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Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea-based on the polygyny threshold model-that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.

The Eurasian Jackdaw is thought to be archetypically monogamous, but recent tagging research uncovered extra-pair copulations in the species. Here we examined extra-pair paternity (genetic monogamy) in Eurasian jackdaws breeding in the Judean Hills, Israel, at the global edge of the species range, using a set of highly polymorphic molecular microsatellites. We found roughly a sixth of nests sampled showed deviations from monogamy, more than previously found in DNA fingerprinting studies of jackdaws, suggesting a mixed mating strategy in this population. These findings support the trend of extra-pair paternity in avian species, even when social monogamy remains the rule, and highlight the importance of continued study of species throughout their geographical range. [ABSTRACT FROM AUTHOR]

The behavior of eating their mates or a part of their mate's body has been studied in sexual cannibalism or nuptial feeding. In these behaviors, only one sex eats the other unilaterally. Within mating pairs of a wood‐feeding cockroach (Salganea taiwanensis), males and females eat the mate's wings each other, which is the first "mutual" case in these behaviors. Because the evolution of sexual cannibalism and nuptial feeding has been explained based on unilaterality, this mutual eating should have a new significance of reproduction. We described this behavior quantitatively and suggest a new hypothesis based on true monogamy, the mating system of S. taiwanensis, copulating with only one mate throughout life. Under true monogamy, the fitness of the mate is the same as own fitness and the pairs are free from sexual conflict. If the wing eating increases the ability of the mate to raise the offspring, this behavior is adaptive for the eater as well as its mate. [ABSTRACT FROM AUTHOR]

While the four species of horseshoe crabs share many common reproductive traits with respect to their reproductive systems, they do differ with respect to their mating behavior (monogamy vs. polygynandry). Past research has attributed these differences to a number of factors including: spawning densities, operational sex ratios (OSR’s), male condition (or age), environmental and/or genetic factors, or a combination thereof. Mating behaviors in the three Asian horseshoe crab species (Tachypleus gigas, T. tridentatus, and Carcinoscorpius rotundicauda) with low spawning densities and 1:1 operational sex ratios are typically monogamous. In Limulus polyphemus, mating behavior is more variable ranging from monogamy to polygynandry. Here we provide evidence, through a long term behavioral study, that variation in mating behavior is influenced by population density in L. polyphemus. Our study population on two beaches in Connecticut (Long Island Sound) have a spawning density 400 times less than that found in Delaware Bay (0.002 females/m2 vs. 0.8 females/m2) but similar operational sex ratios. Between 90%–95% of all spawning females in CT were paired with only one male, thus exhibiting monogamous behavior. In contrast, between 30 and 60% of spawning females in Delaware Bay have more than one mate and produce clutches of eggs with multiple paternities. Male condition played no role in mating behavior in CT populations. We also observed that on average 18% of the females on the spawning beaches are single. These results suggest that population density is an important condition that determines mating behavior. Also, low population density may lead to decreased mate finding ability and lost opportunities for spawning [Current Zoology 56 (5): 634–642, 2010].

Courting, accessing, and/or competing for mates are involved in sexual selection by generating differences in mating success. Although courtship behavior should reflect intensity of mating competition and sexual selection, studies that compare courtship behavior across populations/species with different mating systems subject to differing degrees of mating competition are scanty. Here, we compare courtship behavior between two closely related plover species ( Charadrius spp.): a polygamous population of snowy plovers and a socially monogamous population of Kentish plovers. Consistently with expectations, both males and females spent more time courting in the polygamous plover than in the monogamous one. In addition, courtship behavior of males relative to females increased over the breeding season in the polygamous plover, whereas it did not change in the monogamous one. Our results therefore suggest that courtship behavior is a fine-tuned and informative indicator of sexual selection in nature. [ABSTRACT FROM AUTHOR]

While the four species of horseshoe crabs share many common reproductive traits with respect to their reproductive systems, they do differ with respect to their mating behavior (monogamy vs. polygynandry). Past research has attributed these differences to a number of factors including: spawning densities, operational sex ratios (OSR's), male condition (or age), environmental and/or genetic factors, or a combination thereof. Mating behaviors in the three Asian horseshoe crab species (Tachypleus gigas, T. tridentatus, and Carcinoscorpius rotundicauda) with low spawning densities and 1:1 operational sex ratios are typically monogamous. In Limulus polyphemus, mating behavior is more variable ranging from monogamy to polygynandry. Here we provide evidence, through a long term behavioral study, that variation in mating behavior is influenced by population density in L. polyphemus. Our study population on two beaches in Connecticut (Long Island Sound) have a spawning density 400 timesless than that found in Delaware Bay (0.002 females/m2 vs. 0.8 females/m2) but similar operational sex ratios. Between 90%-95% of all spawning females in CT were paired with only one male, thus exhibiting monogamous behavior. In contrast, between 30 and 60% of spawning females in Delaware Bay have more than one mate and produce clutches of eggs with multiple paternities. Male condition played no role in mating behavior in CT populations. We also observed that on average 18% of the females on the spawning beaches are single. These results suggest that population density is an important condition that determines mating behavior. Also, low population density may lead to decreased mate finding ability and lost opportunities for spawning. [ABSTRACT FROM AUTHOR]

Monogamous prairie voles (Microtus ochrogaster) form mating-based pair bonds. Although wild prairie voles rarely re-pair following loss of a partner, laboratory studies have shown that previous pairing and mating does not negate the ability to form a new partner preference. However, little is known about how prior bond experience may alter the trajectory and display of a new pair bond. In the present study, we disrupted an initial pair bond by separating partners and then varied the amount of time before a new partner was introduced. We assessed how separation time affected the stability of partner preference over time and influenced decision-making in male voles performing a head-to-head partner preference test in which they chose between the first and second partner. We found that the ability to consistently display a preference for the second partner, supplanting the initial pair bond, depended on how long the test animal was separated from their first partner. Prior bonding experience also shaped the subsequent effects of mating on partner preference. Partner preference strength was sensitive to latency to mate with the second partner but not the first partner, irrespective of separation time. These results suggest that the ability to form a consistent, strong preference for a new partner after an initial pair bond depends upon the amount of time that has passed since separation from the first partner. These results provide valuable insight into how social bonds are dynamically shaped by prior social experience and identify variables that contribute to recovery from partner loss and the ability to form a new pair bond. They also delineate a behavioral trajectory essential for future work examining the hormonal and genetic changes that enable recovery from partner loss. • Prairie voles can form sequential pair bonds. • Separation time determines the consistency of subsequent partner preference. • Separation time predicts whether the new preference supplants that for the old partner. • Mating latency predicts long term bond strength for the second but not the first partner. [ABSTRACT FROM AUTHOR]