Assortative Mating Preferences Research Articles

The effectiveness of pseudomagic traits in promoting premating isolation.

Upon the secondary contact of populations, speciation with gene flow is greatly facilitated when the same pleiotropic loci are both subject to divergent ecological selection and induce non-random mating, leading to loci with this fortuitous combination of functions being referred to as 'magic trait' loci. We use a population genetics model to examine whether 'pseudomagic trait' complexes, composed of physically linked loci fulfilling these two functions, are as efficient in promoting premating isolation as magic traits. We specifically measure the evolution of choosiness, which controls the strength of assortative mating. We show that, surprisingly, pseudomagic trait complexes, and to a lesser extent also physically unlinked loci, can lead to the evolution of considerably stronger assortative mating preferences than do magic traits, provided polymorphism at the involved loci is maintained. This is because assortative mating preferences are generally favoured when there is a risk of producing maladapted recombinants, as occurs with non-magic trait complexes but not with magic traits (since pleiotropy precludes recombination). Contrary to current belief, magic traits may not be the most effective genetic architecture for promoting strong premating isolation. Therefore, distinguishing between magic traits and pseudomagic trait complexes is important when inferring their role in premating isolation. This calls for further fine-scale genomic research on speciation genes.

Experimentally testing mate preference in an avian system with unidirectional bill color introgression.

Mating behavior can play a key role in speciation by inhibiting or facilitating gene flow between closely related taxa. Hybrid zones facilitate a direct examination of mating behavior and the traits involved in establishing species barriers. The long-tailed finch (Poephila acuticauda) has two hybridizing subspecies that differ in bill color (red and yellow), and the yellow bill phenotype appears to have introgressed ~350 km eastward following secondary contact. To examine the role of mate choice on bill color introgression, we performed behavioral assays using natural and manipulated bill colors. We found an assortative female mating preference for males of their own subspecies when bill color was not manipulated. However, we did not find this assortative preference in trials based on artificially manipulated bill color. This could suggest that assortative preference is not fixed entirely on bill color and instead may be based on a different trait (e.g., song) or a combination of traits, or alternatively may be due to lower statistical power alongside the bill manipulations being unconvincing to the female choosers. Intriguingly, we find a bias in the inheritance of bill color in captive bred F1 hybrid females. Previous modeling suggests that assortative mate preference and this kind of partial dominance in the underlying genes may together contribute to introgression, making the genetic architecture of bill color in this system a priority for future research.

Profile similarities among romantic partners’ character strengths and their associations with relationship- and life satisfaction

We studied the similarity among partners’ character strengths (i.e., positively valued traits) across two studies. In Study 1, N = 68 couples completed the 240-item VIA Inventory of Strengths and in Study 2, N = 143 couples completed a 24-item brief-form and measures of life- and relationship satisfaction. We computed raw, normative, and distinctive profile similarities for the 24 strengths and found support for partners’ similarity in both studies (normative: rs ≥ 0.84; raw: rs ≥ 0.23; distinctive: rs ≥ 0.06). Actor-Partner Interdependence Model analyses (Study 2) provided no evidence for the notion that similarity relates to couples’ satisfaction. We discuss our findings regarding prior research, assortative mating preferences, and extensions to the study of partner- and ideal partner perceptions.

Never mind I'll find someone like me – Assortative mating preferences on Tinder

Previous literature has identified assortative mating as the most frequent deviation from random mating both in offline dating and on classic online dating websites. However, several recent studies have suggested that assortative mating is fading due to the advent of mobile dating apps. Therefore, in this study we examine whether preferences for assortative mating are still present on the most popular mobile dating app of the moment, Tinder. For this means, we analyze experimental and survey data on 7846 Tinder profile evaluations. We unambiguously find that Tinder users prefer a potential partner whom they perceive to be similar in the personality traits agreeableness and openness to experience. With respect to similarity in perceived age, we find either no assortment or positive assortment, depending on whether we condition on other participant characteristics. Finally, we do not find any evidence for preferences for assortative mating based on attractiveness. We examine heterogeneous preferences by the gender and age of the experiment participants.

Size-dependent mating pattern in a nuptial gift-giving insect.

The reproductive interests of females and males often diverge in terms of the number of mating partners, an individual’s phenotype, origin, genes, and parental investment. This conflict may lead to a variety of sex‐specific adaptations and also affect mate choice in both sexes. We conducted an experiment with the bush‐cricket Pholidoptera griseoaptera (Orthoptera, Tettigoniidae), a species in which females receive direct nutritional benefits during mating. Mated individuals could be assigned due to the genotype of male spermatodoses, which are stored in the female’s spermatheca. After 3 weeks of possible copulations in established mating groups which were random replications with four females and males we did not find consistent assortative mating preference regarding to body size of mates. However, our results showed that the frequency of within‐pair copulations (192 analyzed mating events in 128 possible pairwise combinations) was positively associated with the body size of both mated individuals with significant interaction between sexes (having one mate very large, association between body size and the number of copulations has weaken). Larger individuals also showed a higher degree of polygamy. This suggests that body size of this nuptial gift‐giving insect species is an important sexual trait according to which both sexes choose their optimal mating partner.

Does adaptation to different diets result in assortative mating? Ambiguous results from experiments on Drosophila.

The emergence of behavioural isolation between populations under divergent selection can be crucial for ecological speciation, but the mechanisms underlying such isolation are poorly understood. Several experimental evolution studies have shown that positive assortative mating (preference for similar mates) can arise rapidly in Drosophila laboratory populations reared in different stressful conditions, while other studies failed to confirm this effect. Here, we present the results of an evolution experiment in which outbred lines of Drosophila melanogaster were reared for 1-2years on one of the three different diets (standard, starch based or high salt). We show that nonrandom mating arose in some, but not all lines, and that the manifestations and possible interpretations of this nonrandomness depend strongly on the type of tests used to assess mating preferences. More specifically, multiple-choice four-fly tests revealed positive assortative mating (prevalence of homogamic matings) in some starch-adapted and salt-adapted lines when paired with a control line reared on the standard diet, but competitive three-fly tests rather revealed competitive advantage of control males and females over the flies reared on stressful diets. The results imply that divergent adaptation can result in differences in mating propensity or competitive ability, which, in turn, may either facilitate or hamper speciation depending on the relative frequency of high- vs. low-competition settings in natural habitats of the diverging populations. The results also emphasize the importance of using diverse tests for assessing mating structure in natural and laboratory populations.

Personality assortative female mating preferences in a songbird

Abstract Consistent individual behavioural differences (‘animal personalities’) are documented across a variety of animal taxa. Sexual selection, especially assortative mating has been suggested as a possible mechanism contributing to the maintenance of different personality types within populations but little is known about non-random pair-formation with respect to personality traits in unconstrained choice tests. We here tested whether female mating preferences were non-random with respect to male and female neophobia in zebra finches (Taeniopygia guttata), an important avian model of mate choice and animal personality research. Male and female neophobia was assessed by attaching novel objects to birds’ feeders. Females’ mating preferences were tested with randomly assigned, unfamiliar males in a four-way choice apparatus. Females associated most with males with neophobia scores similar to their own. These results provide evidence that mating preferences and personality traits can covary, supporting evolutionary scenarios of assortative mating contributing to the maintenance of personality traits.

Shifting barriers and phenotypic diversification by hybridisation.

The establishment of hybrid taxa relies on reproductive isolation from the parental forms, typically achieved by ecological differentiation. Here, we present an alternative mechanism, in which shifts in the strength and location of dispersal barriers facilitate diversification by hybridisation. Our case study concerns the highly diverse, stenotopic rock-dwelling cichlids of the African Great Lakes, many of which display geographic colour pattern variation. The littoral habitat of these fish has repeatedly been restructured in the course of ancient lake level fluctuations. Genetic data and an experimental cross support the hybrid origin of a distinct yellow-coloured variant of Tropheus moorii from ancient admixture between two allopatric, red and bluish variants. Deficient assortative mating preferences imply that reproductive isolation continues to be contingent on geographic separation. Linking paleolimnological data with the establishment of the hybrid variant, we sketch a selectively neutral diversification process governed solely by rearrangements of dispersal barriers.

Adaptive, but not condition-dependent, body shape differences contribute to assortative mating preferences during ecological speciation.

Assortative mating is critical for reproductive isolation during speciation; however, the mechanisms underlying mating preferences are often unknown. Assortative mating can be mediated through preferences for condition-dependent and adaptive ("magic") traits, but rigorously testing these hypotheses has been impeded by trait covariation in living organisms. We used computer-generated models to examine the role of body shape in producing association preferences between fish populations undergoing ecological speciation in different habitat types. We demonstrate that body shape can serve as an adaptive trait (variation in head size between populations) and a condition-dependent signal (variation in abdominal distention among individuals). Female preferences for stimuli varying in only one aspect of body shape uncovered evidence for body shape as a magic trait across population pairs, but no evidence for body shape serving as a condition-dependent signal. Evolution of preferences only in females from one habitat type as well as stronger preferences in sympatric nonsulfidic as opposed to allopatric nonsulfidic populations suggests that reinforcement may have played a role in producing the observed patterns.

‘For Richer, For Poorer’: Assortative Mating and Savings Preferences

Do couples share the same values? The social sciences have mainly concentrated on comparing the socioeconomic characteristics of spouses, but rarely consider their attitudes to risk and time. In this paper, we use conventional measurements and an original method of scoring. We find that spouses are very similar in their savings preferences, even when we control for the individual characteristics. Our results suggest that most of this relationship comes from marital sorting. These conclusions are decisive in explaining the decision process within households and its implications for wealth inequalities between households since homogamy causes a divide in the population.

Experimental swap of Anopheles gambiae's assortative mating preferences demonstrates key role of X-chromosome divergence island in incipient sympatric speciation.

Although many theoretical models of sympatric speciation propose that genes responsible for assortative mating amongst incipient species should be associated with genomic regions protected from recombination, there are few data to support this theory. The malaria mosquito, Anopheles gambiae, is known for its sympatric cryptic species maintained by pre-mating reproductive isolation and its putative genomic islands of speciation, and is therefore an ideal model system for studying the genomic signature associated with incipient sympatric speciation. Here we selectively introgressed the island of divergence located in the pericentric region of the X chromosome of An. gambiae s.s. into its sister taxon An. coluzzii through 5 generations of backcrossing followed by two generations of crosses within the introgressed strains that resulted in An. coluzzii-like recombinant strains fixed for the M and S marker in the X chromosome island. The mating preference of recombinant strains was then tested by giving virgin recombinant individuals a choice of mates with X-islands matching and non-matching their own island type. We show through genetic analyses of transferred sperm that recombinant females consistently mated with matching island-type males thereby associating assortative mating genes with the X-island of divergence. Furthermore, full-genome sequencing confirmed that protein-coding differences between recombinant strains were limited to the experimentally swapped pericentromeric region. Finally, targeted-genome comparisons showed that a number of these unique differences were conserved in sympatric field populations, thereby revealing candidate speciation genes. The functional demonstration of a close association between speciation genes and the X-island of differentiation lends unprecedented support to island-of-speciation models of sympatric speciation facilitated by pericentric recombination suppression.

Asymmetric dominance and asymmetric mate choice oppose premating isolation after allopatric divergence.

Assortative mating promotes reproductive isolation and allows allopatric speciation processes to continue in secondary contact. As mating patterns are determined by mate preferences and intrasexual competition, we investigated male–male competition and behavioral isolation in simulated secondary contact among allopatric populations. Three allopatric color morphs of the cichlid fish Tropheus were tested against each other. Dyadic male–male contests revealed dominance of red males over bluish and yellow-blotch males. Reproductive isolation in the presence of male–male competition was assessed from genetic parentage in experimental ponds and was highly asymmetric among pairs of color morphs. Red females mated only with red males, whereas the other females performed variable degrees of heteromorphic mating. Discrepancies between mating patterns in ponds and female preferences in a competition-free, two-way choice paradigm suggested that the dominance of red males interfered with positive assortative mating of females of the subordinate morphs and provoked asymmetric hybridization. Between the nonred morphs, a significant excess of negative assortative mating by yellow-blotch females with bluish males did not coincide with asymmetric dominance among males. Hence, both negative assortative mating preferences and interference of male–male competition with positive assortative preferences forestall premating isolation, the latter especially in environments unsupportive of competition-driven spatial segregation.

GENETIC DIFFERENTIATION AND SELECTION AGAINST MIGRANTS IN EVOLUTIONARILY REPLICATED EXTREME ENVIRONMENTS

We investigated mechanisms of reproductive isolation in livebearing fishes (genus Poecilia) inhabiting sulfidic and nonsulfidic habitats in three replicate river drainages. Although sulfide spring fish convergently evolved divergent phenotypes, it was unclear if mechanisms of reproductive isolation also evolved convergently. Using microsatellites, we found strongly reduced gene flow between adjacent populations from different habitat types, suggesting that local adaptation to sulfidic habitats repeatedly caused the emergence of reproductive isolation. Reciprocal translocation experiments indicate strong selection against immigrants into sulfidic waters, but also variation among drainages in the strength of selection against immigrants into nonsulfidic waters. Mate choice experiments revealed the evolution of assortative mating preferences in females from nonsulfidic but not from sulfidic habitats. The inferred strength of sexual selection against immigrants (RI(s)) was negatively correlated with the strength of natural selection (RI(m)), a pattern that could be attributed to reinforcement, whereby natural selection strengthens behavioral isolation due to reduced hybrid fitness. Overall, reproductive isolation and genetic differentiation appear to be replicated and direct consequences of local adaptation to sulfide spring environments, but the relative contributions of different mechanisms of reproductive isolation vary across these evolutionarily independent replicates, highlighting both convergent and nonconvergent evolutionary trajectories of populations in each drainage.

Speciation of fluvial forms from amphidromous forms of migratory populations

We present a mathematical model of the maintenance of polymorphism of fluvial and amphidromous types in a fish population. Downstream drifting of offspring after hatching and their subsequent upstream migration have an important effect on the maintenance of an upstream population. This model, which assumes a linear relationship of offspring mortality rate, nutritional conditions, and flow rate or inclination with the distance from the river mouth, enables us to calculate the number of recruits to the mother population. From the present analysis, we can predict that the fluvial type producing large embryos is selected in the upper reaches under conditions where there are large differences in offspring mortality and flow rate between the upper and lower reaches, and a small difference in nutritional conditions between these sites. Therefore, the fluvial type can be more easily evolved in tropical regions than temperate regions where the difference in nutritional conditions is relatively larger. This selection is promoted when offspring mortality decreases greatly with their size. Conversely, at the lower reaches of the same river, the amphidromous type producing many small embryos is favored. These two populations can be the polymorphism of a single population species in a river, and can be established as different species in terms of pre- or post-reproductive isolation mechanisms, such as assortative mating or habitat preference, even if their members mate with each other in a river. We can assert that sympatric speciation is common in fluvial environments, when this process really works, because other taxonomic groups, such as Annelida, Crustacea, and Mollusca, also have the same sympatric pair of fluvial and amphidromous species derived from marine origin, that is, so called the evolutionary invasion from marine to terrestrial environments.

The impact of extra-pair mating behavior on hybridization and genetic introgression

Hybridization and genetic introgression can be associated with secondary contact between closely related species. Previous models have examined the ecological and demographic conditions leading to hybridization and introgression, but few have examined the role of behavior. Alternative mating behaviors are common throughout the animal kingdom but have rarely been recognized as a potential mechanism for hybridization. We developed an individual-based genetic model to examine the hypothesis that extra-pair copulations (EPCs) can lead to hybridization and genetic introgression even when assortative mating preferences are intact. Our model showed that female choice, whether pre- or post-copulation, reinforced species boundaries and that hybrids were relatively uncommon when no EPCs occurred. However, when EPCs were introduced into the model, the proportion of hybrids in the population depended on the strength of female mate or sperm choice, the strength of male pursuit of EPCs, and habitat-induced effects on the species composition of the neighborhood. As predicted, male pursuit of EPCs caused extensive introgression, but female preference for conspecific paternity reinforced species differences. Inclusion of mitochondrial markers of species identity revealed significant effects of interspecific and intersexual behavior during EPCs on the direction of introgression. These results suggest that an alternative mating tactic may have major effects on the level of genetic homogenization and can cause local extinction of a species.

Are high-quality mates always attractive? State-dependent mate preferences in birds and humans

Sexual selection theory posits that females should choose mates in a way that maximises their reproductive success. But what exactly is the optimal choice? Most empirical research is based on the assumption that females seek a male of the highest possible quality (in terms of the genes or resources he can provide), and hence show directional preferences for indicators of male quality. This implies that attractiveness and quality should be highly correlated. However, females frequently differ in what they find attractive. New theoretical and empirical insights provide mounting evidence that a female's own quality biases her judgement of male attractiveness, such that male quality and attractiveness do not always coincide. A recent experiment in songbirds demonstrated for the first time that manipulation of female condition can lead to divergent female preferences, with low-quality females actively preferring low-quality males over high-quality males. This result is in line with theory on state-dependent mate choice and is reminiscent of assortative mating preferences in humans. Here we discuss the implications of this work for the study of mate preferences.

ASSORTATIVE MATING PREFERENCES AMONG HYBRIDS OFFERS A ROUTE TO HYBRID SPECIATION

Homoploid speciation generates species without a change in chromosome number via introgressive hybridization and has been considered rare in animals. Heliconius butterflies exhibit bright aposematic color patterns that also act as cues in assortative mating. Heliconius heurippa has a color pattern that can be recreated by introgression of the H. melpomene red band into an H. cydno genetic background. Wild H. heurippa males show assortative mating based on color pattern and we here investigate the origin of this preference by studying first-generation backcross hybrids between H. melpomene and H. cydno that resemble H. heurippa. These hybrids show assortative mating preferences, showing a strong preference for their own color pattern over that of either parental species. This is consistent with a genetic basis to wing pattern preference and implies, first, that assortative mating preferences would facilitate the initial establishment of a homozygous hybrid color pattern by increasing the likelihood that early generation hybrids mate among themselves. Second, once established such a lineage would inherit assortative mating preferences that would lead to partial reproductive isolation from parental lineages.

Symbiotic bacteria affect mating choice in Drosophila melanogaster

Mating preferences depending on Wolbachia infection were studied in two genotypically different strains of Drosophila melanogaster. Females from both strains carry two attached X chromosomes. Males from the red-eyed strain (R) have the wild-type X chromosome compared to males from the white-eyed strain (W), whose X chromosome contains two deleterious mutations (white and singed). Three types of competition tests showed that assortative mating depends on genotype, infection status and their combination in the mating partners. Males of strain R, genetically closer to the wild type, were more successful than males of strain W. Wolbachia infection increased the mating ability of W males but did not affect that of R males. Strain W showed positive assortative mating (preference for ‘self’) with regard to genotype and infection status. In strain R, negative assortative mating (preference for ‘nonself’) was observed. Moreover, the most affected flies (infected W) showed higher preference for ‘self’, while the least affected ones (uninfected R) showed higher preference for ‘nonself’. These results support the idea that mating choice may involve testing the partner for degree of genetic or biochemical similarity with self, based on chemoreception with possible participation of immune system components.

Odor preference in house mice: influences of habitat heterogeneity and chromosomal incompatibility

Theory predicts that when maladaptive hybridization occurs assortative mating preference should evolve. Moreover, habitat characteristics can influence quality of mates that is an important criterion in mate choice. Here we ask how chromosomal compatibility and differences in habitat quality might shape preference for odors of the opposite sex in the house mouse. Our study model is composed of 2 chromosomal races and their narrow hybrid zone that occur in habitats of different qualities. We performed 2-way choice tests during which opposite sex urine mixtures of each race were presented to mice from the 2 races and the hybrid zone. Differential investigation of the odor sources indicated both preference and that the odors differed. The results show that the 2 races carry distinct odors and, irrespective of the race they belonged to, males preferred odors of females from the race occurring in habitats of lower quality (hereafter, race B), whereas females preferred odors of males from the race occurring in habitats of better quality (hereafter, race A). Further, preference in the hybrid zone was for race B odors, which differed significantly from that displayed by the 2 races (i.e., for race A odors). The relative influences of geography, ecology, and chromosomal compatibility are discussed, thus leading us to propose that habitat differences might play the most important role in shaping signal divergence and preference in this system. Key words: habitat variations, hybrid zone, Madeira Island, Mus musculus domesticus, odor preference, Rb chromosomes, urinary signals. [Behav Ecol]

Assortative versus disassortative mating preferences of female zebra finches based on self-referent phenotype matching

Kin recognition abilities allow individuals to treat relatives differently. In mate choice contexts, kin recognition can ensure individuals avoid the costs of inbreeding. However, there is also the potential for assortative preferences for genetic similarity as part of an optimal outbreeding strategy. We tested the kin recognition abilities of captive female zebra finches, Taeniopygia guttata, in standard mate choice trials. A full individual cross-fostering scheme ensured that all subjects grew up in broods of only unrelated nestmates and were raised by unrelated foster parents. Therefore, individuals could use only self-referent phenotype matching (or recognition alleles), since exposure to genetic kin was excluded completely. Females were allowed the simultaneous choice between an unfamiliar genetic brother and unfamiliar, unrelated stimulus males. We used three cohorts of birds (199 females in total) that allowed three independent hypothesis tests. We found a significant avoidance of the unfamiliar brother in the first cohort, but could not replicate this finding in the other two cohorts. This was not easily explained by differences in the treatment of the cohorts, since the difference between cohorts was nonsignificant and testable differences in treatments did not show significant effects. The combined effect size was very low (d = −0.048) and nonsignificant. The initial finding of disassortative preferences may represent a type I error or there may be a true effect that is very weak and not easily reproducible. In any case, we did not find evidence of assortative preferences based on self-referent phenotype matching.