Maternal imprints and the origins of variation

Paternal absence and increased caregiving independently and interactively shape the development of male prairie voles at subadult and adult life stages

The influence of maternal caregiving is a powerful force on offspring development. The absence of a father during early life in biparental species also has profound implications for offspring development, although it is far less studied than maternal influences. Moreover, we have limited understanding of the interactive forces that maternal and paternal caregiving impart on offspring. We investigated if behaviorally upregulating maternal care compensates for paternal absence on prairie vole (Microtus ochrogaster) pup development. We used an established handling manipulation to increase levels of caregiving in father-absent and biparental families, and later measured male offspring behavioral outcomes at sub-adulthood and adulthood. Male offspring raised without fathers were more prosocial (or possibly less socially anxious) than those raised biparentally. Defensive behavior and responses to contextual novelty were also influenced by the absence of fathers, but only in adulthood. Offensive aggression and movement in the open field test changed as a function of life-stage but not parental exposure. Notably, adult pair bonding was not impacted by our manipulations. Boosting parental care produced males that moved more in the open field test. Parental handling also increased oxytocin immunoreactive cells within the supraoptic nucleus of the hypothalamus (SON), and in the paraventricular nucleus (PVN) of biparentally-reared males. We found no differences in vasopressinergic cell groups. We conclude that male prairie voles are contextually sensitive to the absence of fathers and caregiving intensity. Our study highlights the importance of considering the ways early experiences synergistically shape offspring behavioral and neural phenotypes across the lifespan.

Revisiting Carl Jung's archetype theory a psychobiological approach

This paper delves into the concept of archetypes, universal patterns of behavior and cognition, and proposes a novel tripartite model distinguishing between structural, regulatory, and representational archetypes. Drawing on insights from code biology, neuroscience, genetics, and epigenetics, the model provides a nuanced framework for understanding archetypes and their role in shaping cognition and behavior. The paper also explores the interplay between these elements to express representational archetypes. Furthermore, it addresses the informational capacity of the genome and its influence on post-natal development and the psyche. The paper concludes by discussing the future trajectory of psychology, emphasizing the need for an integrative approach that combines our understanding of social constructs with insights into our inherent organizational propensities or archetypes. This exploration holds the potential to advance our understanding of the human condition.

Epigenetics and the return to the great mother archetype

Epigenetics is the study of how signals from the environment can change gene expression through the creation of molecules and chemical bonds that can last a lifetime and, therefore, determine the phenotype (the characteristics of the individual resulting from the interaction of their genotype [genes] with their environment). Research in this field began at McGill University, Canada, where it was observed that rats' mothers who were more nurturing raised more resilient pups. Since then, many studies have been carried out with animals and humans, showing the link between epigenetic changes and the experience of the great mother archetype - with potential consequences for the emotional life of the individual and for society.

Muscarinic regulation of self-grooming behavior and ultrasonic vocalizations in the context of open-field habituation in rats

Laboratory rats repeatedly exposed to an open field (OF) apparatus display increasingly high levels of grooming -especially that characterized by long and complex sequences- which has been taken as an additional index of novelty habituation. We hypothesized that disrupting such a learning process by administering an amnesic drug as the antimuscarinic scopolamine (SCP) could delay the appearance of more complex grooming subtypes. Thus, rats were pretreated either with SCP (15 mg/kg or 30 mg/kg) or vehicle (VEH) upon four one-day apart OF (OF1-4). On a fifth assessment, all rats received VEH to analyze the likely carry-over effect of SCP. Finally, we measured 50-kHz and 22-kHz ultrasonic vocalizations (USVs) as reliable markers of positive and negative emotionality, respectively. We found that SCP increased locomotion during OF1 and reduced rearing on OF1-OF4, causing no disruption in habituation over tests. SCP prevented the increase of total grooming time by inhibiting complex grooming subtypes and promoting short cephalic sequences. Despite the SCP-induced alterations on grooming agreed with our hypotheses, those changes may have resulted from a motor impairment that could have also affected rearing behavior. Additionally, SCP suppressed 50-kHz USVs while marginally increased 22-kHz calls. Once SCP was withdrawn, rearing, grooming, and some 50-kHz USVs subtypes returned to VEH levels, suggesting that novelty habituation occurred despite the SCP administration. Altogether, that mixed profile of SCP-induced behavioral changes may derive from the complex interplay between the contrasting action of SCP on different brain regions and the doses here used.

Intra- and interspecific variability among congeneric Pagellus otoliths

Otolith features are useful tools for studying taxonomy, ecology, paleontology, and fish biology since they represent a permanent record of life history. Nevertheless, the functional morphology of otoliths remains an open research question that is useful to completely understand their eco-morphology. This study aims to deepen the knowledge of intra- and interspecific variation in sagitta morphology in three congeneric seabreams, to understand how such variability could be related to the lifestyles of each species. Therefore, the sagittae (n = 161) of 24 Pagellus bogaraveo, 24 Pagellus acarne, and 37 Pagellus erythrinus specimens, collected from the south Tyrrhenian Sea, were analyzed using scanning electron microscopy and a stereomicroscope to assess morphometric features, variability between otolith pairs and the external crystalline structure the of sulcus acusticus. Statistical analysis demonstrated that, between the species, variability in sagittal otolith rostral length growth and sulcus acusticus features, correlated with increased fish total length and body weight. Moreover, slight differences between otolith pairs were detected in P. acarne and P. erythrinus (P < 0.05). The results confirm changes in otolith morphometry and morphology between different congeneric species and populations of the same species from different habitats.

Raised without a father: monoparental care effects over development, sexual behavior, sexual reward, and pair bonding in prairie voles

Around 5 % of mammals are socially monogamous and both parents provide care to the pups (biparental, BP). Prairie voles are socially monogamous rodents extensively used to understand the neurobiological basis of pair bond formation and the consequences that the absence of one parent has in the offspring. Pair bonding, characterized by selective affiliation with a sexual partner, is facilitated in prairie voles by mating for 6 h or cohabitation without mating for 24 h. It was previously shown that prairie voles raised by their mother alone (monoparental, MP) show delayed pair bond formation upon reaching adulthood. In this study we evaluated the effects of BP and MP care provided on the offspring's development, ability to detect olfactory cues, preference for sexually relevant odors, display of sexual behavior, as well as the rewarding effects of mating. We also measured dopamine and serotonin concentration in the nucleus accumbens (ventral striatum) and dorsal striatum after cohabitation and mating (CM) to determine if differences in these neurotransmitters could underlie the delay in pair bond formation in MP voles. Our data showed that MP voles received less licking/grooming than BP voles, but no developmental differences between groups were found. No differences were found in the detection and discrimination of olfactory cues or preference for sexually relevant odors, as all groups innately preferred opposite sex odors. No differences were found in the display of sexual behavior. However, CM induced reinforcing properties only in BP males, followed by a preference for their sexual partner in BP but not MP males. BP males showed an increase in dopamine turnover (DOPAC/DA and HVA/DA) in the nucleus accumbens in comparison to MP voles. No differences in dopamine, serotonin or their metabolites were found in the dorsal striatum. Our results indicate that MP voles that received less licking behavior exhibit a delay in pair bond formation possibly because the sexual interaction is not rewarding enough.

Appetitive olfactory conditioning in the neonatal male rat facilitates subsequent sexual partner preference

Pairing a neutral odor with a male rat's initial sexual experiences to ejaculation produces a subsequent conditioned ejaculatory preference (CEP) in which males ejaculate preferentially with receptive females that bear the odor relative to unscented receptive females. In 1986, Fillion and Blass reported that neonatal male rats exposed to a neutral lemon odor (citral) painted on their mother's ventrum while nursing ejaculated faster as adults with sexually receptive, citral-scented females compared to unscented receptive females. The present study examined whether the same odor paired with tactile reward in neonatal male rats would alter the subsequent expression of a CEP. Newborn Long-Evans male rats were separated from their mothers each day beginning on Postnatal Day 1 and placed into a Plexiglas cage that contained either unscented or citral-scented bedding (N = 8/group). During each trial, rats were stroked from head to toe with a soft, narrow paintbrush, after which they were returned to their mothers. Males were weaned at 21 days of age and housed in same-treatment pairs for an intervening 50 days. Following habituation to a large open field, males were presented with two sexually receptive Long-Evans females, one scented with citral, and the other unscented, for a 30-min test of copulation. Males in the Paired group copulated and ejaculated preferentially with the scented female whereas males in the Unpaired group showed no preference. Pairing a neutral odor with a reward state in infancy generates a preference in male rats to ejaculate with sexually receptive females bearing the same odor in adulthood.

Methylation of oxytocin related genes and early life trauma together shape the N170 response to human faces

Childhood trauma fundamentally shapes social cognition and basic processing of social cues, which frequently cascade into adverse behavioral outcomes. Recent studies indicate that epigenetic changes in oxytocin functioning might contribute to these long-term effects, although a deeper understanding of the underlying mechanisms is still lacking. The electroencephalographic N170 response to faces might capture a neural response at the core of these interactive effects of oxytocin gene methylation and childhood adversity, given that this response is considered to reflect fundamental face processing, to be susceptible to oxytocin administration and also to be a biomarker of various psychiatric disorders. We assessed the N170 response to neutral faces in relation to participant's (81, women) recalled childhood trauma, methylation of their oxytocin structural (OXTg) and oxytocin receptor (OXTRg) genes, and endogenous levels of cortisol and testosterone. Additionally, we investigated the interactive effect of OXTg methylation and CTQ across three face sets of varying maturity. Methylation of OXTg relates to a weakened N170 response towards adults, children and infants. Moreover, methylation of both OXTRg and OXTg shaped the directionality of adversity effects, predicting a weakened N170 response in those with high methylation and hyper-vigilance with participants with low methylation. Our results are the first to relate OXT(R)g methylation to the N170 response. They shed light on biological processes linking childhood adversity and epigenetic marks to altered behavior and potentially psychopathologies.

Genotypic variation in the persistence of transgenerational responses to seasonal cues

Phenotypes respond to environments experienced directly by an individual, via phenotypic plasticity, or to the environment experienced by ancestors, via transgenerational environmental effects. The adaptive value of environmental effects depends not only on the strength and direction of the induced response but also on how long the response persists within and across generations, and how stably it is expressed across environments that are encountered subsequently. Little is known about the genetic basis of those distinct components, or even whether they exhibit genetic variation. We tested for genetic differences in the inducibility, temporal persistence, and environmental stability of transgenerational environmental effects in Arabidopsis thaliana. Genetic variation existed in the inducibility of transgenerational effects on traits expressed across the life cycle. Surprisingly, the persistence of transgenerational effects into the third generation was uncorrelated with their induction in the second generation. Although environmental effects for some traits in some genotypes weakened over successive generations, others were stronger or even in the opposite direction in more distant generations. Therefore, transgenerational effects in more distant generations are not merely caused by the retention or dissipation of those expressed in prior generations, but they may be genetically independent traits with the potential to evolve independently.

Acute stress differentially affects grooming subtypes and ultrasonic vocalisations in the open-field and home-cage test in rats

Grooming behaviour in rodents has been associated with emotional distress, especially in unfamiliar and aversive contexts. However, the biological function of grooming in such situations is still unclear. We hypothesised that particular grooming subtypes are differentially associated with the stress response. Here, we investigated the effects of an acute stress exposure on grooming and ultrasonic vocalisations (USVs) assessed on different testing contexts varying in the level of familiarity. To this aim, footshocked and non-footshocked rats were tested for 20 min on one of the following conditions: an unfamiliar open-field test, a familiar open-field test, and an individual home cage filled with bedding. We found that footshock stress slightly decreased complex grooming sequences while increased cephalic grooming. Stress induced a negative affective state inferred from an increase and decrease of 22-kHz and 50-kHz calls, respectively. The latter USVs correlated positively with the complex grooming subtypes. Altogether, a detailed analysis of grooming seems necessary for elucidating its diverse biological functions. Nevertheless, footshock stress and testing conditions produced weaker-than-expected effects, possibly because the time elapsed between footshocks and behavioural testing was too short for eliciting a full stress response, and because the simple footshock-chamber experience may have impeded detecting stronger effects of familiarity.

Transgenerational consequences of maternal immune activation

Prenatal exposure to infectious or inflammatory insults is increasingly recognized in the etiology of neuropsychiatric diseases, including schizophrenia, autism, depression and bipolar disorder. New discoveries highlight that maternal immune activation can lead to pathological effects on brain and behavior in multiple generations. This review describes the transgenerational consequences of maternal immune activation in shaping brain and behavior anomalies and disease risk across generations. We discuss potential underlying mechanisms of transmission, by which prenatal immune activation can mediate generation-spanning changes in brain development and functions and how external influences could further determine the specificity of the phenotype across generations. The identification of the underlying mechanisms appears relevant to infection-related neuropsychiatric illnesses independently of existing diagnostic classifications and may help identifying complex patterns of generation-spanning transmission beyond genetic inheritance. The herein described principles emphasize the importance of considering ancestral infectious histories in clinical research aiming at developing new preventive treatment strategies against infection-related neurodevelopmental disorders and mental illnesses.

Strain differences in maternal neuroendocrine and behavioral responses to stress and the relation to offspring cocaine responsiveness

Early life stress exposure, including prenatal stress (PNS), influences subsequent risk for many disorders, including substance abuse, and these effects interact with genetic factors to determine risk for disease. We previously demonstrated gene X environmental interactions across the BXD recombinant inbred mouse strain panel and their progenitor strains in PNS modulation of cocaine-induced reward and locomotion. Critical to dissecting genetic interactions with PNS is consideration of the modes of stress transmission to the offspring. Both maternal neuroendocrine responses during stress and subsequent maternal-offspring interactions following stress may serve as transmission modes for PNS-induced changes in cocaine responsiveness. Therefore, we characterized the maternal stress response by measuring restraint stress-induced plasma corticosterone (CORT) during gestation as well as effects of restraint stress on dam-pup contact in the first 10 postnatal days in BXD and progenitor mouse strains. Restraint stress interacted with strain to affect plasma CORT levels and dam-pup contact, indicating heritable variation of the maternal stress response. Furthermore, strain-level variance in maternal stress response correlated to the impact on cocaine response exhibited by adult offspring. These findings implicate multiple modes of maternal stress response in alterations of offspring drug responsiveness and indicate that assessment of maternal endocrine and behavioral responses during early life can be utilized to dissect the complex intersection of maternal factors, the response of the offspring and genetics.

With a little help from her friends (and family) part II: Non-maternal caregiving behavior and physiology in mammals

The diversity of competing frameworks for explaining the evolution of non-maternal care in mammals (Part I, this issue) reflects the vast range of behaviors and associated outcomes these theories attempt to subsume. Caretaking comprises a wide variety of behavioral domains, and is mediated by an equally large range of physiological systems. In Part II, we provide an overview of how non-maternal care in mammals is expressed, the ways in which it is regulated, and the many effects such care has on both recipients and caretakers. We also discuss the two primary ways in which closer integration of ultimate and proximate levels of explanation can be useful when addressing questions about non-maternal caretaking. Specifically, proximate mechanisms provide important functional clues, and are key to testing theory concerning evolutionary tradeoffs. Finally, we highlight a number of methodological and publication biases that currently shape the literature, which provide opportunities for knowledge advancement in this domain going forward. In this conclusion to our two-part introduction, we provide a broad survey of the behavior and physiology that the contributions to this special issue represent.

Alteration in oxytocin levels induced by early social environment affects maternal behavior and estrogen receptor alpha in mandarin voles (Microtus mandarinus)

Many studies have shown that the early social environment exerts long-term effects on the brain and also the parental behavior of adults. Oxytocin (OXT) is one of the most important neurotransmitters that regulate social behavior; howerve, whether the early social environment affects parental behavior via OXT remains unclear. Using socially monogamous adult mandarin voles (Microtus mandarinus), the present study found that 1) both paternal deprivation and early social deprivation significantly decreased OXT expression in both the paraventricular hypothalamic nucleus (PVN) and the supraoptic nucleus (SON) of F2 generation offspring; 2) systemic neonatal OXT injection in naïve animals promoted maternal but not paternal behavior in adult F2 offspring; 3) systemic neonatal OXT injection significantly increased ERα expression in both the medial preoptic area (MPOA) and the ventro medial hypothalamic nucleus (VMH) in female but not in male mandarin voles; 4) systemic neonatal administration of an OXT antagonist significantly reduced ERα expression in the bed nucleus of the stria terminalis (BNST), VMH, and the arcuate hypothalamic nucleus (Arc) in females and in all examined brain regions in males. In summary, the obtained data demonstrate that the early social environment could affect OXT level, which in turn leads to long-term effects on ERα expression in relevant brain regions, consequently affecting maternal behavior but not paternal behavior.

The paradox of care in behavioral epigenetics: Constructing early-life adversity in the lab

Many epigenetic studies focus on how stress, trauma, and care become molecularly embodied, affect gene expression without changing DNA sequence, and produce changes that influence the health and behavior of individuals, their offspring, and future generations. This article describes how care has become central in research on the epigenetic effects of early-life adversity. My analysis draws on two years of ethnographic research in a behavioral epigenetics laboratory in the United States. Building on traditions in feminist theory and the sociology of science, I document how care is enacted with research samples, experimental protocols, and behavioral endpoints in experiments with model organisms. My findings point to tensions between researchers' care for the data and their measurement of adversity as a discrete variable in the form of maternal interaction, neglect, and abuse. I argue that these tensions suggest a "paradox of care" that is actively shaping how epigenetic knowledge is produced and its impacts in society. My analysis shows how decisions in the lab are shaping new understandings of how early-life experiences influence health, with significant impacts on our expectations of mothers and pregnant women. This study suggests that the more complex explanations of health and development promised by epigenetics are simultaneously constructed and constrained by caring practices in the laboratory.

Why and how the early-life environment affects development of coping behaviours

Understanding the ways in which individuals cope with threats, respond to challenges, make use of opportunities and mediate the harmful effects of their surroundings is important for predicting their ability to function in a rapidly changing world. Perhaps one of the most essential drivers of coping behaviour of adults is the environment experienced during their early-life development. Although the study of coping, defined as behaviours displayed in response to environmental challenges, has a long and rich research history in biology, recent literature has repeatedly pointed out that the processes through which coping behaviours develop in individuals are still largely unknown. In this review, we make a move towards integrating ultimate and proximate lines of coping behaviour research. After broadly defining coping behaviours (1), we review why, from an evolutionary perspective, the development of coping has become tightly linked to the early-life environment (2), which relevant developmental processes are most important in creating coping behaviours adjusted to the early-life environment (3), which influences have been shown to impact those developmental processes (4) and what the adaptive significance of intergenerational transmission of coping behaviours is, in the context of behavioural adaptations to a fast changing world (5). Important concepts such as effects of parents, habitat, nutrition, social group and stress are discussed using examples from empirical studies on mammals, fish, birds and other animals. In the discussion, we address important problems that arise when studying the development of coping behaviours and suggest solutions.

Lost connections: Oxytocin and the neural, physiological, and behavioral consequences of disrupted relationships

In humans and rodent animal models, the brain oxytocin system is paramount for facilitating social bonds, from the formation and consequences of early-life parent-infant bonds to adult pair bond relationships. In social species, oxytocin also mediates the positive effects of healthy social bonds on the partners' well-being. However, new evidence suggests that the negative consequences of early neglect or partner loss may be mediated by disruptions in the oxytocin system as well. With a focus on oxytocin and its receptor, we review studies from humans and animal models, i.e. mainly from the biparental, socially monogamous prairie vole (Microtus ochrogaster), on the beneficial effects of positive social relationships both between offspring and parents and in adult partners. The abundance of social bonds and benevolent social relationships, in general, are associated with protective effects against psycho- and physiopathology not only in the developing infant, but also during adulthood. Furthermore, we discuss the negative effects on well-being, emotionality and behavior, when these bonds are diminished in quality or are disrupted, for example through parental neglect of the young or the loss of the partner in adulthood. Strikingly, in prairie voles, oxytocinergic signaling plays an important developmental role in the ability to form bonds later in life in the face of early-life neglect, while disruption of oxytocin signaling following partner loss results in the emergence of depressive-like behavior and physiology. This review demonstrates the translational value of animal models for investigating the oxytocinergic mechanisms that underlie the detrimental effects of developmental parental neglect and pair bond disruption, encouraging future translationally relevant studies on this topic that is so central to our daily lives.

Preterm behavioral epigenetics: A systematic review

Behavioral epigenetics is revealing new pathways that lead individuals from early adversity exposures to later-in-life detrimental outcomes. Preterm birth constitutes one of the major adverse events in human development. Preterm infants are hospitalized in the Neonatal Intensive Care Unit (NICU) where they are exposed to life-saving yet pain-inducing procedures and to protective care. The application of behavioral epigenetics to the field of preterm studies (i.e., Preterm Behavioral Epigenetics, PBE) is rapidly growing and holds promises to provide valid insights for research and clinical activity. Here, the evidence of the epigenetic correlates of prenatal adversities, NICU-related environment and development of preterm infants is systematically reviewed. The findings suggest that a number of prenatal adverse (e.g., maternal depression and stress) and post-natal (e.g., NICU-related pain-related stress) events affect the developmental trajectories of preterm infants and children via epigenetic alterations of imprinted and stress-related genes. Nonetheless, the potential epigenetic vestiges of early care and protective interventions in NICU have not been investigated yet and this represents a fascinating challenge for future PBE research.

The intrauterine environment affects learning ability of Tokai high avoider rat offspring derived using cryopreservation and embryo transfer-mediated reproduction

Embryo transfer (ET) to recipient female animals is a useful technique in biological and experimental animal studies. While cryopreservation of two-cell stage rat embryos and ET to recipient rats are currently well-defined, it is unknown whether these artificial reproductive techniques and maternal factors affect offspring phenotype, particularly higher brain functions. Therefore, we assessed the effects of cryopreservation, ET, and maternal care on learning behaviour of the offspring, using Tokai high avoider (THA) rats that have a high learning ability phenotype. We found that the high learning ability of THA rat offspring was not replicated following ET to surrogate Wistar rats with a low-avoidance phenotype. Additionally, the characteristic phenotype of offspring obtained through mating of ET-derived rats was similar to that of THA rats. A postnatal cross-fostering investigation with the offspring of Wistar and THA rats showed that maternal behaviour, including postnatal care and lactation traits, did not differ between the dams of low-avoidance Wistar rats and THA rats; therefore, learning behaviour was retained in both Wistar and THA rat offspring. We conclude that the offspring phenotype, although unchanged, has an imperceptible effect on the learning ability of ET-derived THA rats through the intrauterine environment of the recipient.

Maternal immune activation transgenerationally modulates maternal care and offspring depression-like behavior

Gestational infection is increasingly being recognized for its involvement as causative mechanism in severe developmental brain abnormalities and its contribution to the pathogenesis of psychopathologies later in life. First observations in the widely accepted maternal immune activation (MIA) model based upon the systemic administration of the viral mimetic Polyinosinic:polycytidylic acid (poly(I:C)) have recently suggested a transmission of behavioral and transcriptional traits across generations. Although maternal care behavior (MCB) is known as essential mediator of the transgenerational effects of environmental challenges on offspring brain function and behavior, the possible propagation of alterations of MCB resulting from MIA to following generations has not yet been examined. Here we show that poly(I:C) stimulation at embryonic day 12.5 (E12.5) leads to aberrant MCB and that this effect is transmitted to the female F1 offspring. The transgenerational effects on MCB are paralleled by enhanced depression-like behavior in the second generation F2 offspring with contributions of both maternal and paternal heritages. Examination of offspring hippocampal expression of genes known as targets of MCB and relevant for ensuing non-genetic transmission of altered brain function and behavior revealed transgenerationally conserved and modified expressional patterns in the F1 and F2 generation. Collectively these data firstly demonstrate the transgenerational transmission of the impact of gestational immune activation on the reproductive care behavior of the mother. Behavioral and molecular characteristics of first and second generation offspring suggest transgenerationally imprinted consequences of gestational infection on psychopathological traits related to mood disorders which remain to be examined in future cross-fostering experiments.

Wild Peromyscus adjust maternal nest-building behaviour in response to ambient temperature

The heat dissipation limit (HDL) hypothesis suggests that energy output during lactation in mammals might be constrained by their ability to dissipate heat. This hypothesis predicts that wild mammals ought to adjust nest insulation in response to heat load, but these predictions have rarely been tested in wild mammals. Here we developed a simple score of nest-building for wild deer mice (Peromyscus maniculatus (Wagner, 1845)) on an ordinal scale from 0 to 4, based on three qualitative and easy to observe aspects of nest-building behaviour: bedding quality, nest shape, and mouse visibility. We used this measure to track 472 nest-building observations across 14 wild P. maniculatus that were brought into captivity and housed under pseudoambient temperatures across one reproductive event. Our observations of nest-building behaviour of the genus Peromyscus Gloger, 1841 provide varying support for the HDL hypothesis; there is a negative effect of ambient temperature on nest-building behaviour and lactating females became more sensitive to temperature as days post partum increased. However, females generally build more elaborate nests in lactation than other reproductive states and there are no effects of litter size, total pup mass, or days post partum on nest scores during lactation. Our observations have broad implications for quantifying behaviours in nest-building species and metabolic relationships in wild mammals.

Intergenerational transmission of sociality: the role of parents in shaping social behavior in monogamous and non-monogamous species

Social bonds are necessary for many mammals to survive and reproduce successfully. These bonds (i.e. pair-bonds, friendships, filial bonds) are characterized by different periods of development, longevity and strength. Socially monogamous species display certain behaviors not seen in many other mammals, such as adult pair-bonding and male parenting. In our studies of prairie voles (Microtus ochrogaster) and titi monkeys (Callicebus cupreus), we have examined the neurohormonal basis of these bonds. Here, we discuss the evidence from voles that aspects of adolescent and adult social behavior are shaped by early experience, including changes to sensory systems and connections, neuropeptide systems such as oxytocin and vasopressin, and alterations in stress responses. We will compare this with what is known about these processes during development and adulthood in other mammalian species, both monogamous and non-monogamous, and how our current knowledge in voles can be used to understand the development of and variation in social bonds. Humans are endlessly fascinated by the variety of social relationships and family types displayed by animal species, including our own. Social relationships can be characterized by directionality (either uni- or bi-directional), longevity, developmental epoch (infant, juvenile or adult) and strength. Research on the neurobiology of social bonds in animals has focused primarily on 'socially monogamous' species, because of their long-term, strong adult affiliative bonds. In this Review, we attempt to understand how the ability and propensity to form these bonds (or lack thereof), as well as the display of social behaviors more generally, are transmitted both genomically and non-genomically via variation in parenting in monogamous and non-monogamous species.

The endocrinology of human caregiving and its intergenerational transmission

Variation in the quality of parental care has a tremendous impact on a child's social–emotional development. Research investigating the predictors of this variability in human caregiving behavior has mostly focused on learning mechanisms. Evidence is currently accumulating for the complementary underlying role of steroid hormones and neuropeptides. An overview is provided of the hormones and neuropeptides relevant for human caregiving behavior. Then the developmental factors are described that stimulate variability in sensitivity to these hormones and neuropeptides, which may result in variability in the behavioral repertoire of caregiving. The role of genetic variation in neuropeptide and steroid receptors, the role of testosterone and oxytocin during fetal development and parturition, and the impact of experienced caregiving in childhood on functioning of the neuroendocrine stress and oxytocin system are discussed. Besides providing a heuristic framework for further research on the ontogenetic development of human caregiving, a neuroendocrine model is also presented for the intergenerational transmission of caregiving practices. Insight into the underlying biological mechanisms that bring about maladaptive caregiving behavior, such as neglect and insensitive parenting, will hopefully result in more efficient approaches to reduce the high prevalence of such behavior and to minimize the impact on those affected.

Social regulation of adult neurogenesis: A comparative approach

The social environment sculpts the mammalian brain throughout life. Adult neurogenesis, the birth of new neurons in the mature brain, can be up- or down-regulated by various social manipulations. These include social isolation, social conflict, social status, socio-sexual interactions, and parent/offspring interactions. However, socially-mediated changes in neuron production are often species-, sex-, and/or region-specific. In order to reconcile the variability of social effects on neurogenesis, we need to consider species-specific social adaptations and other contextual variables (e.g. age, social status, reproductive status, etc.) that shift the valence of social stimuli. Using a comparative approach to understand how adult-generated neurons in turn influence social behaviors will shed light on how adult neurogenesis contributes to survival and reproduction in diverse species.

Disposable Soma Theory and the Evolution of Maternal Effects on Ageing

Maternal effects are ubiquitous in nature and affect a wide range of offspring phenotypes. Recent research suggests that maternal effects also contribute to ageing, but the theoretical basis for these observations is poorly understood. Here we develop a simple model to derive expectations for (i) if maternal effects on ageing evolve; (ii) the strength of maternal effects on ageing relative to direct environmental effects; and (iii) the predicted relationships between environmental quality, maternal age and offspring lifespan. Our model is based on the disposable soma theory of ageing, and the key assumption is thus that mothers trade off their own somatic maintenance against investment in offspring. This trade-off affects the biological age of offspring at birth in terms of accumulated damage, as indicated by biomarkers such as oxidative stress or telomere length. We find that the optimal allocation between investment in maternal somatic investment and investment in offspring results in old mothers and mothers with low resource availability producing offspring with reduced life span. Furthermore, the effects are interactive, such that the strongest maternal age effects on offspring lifespan are found under low resource availability. These findings are broadly consistent with results from laboratory studies investigating the onset and rate of ageing and field studies examining maternal effects on ageing in the wild.

The role of non-genetic inheritance in evolutionary rescue: epigenetic buffering, heritable bet hedging and epigenetic traps

Rapid environmental change is predicted to compromise population survival, and the resulting strong selective pressure can erode genetic variation, making evolutionary rescue unlikely. Non-genetic inheritance may provide a solution to this problem and help explain the current lack of fit between purely genetic evolutionary models and empirical data. We hypothesize that epigenetic modifications can facilitate evolutionary rescue through 'epigenetic buffering'. By facilitating the inheritance of novel phenotypic variants that are generated by environmental change-a strategy we call 'heritable bet hedging'-epigenetic modifications could maintain and increase the evolutionary potential of a population. This process may facilitate genetic adaptation by preserving existing genetic variation, releasing cryptic genetic variation and/or facilitating mutations in functional loci. Although we show that examples of non-genetic inheritance are often maladaptive in the short term, accounting for phenotypic variance and non-adaptive plasticity may reveal important evolutionary implications over longer time scales. We also discuss the possibility that maladaptive epigenetic responses may be due to 'epigenetic traps', whereby evolutionarily novel factors (e.g. endocrine disruptors) hack into the existing epigenetic machinery. We stress that more ecologically relevant work on transgenerational epigenetic inheritance is required. Researchers conducting studies on transgenerational environmental effects should report measures of phenotypic variance, so that the possibility of both bet hedging and heritable bet hedging can be assessed. Future empirical and theoretical work is required to assess the relative importance of genetic and epigenetic variation, and their interaction, for evolutionary rescue.

The maternal brain and its plasticity in humans

This article is part of a Special Issue "Parental Care". Early mother-infant relationships play important roles in infants' optimal development. New mothers undergo neurobiological changes that support developing mother-infant relationships regardless of great individual differences in those relationships. In this article, we review the neural plasticity in human mothers' brains based on functional magnetic resonance imaging (fMRI) studies. First, we review the neural circuits that are involved in establishing and maintaining mother-infant relationships. Second, we discuss early postpartum factors (e.g., birth and feeding methods, hormones, and parental sensitivity) that are associated with individual differences in maternal brain neuroplasticity. Third, we discuss abnormal changes in the maternal brain related to psychopathology (i.e., postpartum depression, posttraumatic stress disorder, substance abuse) and potential brain remodeling associated with interventions. Last, we highlight potentially important future research directions to better understand normative changes in the maternal brain and risks for abnormal changes that may disrupt early mother-infant relationships.

Early-life object exposure with a habituated mother reduces fear reactions in foals

Fear reactions in horses are a major cause of horse-human accidents, and identification of effective pathways for reduction in fearfulness can help decreasing the frequency of accidents. For a young mammal, the mother is one of the most salient aspects of its environment, and she can have a strong influence on her offspring's behaviour. This study investigated whether fearfulness in foals can be reduced through weekly exposure to usually frightening objects with a habituated mother during the first 8 weeks of life. Prior to foaling, mares (N = 22) were habituated to five initially fear-eliciting situations, including exposure to novel stationary and moving objects. At birth, the foals were randomly assigned to either a Demonstration group (N = 11) or a Control group (N = 11). Demonstration mares demonstrated habituation towards the objects to their foals once per week in weeks 1-8 post-partum. Control mares were inside the empty test arena with their foals for the same amount of time. The foals were tested at 8 weeks and 5 months of age in four standardised fear tests. Demonstration foals showed significantly reduced fear responses (behaviour and heart rate) and increased exploratory behaviour at both 8 weeks and 5 months of age. The effect was likely achieved through a combination of maternal transmission and individual learning. It is concluded that fearfulness in foals may be reduced through exposure to frightening objects together with their habituated mother during the first 8 weeks of life.

Cross-generational impact of a male murine pheromone 2-sec-butyl-4,5- dihydrothiazole in female mice

The current understanding of the activity of mammalian pheromones is that endocrine and behavioural effects are limited to the exposed individuals. Here, we demonstrate that the nasal exposure of female mice to a male murine pheromone stimulates expansion of mammary glands, leading to prolonged nursing of pups. Subsequent behavioural testing of the pups from pheromone-exposed dams exhibited enhanced learning. Sialic acid components in the milk are known to be involved in brain development. We hypothesized that the offspring might have received more of this key nutrient that promotes brain development. The mRNA for polysialyltransferase, which produces polysialylated neural cell adhesion molecules related to brain development,was increased in the brain of offspring of pheromone-exposed dams at post-natal day 10, while it was not different at embryonic stages, indicating possible differential brain development during early post-natal life.

Early-life nutritional effects on the female reproductive system

There is now considerable epidemiological and experimental evidence indicating that early-life environmental conditions, including nutrition, affect subsequent development in later life. These conditions induce highly integrated responses in endocrine-related homeostasis, resulting in persistent changes in the developmental trajectory producing an altered adult phenotype. Early-life events trigger processes that prepare the individual for particular circumstances that are anticipated in the postnatal environment. However, where the intrauterine and postnatal environments differ markedly, such modifications to the developmental trajectory may prove maladaptive in later life. Reproductive maturation and function are similarly influenced by early-life events. This should not be surprising, because the primordial follicle pool is established early in life and is thus vulnerable to early-life events. Results of clinical and experimental studies have indicated that early-life adversity is associated with a decline in ovarian follicular reserve, changes in ovulation rates, and altered age at onset of puberty. However, the underlying mechanisms regulating the relationship between the early-life developmental environment and postnatal reproductive development and function are unclear. This review examines the evidence linking early-life nutrition and effects on the female reproductive system, bringing together clinical observations in humans and experimental data from targeted animal models.

Re-considering the turn to biology in feminist theory

This article argues that feminist theorists should conceive of the life sciences not only as a factual resource but also as a figural resource. It proposes that in shifting our conceptual orientation to biological science from fact to figure, feminists will be able to give theoretical life to scientific findings about the ways in which social environments and material habitats are processes integral to our development, growth, and social and political well-being. The figuration of ourselves as specifically biocultural creatures will enable feminists to gain a stronger theoretical and analytic purchase on the ongoing mutual shaping of the biological and social dimensions of existence. This, in turn, will enable feminists to creatively re-imagine the fields and fora of feminist politics.

The biology of mammalian parenting and its effect on offspring social development

Parents know the transformative nature of having and caring for a child. Among many mammals, giving birth leads from an aversion to infant stimuli to irresistible attraction. Here, we review the biological mechanisms governing this shift in parental motivation in mammals. Estrogen and progesterone prepare the uterus for embryo implantation and placental development. Prolactin stimulates milk production, whereas oxytocin initiates labor and triggers milk ejection during nursing. These same molecules, interacting with dopamine, also activate specific neural pathways to motivate parents to nurture, bond with, and protect their offspring. Parenting in turn shapes the neural development of the infant social brain. Recent work suggests that many of the principles governing parental behavior and its effect on infant development are conserved from rodent to humans.

Cortisol administration increases hippocampal activation to infant crying in males depending on childhood neglect

Animal studies show that exposure to parental neglect alters stress regulation and can lead to neural hyposensitivity or hypersensitivity in response to cortisol, most pronounced in the hippocampus. Cortisol, the end product of the hypothalamic-pituitary-adrenal (HPA) axis, has also been related to parenting more directly, for example, in both sexes, cortisol levels increase when listening to infants crying, possibly to activate and facilitate effective care behavior. Severe trauma is known to negatively affect the HPA-axis in humans; however, it is unknown whether normal variation in parental care in the healthy population can alter sensitivity of the hippocampus to cortisol. Here, we investigate whether variation in experienced neglect changes neural sensitivity to cortisol when humans listen to infant crying, which is an unequivocal signal relevant for care behavior. In a placebo-controlled, within-subject neuroimaging study, we administered 40 mg cortisol to 21 healthy young males without children and used a validated task for measuring neural responses to infant crying. The Dutch version of the Childhood Trauma Questionnaire was used to index participants' early exposure to abuse and neglect. The data show that cortisol markedly increased hippocampal activation toward crying infants, and this effect varied significantly with parental neglect, even in our nonclinical subject sample. Without exposure to severe trauma or neglect, reduced self-experienced quality of parental care in the normal range already substantially increased hippocampal responsivity to cortisol. Altered hippocampal sensitivity to cortisol might be a cross-species marker for the risk of developing later life psychopathology.

Age- and sex-dependent effects of early life stress on hippocampal neurogenesis

Early life stress is a well-documented risk factor for the development of psychopathology in genetically predisposed individuals. As it is hard to study how early life stress impacts human brain structure and function, various animal models have been developed to address this issue. The models discussed here reveal that perinatal stress in rodents exerts lasting effects on the stress system as well as on the structure and function of the brain. One of the structural parameters strongly affected by perinatal stress is adult hippocampal neurogenesis. Based on compiled literature data, we report that postnatal stress slightly enhances neurogenesis until the onset of puberty in male rats; when animals reach adulthood, neurogenesis is reduced as a consequence of perinatal stress. By contrast, female rats show a prominent reduction in neurogenesis prior to the onset of puberty, but this effect subsides when animals reach young adulthood. We further present preliminary data that transient treatment with a glucocorticoid receptor antagonist can normalize cell proliferation in maternally deprived female rats, while the compound had no effect in non-deprived rats. Taken together, the data show that neurogenesis is affected by early life stress in an age- and sex-dependent manner and that normalization may be possible during critical stages of brain development.

Prenatal transport stress, postnatal maternal behavior, and offspring sex differentially affect seizure susceptibility in young rats

Epilepsy is a heterogeneous and chronic neurological condition of undefined etiology in the majority of cases. Similarly, the pathogenesis of the unprovoked seizures that lead to epilepsy is not known. We are interested in the factors that modify inherent seizure susceptibility, with a particular focus on those occurring during the prenatal and early postnatal periods. Female Sprague-Dawley rats were bred in-house or transported during pregnancy at one of two gestational days (G9 or G16). The effects of transport stress, maternal behavior, and offspring sex were then examined in terms of how they were related to provoked seizure susceptibility to kainic acid (KA) or a model of febrile convulsions (FCs) on postnatal day 14 (P14). We also examined the pattern of neuronal activation in the hippocampus and amygdala as indicated by the density of FosB protein immunoreactivity (FosB-ir). Results demonstrated only a small and inconsistent effect of transport alone, suggesting that the groups differed slightly prior to experimental manipulations. However, the influence of maternal behaviors such as licking and grooming (LG), arched back nursing (ABN), and dam-off time (DO) exerted a much stronger effect on the offspring. Dams designated as high LG gave birth to smaller litters, had pups that weighed less, had greater seizure susceptibility and severity, and had more FosB-ir neurons predominantly in the ventral hippocampus and the medial subnucleus of the amygdala (MeA). We also found a sex-dependent effect such that P14 males were smaller than their female littermates and had a greater seizure susceptibility and severity. Taken together, these results suggest an impact of prenatal and postnatal factors, as well as sex, on seizure susceptibility in young animals.

Behavioral and neurochemical characterization of maternal care effects on juvenile Sprague-Dawley rats

Maternal care represents a major constituent of early life environment and has the potential to modulate critical neurobehavioral responses to stress. The aim of the present study was to determine the effects of naturally occurring variations in maternal care on behavioral and neurochemical responses of juvenile Sprague-Dawley rats. A group of dams were classified based on their licking behavior in high and low licking-grooming mothers. Afterwards, the male offspring was tested in a series of behavioral tests: open field test (OFT), elevated plus maze (EPM) and forced swimming test (FST). Additionally, monoamine concentrations were determined post-mortem in three brain regions: hippocampus, ventral striatum and prefrontal cortex. Our findings suggest that maternal care variations have an effect on several anxiety-related behaviors in OFT and EPM but not in depression-like behaviors in FST. Such behavioral differences could be related to an increased DOPAC concentration and 5-HT turnover in prefrontal cortex. These evidences suggest that natural variations in maternal care modified some behavioral and neurochemical parameters related with anxiety and stress in this strain.

Constraints and flexibility in mammalian social behaviour: introduction and synthesis

This paper introduces a Theme Issue presenting the latest developments in research on the interplay between flexibility and constraint in social behaviour, using comparative datasets, long-term field studies and experimental data from both field and laboratory studies of mammals. We first explain our focus on mammals and outline the main components of their social systems, focusing on variation within- and among-species in numerous aspects of social organization, mating system and social structure. We then review the current state of primarily ultimate explanations of this diversity in social behaviour. We approach the question of how and why the balance between behavioural flexibility and continuity is achieved by discussing the genetic, developmental, ecological and social constraints on hypothetically unlimited behavioural flexibility. We introduce the other contributions to this Theme Issue against this background and conclude that constraints are often crucial to the evolution and expression of behavioural flexibility. In exploring these issues, the enduring relevance of Tinbergen's seminal paper 'On aims and methods in ethology', with its advocacy of an integrative, four-pronged approach to studying behaviour becomes apparent: an exceptionally fitting tribute on the 50th anniversary of its publication.

Phenotypic plasticity and integration in the mangrove rivulus (Kryptolebias marmoratus): a prospectus

The mangrove rivulus (Kryptolebias marmoratus) is a small fish native to mangrove ecosystems in Florida, the Caribbean, Central America, and South America. This species is one of only two self-fertilizing, hermaphroditic vertebrates capable of producing offspring that are genetically identical to both the parent and all siblings. Long bouts of selfing result in individuals with completely homozygous genotypes, effectively allowing for the production of "clones." Rivulus is also extremely sensitive to environmental change, both during development and adulthood. Life-history traits, behavior, physiology, morphology, and even sexual phenotype are shaped to a large extent by the interaction of genes with the environment, and many of these traits appear to co-vary. True reaction norms can be generated for this species in much the same way as has been done for clonally reproducing invertebrates and plants that have contributed immensely to our understanding of the evolution of phenotypic plasticity. That is, rivulus provides the opportunity to place individuals with identical genotypes in many different environments at any point during ontogeny or adulthood. In addition, rivulus populations are characterized by high genotypic diversity, a luxury not afforded by many clonal vertebrates, which allows us to evaluate variation among genotypes in the shape of reaction norms and in patterns of covariance among traits. We provide background information on phenotypic plasticity and phenotypic integration, coupled with a description of characteristics that we feel qualify rivulus as a potentially powerful model in which to study the evolution of reaction norms and covariance among traits.

Preliminary genetic imaging study of the association between estrogen receptor-α gene polymorphisms and harsh human maternal parenting

A failure of neural changes initiated by the estrogen surge in late pregnancy to reverse the valence of infant stimuli from aversive to rewarding is associated with dysfunctional maternal behavior in nonhuman mammals. Estrogen receptor-α plays the crucial role in mediating these neural effects of estrogen priming. This preliminary study examines associations between estrogen receptor-α gene polymorphisms and human maternal behavior. Two polymorphisms were associated with human negative maternal parenting. Furthermore, hemodynamic responses in functional magnetic resonance imaging to child stimuli in neural regions associated with social cognition fully mediated the association between genetic variation and negative parenting. This suggests testable hypotheses regarding a biological pathway between genetic variants and dysfunctional human maternal parenting.

Beyond Licking and Grooming: Maternal Regulation of Infant Stress in the Context of Routine Care

Rodent epigenetic models of early maternal care have demonstrated that natural variations in maternal behavior shape the development of stress reactivity and social behavior in offspring. Rodent models have also revealed the "hidden" regulatory functions of specific dimensions of maternal behavior. Here we present research that has extended rodent models of early care to the study of biobehavioral development in human infants. Research showing contemporaneous and predictive associations between quality of maternal caregiving behavior (MCB) and early biobehavioral development is reviewed. New evidence demonstrating the proximal effects of MCB in early infancy on infant stress reactivity is reported and highlights the value of examining early parenting at the specific behavioral level. Future research should extend this domain-specific approach to the study of infant contributions to the early care environment. Implications for intervention are discussed.

Oxytocin and social affiliation in humans

A conceptual model detailing the process of bio-behavioral synchrony between the online physiological and behavioral responses of attachment partners during social contact is presented as a theoretical and empirical framework for the study of affiliative bonds. Guided by an ethological behavior-based approach, we suggest that micro-level social behaviors in the gaze, vocal, affective, and touch modalities are dynamically integrated with online physiological processes and hormonal response to create dyad-specific affiliations. Studies across multiple attachments throughout life are presented and demonstrate that the extended oxytocin (OT) system provides the neurohormonal substrate for parental, romantic, and filial attachment in humans; that the three prototypes of affiliation are expressed in similar constellations of social behavior; and that OT is stable over time within individuals, is mutually-influencing among partners, and that mechanisms of cross-generation and inter-couple transmission relate to coordinated social behavior. Research showing links between peripheral and genetic markers of OT with concurrent parenting and memories of parental care; between administration of OT to parent and infant's physiological readiness for social engagement; and between neuropeptides and the online synchrony of maternal and paternal brain response in social-cognitive and empathy networks support the hypothesis that human attachment develops within the matrix of biological attunement and close behavioral synchrony. The findings have conceptual implications for the study of inter-subjectivity as well as translational implications for the treatment of social disorders originating in early childhood, such as autism spectrum disorders, or those associated with disruptions to early bonding, such as postpartum depression or child abuse and neglect. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Toward understanding how early-life social experiences alter oxytocin- and vasopressin-regulated social behaviors

The early-life social environment has profound effects on brain development and subsequent expression of social behavior. Oxytocin and vasopressin are expressed and released in the brain and are important regulators of social behavior. Accordingly, the early social environment may alter social behaviors via changes in the oxytocin and/or vasopressin systems. To test this hypothesis, and to gain mechanistic insights, rodent models mimicking either a deprived (e.g. maternal separation) or enriched (e.g. neonatal handling) early social environment have been utilized. Findings indeed show that differences in the quality of the early social environment are associated with brain region-specific alterations in oxytocin and vasopressin expression and oxytocin receptor and vasopressin 1a receptor binding. Early social environment-induced changes in oxytocin and vasopressin systems were associated with changes in several forms of social behavior, including maternal care, aggression, play-fighting, and social recognition. First studies provide evidence for a causal link between altered vasopressin responsiveness and impairments in social recognition in rats exposed to maternal separation and a role for epigenetic mechanisms to explain persistent increases in vasopressin expression in mice exposed to maternal separation. Overall, initial findings suggest that oxytocin and vasopressin systems may mediate early social environment-induced alterations in social behavior. Additional comprehensive studies will be necessary to advance our understanding to what extent changes in oxytocin and vasopressin underlie early social environment-induced alterations in social behavior. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.