What cortisol can tell us about the costs of sociality and reproduction among free-ranging rhesus macaque females on Cayo Santiago

Pterion variation in the skulls of rhesus macaques from Cayo Santiago: Inheritance, development, and pathology

The pterion is the sutural juncture of the frontal, parietal, sphenoidal, temporal, and zygomatic bones on the lateral aspect of the cranium. As a craniometric landmark, the pterion has a taxonomic valence, in addition to a common neurosurgical entry point in medicine. Variation in the articulation patterns at the pterion have been documented between primate species yet have a high degree of uniformity within species, suggesting a genetic control for this complex region of the skull. In this study, pterion pattern variation was investigated in 1627 Rhesus macaque crania of the Cayo Santiago colony. The colony's associated skeletal collections accompany known age, sex, and maternal lineages. Pterion pattern prevalence rates were tested against matrilines, as well as cranial shape, and cranial sutural fusion ages (including individuals with prematurely fused sutures). Five patterns were identified, the most prominent being the prevailing Old World Monkey frontotemporal (FT) articulation (83.4%). The relative frequency of those not exhibiting the FT pattern was found to vary considerably between matrilineal families (p = 0.037), ranging from 5.3% to 34.2%. Mothers with the non-FT pterion pattern were three times as likely to bear non-FT offspring. Cranial shape additionally varied with pterion type. Males exhibiting zygomaticotemporal (ZT) and sphenoparietal (SP) articulations possessed a relatively longer and narrower cranium than those with the default FT type (p = < 0.001). Cranial sutural fusion ages were not found to differ between pterion types, though all individuals with craniosynostosis (6; 0.38%) exhibited the FT type. The study provided strong evidence for a genetic source for pterion pattern as well as outlining a relatively novel relationship with cranial shape and sutural fusion ages. A unifying explanation may lie in those genes involved in both sutural and craniofacial development, or in the variation of brain growth processes channeling sutural articulation at the pterion. Both may be heritable and responsible for producing observed matrilineal differences in the pterion.

Visuo-frontal interactions during social learning in freely moving macaques

Social interactions represent a ubiquitous aspect of our everyday life that we acquire by interpreting and responding to visual cues from conspecifics1. However, despite the general acceptance of this view, how visual information is used to guide the decision to cooperate is unknown. Here, we wirelessly recorded the spiking activity of populations of neurons in the visual and prefrontal cortex in conjunction with wireless recordings of oculomotor events while freely moving macaques engaged in social cooperation. As animals learned to cooperate, visual and executive areas refined the representation of social variables, such as the conspecific or reward, by distributing socially relevant information among neurons in each area. Decoding population activity showed that viewing social cues influences the decision to cooperate. Learning social events increased coordinated spiking between visual and prefrontal cortical neurons, which was associated with improved accuracy of neural populations to encode social cues and the decision to cooperate. These results indicate that the visual-frontal cortical network prioritizes relevant sensory information to facilitate learning social interactions while freely moving macaques interact in a naturalistic environment.

Differential effects of early life adversity on male and female rhesus macaque lifespan

Early life adversity predicts shorter adult lifespan in several animal taxa. Yet, work on long-lived primate populations suggests the evolution of mechanisms that contribute to resiliency and long lives despite early life insults. Here, we tested associations between individual and cumulative early life adversity and lifespan on rhesus macaques at the Cayo Santiago Biological Field Station using 50 years of demographic data. We performed sex-specific survival analyses at different life stages to contrast short-term effects of adversity (i.e., infant survival) with long-term effects (i.e., adult survival). Female infants showed vulnerability to multiple adversities at birth, but affected females who survived to adulthood experienced a reduced risk later in life. In contrast, male infants showed vulnerability to a lower number of adversities at birth, but those who survived to adulthood were negatively affected by both early life individual and cumulative adversity. Our study shows profound immediate effects of insults  on female infant cohorts and suggests that affected female adults are more robust. In contrast, adult males who experienced harsh conditions early in life showed an increased mortality risk at older ages as expected from hypotheses within the life course perspective. Our analysis suggests sex-specific selection pressures on life histories and highlights the need for studies addressing the effects of early life adversity across multiple life stages.

Coming to the Caribbean-acclimation of Rhesus macaques (Macaca mulatta) at Cayo Santiago

OBJECTIVES

To investigate whether the Cayo Santiago, Puerto Rico (Latitude: 18.1564°N; temperature range 19°C to 32°C) rhesus macaque population has acclimated to their tropical island conditions since arriving from Lucknow, India (Latitude: 26.8470°N; temperature range 8°C to 41°C) in 1938.

MATERIALS AND METHODS

Using the derived skeletal collection, measurements were taken of long bone lengths, diaphyseal circumference, and body weight using 635 (237 males and 398 females) skeletally mature individuals. Measurements sampled colony members born over a 51-year time span at Cayo Santiago, from 1951 to 2002.

RESULTS

Results demonstrated that body weights and diaphyseal circumferences significantly declined in both males and females. Long bone lengths relative to body weight and diaphyseal circumference also increased in females. Whereas body weight, long bone length and diaphyseal circumference declined at near parallel rates in males.

DISCUSSION

The population has acclimated to homogenous, tropical, conditions of the Caribbean island since their arrival over 80 years ago. Trends in both sexes aligned with Bergmann's rule, though females displayed a greater decline in body weight, as well as greater affinity with Allen's rule, than did males. Buffering effects related to male competition may be responsible for this discrepancy. Overall, the Cayo Santiago populations, as shown over a significant period (1951-2002) of their history, have acclimated to their island conditions by decreasing in size and altering body proportions.

Social roles influence cortisol levels in captive Livingstone's fruit bats (Pteropus livingstonii)

A critical component of conserving and housing species ex situ is an explicit scientific understanding of the physiological underpinnings of their welfare. Cortisol has been repeatedly linked to stress, and therefore used as an indicator of welfare for many species. In order to measure cortisol in the Livingstone's fruit bat (Pteropus livingstonii; a critically endangered keystone species) without disturbing the captive population, we have developed and validated a non-invasive, novel hormone extraction procedure and faecal glucocorticoid assay. A total of 92 faecal samples, 73 from the P. livingstonii breeding colony at Jersey Zoo, Channel Islands and 19 samples from P. livingstonii housed at Bristol Zoological Gardens, UK, have been collected and analyzed. Mixed-effect modelling of the influence of physiological state variables on cortisol concentration revealed that lactating females had higher cortisol levels than non-lactating females, indicating that our assay is measuring biologically relevant hormone concentrations. Males and older bats also had higher cortisol than non-lactating females and younger individuals. Further analysis applied social network methodology to compare the cortisol levels of bats with different social roles. We found that individuals that linked social groups possessed higher than average cortisol levels and conversely, individuals with high-quality, positive relationships had lower cortisol levels. These results demonstrate, for the first time in a bat species, social mediation of stress hormones. Lastly, the frequency of vocalisation was found to positively correlate with cortisol concentration in males, suggesting that this behaviour may be used by animal management as a visual indicator of a bat's hormonal status. Hence, this research has provided unique insights and empirical scientific knowledge regarding the relationship between the physiology and social behaviour of P. livingstonii, therefore allowing for recommendations to be made to optimise bat welfare at the individual level.

Multigenerational Social Housing and Group-Rearing Enhance Female Reproductive Success in Captive Rhesus Macaques (Macaca mulatta)

Simple Summary

It is currently common practice to house non-human primates at biomedical research facilities, e.g., rhesus macaques, in social groups. To enhance female reproductive success, peer groups are formed. In these breeding groups, infants are taken from their mother at an age of ten months and housed with animals of approximately the same age. Yet for welfare, leaving offspring with their mother and allowing multigenerational groups including families is preferred. This argues that a trade-off between female reproductive success and welfare exists. In this retrospective study we investigated the differences in female rhesus macaque reproductive success between peer groups and multigenerational groups. Our results show that females in multigenerational groups have more births per year and have higher offspring survival compared with those in peer groups. Thus, housing rhesus macaques in multigenerational groups provides a win−win situation, rather than a trade-off, in which female reproductive success and animal welfare can simultaneously be optimized.

Abstract

To optimize costs and reproductive success, rhesus macaques in biomedical primate research facilities are often peer-reared. Older, dependent infants are typically removed from their natal group to enhance female reproduction. The minimal husbandry age-norm of infant removal is ten months. These practices deviate from species-specific behavior and may reduce welfare, suggesting a trade-off between female reproduction and welfare. However, the effect of breeding group type and rearing history on female reproductive success (i.e., birth rate; inter-birth interval (IBI); offspring survival) is unclear. This retrospective study investigated whether group type (i.e., peer groups versus multigenerational groups) and rearing history (i.e., peer- or hand-reared; group-reared with peer- or hand-reared mother; group-reared) affected female reproductive success in captive rhesus macaques. Data on female reproduction between 1996 and 2019 were collected at the Biomedical Primate Research Centre, Rijswijk. Birth rates were higher in multigenerational breeding groups than in peer groups. Moreover, group-reared females had higher offspring survival than peer- or hand-reared females. IBI was not affected by breeding group type or female rearing history. However, females in both peer and multigenerational breeding groups typically conceived earlier after giving birth than the husbandry infant removal age-norm of ten months. Thus, infant removal at an age of ten months does not enhance a female’s reproduction. Altogether, female reproduction and non-human primate welfare can simultaneously be optimized through multigenerational breeding groups and group-rearing.

Low rank and primiparity increase fecal glucocorticoid metabolites across gestation in wild geladas

Integrative behavioral ecology requires accurate and non-invasive measures of hormone mediators for the study of wild animal populations. Biologically sensitive assay systems for the measurement of hormones and their metabolites need to be validated for the species and sample medium (e.g. urine, feces, saliva) of interest. Where more than one assay is available for hormone (metabolite) measurement, antibody selection is useful in identifying the assay that tracks changes in an individuaĺs endocrine activity best, i.e., the most biologically sensitive assay. This is particularly important when measuring how glucocorticoids (GCs) respond to the subtle, additive effects of acute stressors during a predictable metabolic challenge, such as gestation. Here, we validate a group-specific enzyme immunoassay, measuring immunoreactive 11β-hydroxyetiocholanolone, for use in a wild primate, geladas (Theropithecus gelada). This group-specific assay produced values correlated with those from a previously validated double-antibody, corticosterone ¹²⁵I radioimmunoassay. However, the results with the group-specific assay showed a stronger response to an ACTH challenge and identified greater variation in gelada immunoreactive fecal glucocorticoid metabolites (iGCMs) compared with the corticosterone assay, indicating a higher biological sensitivity for assessing adrenocortical activity. We then used the group-specific assay to: (1) determine the normative pattern of iGCM levels across gelada gestation, and (2) identify the ecological, social, and individual factors that influence GC output for pregnant females. Using a general additive mixed model, we found that higher iGCM levels were associated with low rank (compared to high rank) and first time mothers (compared to multiparous mothers). This study highlights the importance of assay selection and the efficacy of group-specific assays for hormonal research in non-invasively collected samples. Additionally, in geladas, our results identify some of the factors that increase GC output over and above the already-elevated GC concentrations associated with gestation. In the burgeoning field of maternal stress, these factors can be examined to identify the effects that GC elevations may have on offspring development.

Changes in social behavior and fecal glucocorticoids in a Japanese macaque (Macaca fuscata) carrying her dead infant

Maternal care towards dead infants has been observed in many wild and captive mammals, but the consequences of this behavior for social interactions and the physiological status of the mother remain elusive. Here, we report changes in rates of aggression and grooming time, and fecal glucocorticoid (fGC) levels in a free-ranging female Japanese macaque (Macaca fuscata) that carried her dead infant for 20 days. Our observations revealed that when carrying the dead infant, the mother showed increased rates of grimace, avoidance, and human-directed behaviors, along with reduced allogrooming time and fleeing from other individuals. Postpartum fGC levels were comparable to those of non-pregnant and non-lactating females, suggesting that the energetic costs and stress of carrying a dead infant are low. Our findings indicate that carrying a dead neonate can have three profound consequences on the mother: increased fearful behavior, decreased allogrooming, and a rapid return to baseline fGC levels. We hypothesize that dead infant-carrying may have evolved as a strategy to mitigate stress from infant loss. These findings have implications for our understanding of grief in nonhuman primates and can impact management protocols surrounding deaths in captive social groups.

Repeatable glucocorticoid expression is associated with behavioural syndromes in males but not females in a wild primate

Behavioural syndromes are a well-established phenomenon in human and non-human animal behavioural ecology. However, the mechanisms that lead to correlations among behaviours and individual consistency in their expression at the apparent expense of behavioural plasticity remain unclear. The 'state-dependent' hypothesis posits that inter-individual variation in behaviour arises from inter-individual variation in state and that the relative stability of these states within an individual leads to consistency of behaviour. The endocrine stress response, in part mediated by glucocorticoids (GCs), is a proposed behavioural syndrome-associated state as GC levels are linked to an individual's behavioural responses to stressors. In this study, in wild Barbary macaques (Macaca sylvanus), consistent inter-individual differences were observed in both sexes for GC activity (faecal glucocorticoid, fGC concentrations), but not GC variation (coefficient of variation in fGC concentrations). The expression of the behavioural syndrome 'Excitability' (characterized by the frequencies of brief affiliation or aggressive interactions) was related to GC activity in males but not in females; more 'excitable' males had lower GC activity. There was no relationship in females between any of the behavioural syndromes and GC activity, nor in either sex with GC variation. The negative relationship between GC activity and Excitability in males provides some support for GC expression as a behavioural syndrome-generating state under the state-dependent framework. The absence of this relationship in females highlights that state-behavioural syndrome associations may not be generalizable within a species and that broader sex differences in state need to be considered for understanding the emergence and maintenance of behavioural syndromes.

Postcranial Skeletal Differences in Free-Range and Captive-Born Primates

Skeletal morphology is important in evolutionary, genetic, developmental, physiological, and functional studies. Although samples from free-ranging individuals may be preferable, constraints of sample size, demography, or conservation status may necessitate the inclusion of captive-born individuals. Captivity may be associated with physical, physiological, or behavioral differences that may affect skeletal form. This study assesses differences in postcranial skeletal form between free-range and captive-born Macaca mulatta and Saguinus oedipus. Samples included free-range M. mulatta from Cayo Santiago (Caribbean Primate Research Center) and captive-born macaques from the Wisconsin National Primate Research Center. S. oedipus samples included free-range born and captive-born individuals from the Oak Ridge Associated Universities Marmoset Research Center. Twenty-four dimensions of various bones, including the scapula, upper limb, innominate and lower limb, were recorded for adults. Age of epiphyseal closure was recorded for immature captive-born M. mulatta. Analysis of variance and principal component analyses tested significant differences between free-range born and captive-born individuals in each species. Significant differences were present in size and shape of postcrania between free-range and captive-born within taxa. Free-range macaques were larger than captive-born macaques, but this pattern did not consistently carry over to the Saguinus samples. Shape differences, while present throughout the skeleton, were especially prominent in the scapula. Differences in developmental timing, nutrition, and physical activity can be expected to contribute to the observed differences in postcranial skeletal form. These differences should be considered when captive-born primates are included in morphological or evolutionary studies. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:761-774, 2019. © 2018 Wiley Periodicals, Inc.

Male-inflicted wounds have opposite effects on hair cortisol for captive male and female rhesus macaques (Macaca mulatta) following new group formation

Sexual dimorphism in body size, aggression, and dispersal patterns may affect the degree to which males and females perceive aggression from either sex as stressful. Whereas male macaques typically disperse to new groups at maturity, thus encountering many unfamiliar individuals of both sexes, females are philopatric, usually only encountering unfamiliar males who transfer into their natal groups. In rare circumstances, however, group fusions can expose both males and females to many novel individuals, which often increases aggression. Here, we use a captive new group formation of rhesus macaques (Macaca mulatta) as a model of social instability during fusions and examine differences in male and female chronic stress responses to male-pattern and female-pattern trauma (i.e., trauma inflicted by males or by females, respectively). We found that male- but not female-pattern traumas predicted hair cortisol concentrations during the first 9 months after new group formation, but in opposite ways for males and females. A greater number of male-pattern traumas was linked to elevated hair cortisol concentrations in females but slightly lower hair cortisol concentrations in males. We suggest that the apparent importance of male-pattern trauma, but not female-pattern-trauma, in predicting higher hair cortisol concentrations in females can be attributed to the more acutely intense but less persistent nature of male aggression toward females.

Social and ecological drivers of reproductive seasonality in geladas

Many nonseasonally breeding mammals demonstrate some degree of synchrony in births, which is generally associated with ecological factors that mediate fecundity. However, disruptive social events, such as alpha male replacements, also have the potential to affect the timing of female reproduction. Here, we examined reproductive seasonality in a wild population of geladas (Theropithecus gelada) living at high altitudes in an afro-alpine ecosystem in Ethiopia. Using 9 years of demographic data (2006-2014), we determined that, while females gave birth year-round, a seasonal peak in births coincided with peak green grass availability (their staple food source). This post-rainy season "ecological peak" in births meant that estimated conceptions for these births occurred when temperatures were at their highest and mean female fecal glucocorticoid concentrations were at their lowest. In addition to this ecological birth peak, we also found a separate birth peak that occurred only for females in groups that had experienced a recent replacement of the dominant male (i.e., a takeover). Because new dominant males cause abortions in pregnant females and kill the infants of lactating females, takeovers effectively "reset" the reproductive cycles of females in the group. This "social birth peak" was distinct from the ecological peak and was associated with higher rates of cycling and conceptions overall and higher glucocorticoid levels immediately following a takeover as compared to females that did not experience a takeover. These data demonstrate that social factors (in this case, male takeovers) can contribute to population-level reproductive seasonality above and beyond group-level reproductive synchrony.

Alpha male status and availability of conceptive females are associated with high glucocorticoid concentrations in high-ranking male rhesus macaques (Macaca mulatta) during the mating season

The relationship between male mating opportunities, stress, and glucocorticoid concentrations is complicated by the fact that physiological stress and glucocorticoid concentrations can be influenced by dominance rank, group size, and the stability of the male dominance hierarchy, along with ecological factors. We studied the three highest-ranking males in nine different social groups within the same free-ranging population of rhesus macaques on Cayo Santiago, Puerto Rico, during the mating season, to examine variation in glucocorticoid concentrations in relation to number of females that conceived each month, alpha status, number of adult males in a group, and male rank hierarchy stability. We found that glucocorticoid concentrations were highest in the early mating season period when more females conceived in each group and declined linearly as the mating season progressed and the number of conceptive females decreased. Alpha males had significantly higher mean monthly glucocorticoid concentrations than other high-ranking males throughout the study period. Male age, number of adult males in a group, and hierarchy stability were not significantly associated with glucocorticoid concentrations. Our findings suggest that alpha males may experience significantly higher levels of physiological stress than their immediate subordinates and that this stress coincides with the period of the mating season when most conceptions occur.

Physiologic Correlates of Interactions between Adult Male and Immature Long-tailed Macaques (Macaca fascicularis)

Interactions between adult males and immature members of the same species are rare in most mammals; in contrast, an estimated 40% of primate species are characterized by an involvement of males in the social life of infants and juveniles. The proximate mechanisms of male-infant interactions are largely unstudied, and very few direct benefits for males have been proposed, especially in uniparental species in which the identity of the male parent is uncertain. In this study, we aimed to assess the relationship among behavioral and physiologic stress, health, and various affiliative behaviors initiated by adult males toward infants and juveniles in long-tailed macaques. We hypothesized that males that spent more time with infants and juveniles would have lower physiologic and social stress and better health than males with less interaction. We observed 2 troops of macaques with established social hierarchies (n = 18 in troop 1 and n = 8 in troop 2), each occupying a stable area within the enclosure, for more than 200 h. Fecal samples were used to assess cortisol levels as a measure of physiologic stress, and blood samples were collected to measure oxytocin levels as an index of social responsiveness. Our results indicated that male affiliative behavior directed toward immature animals was significantly higher in the troop characterized by more social conflicts; midranking males interacted more with infants than high- and low-ranking males in both troops. Furthermore, the DHEA:cortisol ratio, a physiologic index of resilience and coping, was positively correlated with males' affiliative responses, suggesting a neuroprotective role of male-infant interactions. In summary, our data support a proximate mechanism of alloparenting or paternal behavior in uniparental species. Interacting with infants and juveniles could provide an immediate neurobiologic benefit to adult males by facilitating adaptive coping responses to social tensions.

Making the Case for 'Power Abuse Disorder' as a Nosologic Entity

The development of societies and cultures arguably is based on the ability of human primates to form hierarchies in which some individuals acquire and wield power, that is, control resources and influence and control the behavior of their conspecifics. In the following, we focus on the type of human primate power wielding that (a) harms and (b) produces excessive negative emotions in (1) the victim(s) of the power wielder and (2) the power wielder her/himself. If such a harmful behavior of the power wielder is not accompanied by an ethically justifiable benefit for the involved human primate groups, it can be considered "power abuse." We propose to term the associated behaviors, cognitions, and emotions of the power wielder as "power abuse disorder" (PAD). This behavior results from what we consider addictive behavior of the power abuse disordered (PADed) power wielder. PAD can be diagnosed on the basis of the World Health Organization's criteria for "dependence syndrome" as listed in the International Classification of Diseases version 10. We will demonstrate that many PADed individuals may very likely carry the Zeitgeist diagnosis "burnout." This article reviews the current understanding of the neural correlates of PAD and suggests future research. Based on the available evidence, PAD seems to be associated with a dysfunction of the mesocorticolimbic dopamine system, rendering PADed individuals vulnerable for psychostimulant abuse/dependence, and suggesting specific pharmacotherapeutic approaches to treat PAD.

An Overly Permissive Extension

In this article, I describe how the current practice of classifying as a stressor any event that is accompanied by a change in any of a number of biological or behavioral measures-even when it is not accompanied by a long-term compromise in an organism's health or capacity to cope with daily challenges-has limited the utility of this concept. This permissive posture, which began with Selye's writings more than 65 years ago, is sustained by the public's desire for a simple term that might explain the tension generated by the threat of terrorists, growing economic inequality, increased competiveness in the workplace or for admission to the best universities, rogue nuclear bombs, and media reports of threats to health in food and water. I believe that the concept stress should be limited to select events that pose a serious threat to an organism's well-being or discarded as too ambiguous to be theoretically useful.

The janus face of stress on reproduction: from health to disease

Parenthood is a fundamental feature of all known life. However, infertility has been recognized as a public health issue worldwide. But even when the offspring are conceived, in utero problems can lead to immediate (abortion), early (birth), and late (adulthood) consequences. One of the most studied factors is stress. However, stress response is, per se, of adaptive nature allowing the organism to cope with challenges. Stressors lead to deterioration if one is faced with too long lasting, too many, and seemingly unsolvable situations. In stress adaptation the hypothalamus-pituitary-adrenocortical axis and the resulting glucocorticoid elevation are one of the most important mechanisms. At cellular level stress can be defined as an unbalance between production of free radicals and antioxidant defenses. Oxidative stress is widely accepted as an important pathogenic mechanism in different diseases including infertility. On the other hand, the goal of free radical production is to protect the cells from infectious entities. This review aims to summarize the negative and positive influence of stress on reproduction as a process leading to healthy progeny. Special emphasis was given to the balance at the level of the organism and cells.