diversity would provide a valuable evolutionary context for the human Y, and would also illuminate sex-biased behaviours, and the effects of the evolutionary pressures exerted by different mating strategies on this male-specific part of the genome. High-quality Y-chromosome sequences are available for human and chimpanzee (and low-quality for gorilla). The chromosomes differ in size, sequence organisation and content, and while retaining a relatively stable set of ancestral single-copy genes, show considerable variation in content and copy number of ampliconic multi-copy genes. Studies of Y-chromosome diversity in other great apes are relatively undeveloped compared to those in humans, but have nevertheless provided insights into speciation, dispersal, and mating patterns. Future studies, including data from larger sample sizes of wild-born and geographically well-defined individuals, and full Y-chromosome sequences from bonobos, gorillas and orangutans, promise to further our understanding of population histories, male-biased behaviours, mutation processes, and the functions of Y-chromosomal genes.

Mathematical modelling for variations of inbreeding populations fitness with single and polygenic traits

BackgroundInbreeding mating has been widely accepted as the key mechanism to enhance homozygosity which normally will decrease the fitness of the population. Although this result has been validated by a large amount of biological data from the natural populations, a mathematical proof of these experimental discoveries is still not complete. A related question is whether we can extend the well-established result regarding the mean fitness from a randomly mating population to inbreeding populations. A confirmative answer may provide insights into the frequent occurrence of self-fertilization populations.ResultsThis work presents a theoretic proof of the result that, for a large inbreeding population with directional relative genotype fitness, the mean fitness of population increases monotonically. However, it cannot be extended to the case with over-dominant genotype fitness. In addition, by employing multiplicative intersection hypothesis, we prove that inbreeding mating does decrease the mean fitness of polygenic population in general, but does not decrease the mean fitness with mixed dominant-recessive genotypes. We also prove a novel result that inbreeding depression depends on not only the mating pattern but also genetic structure of population.ConclusionsFor natural inbreeding populations without serious inbreeding depression, our theoretical analysis suggests the majority of its genotypes should be additive or dominant-recessive genotypes. This result gives a reason to explain why many hermaphroditism populations do not show severe inbreeding depression. In addition, the calculated purging rate shows that inbreeding mating purges the deleterious mutants more efficiently than randomly mating does.

Assortative mating by colored ornaments in blue tits: space and time matter.

Assortative mating is a potential outcome of sexual selection, and estimating its level is important to better understand local adaptation and underlying trait evolution. However, assortative mating studies frequently base their conclusions on small numbers of individuals sampled over short periods of time and limited spatial scales even though spatiotemporal variation is common. Here, we characterized assortative mating patterns over 10 years in four populations of the blue tit (Cyanistes caeruleus), a passerine bird. We focused on two plumage ornaments—the blue crown and the yellow breast patch. Based on data for 1,657 pairs of birds, we found large interannual variation: assortative mating varied from positive to negative. To determine whether there was nonetheless a general trend in the data, we ran a within‐study meta‐analysis. It revealed that assortative mating was moderately positive for both ornaments. It also showed that mating patterns differed among populations and especially between two neighboring populations that displayed phenotypic divergence. Our results therefore underscore that long‐term studies are needed to draw broad conclusions about mating patterns in natural populations. They also call for studying the potential role of assortative mating in local adaptation and evolution of ornaments in both sexes.

Preference Versus Choice in Online Dating.

This study explores factors that influence matches of online dating participants' stated preference for particular characteristics in a potential partner and compares these with the characteristics of the online daters actually contacted. The nature of online dating facilitates exploration of the differences between stated preference and actual choice by participants, as online daters willingly provide a range of demographics on their ideal partner. Using data from the Australian dating website RSVP, we analyze 219,013 contact decisions. We conduct a multivariate analysis using the number of matched variables between the participants' stated preference and the characteristics of the individuals contacted. We find that factors such as a person's age, their education level, and a more social personality all increase the number of factors they choose in a potential partner that match their original stated preference. Males (relative to females) appear to match fewer characteristics when contacting potential love interests. Conversely, age interaction effects demonstrate that males in their late 60's are increasingly more selective (than females) regarding who they contact. An understanding of how technology (the Internet) is impacting human mating patterns and the psychology behind the participants informs the wider social science of human behavior in large-scale decision settings.

The Reversed Gender Gap in Education and Assortative Mating in Europe.

While in the past men received more education than women, the gender gap in education has turned around: in recent years, more highly educated women than highly educated men are reaching the reproductive ages. Using data from the European Social Survey (rounds 1-6), we investigate the implications of this reversed gender gap for educational assortative mating. We fit multilevel multinomial regression models to predict the proportions of men and women living with a partner of a given level of education, contingent on respondents' own educational attainment and on the cohort-specific sex ratio among the population with tertiary education at the country level. We find that highly educated women tend to partner more often "downwards" with less educated men, rather than remaining single more often. Medium educated women are found to partner less often "upwards" with highly educated men. For men, there is no evidence that they are more likely to partner with highly educated women. Rather, they are found to be living single more often. In sum, women's advantage in higher education has affected mating patterns in important ways: while women previously tended to form unions with men who were at least as highly educated as themselves, they now tend to live with men who are at most as highly educated. Along the way, advanced education became a bonus on the mating market for women as well as for men.