Monogamous Pair Bonds Research Articles

The Evolution of Mate Attachment.

AbstractWhether natural selection leads to attachment in monogamous pair bonds has seldom been addressed. Operationally defining attachment as a behavioral modifier that decreases divorce probability with pair duration, we develop a model for the evolution of attachment. If divorce (the ending of a pair bond when both individuals survive to the next breeding season) is more likely to occur out of poor-quality reproductive opportunities (i.e., poor territory or low-quality mate), individuals in experienced pairs are more likely to be found in high-quality opportunities. Consequently, when divorce decisions occur using imperfect information from reproductive success, pair duration provides individuals with information about the quality of their reproductive opportunity and attachment can evolve. We show that high survival rates, divorce propensities, and probabilities of nest failure favor the evolution of attachment. Attachment is also more likely to evolve when individuals can directly assess the quality of their reproductive opportunity (as opposed to relying on imperfect information from reproductive success), when the quality of the reproductive opportunity has adult survival ramifications, and when divorce coevolves with attachment. We show that our core conclusions are robust to a variety of assumptions using individual-based simulations. Our results clarify how attachment can be adaptive and suggest that studying pair bonds as dynamic entities is a promising avenue for future work.

Binding Affinity, Selectivity, and Pharmacokinetics of the Oxytocin Receptor Antagonist L-368,899 in the Coyote (Canis latrans).

L-368,899 is a selective small-molecule oxytocin receptor (OXTR) antagonist originally developed in the 1990s to prevent preterm labor. Although its utility for that purpose was limited, L-368,899 is now one of the most commonly used drugs in animal research for the selective blockade of neural OXTR after peripheral delivery. A growing number of rodent and primate studies have used L-368,899 to evaluate whether certain behaviors are oxytocin dependent. These studies have improved our understanding of oxytocin's function in the brains of rodents and monkeys, but very little work has been done in other mammals, and only a single paper in macaques has provided any evidence that L-368,899 can be detected in the CNS after peripheral delivery. The current study sought to extend those findings in a novel species: coyotes ( Canis latrans ). Coyotes are ubiquitous North American canids that form long-term monogamous pair-bonds. Although monogamy is rare in rodents and primates, all wild canid species studied to date exhibit social monogamy. Coyotes are therefore an excellent model organism for the study of oxytocin and social bonds. Our goal was to determine whether L-368,899 is a viable candidate for future use in behavioral studies in coyotes. We used captive coyotes at the USDA National Wildlife Research Center's Predator Research Facility to evaluate the pharmacokinetics of L-368,899 in blood and CSF during a 90-min time course after intramuscular injection. We then characterized the binding affinity and selectivity of L-368,899 to coyote OXTR and the structurally similar vasopressin 1a receptor. We found that L-368,899 peaked in CSF at 15 to 30 min after intramuscular injection and slowly accumulated in blood. L-368,899 was 40 times more selective for OXTR than vasopressin 1a receptors and bound to the coyote OXTR with an affinity of 12 nM. These features of L-368,899 support its utility in future studies to probe the oxytocin system of coyotes.

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.

Clomiphene citrate treatment during perinatal development alters adult partner preference, mating behaviour and androgen receptor and vasopressin in the male mandarin vole Microtus mandarinus.

During development, many aspects of behaviour, including partner preferences and sexual behaviour, are "organized" by neural aromatization of androgen and oestrogen. This study aimed to analyse these processes in the mandarin vole (Microtus mandarinus); this is a novel mammalian model exhibiting strong monogamous pair bonds. Male pups were treated daily with a sesame oil only (MC) or the oestrogen receptor blocker-clomiphene citrate sesame oil mixture (MT) from prenatal day 14 to postnatal day 10. Female pups were treated daily with sesame oil only (FC). Partner preferences, sexual behaviour, and the expression of androgen receptor (AR) and arginine vasopressin (AVP) were examined when animals were 3months old. The MT and FC groups exhibited male-directed partner preferences and feminized behaviour. AR-immunoreactive neurons (AR-IRs) in the medial preoptic area (mPOA), bed nucleus of stria terminalis (BNST), and medial amygdaloid nucleus (MeA) were reduced in MT males compared to MC males, and there was no significant difference in the number of AR-IRs between MT males and FC females. AVP-immunoreactive neurons (AVP-IRs) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were reduced in MT males compared to MC males, and there were no significant differences in the number of AVP-IRs between MT males and FC females. The results indicate a significant role of hormone signalling in the development of male mate preference in the novel monogamous mammal model.

Automated radio tracking provides evidence for social pair bonds in an obligate brood parasite

Social monogamy predominates in avian mating systems, but this strategy seems unlikely among brood parasites, where the emancipation from parental care should lead to an increase in numbers of mates for both sexes. Despite this, there is great diversity in mating systems in brood parasitic birds. The Screaming CowbirdMolothrus rufoaxillarisis a brood parasite that specializes almost exclusively on one host, the Greyish BaywingAgelaioides badius. Field observations and a radio telemetry study have indicated that male–female pairs spend a great deal of time together through the day, suggesting that they may be socially monogamous. We tested the hypothesis of social monogamy by radio‐tracking male and female Screaming Cowbirds using an array of automated radiotracking receivers to collect data on spatial behaviour and social mating system. Monogamous pair bonds were recorded through social network analysis. These bonds endured throughout the entire breeding season, with males and females remaining associated throughout the day. In accordance with the hypothesis, paired Screaming Cowbirds spent significantly more time in proximity to their mates than to other conspecifics of the opposite sex, and had similar home‐ranges. Social monogamy in the Screaming Cowbird differed markedly from the social polygyny/promiscuity exhibited by the sympatric congener Shiny CowbirdMolothrus bonariensis, a generalist brood parasite.

Causes and consequences of pair-bond disruption in a sex-skewed population of a long-lived monogamous seabird.

Many animals form long‐term monogamous pair bonds, and the disruption of a pair bond (through either divorce or widowhood) can have significant consequences for individual vital rates (survival, breeding, and breeding success probabilities) and life‐history outcomes (lifetime reproductive success [LRS], life expectancy). Here, we investigated the causes and consequences of pair‐bond disruption in wandering albatross (Diomedea exulans). State‐of‐the‐art statistical and mathematical approaches were developed to estimate divorce and widowhood rates and their impacts on vital rates and life‐history outcomes. In this population, females incur a higher mortality rate due to incidental fishery bycatch, so the population is male‐skewed. Therefore, we first posited that males would show higher widowhood rates negatively correlated with fishing effort and females would have higher divorce rates because they have more mating opportunities. Furthermore, we expected that divorce could be an adaptive strategy, whereby individuals improved breeding success by breeding with a new partner of better quality. Finally, we posited that pair‐bond disruptions could reduce survival and breeding probabilities owing to the cost of remating processes, with important consequences for life‐history outcomes. As expected, we showed that males had higher widowhood rates than females and females had higher divorce rates in this male‐skewed population. However, no correlation was found between fishing effort and male widowhood. Secondly, contrary to our expectation, we found that divorce was likely nonadaptive in this population. We propose that divorce in this population is caused by an intruder who outcompetes the original partner in line with the so‐called forced divorce hypothesis. Furthermore, we found a 16.7% and 18.0% reduction in LRS only for divorced and widowed males, respectively, owing to missing breeding seasons after a pair‐bond disruption. Finally, we found that divorced individuals were more likely to divorce again, but whether this is related to specific individual characteristics remains an important area of investigation.

Snails riding mantis shrimps: Ectoparasites evolved from ancestors living as commensals on the host’s burrow wall

The molluscan class Gastropoda includes over 5,000 parasitic species whose evolutionary origins remain poorly understood. Marine snails of the genus Caledoniella (Caledoniellidae) are obligate parasites that live on the abdominal surface of the gonodactylid mantis shrimps. They have highly modified morphological characteristics specialized to the ectoparasitic lifestyle that make it difficult to infer their close relatives, thereby posing a question about their current systematic position in the superfamily Vanikoroidea. In the present study, we performed molecular phylogenetic analyses using three nuclear and three mitochondrial gene sequences to unveil the phylogenetic position of these enigmatic snails. The resulting trees recovered Caledoniella in the superfamily Truncatelloidea and within a subclade of commensal species that live on the burrow wall of marine benthic invertebrates. More specifically, Caledoniella formed the sister clade to a commensal snail species living in mantis-shrimp burrows and they collectively were sister to Sigaretornus planus (formerly in the family Tornidae or Vitrinellidae), a commensal living in echiuran burrows. This topology suggests that the species of Caledoniella achieved their ectoparasitic mode of life through the following evolutionary pathway: (1) invasion into the burrows of benthic invertebrates, (2) specialization to mantis shrimps, and (3) colonization of the host body surface from the host burrow wall with the evolution of the parasitic nature. The final step is likely to have been accompanied by the acquisition of a sucker on the metapodium, the loss of the radula and operculum, and the formation of monogamous pair bonds. The present molecular phylogeny also suggested parallel evolution of planispiral shells in a subclade of Truncatelloidea and enabled us to newly redefine the families Caledoniellidae, Elachisinidae, Teinostomatidae, Tornidae and Vitrinellidae.

Mate fidelity improves survival and breeding propensity of a long-lived bird.

Evolutionary and behavioural ecologists have long been interested in factors shaping the variation in mating behaviour observed in nature. Although much of the research on this topic has focused on the consequences of mate choice and mate change on annual reproductive success, studies of a potential positive link between mate fidelity and adult demographic rates have been comparatively rare. This is particularly true for long-lived birds with multi-year, socially monogamous pair bonds. We used a 26-year capture-mark-recapture dataset of 3,330 black brent Branta bernicla nigricans to test whether breeding with a familiar mate improved future breeding propensity and survival. We predicted that experienced breeders nesting with a new partner would have rates of survival similar to familiar pairs because long-lived species avoid jeopardizing survival since their lifetime fitness is sensitive to this vital rate. In contrast, we expected that any costs of breeding with a new partner would be paid through skipping the subsequent breeding attempt. We found that unfamiliar pairs had lower subsequent breeding propensity than faithful partners. However, contrary to our expectations, individuals breeding with a new mate also suffered reduced survival. These results add to a small number of studies indicating that a positive relationship between mate retention and adult demographic rates may exist in a diverse array of avian species. Given these results, researchers should consider costs of mate change that extend beyond within-season reproductive success to fully understand the potential adaptive basis for perennial social monogamy. We caution that if mate retention enhances survival prospects, improvements in annual reproductive success with pair-bond length could be a secondary factor favouring perennial social monogamy, particularly in species with slower life-history strategies. Furthermore, some cases where annual reproductive success does not improve with pair-bond duration, yet multi-year pair bonds are common, could be explained by benefits afforded by mate fidelity to adult vital rates.

Coppery titi monkey (Plecturocebus cupreus) pairs display coordinated behaviors in response to a simulated intruder.

Mate guarding and coordinated behaviors between partners are important for the maintenance of monogamous pair bonds. To study the effects of a perceived unfamiliar social intruder on females' behavior, we used coppery titi monkeys (Plecturocebus cupreus). We examined the effects of male aggressive temperament on females' behavior and the effects of each behavior performed by the male on the same female behavior. Using a mirror, we simulated a social intruder in the home territory and scored behaviors using an established ethogram. Based on our analysis of self-directed behaviors, females do not recognize themselves in the mirror. We then used general linear mixed models to predict percent change in females' behaviors as a function of (a) males' temperament, (b) males' behavior, and (c) an interaction between males' temperament and behavior. Male temperament did not significantly predict female behavior for any of our best fitting models. For percent change in female lip-smacking, male lip-smacking significantly predicted female lip-smacking (β = 0.74, SE = 0.22, t = 3.39; p = .004). There was a positive correlation between male and female agonistic behaviors such as back-arching/tail-lashing (β = 0.51, SE = 0.23, t = 2.22; p = .04) and for anxiety-related behaviors such as leaving the partner (β = 0.50, SE = 0.19, t = 2.68; p = .015), locomotion duration (β = 0.19, SE = 0.06, t = 2.98; p = .02), and locomotion frequency (β = 0.71, SE = 0.14, t = 5.17; p < .001). These findings on coordination of pair-mate behaviors may explain how titi monkeys display pair bond strength and ensure their reproductive success.

Familiarity enhances moment-to-moment behavioral coordination in zebra finch (Taeniopygia guttata) dyads.

An individual's ability to respond to and align with the behavior of others is a fundamental component of social behavior. Zebra finches form lifelong monogamous pair bonds; however, zebra finches are also gregarious and can form strong social bonds with same-sex conspecifics. Here, we quantified behavior during brief 10-min reunions for males and females in five types of social conditions: monogamously bonded opposite-sex partners, familiar same-sex, familiar opposite-sex, novel same-sex, and novel opposite-sex dyads. We analyzed these interactions in three ways. First, we quantified overall activity levels (call and movement rates) for each individual. Second, we measured how coordinated calls and movements were by calculating (a) the percent difference in activity rates as an estimate of how similar calling and movement activity were between individuals within a dyad, and (b) the sliding correlation coefficients for time-stamped calls and movements for each dyad. Finally, we described multimodal behavioral profiles of coordination using principal component analyses. Overall, females were more active than males. For both females and males, activity levels as well as the coordination of calls and movements were significantly affected by social condition. In general, monogamous partners, female familiar same-sex dyads and familiar opposite-sex dyads were the most coordinated. This effect of familiarity shows that moment-to-moment behavioral coordination can be influenced by prior social experiences. Quantifying patterns of coordination or social synchrony may prove valuable for understanding the effects of social experience on brain and behavior. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

The ‘culture of two’: Communication accommodation in ravens’ (Corvus corax) nonvocal signaling

Abstract The theory of communication accommodation refers to linguistic processes through which human interactants—consciously or subconsciously—shift their speech and gesture styles to resemble those of their conversation partners. This phenomenon represents a crucial feature of human language and is particularly pronounced in affiliative and/or strong relationships. Communication accommodation is suggested to reflect a need for social integration or identification with other individuals and, as such, plays an important role in communication within closely-knit social units and in particular monogamous relationships. Concerning nonhuman animals, the phenomenon of communication accommodation has received relatively little research attention. Here, we tested whether common ravens (Corvus corax), which are known for their sophisticated communicative skills and lifelong monogamous pair bonds, accommodate their nonvocal signals within a relationship (i.e., pair-partners). Specifically, we investigated whether the nonvocal signals exchanged within pairs become synchronized over time. Our results provided evidence that raven pairs matched their repertoires, with recipients reciprocating the signals of their communication partners in relation to time spent together. This study thus strengthens the hypothesis that the motives to form and maintain affiliate relationships may have been crucial in boosting not only cognitive but also communicative abilities, and provides insight into the role social bonding might have played in the evolution of communicative plasticity.

The Impact of Early Postnatal and Juvenile Social Environments on the Effects of Chronic Intranasal Oxytocin in the Prairie Vole.

Interactions between social experiences at different stages of development (e.g., with parents as juveniles and peers as subadults) can profoundly shape the expression of social behavior. Rarely are the influences of more than one stage of developmental sensitivity to social environment investigated simultaneously. Furthermore, oxytocin (OT) has an extraordinary effect on a breadth of social behaviors, activationally or organizationally. The use of intranasal OT (IN-OT) has become increasingly common therapeutically in humans and scientifically in non-human experiments, however very little attention has been paid to the potential developmental consequences on social behavior that might result. We investigated the effects of early-life social environments and the impact of chronic IN-OT on social behavior at different stages of development in male prairie voles (Microtus ochrogaster). We raised animals under two conditions: “socially enriched” (in which they were biparentally reared and then weaned into group housing as subadults), or “socially limited” (in which they were reared by a single-mother, and that were then weaned into social isolation). Males raised under each condition were either administered daily doses of IN-OT or a saline control for 21 days from postnatal day (PND) 21–42. During this time, we assessed the prosocial behavior subjects demonstrated by evaluating juvenile affiliation (as subadults), alloparental care (as adults no longer being exposed to IN-OT), and partner preference tests to assess tendencies to form adult monogamous pairbonds. We found that “socially limited” males, exhibited increased social contact in juvenile affiliation tests at PND 35 and 42. These males were also more likely to form a partner preference than “socially enriched” males and formed stronger partner preferences overall. IN-OT did not alter these behavioral effects. We also found that “socially limited” males exhibited a distinct response to chronic IN-OT treatment. When compared to all other treatment groups, “socially limited” males that received IN-OT exhibited a greater amount of huddling behavior in the alloparental care test. This effect was, in part, explained by an absence of attack behavior, found only in these males. This study contributes to understanding the complex interactions between the developmental social environment, oxytocin, and social behavior.

Extra-pair mating in a socially monogamous and paternal mouth-brooding cardinalfish.

Many vertebrates form monogamous pairs to mate and care for their offspring. However, genetic tools have increasingly shown that offspring oftenarise from matings outside of the monogamous pair bond. Social monogamy is relatively common in coral reef fishes, but there have been few studies that have confirmed monogamy or extra-pair reproduction, either for males or for females. Here, long-term observations and genetic tools were applied to examine the parentage of embryos in a paternally mouth-brooding cardinalfish, Sphaeramia nematoptera. Paternal care in fishes, such as mouth-brooding, is thought to be associated with a high degree of confidence in paternity. Two years of observations confirmed that S.nematoptera form long-term pair bonds within larger groups. However, genetic parentage revealed extra-pair mating by both sexes. Of 105 broods analysed from 64 males, 30.1% were mothered by a female that was not the partner and 11.5% of broods included eggs from two females. Despite the high paternal investment associated with mouth-brooding, 7.6% of broods were fertilized by two males. Extra-pair matings appeared to be opportunistic encounters with individuals from outside the immediate group. We argue that while pair formation contributes to group cohesion, both males and females can maximize lifetime reproductive success by taking advantage of extra-pair mating opportunities.

Female Mate Choice Influences on Monogamous Pair Bond Formation in Prairie Voles

The prairie vole is an established model for social behavior, most notably, the monogamous pair bond formed between a mated pair. The formation of this bond hinges upon estrogen surges in the female shortly after being introduced to a potential mate. Our lab has correlated earlier estrogen surges with earlier achievement of pregnancy, which we have also found to be a determining factor in the formation of a monogamous pair bond for male prairie voles. Currently, our lab is examining how female mate choice influences the formation of a monogamous pair bond via both behavioral and endocrine measures.This study has three objectives: 1) To establish whether endocrine measures provide supporting data for behavioral measures of pair bond formation; 2) To examine whether female prairie voles allowed to pair with a mate of their choice will show an earlier estrogen surge and a shorter latency pregnancy; and 3) To determine if pairing and pregnancy is a greater stressor for animals not paired with their mate of choice.Sexually naïve female prairie voles were allowed to choose between two males and subsequently paired either with the male of their choice or the male they did not choose. An additional group of females was paired randomly with a male outside of the choice paradigm. Fecal samples were collected prior to and immediately after mate choice, and at select time points throughout the next 30 days or until the birth of a litter. Fecal samples were analyzed via ELISA for 17b‐estradiol and corticosterone content to examine sex hormone changes associated with pairing and pregnancy, as well as stress levels throughout pairing and pregnancy. These measures will be combined with partner preference testing on either the female or male subject to establish whether female mate choice can affect endocrine changes that may impact monogamous pair bond formation.Regardless of sex, animals in pairs that include the non‐chosen male tend to display social affiliation patterns that differ from those pairs that include the chosen male or a randomly assigned male. Despite differences in affiliative behavior, latency to birth in all groups was similar. These data suggest that female mate choice may influence pair bond formation, despite the lack of differences in latency to pregnancy.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Alternative Mating Tactics in Socially Monogamous Prairie Voles, Microtus ochrogaster

ABSTRACT: Alternative mating tactics appear to evolve when sexual selection is strong. Because such conditions are usually observed in species with polygynous or polyandrous mating systems, alternative mating tactics in monogamous mating systems are seldom documented and are poorly understood. In prairie voles, Microtus ochrogaster, a species widely known for forming monogamous pair-bonds, the expression of territoriality within each sex is dimorphic, and includes non-territorial “wanderers” as well as territorial “residents.” To explore the variance in fitness, measured in offspring numbers, among breeding individuals expressing these alternative mating tactics, we compiled parentage data over three years for male and female prairie voles from natural populations in Indiana and Kansas, USA. We found that: (1) the average fitnesses of males and females within each population were identical when adjusted by the sex ratio; (2) the variance in fitness in male and female prairie voles was comparable to that of many highly polygynous species; (3) The average fitnesses of male tactics, and of female tactics, were equivalent within and among years within each location; (4) consistent with negative frequency-dependent selection acting on mating phenotypes, the between-tactic variance in fitness for male and female mating tactics decreased with increasing study duration; (5) consistent with negative assortative mating, resident males and wanderer females produced offspring primarily in monogamous partnerships, whereas wanderer males and resident females produced offspring primarily in polygamous partnerships. Our results show that the conditions necessary for the persistence of alternative mating tactics are indistinguishable from those for phenotypically less flexible alternative mating strategies, and that alternative mating tactics can evolve in both sexes in monogamous species when fitness variance within each sex is large.

Committed for the long haul: Do nonapeptides regulate long-term pair maintenance in zebra finches?

The nonapeptides (oxytocin, vasopressin, and their non-mammalian homologs) regulate a number of social behaviors across vertebrates including monogamous pair bonds in mammals. Recent work on zebra finches has shown an important role for these neurohormones in establishing avian pair bonds as well. However, studies on the role of nonapeptides in maintaining pair bonds after pair formation are lacking. The goal of the present study was to investigate the effects of an oxytocin receptor antagonist (OTA) on pair maintenance behaviors in the monogamous zebra finch. I injected established zebra finch pairs over three days with either 5 μg of an OTA or a vehicle control, and separated the partners for one hour, after which partners were reunited and their reunion recorded on video for 30 min. Videos were then coded to measure singing, affiliative (allopreening, clumping, following), and aggressive (pecking) behaviors. These behaviors were also measured both on the day before injections to establish a pre-treatment level and two days after the last injection. Control and antagonist treated birds did not differ in the amount of time spent clumping or the frequency of pecking across the experiment. However, both male and female zebra finches that received OTA significantly reduced the amount of time spent following their partner. Females given the OTA treatment reduced allopreening and males given the OTA treatment reduced the frequency of singing bouts directed at their partners relative to controls. These results suggest that the nonapeptides play a role in regulating some, but not all, pair maintenance behaviors in experienced zebra finches.

Effects of aggressive temperament on endogenous oxytocin levels in adult titi monkeys.

Coordination of oxytocin (OT) activity and partner interactions is important for the facilitation and maintenance of monogamous pair bonds. We used coppery titi monkeys (Callicebus cupreus) to identify the effects of male aggressive temperament on OT activity, affiliative partner-directed behaviors, aggressive partner-directed behaviors, anxiety-related behaviors, and hormone-behavior interactions. We used a mirror technique, simulating an intruder in the home territory of pairs to elicit behavioral responses, and quantified behaviors using an established ethogram. Plasma concentrations of OT (pg/ml) were quantified using enzyme immunoassay. We used general linear mixed models to predict 1) percent change in OT as a function of aggression score, and 2) percent change in behaviors as a function of aggression, OT, and OT by aggression interactions. High-aggressive males exhibited a significant drop in OT concentration relative to control when exposed to the front of the mirror (β = -0.22, SE = 0.10, t = -2.20, p = 0.04). High-aggressive males spent significantly less time in contact with their mates (β = -1.35, SE = 0.60, t = -2.26, p = 0.04) and lip-smacked less (β = -1.02, SE = 0.44, t = -2.32, p = 0.03) relative to control. We also saw a trend toward an interaction effect between OT and proximity such that High-aggressive males displaying a drop in OT exhibited a smaller percent increase in social proximity (β = 6.80, SE = 3.48, t = 1.96, p = 0.07). Males exhibiting a decrease in OT also trended toward back-arching and tail-lashing less in response to the mirror (β = 4.53, SE = 2.5, t = 1.82, p = 0.09). To our knowledge, this is the first empirical study to examine interactions between OT and temperament in adult monogamous primates. Future studies should incorporate measures of pair-mate interactions and early-life experience to further understand variation in responses to social stressors and their effects on pair bonding.

Mate familiarity and social learning in a monogamous lizard.

Social learning is thought to be advantageous as it allows an animal to gather information quickly without engaging in costly trial-and-error learning. However, animals should be selective about when and whom they learn from. Familiarity is predicted to positively influence an animal's reliance on social learning; yet, few studies have empirically tested this theory. We used a lizard (Liopholis whitii) that forms long-term monogamous pair bonds to examine the effects of partner familiarity on social learning in two novel foraging tasks, an association and areversal task. We allowed female lizards to observe trained conspecifics that were either familiar (social mate) or unfamiliar execute these tasks and compared these two groups with control females that did not receive social information. Lizards preferentially relied on trial-and-error learning in the association task. In the reversal task, lizards that were demonstrated by familiar partners learnt in fewer trials compared to control lizards and made more correct choices. Our results provide some evidence for context-dependent learning with lizards differentiating between when they utilize social learning, and, to a limited degree, whom they learnt from. Understanding the role of the social context in which learning occurs provides important insights into the benefits of social learning and sociality more generally.

Non‐invasive, Repeated Measurement of Estrogen Levels within Subjects in Prairie Voles

Prairie voles are a good model for the studying the formation of social bonds; in particular, the formation of monogamous pair bonds. Previous studies in our lab have shown that successful pair bond formation hinges on pregnancy onset within a short time after mating. Female prairie voles only enter estrous when exposed to a potential mate. A surge in estrogen levels induces behavioral estrous and progressive increases in estrogen are seen throughout the course of pregnancy. Measurements of estrogen are generally taken from blood plasma, but collection methods are highly invasive or require the termination of subjects. To better measure estrogen levels in female prairie voles over a time course, a non‐invasive means of collecting samples is needed.We measured estrogen levels in fecal samples collected from female prairie voles over the course of pairing, mating, and pregnancy. Estrogen was extracted from fecal pellets using an organic solvent and ELISAs were run to measure changes in 17b‐estradiol concentrations. Animals that became pregnant showed progressively increasing levels of fecal estrogen over the course of mating and pregnancy, while animals that did not achieve pregnancy showed distinctly less fecal estrogen over the same time course. Our results suggest that measurement of fecal estrogen provides an alternative to more invasive means of measuring changes in sex hormones across time within subjects.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

How the brain codes intimacy: The neurobiological substrates of romantic touch.

Humans belong to a minority of mammalian species that exhibit monogamous pair-bonds, thereby enabling biparental care of offspring. The high reward value of interpersonal closeness and touch in couples is a key proximate mechanism facilitating the maintenance of enduring romantic bonds. However, surprisingly, the neurobiological underpinnings mediating the unique experience of a romantic partner's touch remain unknown. In this randomized placebo (PLC)-controlled, between-group, pharmacofunctional magnetic resonance imaging (fMRI) study involving 192 healthy volunteers (96 heterosexual couples), we intranasally administered 24 IU of the hypothalamic peptide oxytocin (OXT) to either the man or the woman. Subsequently, we scanned the subjects while they assumed that they were being touched by their romantic partners or by an unfamiliar person of the opposite sex, although in reality an identical pattern of touch was always given by the same experimenter. Our results show that intranasal OXT compared to PLC selectively enhanced the subjective pleasantness of the partner's touch. Importantly, intranasal OXT selectively increased responses to partner touch in the nucleus accumbens (NAcc) and anterior cingulate cortex. Under OXT, NAcc activations to partner touch positively correlated with the subjects' evaluation of their relationship quality. Collectively, our results suggest that OXT may contribute to the maintenance of monogamous relationships in humans by concomitantly increasing the reward value of partner touch and diminishing the hedonic quality of stranger touch. Hum Brain Mapp 38:4525-4534, 2017. © 2017 Wiley Periodicals, Inc.