Maternal stress effects on infant development in wild Verreaux's sifaka (Propithecus verreauxi)

All together now: Assessing variation in maternal and nonmaternal handling of wild Colobus vellerosus infants

Primatologists have a long-standing interest in the study of maternal care and nonmaternal handling (NH) of infants stemming from recognition that early social relationships can have enduring consequences. Though maternal care and NH often include expression of similar behaviors, they are regularly studied in isolation from each other with nonoverlapping terminology, thereby overlooking possible interplay between them and obfuscating potential developmental ramifications that ensue from trade-offs made between maternal (MH) and NH during infancy. To that end, identifying how MH and NH patterns interact and contribute to the total handling (TH) infants receive is a critical first step. We present durational handling data collected from 25 wild Colobus vellerosus infants from 2016 to 2017 and assess the relationships between TH, MH, and NH. Patterns of social affiliation are shaped in part by surrounding context, and therefore, we also assess whether NH and TH differ in their responsivity to various infant and social group characteristics. Ninety-four percent of observed handling was MH, while just 5.5% was NH. Young infants who received more MH (excluding nursing) also received more NH; there was no relationship between the two in older infants. Infants in larger groups participated in more handling of all types. Additionally, NH time was associated with infant sex and group stability. Non-nursing TH time was associated with group stability and infant cohort size. Though NH variation likely confers social-networking advantage, in this population NH is not a major contributor to TH and would not effectively replace reduced MH. The positive association between MH and NH during early infancy suggests that colobus mothers may play a mediating role in shaping infant socialization. This is a first step in elucidating how different forms of handling relate to one another in wild primates and in identifying the impact of handling on infant socialization.

Early prenatal but not postnatal glucocorticoid exposure is associated with enhanced HPA axis activity into adulthood in a wild primate

The hypothalamic-pituitary-adrenal (HPA) axis plays a dual role in the biology of developmental plasticity in mammals, including humans-HPA axis activity not only provides the input for, but is also a target of, offspring developmental plasticity. To investigate the understudied effects of exposure timing, this study quantified maternal HPA axis activity during each half of gestation as well as during early lactation and assessed its effect on offspring HPA axis activity in a cross-sectional sample of infant, juvenile and adult Assamese macaques (Macaca assamensis). To add ecological validity to experimental studies under laboratory conditions, macaques were studied in the wild. Increased maternal faecal glucocorticoid (GC) metabolite levels experienced early in gestation, but not postnatal exposure during lactation were associated with increased offspring HPA axis activity from infancy into adulthood. Building on prior findings, this study indicates that significant timing effects not only influence the presence, magnitude and direction, but also the consistency of maternal GC effects on offspring HPA axis function.

Establishment and Validation of Fecal Secretory Immunoglobulin A Measurement for Intestinal Mucosal Health Assessment in Wild Lemurs

The measurement of biomarkers in blood and excreta can enable immune status assessment and provide prognostic information on individual health outcomes. In this respect, the fecal measurement of secretory immunoglobulin A (sIgA), the primary mammalian antibody for mucosal defense, has recently received increased interest in a few anthropoid primates, but a fecal sIgA assay for use in strepsirrhine primates has not yet been reported. Here, we develop and analytically validate a cost-effective in-house sandwich enzyme immunoassay for the extraction and measurement of sIgA in feces of redfronted lemurs (Eulemur rufifrons). We also tested a simple method for sIgA extraction that can be used under remote field conditions and undertook experiments to assess the robustness of sIgA concentrations to variation in processing and storage conditions of fecal extracts. Our analytical validation revealed that the assay recognizes immunoreactive sIgA in redfronted lemur feces, that sIgA can be measured accurately with no potential interference from the fecal matrix, and that assay reagents and performance are highly stable over time. The field-friendly extraction procedure produced sIgA results strongly correlated with those generated by a standard laboratory extraction method. Short-term storage at room temperature resulted in a slight decline in sIgA concentrations, whereas freezing extracts at -20°C kept sIgA levels stable for at least 3 months. Longer-term storage of >5 months, however, led to a significant decline of sIgA concentrations. Multiple freeze-thaw cycles did not affect sIgA levels. This study, therefore, provides the basis for measuring fecal sIgA in lemurs and possibly other strepsirrhines. When samples are processed properly and stored frozen, and when sIgA analysis can be performed within 3 months upon sample collection, fecal sIgA measurements can become a valuable tool for monitoring aspects of immunity and health in both zoo-housed and wild-living lemurs.

DO HEALTHY COQUEREL'S SIFAKAS IN CAPTIVITY HAVE UNUSUALLY LOW CIRCULATING CORTISOL?

Cortisol, and other glucocorticoids, are routinely used as markers of physiological stress in wildlife. Typically, stress activates the hypothalamic-pituitary-adrenal (HPA) axis, with adrenocorticotropic hormone (ACTH) signaling the adrenal glands to release cortisol. Nevertheless, recent anecdotes in captive Coquerel's sifakas (Propithecus coquereli), strepsirrhine primates that are difficult to maintain under human care, may challenge the assumption that physiological stress universally increases circulating cortisol. Here, the authors ask if low circulating cortisol and minimal response to adrenal stimulation might be hallmarks of outwardly healthy sifakas in captivity. Comparative ACTH stimulation or control tests were performed in 10 Coquerel's sifakas and six ring-tailed lemurs (Lemur catta) at the Duke Lemur Center (DLC). At baseline, sifakas had average cortisol concentrations of just 0.67 µg/dl, whereas those of ring-tailed lemurs averaged 12.53 µg/dl. Stressful pre-experiment procedures, including kenneling and handling, activated the HPA axis in ring-tailed lemurs, masking further cortisol release from ACTH administration; however, neither these procedures nor exogenous ACTH raised cortisol concentrations in sifakas. Additionally, cortisol in dozens of serum samples from DLC sifakas banked over 17 yr was assayed. Across samples, cortisol concentrations averaged just 0.49 µg/dl and did not vary by animal sex, age, or housing condition. Comparable samples from two individual sifakas in sepsis at the end of life (4.28 and 21.88 µg/dl) indicate that the assay does capture meaningful variation in cortisol in captive sifakas, although robust biological validation is needed. Currently there is a lack of comparative data from wild Coquerel's sifakas that might determine if these unusual endocrine patterns are characteristic of the species or a function of captivity. If the latter, chronic stress in captivity could lead to a downregulated HPA axis, with persistent hypocortisolism perhaps contributing to the Coquerel's sifaka's susceptibility to infection under human management.

Parasitism in viviparous vertebrates: an overview

The reproductive mode of viviparity has independently evolved in various animal taxa. It refers to the condition in which the embryos or young develop inside the female's body during gestation, providing advantages such as protection, nutrition, and improved survival chances. However, parasites and diseases can be an evolutionary force that limit the host's resources, leading to physiological, morphological, and behavioral changes that impose additional costs on both the pregnant female and her offspring. This review integrates the primary literature published between 1980 and 2021 on the parasitism of viviparous hosts. We describe aspects such as reproductive investment in females, offspring sex ratios, lactation investment in mammals, alterations in birth intervals, current reproductive investment, variations between environments, immune system activity in response to immunological challenges, and other factors that can influence the interaction between viviparous females and parasites. Maintaining pregnancy incurs costs in managing the mother's resources and regulating the immune system's responses to the offspring, while simultaneously maintaining an adequate defense against parasites and pathogens. Parasites can significantly influence this reproductive mode: parasitized females adjust their investment in survival and reproduction based on their life history, environmental factors, and the diversity of encountered parasites.

Conceptual and analytical approaches for modelling the developmental origins of inequality

In many species, individuals that experience harsh conditions during development have poor health and fitness outcomes in adulthood, compared with peers that do not. These early-life contributions to inequality are often attributed to two classes of evolutionary hypotheses: Developmental Constraints (DC) models, which focus on the deleterious effects of low-quality early-life environments, and Predictive Adaptive Response (PAR) hypotheses, which emphasize the costs individuals incur when they make incorrect predictions about conditions in adulthood. Testing these hypotheses empirically is difficult for conceptual and analytical reasons. Here, we help resolve some of these difficulties by providing mathematical definitions for DC, PAR (particularly focusing on 'external' PAR) and related concepts. We propose a novel, quadratic regression-based statistical test derived from these definitions. Our simulations show that this approach markedly improves the ability to discriminate between DC and PAR hypotheses relative to the status quo approach, which uses interaction effects. Simulated data indicate that the interaction effects approach often conflates PAR with DC, while the quadratic regression approach yields high sensitivity and specificity for detecting PAR. Our results highlight the value of linking verbal and visual models to a formal mathematical treatment for understanding the developmental origins of inequitable adult outcomes. This article is part of the theme issue 'Evolutionary ecology of inequality'.

Sex and dominance: How to assess and interpret intersexual dominance relationships in mammalian societies

The causes and consequences of being in a particular dominance position have been illuminated in various animal species, and new methods to assess dominance relationships and to describe the structure of dominance hierarchies have been developed in recent years. Most research has focused on same-sex relationships, however, so that intersexual dominance relationships and hierarchies including both sexes have remained much less studied. In particular, different methods continue to be employed to rank males and females along a dominance hierarchy, and sex biases in dominance are still widely regarded as simple byproducts of sexual size dimorphism. However, males and females regularly compete over similar resources when living in the same group, and sexual conflict takes a variety of forms across societies. These processes affect the fitness of both sexes, and are mitigated by intersexual hierarchies. In this study, we draw on data from free-ranging populations of nine species of mammals that vary in the degree to which members of one sex dominate members of the other sex to explore the consequences of using different criteria and procedures for describing intra- and intersexual dominance relationships in these societies. Our analyses confirmed a continuum in patterns of intersexual dominance, from strictly male-dominated species to strictly female-dominated species. All indices of the degree of female dominance were well correlated with each other. The rank order among same-sex individuals was highly correlated between the intra- and intersexual hierarchies, and such correlation was not affected by the degree of female dominance. The relative prevalence of aggression and submission was sensitive to variation in the degree of female dominance across species, with more submissive signals and fewer aggressive acts being used in societies where female dominance prevails. Thus, this study provides important insights and key methodological tools to study intersexual dominance relationships in mammals.

Maternal stress effects on infant development in wild Verreaux's sifaka (Propithecus verreauxi)

Abstract

Maternal effects mediated by nutrients or specific endocrine states of the mother can affect infant development. Specifically, pre- and postnatal maternal stress associated with elevated glucocorticoid (GC) output is known to influence the phenotype of the offspring, including their physical and behavioral development. These developmental processes, however, remain relatively poorly studied in wild vertebrates, including primates with their relatively slow life histories. Here, we investigated the effects of maternal stress, assessed by fecal glucocorticoid output, on infant development in wild Verreaux’s sifakas (Propithecus verreauxi), a group-living Malagasy primate. In a first step, we investigated factors predicting maternal fecal glucocorticoid metabolite (fGCM) concentrations, how they impact infants’ physical and behavioral development during the first 6 months of postnatal life as well as early survival during the first 1.5 years of postnatal life. We collected fecal samples of mothers for hormone assays and behavioral data of 12 infants from two birth cohorts, for which we also assessed growth rates. Maternal fGCM concentrations were higher during the late prenatal but lower during the postnatal period compared to the early/mid prenatal period and were higher during periods of low rainfall. Infants of mothers with higher prenatal fGCM concentrations exhibited faster growth rates and were more explorative in terms of independent foraging and play. Infants of mothers with high pre- and postnatal fGCM concentrations were carried less and spent more time in nipple contact. Time mothers spent carrying infants predicted infant survival: infants that were more carried had lower survival, suggesting that they were likely in poorer condition and had to be cared for longer. Thus, the physical and behavioral development of these young primates were impacted by variation in maternal fGCM concentrations during the first 6 months of their lives, presumably as an adaptive response to living in a highly seasonal, but unpredictable environment.

Significance statement

The early development of infants can be impacted by variation in maternal condition. These maternal effects can be mediated by maternal stress (glucocorticoid hormones) and are known to have downstream consequences for behavior, physiology, survival, and reproductive success well into adulthood. However, the direction of the effects of maternal physiological GC output on offspring development is highly variable, even within the same species. We contribute comparative data on maternal stress effects on infant development in a Critically Endangered primate from Madagascar. We describe variation in maternal glucocorticoid output as a function of ecological and reproductive factors and show that patterns of infant growth, behavioral development, and early survival are predicted by maternal glucocorticoids. Our study demonstrates how mothers can influence offspring fitness in response to challenging environmental conditions.