Benefits of Pair-Bond Duration on Reproduction in a Lifelong Monogamous Cooperative Passerine.

AbstractLong-term social and genetic monogamy is rare in animals except birds, but even in birds it is infrequent and poorly understood. We investigated possible advantages of monogamy in a colonial, facultative cooperatively breeding bird from an arid, unpredictable environment, the sociable weaver (Philetairus socius). We documented divorce and extrapair paternity of 703 pairs over 10 years and separated effects of pair duration from breeding experience by analyzing longitudinal and cross-sectional datasets. Parts of the colonies were protected from nest predation, thereby limiting its stochastic and thus confounding effect on fitness measures. We found that 6.4% of sociable weaver pairs divorced and 2.2% of young were extrapair. Longer pair-bonds were associated with more clutches and fledglings per season and with reproducing earlier and later in the season, when snake predation is lower, but not with increased egg or fledgling mass or with nestling survival. Finally, the number of helpers at the nest increased with pair-bond duration. Results were similar for protected and unprotected nests. We suggest that long-term monogamy is associated with a better capacity for exploiting a temporally unpredictable environment and helps to form larger groups. These results can contribute to our understanding of why long-term monogamy is frequently associated with unpredictable environments and cooperation.

Tighter Constraints of Multi-Qubit Entanglement in Terms of Nonconvex Entanglement Measures LCREN and LCRENoA.

The monogamy property of entanglement is an intriguing feature of multipartite quantum entanglement. Most entanglement measures satisfying the monogamy inequality have turned out to be convex. Whether nonconvex entanglement measures obey the monogamy inequalities remains less known at present. As a well-known measure of entanglement, the logarithmic negativity is not convex. We elucidate the constraints of multi-qubit entanglement based on the logarithmic convex-roof extended negativity (LCREN) and the logarithmic convex-roof extended negativity of assistance (LCRENoA). Using the Hamming weight derived from the binary vector associated with the distribution of subsystems, we establish monogamy inequalities for multi-qubit entanglement in terms of the αth-power (α≥4ln2) of LCREN, and polygamy inequalities utilizing the αth-power (0≤α≤2) of LCRENoA. We demonstrate that these inequalities give rise to tighter constraints than the existing ones. Furthermore, our monogamy inequalities are shown to remain valid for the high-dimensional states that violate the CKW monogamy inequality. Detailed examples are presented to illustrate the effectiveness of our results in characterizing the multipartite entanglement distributions.

Nucleus accumbens dopamine release reflects the selective nature of pair bonds.

In monogamous species, prosocial behaviors directed toward partners are dramatically different from those directed toward unknown individuals and potential threats. Dopamine release in the nucleus accumbens has a well-established role in social reward and motivation, but how this mechanism may be engaged to drive the highly divergent social behaviors directed at a partner or unfamiliar conspecific remains unknown. Using monogamous prairie voles, we first employed receptor pharmacology in partner preference and social operant tasks to show that dopamine is critical for the appetitive drive for social interaction but not for low-effort, unconditioned consummatory behaviors. We then leveraged the subsecond temporal resolution of the fluorescent biosensor, GRABDA, to ask whether differential dopamine release might distinguish between partner and novel social access and interaction. We found that partner seeking, anticipation, and interaction resulted in more accumbal dopamine release than the same events directed toward a novel vole. Further, partner-associated dopamine release decreased after prolonged partner separation. Our results are consistent with a model in which dopamine signaling plays a prominent role in the appetitive aspects of social interactions. Within this framework, differences in partner- and novel-associated dopamine release reflect the selective nature of pair bonds and may drive the partner- and novel-directed social behaviors that reinforce and cement bonds over time. This provides a potential mechanism by which highly conserved reward systems can enable selective, species-appropriate social behaviors.

Your Happiness Is My Happiness: Predicting Positive Feelings for a Partner's Consensual Extra-Dyadic Intimate Relations.

This quantitative study tested hypotheses derived from a previous qualitative study of the factors that facilitated and hindered compersion (the positive feelings derived from one's partner's intimate relations with others) in consensually non-monogamous (CNM) relationships. A total of 255 participants recruited from online CNM and Alt-Sex communities reported on demographic and relationship characteristics as well as individual, relationship, and metamour-related variables in an online anonymous survey. In Flicker et al. (2022), we identified various factors that predicted three subtypes of compersion: contentment with one's partner's relationships with established metamours (intimate partners of one's partners), excitement sparked by one's partner's new/potentially new intimate connections, and sexual excitement elicited by thinking about one's partner with another person. The current findings were consistent with the Flicker et al. qualitative study, with some hypotheses from the previous study more strongly supported than others. The predictors of compersion most strongly supported by the current data include closeness with one's metamour and knowledge about the partner/metamour relationship, in a positive direction, as well as jealousy, envy, and attachment anxiety, in a negative direction. Individual-level predictors were weak predictors of compersion. The sexual arousal subtype of compersion was weakly endorsed by the current sample and predictors of this subtype were distinct from predictors of the other subtypes of compersion. The findings suggest that the development of new interventions that target reducing jealousy and envy and increasing attachment security within the unique context of CNM relationships could have the added benefit of increasing compersion. The development of these interventions stands to benefit a growing population of individuals involved in CNM relationships.

A Narrative Review of the Dichotomy Between the Social Views of Non-Monogamy and the Experiences of Consensual Non-Monogamous People.

Monogamy is deeply rooted in most Western societies, shaping how people construe and behave in romantic relationships. These normative views facilitate the emergence of negative perceptions and evaluations when people choose not to adhere to mononormativity. Even though people in consensual non-monogamous (CNM) relationships are targets of stigmatization, research shows a dichotomy between these negative views and the relational experiences of CNM people. Indeed, people in CNM and monogamous relationships have comparable relationship functioning and quality and struggle with similar relationship problems. One of the differences is that CNM relationships afford people to explore their sexuality and fulfill their needs with multiple partners, without agreed-upon extradyadic behavior being perceived as infidelity or having deleterious consequences to relationship maintenance. These positive experiences notwithstanding, CNM people are continuously pressured by mononormativity and stigmatization, increasing the risk of internalized CNM negativity and worse personal and relational outcomes. One possible way to counteract CNM stigmatization and improve the lives of CNM people is by changing discourses surrounding non-monogamy and improving acceptance, not only in professional settings but also in the general population. Another strategy is to understand how the relationship beliefs and scripts of younger generations can help promote more inclusive and diverse societies.

Examining the Role of Mononormative Beliefs, Stigma, and Internalized Consensual Non-Monogamy Negativity for Dehumanization.

Interest in consensually non-monogamous (CNM) relationships has been increasing in the general population in recent years. However, given the cultural dominance of monogamy and the normative expectations often imposed through socialization (i.e., mononormativity), people in CNM relationships may experience negativity, which can become internalized and harm their individual and relationship health. The present study investigated if mononormativity beliefs and CNM relationship stigma were associated with more dehumanization and if internalized CNM negativity was an underlying mechanism for these associations. Results showed that participants who endorsed more mononormative beliefs and CNM relationship stigma also reported more internalized CNM negativity. In turn, participants who experienced more internalized CNM negativity attributed more negative (vs. positive) emotions to themselves and treated their partners as more immature, unrefined, exploitable, and emotionless. These results show that mononormativity and internalized negativity can shape the attitudes, perceptions, and behaviors of CNM individuals toward themselves and their partners.

Evidence for individual vocal recognition in a pair-bonding poison frog, Ranitomeya imitator.

Individually distinctive vocalizations are widespread in nature, although the ability of receivers to discriminate these signals has only been explored through limited taxonomic and social lenses. Here, we asked whether anuran advertisement calls, typically studied for their role in territory defense and mate attraction, facilitate recognition and preferential association with partners in a pair-bonding poison frog (Ranitomeya imitator). Combining no- and two-stimulus choice playback experiments, we evaluated behavioral responses of females to male acoustic stimuli. Virgin females oriented to and approached speakers broadcasting male calls independent of caller identity, implying that females are generally attracted to male acoustic stimuli outside the context of a pair bond. When pair-bonded females were presented with calls of a mate and a stranger, they showed significant preference for calls of their mate. Moreover, behavioral responses varied with breeding status: females with eggs were faster to approach stimuli than females that were pair bonded but did not currently have eggs. Our study suggests a potential role for individual vocal recognition in the formation and maintenance of pair bonds in a poison frog and raises new questions about how acoustic signals are perceived in the context of monogamy and biparental care.

Polygamous Interest in a Mononormative Nation: The Roles of Sex and Sociosexuality in Polygamous Interest in a Heterosexual Sample from the UK.

Polygamy is a form of "one-sided" consensually non-monogamous relationship where one person has multiple committed partners, each of whom is only involved with that one person. It was likely a reoccurring feature of ancestral mating that posed adaptive problems for our ancestors. Yet polygamy, and multi-partnering more generally, is understudied in Western cultures, raising questions about the existence of polygamous interest and whether this is calibrated adaptively to personal conditions. In two studies, we examined polygamous interest in two heterosexual online samples from the UK. In Study 1 (N = 393), modest interest was found for polygamous relationships overall. Men were six times more open to polygyny than women, but there was little sex difference in openness to polyandry. Further analysis revealed that all forms of multi-partnering were undesirable relative to singlehood and monogamy; however, consensual multi-partner relationships were less undesirable than non-consensual ones. Sex differences were largest for polygyny and arrangements where men had agreed access to a casual partner alongside a committed one, yet these were two of the most acceptable forms of multi-partnering when men and women's responses were combined. Sociosexuality positively predicted interest in most forms of multi-partnering. Study 2 (N = 735) focused on polygyny and added status-linked traits as predictors. The results of Study 1 were broadly replicated, though the status-linked traits did not predict polygynous interest specifically. Instead, sociosexuality and male intrasexual competitiveness uniquely predicted general interest in multi-partner relationships. Overall, interest in polygamy appears to emerge despite social discouragement and sex differences in interest track the relative costs and benefits associated with it. However, there is no strong evidence that polygamous interest is uniquely calibrated to personal conditions when compared to other forms of multi-partnering.

Initial Motivations for Engaging in Polyamorous Relationships.

Polyamory is a relationship style in which partners consensually agree to engage in sexual and/or emotional relationships with concurrent partners. Compared with other forms of consensual non-monogamy (CNM), polyamory practitioners tend to report greater relationship satisfaction and less jealousy. However, the unique motivations leading people to engage with polyamory are less understood. Previous research has examined motivations for engaging in CNM relationship styles, in general, but no research has focused exclusively on the motivations of polyamory practitioners. The present study draws on the open-ended responses of 63 U.S. American adults who reported previous or current engagement in at least one consensually polyamorous relationship. Thematic analyses revealed four themes guiding participants' initial motivations for polyamory engagement: values alignment, relationship factors, external triggers, and sexuality. The study's themes are discussed in the context of self-determination theory and situated in the existing body of CNM and polyamory research. Directions for future research provide next steps for examining outcomes associated with specific polyamory motivations.

Primate social organization evolved from a flexible pair-living ancestor.

Explaining the evolution of primate social organization has been fundamental to understand human sociality and social evolution more broadly. It has often been suggested that the ancestor of all primates was solitary and that other forms of social organization evolved later, with transitions being driven by various life history traits and ecological factors. However, recent research showed that many understudied primate species previously assumed to be solitary actually live in pairs, and intraspecific variation in social organization is common. We built a detailed database from primary field studies quantifying the number of social units expressing different social organizations in each population. We used Bayesian phylogenetic models to infer the probability of each social organization, conditional on several socioecological and life history predictors. Here, we show that when intraspecific variation is accounted for, the ancestral social organization of primates was inferred to be variable, with the most common social organization being pair-living but with approximately 10 to 20% of social units of the ancestral population deviating from this pattern by being solitary living. Body size and activity patterns had large effects on transitions between types of social organizations. As in other mammalian clades, pair-living is closely linked to small body size and likely more common in ancestral species. Our results challenge the assumption that ancestral primates were solitary and that pair-living evolved afterward emphasizing the importance of focusing on field data and accounting for intraspecific variation, providing a flexible statistical framework for doing so.

Bonding against the odds: Male prairie vole response to the "widow effect" among females.

Although pair bonding is the preferred mating tactic among socially monogamous prairie voles, naturalistic observations have demonstrated many males remain non-bonded. Moreover, although males readily re-bond after the loss of a partner, females do not (i.e., the "widow effect'). Few studies have attempted to address why so many males remain non-bonded or if a reluctance of re-bonding in females contributes to this outcome. We investigate how female bonding history impacts male pair bond formation. Specifically, we test two alternative hypotheses for how sexually naïve males will behave when paired with widow females. The fecundity hypothesis predicts males will avoid bonding with widow females and be more receptive to novel bond-naïve females. The preference to bond hypothesis predicts males will choose to bond and express a partner preference, irrespective of if a pair-mate is a widow or sexually naïve. Our results demonstrated that males expressed a partner preference for females regardless of their social history. These data support the preference to bond hypothesis and suggest natural variation in bonding may not be strongly due to males forgoing bonding opportunities.

Varied impacts of social relationships on neuroendocrine state.

Social relationships, affiliative social attachments, are important for many species. The best studied types of relationships are monogamous pair bonds. However, it remains unclear how generalizable models of pair bonding are across types of social attachments. Zebra finches are a fascinating system to explore the neurobiology of social relationships because they form various adult bonds with both same- and opposite-sex partners. To test whether different bonds are supported by a single brain network, we quantified individuals' neuroendocrine state after either 24 h or 2 weeks of co-housing with a novel same- or opposite-sex partner. We defined neuroendocrine state by the expression of 22 genes related to 4 major signaling pathways (dopamine, steroid, nonapeptide, and opioid) in six brain regions associated with affiliation or communication [nucleus accumbens (NAc), nucleus taeniae of the amygdala (TnA), medial preoptic area (POM), and periaqueductal gray (PAG), ventral tegmental area, and auditory cortex]. Overall, we found dissociable effects of social contexts (same- or opposite-sex partnerships) and duration of co-housing. Social bonding impacted the neuroendocrine state of four regions in males (NAc, TnA, POM, and PAG) and three regions in females (NAc, TnA, and POM). Monogamous pair bonding specifically appeared to impact male NAc. However, the patterns of gene expression in zebra finches were different than has previously been reported in mammals. Together, our results support the view that there are numerous mechanisms regulating social relationships and highlight the need to further our understanding of how social interactions shape social bonds.

Descent, marriage, and residence practices of a 3,800-year-old pastoral community in Central Eurasia.

Our understanding of prehistoric societal organization at the family level is still limited. Here, we generated genome data from 32 individuals from an approximately 3,800-y-old burial mound attributed to the Bronze Age Srubnaya-Alakul cultural tradition at the site of Nepluyevsky, located in the Southern Ural region of Central Eurasia. We found that life expectancy was generally very low, with adult males living on average 8 y longer than females. A total of 35 first-degree, 40 second-degree, and 48 third-degree biological relationships connected 23 of the studied individuals, allowing us to propose a family tree spanning three generations with six brothers at its center. The oldest of these brothers had eight children with two women and the most children overall, whereas the other relationships were monogamous. Notably, related female children above the age of five were completely absent from the site, and adult females were more genetically diverse than males. These results suggest that biological relationships between male siblings played a structural role in society and that descent group membership was based on patrilineality. Women originated from a larger mating network and moved to join the men, with whom they were buried. Finally, the oldest brother likely held a higher social position, which was expressed in terms of fertility.

A matter of time: Bateman's principles and mating success as count and duration across social strata in contemporary Finland.

Bateman's principles heavily influence the understanding of human reproductive behaviour. Yet, few rigorous studies on Bateman's principles in contemporary industrialized populations exist. Most studies use small samples, exclude non-marital unions, and disregard recent insights on within-population heterogeneity in mating strategies. We assess mating success and reproductive success using population-wide Finnish register data on marital and non-marital cohabitations and fertility. We examine variability across social strata in the Bateman principles and analyse the mate count, the cumulated duration with a mate, and the association with reproductive success. Results support Bateman's first and second principles. Regarding Bateman's third principle, the number of mates is more positively associated with reproductive success for men than women, but this association is driven by ever having a mate. Having more than one mate is on average associated with lower reproductive success. However, for men in the lowest income quartile, having more than one mate positively predicts reproductive success. Longer union duration is associated with higher reproductive success, and more so for men. We note that sex differences in the relationship between mating success and reproductive success differ by social strata, and argue that mate duration may be an important component of mating success alongside mate count.

Male-male relationships in chimpanzees and the evolution of human pair bonds.

The evolution of monogamy has been a central question in biological anthropology. An important avenue of research has been comparisons across "socially monogamous" mammals, but such comparisons are inappropriate for understanding human behavior because humans are not "pair living" and are only sometimes "monogamous." It is the "pair bond" between reproductive partners that is characteristic of humans and has been considered unique to our lineage. I argue that pair bonds have been overlooked in one of our closest living relatives, chimpanzees. These pair bonds are not between mates but between male "friends" who exhibit enduring and emotional social bonds. The presence of such bonds in male-male chimpanzees raises the possibility that pair bonds emerged earlier in our evolutionary history. I suggest pair bonds first arose as "friendships" and only later, in the human lineage, were present between mates. The mechanisms for these bonds were co-opted for male-female bonds in humans.

Reproductive inequality in humans and other mammals.

To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women's fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species-including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.

Is the pair bond a human universal? An analytical essay.

I argue the impulse to form a dyadic love bond and not the desire for sexual release accounts for the formation of a universality of the pair bond. This impulse is not recent but has been a pervasive force throughout human history. Recently, a reversionist position has argued we are more of a hybrid species that easily and readily shifts between a pair bond and a plural partner family arrangement. Although most humans live out their lives in a sexually monogamous union, it is not something that comes easily or naturally. Sexual monogamy requires adopting an ethical stance and personal dedication to maintain it. This raises the question: if humans need to be vigilant in their moral commitment to remain sexually faithful, does this vigilance extend also to the domain of love? Is it possible to find greater contentment and life-satisfaction in forming simultaneously sexual and emotional unions with a variety of individuals. This is the central question that lies at the core of the pair bond deniers who insist humans are not a pair bond species and can find fulfilment in a pluralistic love bond. I probe (below) the social and emotional nuances associated with what it means to be in an enduring love bond through exploring the social and psychological complexities often associated with being in love. I will then discuss efforts by groups and individuals who have sought to establish social bonds not organised around an exclusive pair bond, and what their efforts reveal about underlying human psychology. My analysis concludes with rendering an assessment of the relative success of the social and personal experiments in the search to find a more fulfilling arena for love.

Sexual boredom and sexual desire in long-term relationships: a latent profile analysis.

BACKGROUND: Research suggests a general link between sexual boredom and sexual desire, but its understanding is currently very limited. AIM: To identify distinct (latent) groups of women and men in long-term relationships based on their reported levels of sexual boredom and sexual desire. METHODS: Latent profile analysis (LPA) was conducted in an online sample of 1223 Portuguese participants aged 18 and 66 years (mean ± SD, 32.75 ± 6.11), using indicators of sexual boredom and partner-related, attractive other-related, and solitary sexual desire to categorize participants. Multinomial logistic regression analysis was carried out to explore predictors and correlates of the latent profiles. OUTCOMES: Sexual boredom was assessed by the Sexual Boredom Scale, while sexual desire was measured with the Sexual Desire Inventory. RESULTS: As compared with women, men reported higher levels of sexual boredom and sexual desire. LPA indicated 3 profiles in women and 2 profiles in men. Among women, P1 was characterized by above-average sexual boredom, below-average partner- and attractive other-related sexual desire, and very low solitary sexual desire; P2 by below-average sexual boredom, attractive other-related sexual desire, and solitary sexual desire and above-average partner-related sexual desire; and P3 by above-average sexual boredom, attractive other-related sexual desire, and solitary sexual desire and below-average partner-related sexual desire. In men, P1 was characterized by high sexual boredom, above-average partner-related sexual desire, and high attractive other-related and solitary sexual desire and P2 by below-average sexual boredom and above-average partner-related, attractive other-related, and solitary sexual desire. The latent profiles did not differ according to relationship duration. Overall, the sole consistent correlate of the latent categorization was sexual satisfaction. CLINICAL IMPLICATIONS: In women, above-average levels of sexual boredom were linked to below-average levels of partner-related desire, which suggests likely benefits of helping the couple to minimize or cope better with their sexual routines. In men, participants in the 2 profiles did not differ in partner-related sexual desire, suggesting that clinical interventions dealing with male sexual boredom should investigate factors beyond the current relationship. STRENGTHS AND LIMITATIONS: This study explored different facets of sexual desire and used LPA, rendering advantages over previous research. The male sample has lower statistical power than the female sample. CONCLUSION: Patterns of sexual boredom and sexual desire among individuals in long-term monogamous relationships are distinct and consistently related to sexual satisfaction in women and men and to relationship satisfaction among only women, which have important clinical ramifications.

Effects of oxytocin receptor blockade on dyadic social behavior in monogamous and non-monogamous Eulemur.

A prominent body of research spanning disciplines has been focused on the potential underlying role for oxytocin in the social signatures of monogamous mating bonds. Behavioral differences between monogamous and non-monogamous vole species, putatively mediated by oxytocinergic function, constitute a key source of support for this mechanism, but it is unclear to what extent this hormone-behavior linkage extends to the primate order. In a preregistered experiment, we test if oxytocin receptor blockade affects affiliative behavior in mixed-sex pairs of Eulemur, a genus of strepsirrhine primate containing both monogamous and non-monogamous species. Inconsistent with past studies in monogamous voles or monkeys, we do not find confirmatory evidence in Eulemur that monogamous pairs affiliate more than non-monogamous pairs, nor that oxytocin receptor blockade of one pair member selectively corresponds to reduced affiliative or scent-marking behavior in monogamous species. We do, however, find exploratory evidence of a pattern not previously investigated: simultaneously blocking oxytocin receptors in both members of a monogamous pair predicts lower rates of affiliative behavior relative to controls. Our study demonstrates the value of non-traditional animal models in challenging generalizations based on model organisms, and of methodological reform in providing a potential path forward for behavioral oxytocin research.

Lasting consequences on physiology and social behavior following cesarean delivery in prairie voles.

Cesarean delivery is associated with diminished plasma levels of several 'birth-signaling' hormones, such as oxytocin and vasopressin. These same hormones have been previously shown to exert organizational effects when acting in early life. For example, our previous work found a broadly gregarious phenotype in prairie voles exposed to oxytocin at birth. Meanwhile, cesarean delivery has been previously associated with changes in social behavior and metabolic processes related to oxytocin and vasopressin. In the present study, we investigated the long-term neurodevelopmental consequences of cesarean delivery in prairie voles. After cross-fostering, vole pups delivered either via cesarean or vaginal delivery were studied throughout development. Cesarean-delivered pups responded to isolation differently in terms of their vocalizations (albeit in opposite directions in the two experiments), huddled in less cohesive groups under warmed conditions, and shed less heat. As young adults, we observed no differences in anxiety-like or alloparental behavior. However, in adulthood, cesarean-delivered voles of both sexes failed to form partner preferences with opposite sex conspecifics. In a follow-up study, we replicated this deficit in partner-preference formation among cesarean-delivered voles and were able to normalize pair-bonding behavior by treating cesarean-delivered vole pups with oxytocin (0.25 mg/kg) at delivery. Finally, we detected minor differences in regional oxytocin receptor expression within the brains of cesarean-delivered voles, as well as microbial composition of the gut. Gene expression changes in the gut epithelium indicated that cesarean-delivered male voles have altered gut development. These results speak to the possibility of unintended developmental consequences of cesarean delivery, which currently accounts for 32.9 % of deliveries in the U.S. and suggest that further research should be directed at whether hormone replacement at delivery influences behavioral outcomes in later life.