Testosterone response to courtship predicts future paternal behavior in the California mouse, Peromyscus californicus

Behavioral convergence in defense behaviors in pair bonded individuals correlates with neuroendocrine receptors in the medial amygdala

Monogamous, pair-bonded animals coordinate intra-pair behavior for spatially separated challenges including territorial defense and nest attendance. Paired California mice, a monogamous, territorial and biparental species, approach intruders together or separately, but often express behavioral convergence across intruder challenges. To gain a more systems-wide perspective of potential mechanisms contributing to behavioral convergence across two conspecific intruder challenges, we conducted an exploratory study correlating behavior and receptor mRNA (Days 10 and 17 post-pairing). We examined associations between convergence variability in pair time for intruder-oriented behaviors with a pair mRNA index for oxytocin (OXTR), androgen (AR), and estrogen alpha (ERα) receptors within the medial amygdala (MeA) and the anterior olfactory nucleus (AON), brain regions associated with social behavior. An intruder behavior index revealed a bimodal distribution of intruder-related behaviors in Challenge 1 and a unimodal distribution in Challenge 2, suggesting population behavioral convergence, but no significant correlations with neuroendocrine measures. However, OXTR, AR, and ERα mRNA in the MeA were positively associated with convergence in individual intruder-related behaviors, suggesting multiple mechanisms may influence convergence. Mice could also occupy the nest during intruder challenges and convergence in nest attendance was positively correlated with MeA OXTR. At an individual level, nest attendance was positively associated with MeA ERα. Vocalizations were positively associated with AR and ERα mRNA. No positive associations were found in the AON. Overall, neuroendocrine receptors were implicated in convergence of a monogamous pair's defense behavior, highlighting the potential importance of the MeA as part of a circuit underlying convergence.

Estrogen-responsive neural circuits governing male and female mating behavior in mice

Decades of knockout analyses have highlighted the crucial involvement of estrogen receptors and downstream genes in controlling mating behaviors. More recently, advancements in neural circuit research have unveiled a distributed subcortical network comprising estrogen-receptor or estrogen-synthesis-enzyme-expressing cells that transforms sensory inputs into sex-specific mating actions. This review provides an overview of the latest discoveries on estrogen-responsive neurons in various brain regions and the associated neural circuits that govern different aspects of male and female mating actions in mice. By contextualizing these findings within previous knockout studies of estrogen receptors, we emphasize the emerging field of "circuit genetics", where identifying mating behavior-related neural circuits may allow for a more precise evaluation of gene functions within these circuits. Such investigations will enable a deeper understanding of how hormone fluctuation, acting through estrogen receptors and downstream genes, influences the connectivity and activity of neural circuits, ultimately impacting the manifestation of innate mating actions.

Plasticity in auditory cortex during parenthood

Most animals display robust parental behaviors that support the survival and well-being of their offspring. The manifestation of parental behaviors is accompanied by physiological and hormonal changes, which affect both the body and the brain for better care giving. Rodents exhibit a behavior called pup retrieval - a stereotyped sequence of perception and action - used to identify and retrieve their newborn pups back to the nest. Pup retrieval consists of a significant auditory component, which depends on plasticity in the auditory cortex (ACx). We review the evidence of neural changes taking place in the ACx of rodents during the transition to parenthood. We discuss how the plastic changes both in and out of the ACx support the encoding of pup vocalizations. Key players in the mechanism of this plasticity are hormones and experience, both of which have a clear dynamic signature during the transition to parenthood. Mothers, co caring females, and fathers have been used as models to understand parental plasticity at disparate levels of organization. Yet, common principles of cortical plasticity and the biological mechanisms underlying its involvement in parental behavior are just beginning to be unpacked.

Flexibility of neural circuits regulating mating behaviors in mice and flies

Mating is essential for the reproduction of animal species. As mating behaviors are high-risk and energy-consuming processes, it is critical for animals to make adaptive mating decisions. This includes not only finding a suitable mate, but also adapting mating behaviors to the animal's needs and environmental conditions. Internal needs include physical states (e.g., hunger) and emotional states (e.g., fear), while external conditions include both social cues (e.g., the existence of predators or rivals) and non-social factors (e.g., food availability). With recent advances in behavioral neuroscience, we are now beginning to understand the neural basis of mating behaviors, particularly in genetic model organisms such as mice and flies. However, how internal and external factors are integrated by the nervous system to enable adaptive mating-related decision-making in a state- and context-dependent manner is less well understood. In this article, we review recent knowledge regarding the neural basis of flexible mating behaviors from studies of flies and mice. By contrasting the knowledge derived from these two evolutionarily distant model organisms, we discuss potential conserved and divergent neural mechanisms involved in the control of flexible mating behaviors in invertebrate and vertebrate brains.

Intranasal oxytocin reduces pre-courtship aggression and increases paternal response in California mice (Peromyscus californicus)

Oxytocin (OXT) is a neuropeptide that can facilitate prosocial behavior and decrease social stress and anxiety but can also increase aggression in some contexts. We investigated whether acute pulses of intranasal (IN) OXT influenced social behavior during social challenges that are likely to occur throughout the lifespan of a wild mouse. To test this, we examined the acute effects of IN OXT in the male California mouse (Peromyscus californicus), a monogamous, biparental, and territorial rodent, using a within-subjects longitudinal design. Social challenges included a pre-courtship male-female encounter conducted during the (1) initial aggressive and not the following affiliative phase of courtship, (2) same-sex resident intruder test, and (3) parental care test. Consecutive tests and doses were separated by at least two weeks. Males were treated with intranasal infusions of 0.8 IU/kg OXT or saline controls 5-min before each behavioral test, receiving a total of three treatments of either IN OXT or saline control. We predicted that IN OXT would 1) decrease aggression and increase affiliation during the pre-courtship aggression phase, 2) increase aggression during resident intruder paradigms, and 3) increase paternal care and vocalizations during a paternal care test. As predicted, during pre-courtship aggression with a novel female, IN OXT males displayed less contact aggression than control males, although with no change in affiliative behavior. However, post-pairing, during the resident intruder test, IN OXT males did not differ from control males in contact aggression. During the paternal care test, IN OXT males were quicker to approach their pups than control males but did not differ in vocalizations produced, unlike our previous research demonstrating an effect on vocalizations in females. In summary, during pre-courtship aggression and the paternal care test, IN OXT reduced antisocial behavior; however, during the resident intruder test, IN OXT did not alter antisocial behavior. These data suggest that IN OXT promotes prosocial behavior specifically in social contexts that can lead to affiliation.

Testosterone pulses paired with a location induce a place preference to the nest of a monogamous mouse under field conditions

Changing social environments such as the birth of young or aggressive encounters present a need to adjust behavior. Previous research examined how long-term changes in steroid hormones mediate these adjustments. We tested the novel concept that the rewarding effects of transient testosterone pulses (T-pulses) in males after social encounters alters their spatial distribution on a territory. In free-living monogamous California mice (Peromyscus californicus), males administered three T-injections at the nest spent more time at the nest than males treated with placebo injections. This mimics T-induced place preferences in the laboratory. Female mates of T-treated males spent less time at the nest but the pair produced more vocalizations and call types than controls. Traditionally, transient T-changes were thought to have transient behavioral effects. Our work demonstrates that in the wild, when T-pulses occur in a salient context such as a territory, the behavioral effects last days after T-levels return to baseline.

Mean Girls: Social Stress Models for Female Rodents

Social stressors are known to have strong negative impacts on mental health. There is a long history of preclinical social defeat stress studies in rodents focusing on males that has produced important insights into the neural mechanisms that modulate depression- and anxiety-related behavior. Despite these impressive results, a historical weakness of rodent social stress models has been an under-representation of studies in females. This is problematic because rates of depression and anxiety are higher in women versus men. Recently there has been a surge of interest in adapting social stress methods for female rodents. Here we review new rodent models that have investigated numerous facets of social stress in females. The different models have different strengths and weaknesses, with some model systems having stronger ethological validity with other models having better access to molecular tools to manipulate neural circuits. Continued use and refinement of these complementary models will be critical for addressing gaps in understanding the function of neural circuits modulating depression- and anxiety-related behavior in females.

Intranasal oxytocin drives coordinated social approach

Coordinated responses to challenge are essential to survival for bonded monogamous animals and may depend on behavioral compatibility. Oxytocin (OT) context-dependently regulates social affiliation and vocal communication, but its role in pair members' decision to jointly respond to challenge is unclear. To test for OT effects, California mouse females received an intranasal dose of OT (IN-OT) or saline after bonding with males either matched or mismatched in their approach response to an aggressive vocal challenge. Pair mates were re-tested jointly for approach response, time spent together, and vocalizations. Females and males converged in their approach after pairing, but mismatched pairs with females given a single dose of IN-OT displayed a greater convergence that resulted from behavioral changes by both pair members. Unpaired females given IN-OT did not change their approach, indicating a social partner was necessary for effects to emerge. Moreover, IN-OT increased time spent approaching together, suggesting behavioral coordination beyond a further increase in bonding. This OT-induced increase in joint approach was associated with a decrease in the proportion of sustained vocalizations, a type of vocalization that can be associated with intra-pair conflict. Our results expand OT's effects on behavioral coordination and underscore the importance of emergent social context.

Neural and Hormonal Control of Sexual Behavior

Gonadal hormones contribute to the sexual differentiation of brain and behavior throughout the lifespan, from initial neural patterning to "activation" of adult circuits. Sexual behavior is an ideal system in which to investigate the mechanisms underlying hormonal activation of neural circuits. Sexual behavior is a hormonally regulated, innate social behavior found across species. Although both sexes seek out and engage in sexual behavior, the specific actions involved in mating are sexually dimorphic. Thus, the neural circuits mediating sexual motivation and behavior in males and females are overlapping yet distinct. Furthermore, sexual behavior is strongly dependent on circulating gonadal hormones in both sexes. There has been significant recent progress on elucidating how gonadal hormones modulate physiological properties within sexual behavior circuits with consequences for behavior. Therefore, in this mini-review we review the neural circuits of male and female sexual motivation and behavior, from initial sensory detection of pheromones to the extended amygdala and on to medial hypothalamic nuclei and reward systems. We also discuss how gonadal hormones impact the physiology and functioning of each node within these circuits. By better understanding the myriad of ways in which gonadal hormones impact sexual behavior circuits, we can gain a richer and more complete appreciation for the neural substrates of complex behavior.

Do olfactory cues from males with different avpr1a genotypes affect female mate choice in prairie voles, Microtus ochrogaster?

Multiple hypotheses have been proposed to explain female mate choice and some of the mechanisms underlying these choices. Females prairie voles display social and mating preferences for males with longer avpr1a microsatellite alleles, which provide more paternal care and exhibit less interest in novel females compared to males with shorter avpr1a microsatellite alleles. The cues females use to differentiate among males with different avpr1a genotypes are unknown, so the objective of our study was to determine if females can discriminate among males with different avpr1a genotypes using only male olfactory cues. In a laboratory choice test, females simultaneously presented with soiled bedding from a male with short versus long avpr1a microsatellite alleles showed no significant difference in the total time spent investigating each type of bedding. Nor did a greater number of females spend more time investigating soiled bedding from males with short versus long avpr1a microsatellite alleles. These findings were not influenced by female estrous status or their own avpr1a genotype. Our results suggest olfactory cues alone are insufficient to explain a female's ability to discriminate between males with different avpr1a genotypes and future research should focus on different cues or a combination of cues.

The challenge hypothesis revisited: Focus on reproductive experience and neural mechanisms

Our review focuses on findings from mammals as part of a Special Issue "30th Anniversary of the Challenge Hypothesis". Here we put forth an integration of the mechanisms through which testosterone controls territorial behavior and consider how reproductive experience may alter these mechanisms. The emphasis is placed on the function of socially induced increases in testosterone (T) pulses, which occur in response to social interactions, as elegantly developed by Wingfield and colleagues. We focus on findings from the monogamous California mouse, as data from this species shows that reproductive status is a key factor influencing social interactions, site fidelity, and vigilance for offspring defense. Specifically, we examine differences in T pulses in sexually naïve versus sexually experienced pair bonded males. Testosterone pulses influence processes such as social decision making, the winner-challenge effect, and location preferences through rewarding effects of T. We also consider how social and predatory vigilance contribute to T pulses and how these interactions contribute to a territory centered around maximizing reproduction. Possible underlying mechanisms for these effects include the nucleus accumbens (rewarding effects of testosterone), hippocampus (spatial memories for territories), and the bed nucleus of the stria terminalis (social vigilance). The development of the challenge effect has provided an ideal framework for understanding the complex network of behavioral, environmental, physiological and neural mechanisms that ultimately relates to competition and territoriality across taxa. The opportunity to merge research on the challenge effect using both laboratory and field research to understand social behavior is unparalleled.

Rapid effects of testosterone on social decision-making in a monogamous California mice (Peromyscus californicus)

Social animals must cope with challenges and opportunities by adjusting how they react to a salient stimulus. Here we use California mice (Peromyscus californicus) and investigate the mechanisms underlying social decision-making by studying (i) rapid effects of testosterone (T) pulses on a male's decisions to approach a novel male (challenge) versus a receptive female (opportunity), and (ii) whether social experience shapes how such effects are manifested. In Experiment 1, we found that sexually naïve males administered saline injections preferentially approached unfamiliar females over unfamiliar males, in contrast, 10 min after receiving a single T-injection, males expressed a preference for approaching unfamiliar males. Such an effect of T only occurred in sexually naïve males, but not pair-bonded males, suggesting that the rapid effects of T on approach behavior may rely on the pair-bonding experiences. Experiment 2 investigated social decision-making across three repeated exposures to the challenge/opportunity situations. Only the initial decision, approach to the challenge, predicted future aggressive behaviors, and such an effect relied on the rapid actions of T. We also found that experience with the controlled challenge situation (the male intruder was restrained behind a wire mesh) dampened the approach to the male side (potential threat) when later exposed to the same conditions. This suggests that a resident's motivation to defend against a threatening individual may decrease as the threat posed by the "neighbors" is reduced. Overall rapid effects of post-encounter T pulses may play important roles in influencing behavioral decisions during social interactions.

Effects of social defeat on paternal behavior and pair bonding behavior in male California mice (Peromyscus californicus)

Male parental care is an important social behavior for several mammalian species. Psychosocial stress is usually found to inhibit maternal behavior, but effects on paternal behavior have been less consistent. We tested the effects of social defeat stress on pair bond formation and paternal behavior in the monogamous California mouse (Peromyscus californicus). Social defeat reduced time spent in a chamber with a stranger female during a partner preference test conducted 24h after pairing, but increased latency to the first litter. In 10min partner preference tests conducted after the birth of pups, both control and stressed males exhibited selective aggression towards stranger females. Unlike prairie voles, side by side contact was not observed in either partner preference test. Stressed male California mice engaged in more paternal behavior than controls and had reduced anxiety-like responses in the open-field test. Defeat stress enhanced prodynorphin and KOR expression in the medial preoptic area (MPOA) but not PVN. Increased KOR signaling has been linked to increased selective aggression in prairie voles. Together the results show that defeat stress enhances behaviors related to parental care and pair bonding in male California mice.

Functional significance of men's testosterone reactivity to social stimuli

Rapid testosterone fluctuations in response to social stimuli are observed across a wide range of species, and the highly conserved nature of these fluctuations suggests an adaptive function. This paper reviews the current literature on testosterone reactivity, primarily in human males, and illustrates how life-history theory provides an adequate theoretical framework to interpret findings. The review is structured around supporting evidence suggesting that situations implicated in mating effort either directly (e.g., interactions with a mate) or indirectly (e.g., intrasexual competition) are generally associated with a brief elevation of testosterone, while situations implicated in parenting effort (e.g., nurturant interactions with offspring) are generally associated with a decline in testosterone. Further, we discuss how these fluctuations in testosterone have been linked to future behaviors, and how situational, motivational, and physiological variables moderate the interplay between social stimuli, testosterone reactivity, and behavior. Supporting the notion that testosterone can play a causal role in modulating behavior in response to social stimuli, we also summarize recent single administration studies examining the effects of testosterone on physiology, neurobiology, and behavior. A conceptual model provides links between supported findings, and hypothesized pathways requiring future testing.

Social and physical environments as a source of individual variation in the rewarding effects of testosterone in male California mice (Peromyscus californicus)

Despite extensive research revealing the occurrence of testosterone (T) pulses following social encounters, it is unclear how they lead to varied behavioral responses. We investigated the influence of residency (home versus unfamiliar environment) and social/sexual experience (pair-bonded, isolated or housed with siblings) on the plasticity of T's rewarding effects by measuring the development of conditioned place preferences (CPPs), a classical paradigm used to measure the rewarding properties of drugs. For pair-bonded males, T-induced CPPs were only produced in the environment wherein the social/sexual experience was accrued and residency status had been achieved. For isolated males, the T-induced CPPs only occurred when the environment was unfamiliar. For males housed with a male sibling, the T-induced CPPs were prevented in both the home and unfamiliar chambers. Our results reveal the plasticity of T's rewarding effects, and suggest that the behavioral functions of T-pulses can vary based on social/sexual experience and the environment in which residency was established. The formation of CPPs or reward-like properties of drugs and natural compounds can therefore exhibit malleability based on past experience and the current environment.

Male prairie voles with different avpr1a microsatellite lengths do not differ in courtship behaviour

Females are generally expected to be selective when choosing their social and sexual partners. In a previous laboratory study, female prairie voles (Microtus ochrogaster) showed significant social and sexual preferences for males with longer microsatellite DNA within the avpr1a gene encoding the vasopressin 1a receptor, as predicted if females select mates whose parental behaviour should increase female reproductive success. We tested the hypothesis that males with short versus long avpr1a microsatellite alleles exhibit differences in courtship behaviour, which could act as cues for female mate preference. The only behavioural difference we detected between males with short versus long avpr1a microsatellite alleles in mate preference trials was that males with short avpr1a microsatellite alleles sniffed the anogenital region of females more frequently during the first two days of the trials. Our results did not strongly support the hypothesis that a male's avpr1a genotype predicts the courtship behaviours we measured and suggests that other courtship behaviours or traits, such as odour and vocalizations, may be more important to female prairie voles when choosing mates. Additional studies using a wider array of species are needed to assess the degree to which male mammal courtship behaviour provides information on mate quality to females.

Estrogen Receptor Alpha Distribution and Expression in the Social Neural Network of Monogamous and Polygynous Peromyscus

In microtine and dwarf hamsters low levels of estrogen receptor alpha (ERα) in the bed nucleus of the stria terminalis (BST) and medial amygdala (MeA) play a critical role in the expression of social monogamy in males, which is characterized by high levels of affiliation and low levels of aggression. In contrast, monogamous Peromyscus males display high levels of aggression and affiliative behavior with high levels of testosterone and aromatase activity. Suggesting the hypothesis that in Peromyscus ERα expression will be positively correlated with high levels of male prosocial behavior and aggression. ERα expression was compared within the social neural network, including the posterior medial BST, MeA posterodorsal, medial preoptic area (MPOA), ventromedial hypothalamus (VMH), and arcuate nucleus in two monogamous species, P. californicus and P. polionotus, and two polygynous species, P. leucopus and P. maniculatus. The results supported the prediction, with male P. polionotus and P. californicus expressing higher levels of ERα in the BST than their polygynous counter parts, and ERα expression was sexually dimorphic in the polygynous species, with females expressing significantly more than males in the BST in both polygynous species and in the MeA in P. leucopus. Peromyscus ERα expression also differed from rats, mice and microtines as in neither the MPOA nor the VMH was ERα sexually dimorphic. The results supported the hypothesis that higher levels of ERα are associated with monogamy in Peromyscus and that differential expression of ERα occurs in the same regions of the brains regardless of whether high or low expression is associated with social monogamy. Also discussed are possible mechanisms regulating this differential relationship.

Beyond aggression: Androgen-receptor blockade modulates social interaction in wild meerkats

In male vertebrates, androgens are inextricably linked to reproduction, social dominance, and aggression, often at the cost of paternal investment or prosociality. Testosterone is invoked to explain rank-related reproductive differences, but its role within a status class, particularly among subordinates, is underappreciated. Recent evidence, especially for monogamous and cooperatively breeding species, suggests broader androgenic mediation of adult social interaction. We explored the actions of androgens in subordinate, male members of a cooperatively breeding species, the meerkat (Suricata suricatta). Although male meerkats show no rank-related testosterone differences, subordinate helpers rarely reproduce. We blocked androgen receptors, in the field, by treating subordinate males with the antiandrogen, flutamide. We monitored androgen concentrations (via baseline serum and time-sequential fecal sampling) and recorded behavior within their groups (via focal observation). Relative to controls, flutamide-treated animals initiated less and received more high-intensity aggression (biting, threatening, feeding competition), engaged in more prosocial behavior (social sniffing, grooming, huddling), and less frequently initiated play or assumed a 'dominant' role during play, revealing significant androgenic effects across a broad range of social behavior. By contrast, guarding or vigilance and measures of olfactory and vocal communication in subordinate males appeared unaffected by flutamide treatment. Thus, androgens in male meerkat helpers are aligned with the traditional trade-off between promoting reproductive and aggressive behavior at a cost to affiliation. Our findings, based on rare endocrine manipulation in wild mammals, show a more pervasive role for androgens in adult social behavior than is often recognized, with possible relevance for understanding tradeoffs in cooperative systems.

Male fidelity expressed through rapid testosterone suppression of ultrasonic vocalizations to novel females in the monogamous California mouse

The steroid hormone testosterone (T) is a well-known mediator of male sexual behavior in vertebrates. However, less is known about T's rapid effects on sexual behavior, particularly those involving ultrasonic vocalizations (USVs), a mode of communication that can influence mate acquisition in rodents. Using the monogamous California mouse, Peromyscus californicus, we tested whether T rapidly alters male USV production by giving T or saline injections to non-paired (sexually naïve) males and paired (paternally experienced and pair-bonded) males immediately prior to a brief exposure to an unrelated, novel female. Among non-paired males, no differences in the total number of USVs were observed; however, T increased the proportion of simple sweeps produced. Among paired males, T decreased the number of USVs produced, and this change was driven by a reduction in simple sweeps. These results suggest a differential rapid effect of T pulses between non-paired and paired males upon exposure to a novel female. Additionally, we observed a positive correlation in the production of USVs made between males and novel females, and this relationship was altered by T. Given the importance of USVs in sexual communication, our study supports an essential concept of monogamy in that mate fidelity is reinforced by decreased responsiveness to prospective mates outside of the pair bond. The central mechanism in pair bonded males that decreases their responsiveness to novel females appears to be one that T can trigger. This is among the first studies to demonstrate that T can inhibit sexually related behaviors and do so rapidly.

Pair bonding prevents reinforcing effects of testosterone in male California mice in an unfamiliar environment

Testosterone (T) can be released by stimuli such as social interactions, and thereby influence future social behaviours. Because the reinforcing effects of T can induce preferences for specific environmental locations, T has the potential to alter behaviour through space use. In a monogamous species, this T pulse may contribute differently to space use in sexually naive (SN) and pair-bonded (PB) males: SN males may be more likely to explore new areas to set up a territory than PB males, which are more likely to defend an existing, established territory. In this study, we test for variation in T-driven space use by examining variation in the formation of conditioned place preferences (CPPs) in SN and PB male California mice. In the three-chambered CPP apparatus, subcutaneous administrations of physiological levels of T were used to repeatedly condition SN and PB males to a side chamber, which is an unfamiliar/neutral environment. The final tests revealed that T-induced CPPs in the side chamber are developed in SN, but not PB males. This study fills a gap in our knowledge about plasticity in the rewarding nature of T pulses, based on past social experience.

Oxytocin administration, salivary testosterone, and father-infant social behavior

The growing involvement of fathers in childcare is followed by an increased interest in the neurobiology of fatherhood; yet, experimental work on the neuroendocrine basis of paternal care in humans is limited. The steroid Testosterone (T) and the neuropeptide Oxytocin (OT) have each been implicated in complex social behavior including parenting. However, no study to date explored the interaction between these two hormones in the context of fathering. In the current study we first test the relationship between father's basal salivary T and father and infant's social behaviors during parent-child interaction. Second, we examine the effects of intranasal OT administration on father's T production, and, finally, address the relations between OT-induced change in father's T with father-infant social behavior. Thirty-five fathers and their infants participated in a double-blind, placebo-controlled, within-subject study. Father-infant interaction was micro-coded for paternal and infant social behavior and synchrony was measured as the coordination between their gaze, affect, and vocalizations. Father's salivary T levels were measured at baseline and three times after administration. Results indicate that lower baseline T correlated with more optimal father and infant's behaviors. OT administration altered T production in fathers, relative to the pattern of T in the placebo condition. Finally, OT-induced change in T levels correlated with parent-child social behaviors, including positive affect, social gaze, touch, and vocal synchrony. Findings support the view that neuroendocrine systems in human males evolved to support committed parenting and are the first to describe the dynamic interactions between OT and T within a bio-behavioral synchrony model.

Parental care, loss of paternity and circulating levels of testosterone and corticosterone in a socially monogamous song bird

Introduction

In biparental birds testosterone levels of males are typically high during the mating phase and decrease during the parental phase. Testosterone implants may enhance mating behaviors, increase the likelihood of males to engage in extra-pair mating behavior and may reduce paternal care. Thus, sex steroids such as testosterone influence reproductive behaviors. Little is known, however, as to whether the more subtle differences in physiological concentrations of testosterone that occur between individuals are related to differences in paternal care, extra-pair behavior, and genetic paternity between those males. Here, we investigate these relationships in the male black redstart (Phoenicurus ochruros), a socially monogamous songbird with a low breeding synchrony. We used nestling provisioning as a proxy for parental care behavior and genetic paternity loss as a proxy for the efficiency of mate-guarding.

Results

There was no relationship between nestling provisioning and paternity loss of males. Baseline and gonadotropin releasing hormone (GnRH)-induced levels of testosterone, but not baseline corticosterone, were significantly higher during the mating than during the provisioning phase. Males fed more often when temperatures decreased and fed less when they sang more, but we found no correlation between parental behavior and baseline or GnRH-induced testosterone, and baseline corticosterone – both measured during either the mating or the parental phase. However, males that experienced loss of paternity had lower levels of testosterone during the provisioning phase than males that did not lose paternity. Further, males that lost paternity also expressed higher baseline levels of corticosterone.

Conclusions

Physiological differences in testosterone or baseline corticosterone were not related to differences in parental care, suggesting that the variation of testosterone within a physiological range may not relate to the degree of paternal care in this species. However, the profile of both hormones may indicate quality traits that influence the likelihood of the respective male to lose paternity.

Interactions between parents and parents and pups in the monogamous California mouse (Peromyscus californicus)

The California mouse (Peromyscuscalifornicus) may be a valuable animal model to study parenting as it is one of the few monogamous and biparental rodent species. By using automated infra-red imaging and video documentation of established pairs spanning two days prior to birth of the litter until d 5 of post natal development (PND), it was possible to follow interactions between parents and between parents and pups. The paired males were attentive to their partners in the form of grooming and sniffing throughout the time period studied. Both these and other activities of the partners, such as eating and drinking, peaked during late light/ mid-dark period. Beginning the day before birth, and most significantly on PND 0, the female made aggressive attempts to exclude the male from nest-attending, acts that were not reciprocated by the male, although he made repeated attempts to mate his partner during that period. By PND 1, males were permitted to return to the nest, where they initiated grooming, licking, and huddling over the litter, although time spent by the male on parental care was still less than that of the female. Male and female pups were of similar size and grew at the same rate. Pups, which are believed to be exothermic for at least the first two weeks post-natally, maintained a body temperature higher than that of their parents until PND 16. Data are consistent with the inference that the male California mouse parent is important in helping retain pup body heat and permit dams increased time to procure food to accommodate her increased energy needs for lactation. These assessments provide indices that may be used to assess the effects of extrinsic factors, such as endocrine disrupting chemicals, on biparental behaviors and offspring development.

Non-genomic transmission of paternal behaviour between fathers and sons in the monogamous and biparental California mouse

Maternal behaviour has profound, long-lasting implications for the health and well-being of developing offspring. In the monogamous California mouse (Peromyscus californicus), care by both parents is critical for offspring survival. We tested the hypothesis that similar to maternal care in rodents, paternal huddling and grooming (HG) behaviour can be transmitted to future generations via behavioural mechanisms. In California mice, testosterone maintains paternal HG behaviour. In the present study, we randomly assigned a group of male California mice to castration or sham-operated conditions and allowed them to raise their offspring normally. Adult sons of these males were paired with a female, and they were observed interacting with their own offspring. We found that like their fathers, the sons of castrated males huddled and groomed their young at lower levels than the sons of sham-operated fathers. The sons of castrates also retrieved pups more frequently. When both parents were present, the sons of castrates also showed a trend towards engaging in less exploratory behaviour. These data support the hypothesis that paternal behaviour, like maternal behaviour, can be transferred to future generations via epigenetic mechanisms and suggest that in a biparental species both parents contribute to offspring behavioural development.

Compatibility drives female preference and reproductive success in the monogamous California mouse (Peromyscus californicus) more strongly than male testosterone measures

Female assessment of male attractiveness and how preferred qualities impact reproductive success is central to the study of mate choice. Male attractiveness may depend on traits beneficial to the reproductive success (RS) of any female, termed 'universal quality', and/or on behavioral and biological interactions between potential mates that reflect 'compatibility'. The steroid hormone testosterone (T) often underlies male attractiveness in rodents and is associated with enhanced paternal care in the monogamous and biparental California mouse (Peromyscus californicus). We hypothesized that (1) T-characteristics are universally attractive to female California mice and that (2) if reproductive success is higher for females mated with preferred males, then females mated with males preferred by other females will also have higher reproductive success. Alternatively, we speculated that pair compatibility, based on emergent pair qualities, is important for a species with coordinated offspring care. We assessed individual T-characteristics in three ways: (1) T-response to GnRH challenges (2) baseline T-level and (3) T-response to a female. Testosterone-response did not predict female preference, but females spent more time investigating males with higher baseline T (accounting for only 9.6% of the variation in investigation time). None of the T-measures was associated with RS. Females paired with males they preferred produced litters more quickly and had higher RS than females paired with their non-preferred males. Naïve females who did not undergo preference tests had equivalent RS regardless of whether their mate was preferred or non-preferred by another female. These data suggest that higher male T elicits investigation, but female preference in the California mouse is more strongly linked with compatibility because individual preference was a better predictor of RS than any T measure.