Oxytocin-like receptors mediate pair bonding in a socially monogamous songbird

Although many species form socially monogamous pair bonds, relevant neural mechanisms have been described for only a single species, the prairie vole (Microtus ochrogaster). In this species, pair bonding is strongly dependent upon the nonapeptides oxytocin (OT) and vasopressin, in females and males, respectively. Because monogamy has evolved many times in multiple lineages, data from additional species are required to determine whether similar peptide mechanisms modulate bonding when monogamy evolves independently. Here we test the hypothesis that OT-like receptor activation is required for pair bond formation in the socially monogamous zebra finch (Taeniopygia guttata). Males and females were administered chronic intracerebroventricular infusions of saline or an OT receptor antagonist and were observed twice daily for 3 days in a colony environment. A variety of affiliative, aggressive and other behaviours were quantified. The antagonist produced significant and selective effects on pair bonding (latency to pair; number of sessions paired; stable pairing) and the associated behaviour of allopreening. Importantly, findings for males follow the trends of females; this yields main effects of treatment in two-way ANOVAs, although within-sex analyses are significant only for females. These data provide evidence for both convergent evolution and species diversity in the neuroendocrine mechanisms of pair bonding.     

Endogenous vasotocin exerts context-dependent behavioral effects in a semi-naturalistic colony environment

Arginine vasotocin (VT), and its mammalian homologue arginine vasopressin (VP), are neuropeptides involved in the regulation of social behaviors and stress responsiveness. Previous research has demonstrated opposing effects of VT/VP on aggression in different species. However, these divergent effects were obtained in different social contexts, leading to the hypothesis that different populations of VT/VP neurons regulate behaviors in a context-dependent manner. We here use VP antagonists to block endogenous VT function in male zebra finches (Taeniopygia guttata) within a semi-natural, mixed-sex colony setting. We examine the role of VT in the regulation of aggression and courtship, and in pair bond formation and maintenance, over the course of three days. Although our results confirm previous findings, in that antagonist treatment reduces aggressive mate competition during an initial behavioral session during which males encounter novel females, we find that the treatment effects are completely reversed within hours of colony establishment, and the antagonist treatment instead facilitates aggression in later sessions. This reversal occurs as aggression shifts from mate competition to nest defense, but is not causally associated with pairing status per se. Instead, we hypothesize that these divergent effects reflect context-specific activation of hypothalamic and amygdalar VT neurons that exert opposing influences on aggression. Across contexts, effects were highly specific to aggression and the antagonist treatment clearly failed to alter latency to pair bond formation, pair bond stability, and courtship. However, VT may still potentially influence these behaviors via promiscuous oxytocin-like receptors, which are widely distributed in the zebra finch brain.     

Behavioral and adrenocortical responses to mate separation and reunion in the zebra finch

The adaptive value of social affiliation has been well established. It is unclear, however, what endogenous mechanisms may mediate affiliative behavior. The Australian zebra finch (Taeniopygia guttata) breeds colonially and adults maintain lifelong pair bonds that may be disrupted in the wild due to high mortality rates. Many of its natural, social behaviors are maintained in laboratory conditions, making this species well suited for studying the mechanisms of affiliation. This study examines the behavioral and neuroendocrine responses to pair mate separation and reunion in zebra finches. We measured plasma corticosterone (CORT) and behavioral changes following separation from a pair bonded mate, and again upon reintroducing the mate or an opposite-sex cagemate. Plasma CORT concentrations were: (1). elevated during pair mate separation, even in the presence of other same-sex individuals, and (2). reduced to baseline upon reunion with the pair mate but not upon re-pairing with a new opposite-sex partner. These findings show that zebra finches exhibit hormonal responses to separation and reunion specifically with a bonded pair mate and not with other familiar conspecifics. In addition, alterations in behavior during separation and reunion are consistent with monogamous pair bond maintenance. This study presents evidence for adrenocortical involvement in avian pair bonding, and for hypothalamic-pituitary-adrenal activation in response to an ecologically relevant social stressor.     

Cellular mechanisms of social attachment

Pharmacological studies in prairie voles have suggested that the neuropeptides oxytocin and vasopressin play important roles in behaviors associated with monogamy, including affiliation, paternal care, and pair bonding. Our laboratory has investigated the cellular and neuroendocrine mechanisms by which these peptides influence affiliative behavior and social attachment in prairie voles. Monogamous prairie voles have a higher density of oxytocin receptors in the nucleus accumbens than do nonmonogamous vole species; blockade of these receptors by site-specific injection of antagonist in the female prairie vole prevents partner preference formation. Prairie voles also have a higher density of vasopressin receptors in the ventral pallidal area, which is the major output of the nucleus accumbens, than montane voles. Both the nucleus accumbens and ventral pallidum are key relay nuclei in the brain circuits implicated in reward, such as the mesolimbic dopamine and opioid systems. Therefore, we hypothesize that oxytocin and vasopressin may be facilitating affiliation and social attachment in monogamous species by modulating these reward pathways.     

Central oxytocin receptors mediate mating-induced partner preferences and enhance correlated activation across forebrain nuclei in male prairie voles

Oxytocin (OT) is a deeply conserved nonapeptide that acts both peripherally and centrally to modulate reproductive physiology and sociosexual behavior across divergent taxa, including humans. In vertebrates, the distribution of the oxytocin receptor (OTR) in the brain is variable within and across species, and OTR signaling is critical for a variety of species-typical social and reproductive behaviors, including affiliative and pair bonding behaviors in multiple socially monogamous lineages of fishes, birds, and mammals. Early work in prairie voles suggested that the endogenous OT system modulates mating-induced partner preference formation in females but not males; however, there is significant evidence that central OTRs may modulate pair bonding behavior in both sexes. In addition, it remains unclear how transient windows of central OTR signaling during sociosexual interaction modulate neural activity to produce enduring shifts in sociobehavioral phenotypes, including the formation of selective social bonds. Here we re-examine the role of the central OT system in partner preference formation in male prairie voles using a selective OTR antagonist delivered intracranially. We then use the same antagonist to examine how central OTRs modulate behavior and immediate early gene (Fos) expression, a metric of neuronal activation, in males during brief sociosexual interaction with a female. Our results suggest that, as in females, OTR signaling is critical for partner preference formation in males and enhances correlated activation across sensory and reward processing brain areas during sociosexual interaction. These results are consistent with the hypothesis that central OTR signaling facilitates social bond formation by coordinating activity across a pair bonding neural network.     

以田鼠作为动物模型来研究社会行为的进化:基因、脑与行为

田鼠属的一些近缘种间具有独特的社会行为多态性。例如Microtusochrogaster和M .pinetorum为一夫一妻制 ,而M .montanus和M .pennsylvanicus则为独居和一夫多妻制。无论是在野外还是人工饲养的条件下 ,单配制的田鼠其雌、雄成年个体一经交配即在两者之间形成长期的配偶关系并且双亲共同哺育后代。已证明神经多肽加压素 (Vasopressin)参与了田鼠单配制行为的神经调控。本篇综述了过去以及近期关于加压素调控田鼠配偶关系形成的研究结果和进展。首先 ,阐述了加压素V1a受体 (V1aR)在脑分布的种间差异 ,并以此来鉴别特定脑区在配偶关系形成中的功能 ;其次 ,探讨了运用V1aR拮抗物的药理学方法来决定究竟哪些脑区参与配偶关系的形成 ,还描述了田鼠种间V1aR基因结构和功能的不同 ,以及这些不同对V1aR在大脑的分布和行为调控潜在的作用机制 ;最后 ,讨论了最新的研究结果 ,即对一夫多妻制田鼠进行脑V1aR基因的改造 ,从而使之表现出一夫一妻制田鼠的行为。总之 ,了解复杂的社会性行为的遗传和神经机制可以加深我们对种间和种内行为分歧进化的理解     

Sex-specific activity and function of hypothalamic nonapeptide neurons during nest-building in zebra finches

Vertebrate species from fish to humans engage in a complex set of preparatory behaviors referred to as nesting; yet despite its phylogenetic ubiquity, the physiological and neural mechanisms that underlie nesting are not well known. We here test the hypothesis that nesting behavior is influenced by the vasopressin–oxytocin (VP–OT) peptides, based upon the roles they play in parental behavior in mammals. We quantified nesting behavior in male and female zebra finches following both peripheral and central administrations of OT and V_1a receptor (OTR and V1aR, respectively) antagonists. Peripheral injections of the OTR antagonist profoundly reduce nesting behavior in females, but not males, whereas comparable injections of V1aR antagonist produce relatively modest effects in both sexes. However, central antagonist infusions produce no effects on nesting, and OTR antagonist injections into the breast produce significantly weaker effects than those into the inguinal area, suggesting that antagonist effects are mediated peripherally, likely via the oviduct. Finally, immunocytochemistry was used to quantify nesting-induced Fos activation of nonapeptide neurons in the paraventricular and supraoptic nuclei of the hypothalamus and the medial bed nucleus of the stria terminalis. Nest-building induced Fos expression within paraventricular VP neurons of females but not males. Because the avian forms of OT (Ile⁸-OT; mesotocin) and VP (Ile³-VP; vasotocin) exhibit high affinity for the avian OTR, and because both peptide forms modulate uterine contractility, we hypothesize that nesting-related stimuli induce peptide release from paraventricular vasotocin neurons, which then promote female nesting via peripheral feedback from OTR binding in the oviduct uterus.     

The role of sex steroids in courtship, pairing and pairing behaviors in the socially monogamous zebra finch

The purpose of this study was to test whether sex steroid actions are necessary for courtship and pairing in socially monogamous birds. We examined the effects of an aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), combined with an anti-androgen, flutamide (F), on the behavior and pairing status of initially unpaired male and female zebra finches (Taeniopygia guttata). In the first experiment, 24 adult males were implanted with either a combination of ATD and flutamide or empty implants. Two weeks after implantation, birds were housed in aviaries containing 3 ATD + F males, 3 control males, and 3 females and allowed 2 weeks to pair, with observations 7 times during the 2-week period. A second experiment tested the effects of these same treatments in females. During the first 4 days of testing, ATD + F males were less likely to attack conspecifics than were control males. ATD + F males were also less likely to "greet," or approach, females than were control males, but other courtship behaviors, including directed singing, were unaffected. ATD + F females did not differ from control females on any courtship behavior measured. Furthermore, these treatments did not affect pairing behaviors (time spent clumping or in a nest box together) or the likelihood of pairing with a partner of the opposite sex. ATD + F treatments in females did, however, increase the likelihood of same-sex pairing. This suggests that, although sex steroids may regulate some courtship behaviors in males, they do not regulate pairing behaviors and have little effect on the likelihood that a male or female will be chosen as a mate by a bird of the opposite sex.     

Small sex differences in song control dendrites are associated with minimal differences in song capacity

Previous work on canaries and zebra finches has shown that large differences between the sexes exist in the structure of dendrites in n. robustus archistriatalis (RA), one of the principal nuclei involved in the control of song. This sex difference is associated with a general or complete absence of song in females. If dendritic morphology in RA is causally related to capacity for song, large sex differences in structure should not occur in avian species in which both sexes sing. We now report this prediction confirmed for buff-breasted wrens (Thryothorus leucotis), a species in which the members of a breeding pair sing duets with each other. Total dendritic length and number of dendritic branches in RA do not differ in this species. Dendrites from males project about 8 μm further from the cell body than dendrites from females, apparently because of longer dendritic segments near the cell body. We argue that this suggests that differential influences on the structure of RA occurred early in the lives of the wrens.     

Developmental effects of vasotocin and nonapeptide receptors on early social attachment and affiliative behavior in the zebra finch

Zebra finches demonstrate selective affiliation between juvenile offspring and parents, which, like affiliation between pair partners, is characterized by proximity, vocal communication and contact behaviors. This experiment tested the hypothesis that the nonapeptide arginine vasotocin (AVT, avian homologue of vasopressin) and nonapeptide receptors play a role prior to fledging in the development of affiliative behavior. Zebra finch hatchlings of both sexes received daily intracranial injections (post-hatch days 2–8) of either AVT, Manning Compound (MC, a potent V1a receptor antagonist) or saline (vehicle control). The social development of both sexes was assessed by measuring responsiveness to isolation from the family and subsequent reunion with the male parent after fledging. In addition, we assessed the changes in affiliation with the parents, unfamiliar males, and unfamiliar females each week throughout juvenile development. Compared to controls, MC subjects showed decreased attachment to the parents and MC males did not show the normal increase in affiliative interest in opposite sex individuals as they reached reproductive maturity. In contrast, AVT subjects showed a sustained affiliative interest in parents throughout development, and males showed increased interest in opposite sex conspecifics as they matured. These results provide the first evidence suggesting that AVT and nonapeptide receptors play organizational roles in social development in a bird.     

Variation in oxytocin is related to variation in affiliative behavior in monogamous, pairbonded tamarins

Oxytocin plays an important role in monogamous pairbonded female voles, but not in polygamous voles. Here we examined a socially monogamous cooperatively breeding primate where both sexes share in parental care and territory defense for within species variation in behavior and female and male oxytocin levels in 14 pairs of cotton-top tamarins (Saguinus oedipus). In order to obtain a stable chronic assessment of hormones and behavior, we observed behavior and collected urinary hormonal samples across the tamarins’ 3-week ovulatory cycle. We found similar levels of urinary oxytocin in both sexes. However, basal urinary oxytocin levels varied 10-fold across pairs and pair-mates displayed similar oxytocin levels. Affiliative behavior (contact, grooming, sex) also varied greatly across the sample and explained more than half the variance in pair oxytocin levels. The variables accounting for variation in oxytocin levels differed by sex. Mutual contact and grooming explained most of the variance in female oxytocin levels, whereas sexual behavior explained most of the variance in male oxytocin levels. The initiation of contact by males and solicitation of sex by females were related to increased levels of oxytocin in both. This study demonstrates within-species variation in oxytocin that is directly related to levels of affiliative and sexual behavior. However, different behavioral mechanisms influence oxytocin levels in males and females and a strong pair relationship (as indexed by high levels of oxytocin) may require the activation of appropriate mechanisms for both sexes.     

Behavioral effects of progesterone on pair bonding and partner preference in the female zebra finch (Taeniopygia guttata)

Progesterone is a sex steroid known to be involved in reproduction, but its role in pair relationships is not well understood. This study explored the effects of exogenous progesterone (P4) on courtship and pairing behaviors in female zebra finches (Taeniopygia guttata) in two separate experiments: the first focused on courtship and initial pair formation and the second examined the effects on pair maintenance. In these experiments, we tested the hypothesis that P4 increases pairing behaviors and consequently influences their partner preference. In Experiment 1, animals engaged in significantly more pairing behaviors when they were treated with P4 than when they received the vehicle. However, this effect was not partner-specific, since the association index (a marker for female partner preference) did not differ between treatment conditions. In Experiment 2, females were given two weeks to form a pair and then injected with P4 or vehicle. Pairs were observed that day and the subsequent day to determine if P4 caused a decrease in mate-directed behavior and an increase in extra pair behavior. P4 did not affect the quality of the pair relationship and did not increase extra pair behavior. These results suggest that P4 influences the overall quantity of initial pairing behaviors and may slightly increase the likelihood of partner preference formation over short time courses. However, P4 does not alter a previously established bond, suggesting there are likely separate mechanisms for initial pairing behaviors and pair maintenance.     

The neurobiology of social attachment: A comparative approach to behavioral, neuroanatomical, and neurochemical studies

The formation and maintenance of social bonds in adulthood is an essential component of human health. However studies investigating the underlying neurobiology of such behaviors have been scarce. Microtine rodents offer a unique comparative animal model to explore the neural processes responsible for pair bonding and its associated behaviors. Studies using monogamous prairie voles and other related species have recently offered insight into the neuroanatomical, neurobiological, and neurochemical underpinnings of social attachment. In this review, we will discuss the utility of the microtine rodents in comparative studies by exploring their natural history and social behavior in the laboratory. We will then summarize the data implicating vasopressin, oxytocin, and dopamine in the regulation of pair bonding. Finally, we will discuss the ways in which these neurochemical systems may interact to mediate this complex behavior.     

The Strength of Species Recognition in Captive Female Zebra Finches (Taeniopygia guttata): A Comparison Across Estrildid Heterospecifics

Conspecific recognition is essential for sexually reproducing species. Captive zebra finches ( Taeniopygia guttata ) are a model system in which the behavioural, ontogenetic and neurobiological bases of own-species (conspecific) recognition have been studied in detail. To assess the potential role of phylogeographic effects on species recognition, we examined the spatial preferences of unmated captive-bred female zebra finches between unfamiliar captive males of conspecific and estrildid heterospecific male stimuli. In accordance with prior studies using domesticated Bengalese finches ( Lonchura striata vars. domestica ), we found significant spatial and behavioural preference for conspecific males by female zebra finches, irrespective of heterospecific male phylogeographic origin mating status, or individual behaviour. This result has ramifications for the interpretation of social and mate preferences in this model species as it implies a consistency of species discrimination by captive female zebra finches.     

Does Foraging Behaviour Affect Female Mate Preferences and Pair Formation in Captive Zebra Finches?

Background

Successful foraging is essential for survival and reproductive success. In many bird species, foraging is a learned behaviour. To cope with environmental change and survive periods in which regular foods are scarce, the ability to solve novel foraging problems by learning new foraging techniques can be crucial. Although females have been shown to prefer more efficient foragers, the effect of males'' foraging techniques on female mate choice has never been studied. We tested whether females would prefer males showing the same learned foraging technique as they had been exposed to as juveniles, or whether females would prefer males that showed a complementary foraging technique.

Methodology/Principal Findings

We first trained juvenile male and female zebra finches (Taeniopygia guttata) to obtain a significant proportion of their food by one of two foraging techniques. We then tested whether females showed a preference for males with the same or the alternative technique. We found that neither a male''s foraging technique nor his foraging performance affected the time females spent in his proximity in the mate-choice apparatus. We then released flocks of these finches into an aviary to investigate whether assortative pairing would be facilitated by birds taught the same technique exploiting the same habitat. Zebra finches trained as juveniles in a specific foraging technique maintained their foraging specialisation in the aviary as adults. However, pair formation and nest location were random with regard to foraging technique.

Conclusions/Significance

Our findings show that zebra finches can be successfully trained to be foraging specialists. However, the robust negative results of the conditions tested here suggest that learned foraging specializations do not affect mate choice or pair formation in our experimental context.     

Early Administration of 17β-Estradiol Partially Masculinizes Song Control Regions and α2-Adrenergic Receptor Distribution in European Starlings (Sturnus vulgaris)

The vocal control system in many songbird species is a sexually dimorphic neural circuit that mediates learning and production of song. The mechanism by which this system is sexually differentiated has been investigated in only one species, the zebra finch (Taeniopygia guttata). Estradiol may be involved in the sexual differentiation of this system, as female zebra finches treated with estradiol as nestlings develop a male-like song system; however, blocking estradiol action in embryonic and nestling male zebra finches does not demasculinize the song system. Therefore, the role of estradiol in song system development is unclear. The role of estradiol in song system sexual differentiation was assessed in European starlings (Sturnus vulgaris). This species is of potential interest because it is less extreme in the degree of sexual dimorphism of the song system and song behavior than zebra finches. While in the field, starling nestlings were implanted with 500 μg of estradiol at 3 days of age. These birds were brought into the laboratory at Day 11 and hand-reared. In females, estradiol produces significant increases in the volumes of song control regions defined by Nissl stain, as well as by autoradiography for α₂-adrenergic receptors; however, these estradiol-treated females have song systems that more closely resemble those of control females than control males. Estradiol-treated males exhibit significant hypermasculinization at 210 days of age, but this effect is transient and hypermasculinization is no longer evident at Day 345. The role of estradiol in sexual differentiation of the neural circuit mediating song behavior remains enigmatic.     

小型田鼠:研究单配制进化与调控的模型

哺乳动物的单配制通常被认为是社会性单配制,它不是单纯地由性行为来决定,而是由诸多因素,包括长期的pair bond、夫妻双方共同抚育后代、免近亲交配以及雌雄两性相似等来决定的。在这篇综述中,我们论述了如何以啮齿类田鼠属(Microtus)为模型,通过比较研究来帮助我们理解社会性单配制的进化以及其神经调控机制。对田鼠属的研究不仅证实了单配制起源于艰苦的生存条件的假说,而且还证实了雌性性选择可能有利于维持单配制。不仅如此,哺乳动物单配制的进化还需要雄性的prosocial行为的不断强化。例如,亲近行为可以促进pairbond的形成并强化雄性对后代的哺育行为,而这种强化则来源于神经多肽催产素(OT)和加压素(AVP)与类固醇类激素的相互作用。催产素和加压素调控pairbond和双亲哺育行为的表达,而单配制和多配制田鼠的催产素和加压素受体在脑内的分布有显的不同。比较研究揭示了小型田鼠单配制的调控机制,而种内差异和行为上的可塑性则有助于我们进一步理解这种机制。比如,在某些条件下,多配制的草原田鼠(Microtus pennsylvanicu)的雄性个体具有哺育后代的行为。尽管草原田鼠的加压素Vla受体在脑内的分布与其他多配制的田鼠相似,但是如果脑室注射加压素,仍可以诱发其哺育后代的行为。同样是单配制的橙腹田鼠(Microtus ochrogaster),生活在：Illnois的显示出高水平的prosocial行为,而生活在Kansas的则表现出较低水平的社会性行为。即使两个种群的催产素或加压素Vla受体在脑内的分布相同,它们的雌激素受体表达水平显不同,这在雄性个体表现尤其明显。与Kansas的雄性个体相比,在终纹床核(bed rucleus of the stria tenninalis)和杏仁核中区(medial amygdala)这两个调控亲近行为和攻击行为的脑区,Illinois的雄性个体的α雌激素受体的水平要低得多。这些研究表明对雌激素的低敏感程度有利于高水平地表达prosocial行为并降低特定类型的攻击行为。     

Effects of central vasotocin and mesotocin manipulations on social behavior in male and female zebra finches

Male and female zebra finches (Taeniopygia guttata; total n = 40) were fitted with chronic guide cannulae directed at the lateral ventricle and were tested for aggression, affiliation, and partner preference following infusions of mesotocin (MT), vasotocin (VT), their antagonists, and vehicle control. Aggressive behavior was tested in a mate competition paradigm and tests of intersexual affiliation and partner preference were conducted following 1 day of cohabitation with an opposite-sex individual. These tests also provided data on male courtship singing. The results demonstrate a modest dose-dependent facilitation of aggression by VT, but not MT, in both male and female finches. However, only males were sensitive to infusions of a vasopressin antagonist, suggesting that endogenous VT is more important for behavioral modulation in males. Peptide effects were specific to aggression, as no treatments influenced intersexual affiliation, partner preference, or male courtship singing. Thus, in contrast to rodents, partner preference is not readily induced by VT or MT in this species. However, the potential necessity of endogenous VT and MT for natural pair-bond formation remains to be tested.     

Does sex matter? Differential responses to corticosterone administration in the zebra finch

Because of potentially deleterious effects of chronic stress, physiological measurements of stress hormones (in birds, corticosterone (CORT)) are often used to determine the consequences of natural or human-induced change. Often, it is assumed that CORT levels will be similar between the sexes and the results are pooled. However, recent studies have reported sex differences in CORT concentrations in avian species. As zebra finches (Taeniopygia guttata) are one of the most widely used bird species in laboratory studies worldwide, potential sex-specific differences in hormone metabolism, as well as the clearance rate of oral doses of exogenous CORT, are highly relevant. The results of this study show that female zebra finches have a significantly higher baseline CORT than males, which could partially be a product of differential responses to semi-isolation. In addition, a single dose of exogenous CORT resulted in different blood profiles between the sexes over time, though exogenous CORT was cleared from blood within 90 min following treatment in both sexes. Interestingly, exposure to multiple doses of exogenous CORT resulted in elevated CORT levels 24 h after treatment in both sexes. These results highlight the need for further investigations into potential sex differences in hormone metabolism, as well as possible cumulative effects of repeated stress.