Maternal stress alters the phenotype of the mother, her eggs and her offspring in a wild-caught lizard

Multiple behavioral mechanisms shape development in a highly social cichlid fish

Early-life social experiences shape adult phenotype, yet the underlying behavioral mechanisms remain poorly understood. We manipulated early-life social experience in the highly social African cichlid fish Astatotilapia burtoni to investigate the effects on behavior and stress axis function in juveniles. Juveniles experienced different numbers of social partners in stable pairs (1 partner), stable groups (6 fish; 5 partners), and socialized pairs (a novel fish was exchanged every 5 days; 5 partners). Treatments also differed in group size (groups vs. pairs) and stability (stable vs. socialized). We then measured individual behavior and water-borne cortisol to identify effects of early-life experience. We found treatment differences in behavior across all assays: open field exploration, social cue investigation, dominant behavior, and subordinate behavior. Treatment did not affect cortisol. Principal components (PC) analysis revealed robust co-variation of behavior across contexts, including with cortisol, to form behavioral syndromes sensitive to early-life social experience. PC1 (25.1 %) differed by social partner number: juveniles with more partners (groups and socialized pairs) were more exploratory during the social cue investigation, spent less time in the territory, and were more interactive as dominants. PC5 (8.5 %) differed by stability: socialized pairs were more dominant, spent less time in and around the territory, were more socially investigative, and had lower cortisol than stable groups or pairs. Observations of the home tanks provided insights into the social experiences that may underlie these effects. These results contribute to our understanding of how early-life social experiences are accrued and exert strong, lasting effects on phenotype.

The effects of early-life and intergenerational stress on the brain

Stress experienced during ontogeny can have profound effects on the adult phenotype. However, stress can also be experienced intergenerationally, where an offspring's phenotype can be moulded by stress experienced by the parents. Although early-life and intergenerational stress can alter anatomy, physiology, and behaviour, nothing is known about how these stress contexts interact to affect the neural phenotype. Here, we examined how early-life and intergenerational stress affect the brain in eastern fence lizards (Sceloporus undulatus). Some lizard populations co-occur with predatory fire ants, and stress from fire ant attacks exerts intergenerational physiological and behavioural changes in lizards. However, it is unclear if intergenerational stress, or the interaction between intergenerational and early-life stress, modulates the brain. To test this, we captured gravid females from fire ant invaded and uninvaded populations, and subjected offspring to three early-life stress treatments: (1) fire ant attack, (2) corticosterone, or (3) a control. Corticosterone and fire ant attack decreased some aspects of the neural phenotype while population of origin and the interaction of early-life stress and population had no effects on the brain. These results suggest that early-life stressors may better predict adult brain variation than intergenerational stress in this species.

What are the contributions of maternal and paternal traits to fecundity and offspring development? A case study in an amphibian species, the spined toad Bufo spinosus

Assessing the determinants of reproductive success is critical but often complicated because of complex interactions between parental traits and environmental conditions occurring during several stages of a reproductive event. Here, we used a simplified ecological situation-an amphibian species lacking post-oviposition parental care-and a laboratory approach to investigate the relationships between parental (both maternal and paternal) phenotypes (body size and condition) and reproductive success (fecundity, egg size, embryonic and larval duration, larval and metamorphic morphology). We found significant effects of maternal phenotype on fecundity, hatching success, and tadpole size, as well as on the duration of larval development. Interestingly, and more surprisingly, we also found a potential contribution of the paternal phenotype occurring during early (embryonic development duration) offspring development. Although our study focused on life-history traits such as body size and development duration, additional mechanisms involving physiological costs of development may well mediate the relationships between parental phenotypes and offspring development. Future studies are required to decipher the mechanisms underlying our findings in order to clarify the mechanistic basis of the links between parental phenotypes and offspring development.

Stress in the social context: a behavioural and eco-evolutionary perspective

The social environment is one of the primary sources of challenging stimuli that can induce a stress response in animals. It comprises both short-term and stable interactions among conspecifics (including unrelated individuals, mates, potential mates and kin). Social stress is of unique interest in the field of stress research because (1) the social domain is arguably the most complex and fluctuating component of an animal's environment; (2) stress is socially transmissible; and (3) stress can be buffered by social partners. Thus, social interactions can be both the cause and cure of stress. Here, we review the history of social stress research, and discuss social stressors and their effects on organisms across early life and adulthood. We also consider cross-generational effects. We discuss the physiological mechanisms underpinning social stressors and stress responses, as well as the potential adaptive value of responses to social stressors. Finally, we identify outstanding challenges in social stress research, and propose a framework for addressing these in future work.

Unpredictability of maternal environment shapes offspring behaviour without affecting stress-induced cortisol in an annual vertebrate

Exposure of females to stressful conditions during pregnancy or oogenesis has a profound effect on the phenotype of their offspring. For example, offspring behavioural phenotype may show altered patterns in terms of the consistency of behavioural patterns and their average level of performance. Maternal stress can also affect the development of the stress axis in offspring leading to alterations in their physiological stress response. However, the majority of evidence comes from studies utilising acute stressors or exogenous glucocorticoids, and little is known about the effect of chronic maternal stress, particularly in the context of stress lasting throughout entire reproductive lifespan. To bridge this knowledge gap, we exposed female sticklebacks to stressful and unpredictable environmental conditions throughout the breeding season. We quantified the activity, sheltering and anxiety-like behaviour of offspring from three successive clutches of these females, and calculated Intra-class Correlation Coefficients for these behaviours in siblings and half-siblings. We also exposed offspring to an acute stressor and measured their peak cortisol levels. An unpredictable maternal environment had no modifying effect on inter-clutch acute stress responsivity, but resulted in diversification of offspring behaviour, indicated by an increased between-individual variability within families. This may represent a bet-hedging strategy, whereby females produce offspring differing in behavioural phenotype, to increase the chance that some of these offspring will be better at coping with the anticipated conditions.

Baseline corticosterone levels in spadefoot toads reflect alternate larval diets one year later

Early-life environmental variation can influence later-life physiology, such as the regulation of glucocorticoids. However, characterizing the effects of environmental factors on hormone regulation can be hampered when assessing animals that are small and require destructive sampling to collect blood. Using spadefoot toads (genus Spea), we evaluated whether waterborne corticosterone (CORT) measures could be used as a proxy for plasma CORT measures, detect stress-induced levels of CORT, and detect larval diet-induced changes in CORT regulation after metamorphosed individuals were maintained for 1 year under common garden conditions. We found that waterborne CORT measures were correlated with plasma CORT measures and could be used to detect stress-induced levels of CORT. Further, larval diet type significantly influenced baseline plasma CORT levels 1-year post-metamorphosis: adults that had consumed live prey as larvae had higher plasma CORT levels than adults that had consumed detritus as larvae. However, waterborne measures failed to reflect these differences, possibly due to low sample size. Our study demonstrates the utility of the waterborne hormone assay in assessing variation in baseline and stress-induced CORT levels in adult spadefoots. However, resolving more subtle differences that arise through developmental plasticity will require larger samples sizes when using the waterborne assay.

Frank Beach Award Winner: The centrality of the hypothalamic-pituitary-adrenal axis in dealing with environmental change across temporal scales

Understanding if and how individuals and populations cope with environmental change is an enduring question in evolutionary ecology that has renewed importance given the pace of change in the Anthropocene. Two evolutionary strategies of coping with environmental change may be particularly important in rapidly changing environments: adaptive phenotypic plasticity and/or bet hedging. Adaptive plasticity could enable individuals to match their phenotypes to the expected environment if there is an accurate cue predicting the selective environment. Diversifying bet hedging involves the production of seemingly random phenotypes in an unpredictable environment, some of which may be adaptive. Here, I review the central role of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) in enabling vertebrates to cope with environmental change through adaptive plasticity and bet hedging. I first describe how the HPA axis mediates three types of adaptive plasticity to cope with environmental change (evasion, tolerance, recovery) over short timescales (e.g., 1-3 generations) before discussing how the implications of GCs on phenotype integration may depend upon the timescale under consideration. GCs can promote adaptive phenotypic integration, but their effects on phenotypic co-variation could also limit the dimensions of phenotypic space explored by animals over longer timescales. Finally, I discuss how organismal responses to environmental stressors can act as a bet hedging mechanism and therefore enhance evolvability by increasing genetic or phenotypic variability or reducing patterns of genetic and phenotypic co-variance. Together, this emphasizes the crucial role of the HPA axis in understanding fundamental questions in evolutionary ecology.

Egg viability and egg mass underlie immune tradeoffs and differences between urban and rural lizard egg yolk physiology

Urbanization can cause innumerable abiotic and biotic changes that have the potential to influence the ecology, behavior, and physiology of native resident organisms. Relative to their rural conspecifics, urban Side-blotched Lizard (Uta stansburiana) populations in southern Utah have lower survival prospects and maximize reproductive investment via producing larger eggs and larger clutch sizes. While egg size is an important predictor of offspring quality, physiological factors within the egg yolk are reflective of the maternal environment and can alter offspring traits, especially during energetically costly processes, such as reproduction or immunity. Therefore, maternal effects may represent an adaptive mechanism by which urban-dwelling species can persist within a variable landscape. In this study, we assess urban and rural differences in egg yolk bacterial killing ability (BKA), corticosterone (CORT), oxidative status (d-ROMs), and energy metabolites (free glycerol and triglycerides), and their association with female immune status and egg quality. Within a laboratory setting, we immune challenged urban lizards via lipopolysaccharide injection (LPS) to test whether physiological changes associated with immune system activity impacted egg yolk investment. We found urban females had higher mite loads than rural females, however mite burden was related to yolk BKA in rural eggs, but not urban eggs. While yolk BKA differed between urban and rural sites, egg mass and egg viability (fertilized vs. unfertilized) were strong predictors of yolk physiology and may imply tradeoffs exist between maintenance and reproduction. LPS treatment caused a decrease in egg yolk d-ROMs relative to the control treatments, supporting results from previous research. Finally, urban lizards laid a higher proportion of unfertilized eggs, which differed in egg yolk BKA, CORT, and triglycerides in comparison to fertilized eggs. Because rural lizards laid only viable eggs during this study, these results suggest that reduced egg viability is a potential cost of living in an urban environment. Furthermore, these results help us better understand potential downstream impacts of urbanization on offspring survival, fitness, and overall population health.

Embryonic heart rate is affected by yolk androgens and egg laying sequence, and correlates with embryonic tissue growth: A study in rock pigeons

Maternal androgen exposure can have crucial effects on offspring development. Bird eggs are frequently used for studying these effects and virtually all research in this field has focused on post-hatching offspring traits. Yet, much of the yolk, in which the maternal hormones are deposited, is consumed during the embryonic phase. Here, we studied the effects of yolk androgens during this prenatal period. As there is evidence that androgens stimulate post-hatching traits such as increased growth, we measured heart rate throughout incubation as a proxy for prenatal metabolism. Rock pigeons (Columba livia) typically lay 2-egg clutches with yolk androgen levels in second-laid eggs being consistently higher than in first-laid eggs. We investigated whether embryonic heart rate was higher in second- than first-laid eggs. Additionally, we increased yolk androgen levels (testosterone and androstenedione) with the mean difference between those in first- and second-laid eggs, to investigate whether the effects of androgens are egg sequence dependent. As expected, embryonic heart rate predicted body embryo organ- and body mass, and body dimensions, with body mass being significantly higher in second- than first-laid eggs. Androgen treated first-laid eggs increased heart rate to that of second-laid control eggs only temporally, yet it had an overall positive effect on embryo body dimensions but not on tissue mass. Our findings indicate that embryos from different egg laying sequence differed in heart rate and prenatal development outcomes but this can only partially be explained by their difference in maternal androgen levels.

Urbanization and maternal hormone transfer: Endocrine and morphological phenotypes across ontogenetic stages

The phenotypes observed in urban and rural environments are often distinct; however, it remains unclear how these novel urban phenotypes arise. Hormone-mediated maternal effects likely play a key role in shaping developmental trajectories of offspring in different environments. Thus, we measured corticosterone (Cort) and testosterone (T) concentrations in eggs across the laying sequence in addition to Cort concentrations in nestling and adult female house wrens (Troglodytes aedon) at one urban and one rural site. We found that egg T concentrations were not different between birds from urban and rural sites. However, across all life stages (egg, nestling, and adult female), Cort concentrations were higher at the urban site. Additionally, urban nestling Cort concentrations, but not rural, correlated with fine-scale urban density scores. Furthermore, rural egg volume increased over the laying sequence, but urban egg volume leveled off mid-sequence, suggesting either that urban mothers are resource limited or that they are employing a different brood development strategy than rural mothers. Our study is one of the first to show that egg hormone concentrations differ in an urban environment with differences persisting in chick development and adult life stages. We suggest that maternal endocrine programing may shape offspring phenotypes in urban environments and are an overlooked yet important aspect underlying mechanisms of urban evolution.

Transgenerational effects of maternal corticosterone across early life in a viviparous snake

Glucocorticoids (GCs) are central mediators of vertebrate responses to intrinsic and extrinsic stimuli. Among the sources of variation in circulating GCs are transgenerational effects mediated by mothers. Here we studied potential maternal effects mediated by GCs on offspring phenotype in a live-bearing reptile, the western terrestrial garter snake (Thamnophis elegans). We evaluated the association between baseline corticosterone (CORT) levels during gestation (i.e., preparturition) in field-captured mothers and 1) reproductive success and offspring sex ratios, 2) birth phenotypic traits of offspring born under common-garden laboratory conditions, and 3) neonate (age 3 months) and juvenile (age 12 months) traits of offspring raised under two thermal regimes ('warm' and 'cool') during their first year of life. Reproductive success and offspring sex ratios were not associated with preparturition maternal CORT, but pregnant snakes with higher CORT levels gave birth to smaller, lighter offspring, which tended to grow faster to age three months. Neonate baseline CORT varied with preparturition maternal CORT in a sex-specific manner (positive trend for females, negative for males). Maternal CORT effects on offspring phenotype were no longer detectable in juveniles at age one year. Instead, juvenile phenotypes were most influenced by rearing environment, with offspring raised under the cool regime showing higher baseline CORT and slower growth than those raised under warmer conditions. Our findings support the notion that offspring phenotype might be continuously adjusted in response to environmental cues -both pre- and post-natal- and that the strength of maternal CORT effects declines as offspring develop and experience unique environmental challenges. Our results contribute to a growing literature on transgenerational effects of hormones and help to fill a gap in our knowledge of these effects in ectothermic amniotes.

Experimental evidence that chronic outgroup conflict reduces reproductive success in a cooperatively breeding fish

Conflicts with conspecific outsiders are common in group-living species, from ants to primates, and are argued to be an important selective force in social evolution. However, whilst an extensive empirical literature exists on the behaviour exhibited during and immediately after interactions with rivals, only very few observational studies have considered the cumulative fitness consequences of outgroup conflict. Using a cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher), we conducted the first experimental test of the effects of chronic outgroup conflict on reproductive investment and output. ‘Intruded’ groups received long-term simulated territorial intrusions by neighbours that generated consistent group-defence behaviour; matched ‘Control’ groups (each the same size and with the same neighbours as an Intruded group) received no intrusions in the same period. Intruded groups had longer inter-clutch intervals and produced eggs with increasingly less protein than Control groups. Despite the lower egg investment, Intruded groups provided more parental care and achieved similar hatching success to Control groups. Ultimately, however, Intruded groups had fewer and smaller surviving offspring than Control groups at 1-month post-hatching. We therefore provide experimental evidence that outgroup conflict can decrease fitness via cumulative effects on reproductive success, confirming the selective potential of this empirically neglected aspect of sociality.

Vasopressin mediates nonapeptide and glucocorticoid signaling and social dynamics in juvenile dominance hierarchies of a highly social cichlid fish

Early-life social experience can strongly affect adult behavior, yet the behavioral mechanisms underlying developmental trajectories are poorly understood. Here, we use the highly social cichlid, Burton's Mouthbrooder (Astatotilapia burtoni) to investigate juvenile social status and behavior, as well as the underlying neuroendocrine mechanisms. We placed juveniles in pairs or triads and found that they readily establish social status hierarchies, with some group structural variation depending on group size, as well as the relative body size of the group members. Next, we used intracerebroventricular injections to test the hypothesis that arginine vasopressin (AVP) regulates juvenile social behavior and status, similar to adult A. burtoni. While we found no direct behavioral effects of experimentally increasing (via vasotocin) or decreasing (via antagonist Manning Compound) AVP signaling, social interactions directed at the treated individual were significantly altered. This group-level effect of central AVP manipulation was also reflected in a significant shift in whole brain expression of genes involved in nonapeptide signaling (AVP, oxytocin, and oxytocin receptor) and the neuroendocrine stress axis (corticotropin-releasing factor (CRF), glucocorticoid receptors (GR) 1a and 1b). Further, social status was associated with the expression of genes involved in glucocorticoid signaling (GR1a, GR1b, GR2, mineralocorticoid receptor), social interactions with the dominant fish, and nonapeptide signaling activity (AVP, AVP receptor V1aR2, OTR). Together, our results considerably expand our understanding of the context-specific emergence of social dominance hierarchies in juveniles and demonstrate a role for nonapeptide and stress axis signaling in the regulation of social status and social group dynamics.

Fitness consequences of outgroup conflict

In social species across the animal kingdom, conspecific outsiders threaten the valuable resources of groups and their members. This outgroup conflict is recognised as a powerful selection pressure, but we argue that studies explicitly quantifying the fitness consequences need to be broader in scope: more attention should be paid to delayed, cumulative, and third-party fitness consequences, not just those arising immediately to group members involved in physical contests. In the first part of this review, we begin by documenting how single contests can have survival and reproductive consequences either immediately or with a delay. Then, we step beyond contests to describe fitness consequences that can also result from interactions with cues of rival presence and the general landscape of outgroup threat, and beyond single interactions to describe cumulative effects of territorial pressure and elevated outgroup-induced stress. Using examples from a range of taxa, we discuss which individuals are affected negatively and positively, considering both interaction participants and third-party group members of the same or the next generation. In the second part of the review, we provide suggestions about how to move forward. We highlight the importance of considering how different types of outgroup conflict can generate different selection pressures and of investigating variation in fitness consequences within and between species. We finish by discussing the value of theoretical modelling and long-term studies of natural populations, experimental manipulations, and meta-analyses to develop further our understanding of this crucial aspect of sociality.

Prenatal maternal stress is associated with behavioural and epigenetic changes in Japanese quail

Prenatal maternal stress (PMS) influences many facets of offspring's phenotype including morphology, behaviour and cognitive abilities. Recent research suggested that PMS also induced epigenetic modifications. In the present study, we analysed, in the Japanese quail, the effects of PMS on the emotional reactivity and cognitive abilities of the F1 offspring. We also investigated in the hippocampus, the paraventricular hypothalamic nucleus and subnuclei of the arcopallium/amygdala the level of two histone post-translational modifications, H3K4me2 and H3K27me3, known to be impacted by stress. We found that PMS does not affect F1 quail's learning abilities but increases their emotional reactivity. Moreover, we demonstrated that PMS induced an increased density of H3K27me3 positive cells, in the hippocampus, paraventricular hypothalamic nucleus and dorsal nucleus of the amygdala, but not variations of H3K4me2. As these brain regions are involved in the control of vertebrates' emotional responses, the effect of PMS on the epigenetic mark H3K27me3 could possibly be a mechanism involved in the behavioural effects we observed in F1 quail.

Fitness Costs of Maternal Ornaments and Prenatal Corticosterone Manifest as Reduced Offspring Survival and Sexual Ornament Expression

Colorful traits (i.e., ornaments) that signal quality have well-established relationships with individual condition and physiology. Furthermore, ornaments expressed in females may have indirect fitness effects in offspring via the prenatal physiology associated with, and social consequences of, these signaling traits. Here we examine the influence of prenatal maternal physiology and phenotype on condition-dependent signals of their offspring in adulthood. Specifically, we explore how prenatal maternal testosterone, corticosterone, and ornament color and size correlate with female and male offspring survival to adulthood and ornament quality in the lizard Sceloporus undulatus. Offspring of females with more saturated badges and high prenatal corticosterone were less likely to survive to maturity. Badge saturation and area were negatively correlated between mothers and their male offspring, and uncorrelated to those in female offspring. Maternal prenatal corticosterone was correlated negatively with badge saturation of male offspring in adulthood. Our results indicate that maternal ornamentation and prenatal concentrations of a stress-relevant hormone can lead to compounding fitness costs by reducing offspring survival to maturity and impairing expression of a signal of quality in surviving males. This mechanism may occur in concert with social costs of ornamentation in mothers. Intergenerational effects of female ornamentation and prenatal stress may be interdependent drivers of balancing selection and intralocus sexual conflict over signaling traits.

Compensating for a stressful pregnancy? Glucocorticoid treatment during gravidity reduces metabolic rate in female fence lizards post-parturition

Reproduction is a critical part of an animal's life history, but one which incurs significant costs to survival and future reproductive potential. These physiological consequences are likely to be influenced by context - for example, if an individual is subject to environmental stressors, physiological and behavioral changes associated with reproduction may be altered. Glucocorticoids, hormones produced as part of the physiological response to stressors, may alter how reproduction affects female physiology and behavior, and therefore the outcomes of reproductive trade-offs. Glucocorticoids prioritize immediate survival over reproduction, for example through changes in immune function, metabolic rate, and foraging, which may reduce energy expenditure or increase energy gain. However, we previously found that female eastern fence lizards (Sceloporus undulatus) experiencing elevated glucocorticoid levels during gestation were nevertheless able to maintain reproductive output and body condition. Here we investigate compensatory mechanisms by which eastern fence lizard females may maintain reproduction under experimental increases in a glucocorticoid, corticosterone (CORT). We found that, although CORT-treated females had similar immune function and behavior, they had reduced metabolic rates 3-5 days post-parturition compared to control females. Given that CORT-treated females spent a similar time basking and had equal food intake compared to control females, we suggest that the reduced metabolic rate is a mechanism by which CORT-treated females maintain their energy balance and reduce the energetic costs of gestation during periods of stress. This study suggests that physiological responses to reproduction may be context-dependent and could act to minimize costs of reproduction in situations where CORT is elevated (such as during periods of environmental stress).

Context-dependent effects of glucocorticoids on the lizard gut microbiome

The vertebrate gut microbiota (bacterial, archaeal and fungal communities of the gastrointestinal tract) can have profound effects on the physiological processes of their hosts. Although relatively stable, changes in microbiome structure and composition occur due to changes in the environment, including exposure to stressors and associated increases in glucocorticoid hormones. Although a growing number of studies have linked stressor exposure to microbiome changes, few studies have experimentally explored the specific influence of glucocorticoids on the microbiome in wild animals, or across ecologically important processes (e.g., reproductive stages). Here we tested the response of the gut microbiota of adult female Sceloporus undulatus across gestation to ecologically relevant elevations of a stress-relevant glucocorticoid hormone (CORT) in order to determine (i) how experimentally elevated CORT influenced microbiome characteristics, and (ii) whether this relationship was dependent on reproductive context (i.e., whether females were gravid or not, and, in those that were gravid, gestational stage). We show that the effects of CORT on gut microbiota are complex and depend on both gestational state and stage. CORT treatment altered microbial community membership and resulted in an increase in microbiome diversity in late-gestation females, and microbial community membership varied according to treatment. In nongravid females, CORT treatment decreased interindividual variation in microbial communities, but this effect was not observed in late-gestation females. Our results highlight the need for a more holistic understanding of the downstream physiological effects of glucocorticoids, as well as the importance of context (here, gestational state and stage) in interpreting stress effects in ecology.

Prenatal stress and increased susceptibility to anxiety-like behaviors: role of neuroinflammation and balance between GABAergic and glutamatergic transmission

Neuroplasticity during the prenatal period allows neurons to regenerate anatomically and functionally for re-programming the brain development. During this critical period of fetal programming, the fetus phenotype can change in accordance with environmental stimuli such as stress exposure. Prenatal stress (PS) can exert important effects on brain development and result in permanent alterations with long-lasting consequences on the physiology and behavior of the offspring later in life. Neuroinflammation, as well as GABAergic and glutamatergic dysfunctions, has been implicated as potential mediators of behavioral consequences of PS. Hyperexcitation, due to enhanced excitatory transmission or reduced inhibitory transmission, can promote anxiety. Alterations of the GABAergic and/or glutamatergic signaling during fetal development lead to a severe excitatory/inhibitory imbalance in neuronal circuits, a condition that may account for PS-precipitated anxiety-like behaviors. This review summarizes experimental evidence linking PS to an elevated risk to anxiety-like behaviors and interprets the role of the neuroinflammation and alterations of the brain GABAergic and glutamatergic transmission in this phenomenon. We hypothesize this is an imbalance in GABAergic and glutamatergic circuits (as a direct or indirect consequence of neuroinflammation), which at least partially contributes to PS-precipitated anxiety-like behaviors and primes the brain to be vulnerable to anxiety disorders. Therefore, pharmacological interventions with anti-inflammatory activities and with regulatory effects on the excitatory/inhibitory balance can be attributed to the novel therapeutic target for anxiety disorders.

Honest signals and sexual conflict: Female lizards carry undesirable indicators of quality

Sex differences in animal coloration often result from sex-dependent regulatory mechanisms. Still, some species exhibit incomplete sexual dimorphism as females carry a rudimentary version of a costly male trait, leading to intralocus sexual conflict. The underlying physiology and condition dependence of these traits can inform why such conflicts remain unresolved. In eastern fence lizards (Sceloporus undulatus), blue iridophore badges are found in males and females, but melanin pigmentation underneath and surrounding badges is male-exclusive. We track color saturation and area of badges across sexual maturity, and their relationship to individual quality (body condition and immunocompetence) and relevant hormones (testosterone and corticosterone). Saturation and testosterone were positively correlated in both sexes, but hormone and trait had little overlap between males and females. Saturation was correlated with body condition and immunocompetence in males but not in females. Co-regulation by androgens may have released females from resource allocation costs of color saturation, even when in high condition. Badge area was independent of testosterone, but associated with low corticosterone in females, indicating that a nonsex hormone underlies incomplete sexual dimorphism. Given the evidence in this species for female reproductive costs associated with ornamentation, this sex-nonspecific regulation of an honest signal may underlie intralocus sexual conflict.

Acoustic developmental programming: a mechanistic and evolutionary framework

Conditions experienced prenatally, by modulating developmental processes, have lifelong effects on individual phenotypes and fitness, ultimately influencing population dynamics. In addition to maternal biochemical cues, prenatal sound is emerging as a potent alternative source of information to direct embryonic development. Recent evidence suggests that prenatal acoustic signals can program individual phenotypes for predicted postnatal environmental conditions, which improves fitness. Across taxonomic groups, embryos have now been shown to have immediate adaptive responses to external sounds and vibrations, and direct developmental effects of sound and noise are increasingly found. Establishing the full developmental, ecological, and evolutionary impact of early soundscapes will reveal how embryos interact with the external world, and potentially transform our understanding of developmental plasticity and adaptation to changing environments.

Elevated glucocorticoids during gestation suggest sex-specific effects on offspring telomere lengths in a wild lizard

The effects of maternal glucocorticoids (e.g. corticosterone, CORT) on offspring interest biologists due to increasing environmental perturbations. While little is known about the impact of maternal CORT on offspring fitness, it may modulate telomere length and compromise offspring health. Here, we use a modified real-time quantitative PCR assay to assess telomere length using small DNA quantities (<60 ng). We tested the hypothesis that increased maternal CORT during gestation decreases offspring telomere length. While CORT-driven telomere shortening is well established within individuals, cross-generational effects remain unclear. We treated wild-caught gravid female eastern fence lizards (Sceloporus undulatus) with daily transdermal applications of CORT, at ecologically relevant levels, from capture to laying. Maternal CORT treatment did not alter maternal telomere length, although baseline maternal CORT concentrations had a weak, negative correlation with maternal telomere length. There was no relation between mother and offspring telomere length. There was a trend for maternal CORT treatment to shorten telomeres of sons but not daughters. Our treatment replicated exposure to a single stressor per day, likely underestimating effects seen in the wild where stressors may be more frequent. Future research should further explore fitness consequences of maternal CORT effects.

Maternal Temperature, Corticosterone, and Body Condition as Mediators of Maternal Effects in Jacky Dragons (Amphibolurus muricatus)

AbstractTemperature is a crucial environmental component that imposes physiological constraints and ultimately produces variation in life-history traits. Temperatures experienced by mothers can influence offspring phenotypes, including growth and sex ratios, especially in ectothermic species. However, mechanisms by which thermal information can be passed onto offspring have been underexplored. Here, we investigated corticosterone as a potential mediator of thermal maternal effects. We held female jacky dragons (Amphibolurus muricatus) in two different thermal regimes (short [7 h] or long [11 h] basking treatments), then quantified plasma corticosterone levels and tested for correlations between the resulting corticosterone levels and reproductive outputs. Lizards in the long-bask treatment had significantly higher corticosterone levels than those in the short-bask treatment. Maternal corticosterone, in turn, had sex-dependent effects on offspring hatching size but was not associated with maternal reproductive effort or offspring sex or growth. In contrast, maternal body condition was strongly positively related to both reproductive output (including clutch size and total number of eggs) and offspring size at hatching but had no effect on offspring growth. Basking treatment also interacted with condition and corticosterone to affect egg mass and hatchling snout-vent length, respectively. When we tested for relationships between corticosterone levels and body condition, we found corticosterone to be negatively related to condition in long-bask lizards but only in the postbreeding season. These findings indicate that thermal opportunity alters physiology, with potential consequences for fitness. Moreover, the results suggest interactive influences of temperature, corticosterone, and condition as mediators of maternal effects.

Survival is negatively associated with glucocorticoids in a wild ungulate neonate

It is unknown how ungulate physiological responses to environmental perturbation influence overall population demographics. Moreover, neonatal physiological responses remain poorly studied despite the importance of neonatal survival to population growth. Glucocorticoid (GC) hormones potentially facilitate critical physiological and behavioral responses to environmental perturbations. However, elevated GC concentrations over time may compromise body condition and indirectly reduce survival. We evaluated baseline salivary cortisol (CORT; a primary GC in mammals) concentrations in 19 wild neonatal white-tailed deer (Odocoileus virginianus) in a northern (NS) and southern (SS) area in Pennsylvania. After ranking survival models consisting of variables hypothesized to influence neonate survival (i.e. weight, sex), the probability of neonate survival was best explained by CORT concentrations, where elevated CORT concentrations were associated with reduced survival probability to 12 weeks of age. Cortisol concentrations were greater in the SS where predation rates and predator densities were lower. As the first evaluation of baseline CORT concentrations in an ungulate neonate to our knowledge, this is also the first study to demonstrate CORT concentrations are negatively associated with ungulate survival at any life stage. Glucocorticoid hormones could provide a framework in which to better understand susceptibility to mortality in neonatal white-tailed deer.

Effects of temperature on plasma corticosterone in a native lizard

The glucocorticoid stress response is frequently used to indicate vertebrate response to the environment. Body temperature may affect glucocorticoid concentrations, particularly in ectotherms. We conducted lab manipulations and field measurements to test the effects of body temperature on plasma corticosterone (predominant glucocorticoid in reptiles) in eastern fence lizards (Sceloporus undulatus). First, we acclimated lizards to one of 4 treatments: 22 °C, 29 °C, 33 °C, or 36 °C, and measured cloacal temperatures and plasma corticosterone concentrations at baseline and after exposure to a standardized stressor (cloth bag). Both baseline and stress-induced corticosterone concentrations were lower in lizards with lower body temperatures. Second, we acclimated lizards to 22 °C or 29 °C and exposed them to a standardized (cloth bag) stressor for 3 to 41 min. Lizards acclimated to 29 °C showed a robust increase in plasma corticosterone concentrations with restraint stress, but those at 22 °C showed no such increases in corticosterone concentrations. Third, we measured lizards upon capture from the field. There was no correlation between body temperature and baseline plasma corticosterone in field-caught lizards. These results suggest body temperature can significantly affect plasma corticosterone concentrations in reptiles, which may be of particular concern for experiments conducted under laboratory conditions but may not translate to the field.

Multiple Environmental Stressors Induce an Adaptive Maternal Effect

AbstractEvolution of adaptation requires predictability and recurrence of functional contexts. Yet organisms live in multifaceted environments that are dynamic and ever changing, making it difficult to understand how complex adaptations evolve. This problem is particularly apparent in the evolution of adaptive maternal effects, which are often assumed to require reliable and discrete cues that predict conditions in the offspring environment. One resolution to this problem is if adaptive maternal effects evolve through preexisting, generalized maternal pathways that respond to many cues and also influence offspring development. Here, we assess whether an adaptive maternal effect in western bluebirds is influenced by maternal stress pathways across multiple challenging environments. Combining 18 years of hormone sampling across diverse environmental contexts with an experimental manipulation of the competitive environment, we show that multiple environmental factors influenced maternal corticosterone levels, which, in turn, influenced a maternal effect on aggression of sons in adulthood. Together, these results support the idea that multiple stressors can induce a known maternal effect in this system. More generally, they suggest that activation of general pathways, such as the hypothalamic-pituitary-adrenal axis, may simplify and facilitate the evolution of adaptive maternal effects by integrating variable environmental conditions into preexisting maternal physiological systems.

A complex regulating pattern induced by the effects of predation and parasites on root vole (Microtus oeconomus) populations during the breeding season

Predators and parasites have synergistic effects on the phenotype of the species they share as prey and host. Experimental studies that incorporate the interactions between predation and parasitism are, however, scarce in small-mammal populations. Our previous work has shown that the combined effects of predation and coccidian infection reduce overwinter survival and population density in root voles (Microtus oeconomus). Here, we examined the separate and combined effects of these two drivers on the population growth of root voles during the breeding season. We carried out a two-level factorial experiment, in which we manipulated predator exclusion and the removal of parasites in enclosures and measured survival, fecal corticosterone metabolite (FCM) concentration, recruitment, and population density. An expected synergistic effect of predators and parasites on vole population was not found, due to no effect of parasites on FCM level and recruitment rate during the period of the experiment. Instead, we found phase-related effects of predation on demography. Predation reduced the survival rate of voles in spring, which was intensified by parasite infection. Predation risk reduced recruitment rate in early summer by elevating FCM levels. Consequently, both direct and indirect effects of predation lowered population density during the experimental period. In addition, for populations free of predators, the peak density that occurred in early autumn elevated FCM level of adult voles, which reduced recruitment rates and halted population growth. Moreover, predation, parasites, and density affected the quality of the offspring. Our study suggests that multiple regulation processes influence population fluctuations during the breeding season. We conclude that a population experiencing stress acts as a common interface through which interactions between intrinsic and extrinsic factors can be important determinants of fluctuations. We propose a new hypothesis of integrative stress effects to explain small-mammal population fluctuations.

Maternal predation risk increases offspring’s exploration but does not affect schooling behavior

The environment that parents experience can influence their reproductive output and their offspring’s fitness via parental effects. Perceived predation risk can affect both parent and offspring phenotype, but it remains unclear to what extent offspring behavioral traits are affected when the mother is exposed to predation risk. This is particularly unclear in live-bearing species where maternal effects could occur during embryogenesis. Here, using a half-sib design to control for paternal effects, we experimentally exposed females of a live-bearing fish, the guppy (Poecilia reticulata), to visual predator cues and conspecific alarm cues during their gestation. Females exposed to predation risk cues increased their antipredator behaviors throughout the entire treatment. Offspring of mothers exposed to the predation stimuli exhibited more pronounced exploratory behavior, but did not show any significant differences in their schooling behavior, compared to controls. Thus, while maternally perceived risk affected offspring’s exploration during early stages of life, offspring’s schooling behavior could be influenced more by direct environmental experience rather than via maternal cues. Our results suggest a rather limited role in predator-induced maternal effects on the behavior of juvenile guppies.

Parents know best: transgenerational predator recognition through parental effects

In highly biodiverse systems, such as coral reefs, prey species are faced with predatory threats from numerous species. Recognition of predators can be innate, or learned, and can help increase the chance of survival. Research suggests that parental exposure to increased predatory threats can affect the development, behaviour, and ultimately, success of their offspring. Breeding pairs of damselfish (Acanthochromis polyacanthus) were subjected to one of three olfactory and visual treatments (predator, herbivore, or control), and their developing embryos were subsequently exposed to five different chemosensory cues. Offspring of parents assigned to the predator treatment exhibited a mean increase in heart rate two times greater than that of offspring from parents in herbivore or control treatments. This increased reaction to a parentally known predator odour suggests that predator-treated parents passed down relevant threat information to their offspring, via parental effects. This is the first time transgenerational recognition of a specific predator has been confirmed in any species. This phenomenon could influence predator-induced mortality rates and enable populations to adaptively respond to fluctuations in predator composition and environmental changes.

Contrasting Responses of Lizards to Divergent Ecological Stressors Across Biological Levels of Organization

It is frequently hypothesized that animals employ a generalized "stress response," largely mediated by glucocorticoid (GC) hormones, such as corticosterone, to combat challenging environmental conditions. Under this hypothesis, diverse stressors are predicted to have concordant effects across biological levels of an organism. We tested the generalized stress response hypothesis in two complementary experiments with juvenile and adult male Eastern fence lizards (Sceloporus undulatus). In both experiments, animals were exposed to diverse, ecologically-relevant, acute stressors (high temperature or red imported fire ants, Solenopsis invicta) and we examined their responses at three biological levels: behavioral; physiological (endocrine [plasma corticosterone and blood glucose concentrations] and innate immunity [complement and natural antibodies]); and cellular responses (gene expression of a panel of five heat-shock proteins in blood and liver) at 30 or 90 min post stress initiation. In both experiments, we observed large differences in the cellular response to the two stressors, which contrasts the similar behavioral and endocrine responses. In the adult experiment for which we had innate immune data, the stressors affected immune function independently, and they were correlated with CORT in opposing directions. Taken together, these results challenge the concept of a generalized stress response. Rather, the stress response was context specific, especially at the cellular level. Such context-specificity might explain why attempts to link GC hormones with life history and fitness have proved difficult. Our results emphasize the need for indicators at multiple biological levels and whole-organism examinations of stress.

Maternal diet affects juvenile Carpetan rock lizard performance and personality

Differences in both stable and labile state variables are known to affect the emergence and maintenance of consistent interindividual behavioral variation (animal personality or behavioral syndrome), especially when experienced early in life. Variation in environmental conditions experienced by gestating mothers (viz. nongenetic maternal effects) is known to have significant impact on offspring condition and behavior; yet, their effect on behavioral consistency is not clear. Here, by applying an orthogonal experimental design, we aimed to study whether increased vitamin D3 content in maternal diet during gestation (vitamin-supplemented vs. vitamin control treatments) combined with corticosterone treatment (corticosterone-treated vs. corticosterone control treatments) applied on freshly hatched juveniles had an effect on individual state and behavioral consistency of juvenile Carpetan rock lizards (Iberolacerta cyreni). We tested the effect of our treatments on (a) climbing speed and the following levels of behavioral variation, (b) strength of animal personality (behavioral repeatability), (c) behavioral type (individual mean behavior), and (d) behavioral predictability (within-individual behavioral variation unrelated to environmental change). We found higher locomotor performance of juveniles from the vitamin-supplemented group (42.4% increase), irrespective of corticosterone treatment. While activity personality was present in all treatments, shelter use personality was present only in the vitamin-supplemented × corticosterone-treated treatment and risk-taking personality was present in corticosterone control treatments. Contrary to our expectations, behavioral type was not affected by our treatments, indicating that individual quality can affect behavioral strategies without affecting group-level mean behavior. Behavioral predictability decreased in individuals with low climbing speed, which could be interpreted as a form of antipredator strategy. Our results clearly demonstrate that maternal diet and corticosterone treatment have the potential to induce or hamper between-individual variation in different components of boldness, often in interactions.

History of predator exposure affects cell-mediated immunity in female eastern fence lizards, Sceloporus undulatus (Squamata: Phrynosomatidae)

On exposure to stressors, energy is diverted from non-urgent functions towards those important for immediate survival. The degree and nature of reallocation may be affected by the evolutionary history of the animal. The eastern fence lizard (Sceloporus undulatus) coexists in parts of its range with invasive fire ants (Solenopsis invicta), which attack and wound lizards and elevate stress-relevant hormones (corticosterone), whereas other populations have never been exposed to fire ants. We examined how a history of fire ant invasion affected the immune response in female lizards after exposure to exogenous corticosterone (mimicking exposure to a stressor) during gestation (dosing regimens differed among corticosterone-exposed lizards owing to the constraints of the original studies, but we found no evidence that this affected the outcome of the present study). A history of exposure to predatory stressors (fire ants) and corticosterone treatment affected cell-mediated immunity. Lizards from fire ant-invaded sites had a reduced immune response compared with those from uninvaded sites. Corticosterone treatment had no effect on the immune response of lizards from invaded sites but reduced the immune response of lizards from uninvaded sites. This suggests that an evolutionary history of exposure to wounding alters the immune response to corticosterone. Future work on how the immune system responds to environmental threats will be informative for the prediction and management of these threats.

Maternal corticosterone increases thermal sensitivity of heart rate in lizard embryos

While it is well established that maternal stress hormones, such as corticosterone (CORT), can induce transgenerational phenotypic plasticity, few studies have addressed the influence of maternal CORT on pre-natal life stages. We tested the hypothesis that experimentally increased CORT levels of gravid female eastern fence lizards ( Sceloporus undulatus) would alter within-egg embryonic phenotype, particularly heart rates. We found that embryos from CORT-treated mothers had heart rates that increased faster with increasing temperature, resulting in higher heart rates at developmentally relevant temperatures but similar heart rates at maintenance relevant temperatures, compared with embryos of control mothers. Thus, maternal CORT appears to alter the physiology of pre-natal offspring. This may speed development and decrease the amount of time spent in eggs, the most vulnerable stage of life.

Maternal food supplementation and perceived predation risk modify egg composition and eggshell traits but not offspring condition

Mothers may vary resource allocation to eggs and embryos, which may affect offspring fitness and prepare them for future environmental conditions. The effects of food availability and predation risk on reproduction have been extensively studied, yet their simultaneous impacts on reproductive investment and offspring early life conditions are still unclear. We experimentally manipulated these key environmental elements using a 2×2 full factorial design in wild, free-living pied flycatchers (Ficedula hypoleuca), and measured egg composition, eggshell traits and offspring condition. Eggs laid in food-supplemented nests had larger yolks and thicker shells independently of predation risk, while eggs laid in nests exposed to predator cues had lower levels of immunoglobulins, independent of food supplementation. In nests without predator cues, shell biliverdin content was higher in eggs laid in food-supplemented nests. Incubation was 1 day shorter in food-supplemented nests and shorter incubation periods were associated with higher hatching success, but there were no direct effects of maternal treatment on hatching success. To investigate the impact of maternal treatment (via egg composition) on the offspring, we performed full brood cross-fostering after hatching to unmanipulated nests. Maternal treatment did not significantly affect body mass and immunoglobulin levels of offspring. Our results suggest that although prenatal maternal cues affected egg composition, these egg-mediated effects may not have detectable consequences for offspring growth or immune capacity. Unpredictable environmental stressors may thus affect parental investment in the eggs, but parental care may level off costs and benefits of differential maternal egg allocation.

Early-life social environment alters juvenile behavior and neuroendocrine function in a highly social cichlid fish

Early-life experiences can shape adult behavior, with consequences for fitness and health, yet fundamental questions remain unanswered about how early-life social experiences are translated into variation in brain and behavior. The African cichlid fish Astatotilapia burtoni, a model system in social neuroscience, is well known for its highly plastic social phenotypes in adulthood. Here, we rear juveniles in either social groups or pairs to investigate the effects of early-life social environments on behavior and neuroendocrine gene expression. We find that both juvenile behavior and neuroendocrine function are sensitive to early-life effects. Behavior robustly co-varies across multiple contexts (open field, social cue investigation, and dominance behavior assays) to form a behavioral syndrome, with pair-reared juveniles towards the end of syndrome that is less active and socially interactive. Pair-reared juveniles also submit more readily as subordinates. In a separate cohort, we measured whole brain expression of stress and sex hormone genes. Expression of glucocorticoid receptor 1a was elevated in group-reared juveniles, supporting a highly-conserved role for the stress axis mediating early-life effects. The effect of rearing environment on androgen receptor α and estrogen receptor α expression was mediated by treatment duration (1 vs. 5 weeks). Finally, expression of corticotropin-releasing factor and glucocorticoid receptor 2 decreased significantly over time. Rearing environment also caused striking differences in gene co-expression, such that expression was tightly integrated in pair-reared juveniles but not group-reared or isolates. Together, this research demonstrates the important developmental origins of behavioral phenotypes and identifies potential behavioral and neuroendocrine mechanisms.

Acute emotional stress as a trigger for intraocular pressure elevation in Glaucoma

Background

Stress-induced activation of the sympathetic nervous system leads to a cascade of metabolic reactions. Emotional stress is a more specific form of stress in which the stressor is a psychological response to a situation subjectively perceived as traumatic. Stress hormones can have a wide range of effects on the body, however, it is still unclear if and how it can affect ophthalmic physiology. This report presents a case of severe ocular hypertension in which emotional stress was the only cause elicited, and explores potential aggravating factors.

Case presentation

A 78-year-old, personality type A, lady with a history of pseudo-exfoliative glaucoma presented with an acute asymmetrical raise in intraocular pressure (IOP) immediately following a family breakdown. Her IOP had previously remained stable following a deep sclerectomy in the right eye and an Ex-PRESS shunt in the left eye. Her examination was entirely normal otherwise, with a patent filtration and diffuse bleb as confirmed with anterior segment OCT imaging. Near-normalisation of her IOP was observed within 24 h, concomitantly with the reduction of her stress levels. No other cause for the transient acute hypertensive episode were found.

Conclusions

This case report suggests that acute emotional stress could severely affect IOP in patients suffering from glaucoma. This could be important when looking after glaucoma patients. It would also suggest that the personnality types, and the emotional and social context are more factors to take into account in glaucoma studies. These observations are based on a single case report and would need to be verified on a larger scale.