Unpredictable mild stressors on laying females influence the composition of Japanese quail eggs and offspring's phenotype

Maternal stress effects across generations in a precocial bird

Prenatal maternal stress (PMS) is known to shape the phenotype of the first generation offspring (F1) but according to some studies, it could also shape the phenotype of the offspring of the following generations. We previously showed in the Japanese quail that PMS increased the emotional reactivity of F1 offspring in relation to (i) a variation in the levels of some histone post-translational modification (H3K27me3) in their brains and (ii) a modulation of the hormonal composition of the eggs from which they hatched. Here, we wondered whether PMS could also influence the behaviour of the second (F2) and third (F3) generation offspring due to the persistence of the specific marks we identified. Using a principal component analysis, we found that PMS influenced F2 and F3 quail profiles with subtle differences between generations. It increased F2 neophobia, F3 fearfulness and F3 neophobia but only in females. Interestingly, we did not find any variations in the level of histone post-translational modification in F3 brains and we observed inconsistent modulations of androstenedione levels in F1 and F2 eggs. Although they may vary over generations, our results demonstrate that PMS can have phenotypical effects into the third generation.

Growing up in a crowd: social environment shapes the offspring's early exploratory phenotype in a colonial breeding species

In colonial breeding species, the number of adverse social interactions during early life typically varies with breeding density. Phenotypic plasticity can help deal with this social context, by allowing offspring to adjust their behaviour. Furthermore, offspring may not be unprepared since mothers can allocate resources to their embryos that may pre-adjust them to the post-hatching conditions. Thus, we hypothesize that lesser black-backed gull chicks raised in dense breeding areas, with greater exposure to intra-specific aggression, show higher levels of anxiety and lower levels of exploration compared to chicks in low-density areas, and that this is facilitated by prenatal effects. To test this, we cross-fostered clutches within and across pre-defined high- and low-breeding density areas. We measured chicks' anxiety and exploration activity in an open-field test that included a novel and a familiar object. We found that both pre- and post-natal social environment contributed nearly equally and shaped the offspring's exploratory behaviour, but not its anxiety, in an additive way. Post-natal effects could reflect a learned avoidance of intra-specific aggression, yet identifying the pathways of the prenatal effects will require further study.

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.

Training level reveals a dynamic dialogue between stress and memory systems in birds

Chronic stress profoundly affects forms of declarative memory, such as spatial memory, while it may spare non-declarative memory, such as cue-based memory. It is known, however, that the effects of chronic stress on memory systems may vary according to the level of training of an individual was submitted. Here, we investigated, in birds, how chronic stress impact spatial and cue-based memories according to training level. For that, control and chronically stressed Japanese quail were trained in a task that could be solved using spatial and cue-based memory and tested for their memory performance after 5 and 15 training days (initial training and overtraining, respectively) and following an emotional challenge (exposure to an open field). Our results showed that, compared to control quail, chronic stress impacted negatively spatial memory performances in stressed birds after initial training, but these differences were lowered after overtraining. Control birds seemed to shift from spatial to cue-based memory to solve the task across overtraining. However, an emotional challenge before testing reinstated the negative impact of chronic stress on spatial memory performances between the groups, revealing that chronic stress/overtraining did not eliminate the spatial memory and differences caused by stressors can reemerge depending on the individual's immediate psychological state. Contrary to spatial memory, cue-based memory was not affected in chronically stressed birds compared to control birds in any test occasion, confirming its resistance against the negative effects of chronic stress. Altogether these findings reveal a dynamic dialogue between stress, training level, and memory systems in birds.

Effects of acute stressors experienced by five strains of layer breeders on measures of stress and fear in their offspring

Stressors experienced by layer breeders during egg production can lead to changes in the egg hormone content, potentially impacting their offspring, the commercial layers. Genetic differences might also affect the offspring's susceptibility to maternal experiences. In this study, we tested if maternal stress affects measures of stress and fear in five strains of layer breeders: commercial brown 1 & 2, commercial white 1 & 2 and a pure line White Leghorn. Each strain was equally separated into two groups: "Maternal Stress" (MS), where hens were subjected to a series of 8 consecutive days of acute psychological stressors, and "Control," which received routine husbandry. Additional eggs from Control were injected either with corticosterone diluted in a vehicle solution ("CORT") or just "Vehicle." Stress- and fear-responses of the offspring were measured in a plasma corticosterone test and a combined human approach and novel object test. While the stress treatments did not  affect the measured endpoints in the offspring, significant strain differences were found. The offspring of the white strains showed a higher physiological response compared to brown strains and the White 2 offspring was the least fearful strain in the human approach test. Our study found that neither the acute psychological stressors experienced by layer breeders nor the egg injections of corticosterone affected the parameters tested in their offspring. Post hoc power analyses suggest that the lack of treatment effects might be due to a small sample size (type II error). Although studies on larger flocks of layers are still needed, our results provide an initial understanding of an important subject, as in poultry production, layer breeders are often subjected to short-term stressors. In addition, our results suggest the dissociation between the physiological and behavioural parameters of stress response in laying hens, showing that increased concentrations of plasma corticosterone in response to stress might not be directly associated with high levels of fear.

Modulating offspring responses: concerted effects of stress and immunogenic challenge in the parental generation

The perception, processing and response to environmental challenges involves the activation of the immuno-neuroendocrine (INE) interplay. Concerted environmental challenges might induce trade-off when resource allocation to one trait occurs at the expense of another, also producing potential transgenerational effects in the offspring. We evaluated whether concerted challenges, in the form of an immune inoculum against inactivated Salmonella enteritidis (immune challenge, ICH) and a chronic heat stress (CHS) exposure on adult Japanese quail, modulate the INE responses of the parental generation and their offspring. Adults were inoculated and later exposed to a CHS along nine consecutive days. For the last 5 days of the CHS, eggs were collected for incubation. Chicks were identified according to their parental treatments and remained undisturbed. Induced inflammatory response, heterophil/lymphocyte (H/L) ratio and specific humoral response against sheep red blood cells (SRBC) were evaluated in both generations. Regardless of the ICH, stressed adults showed a reduced inflammatory response and an elevated H/L ratio compared with controls. In offspring, the inflammatory response was elevated and the specific SRBC antibody titres were diminished in those chicks prenatally exposed to CHS, regardless of the ICH. No differences were found in the H/L ratio of the offspring. Together, our results suggest that CHS exposure influences the INE interplay of adult quail, establishing trade-offs within their immune system. Moreover, CHS not only affected parental INE responses but also modulated their offspring INE responses, probably affecting their potential to respond to future challenges. The adaptability of the developmental programming of offspring would depend on the environment encountered.

Effects of Maternal Stress on Measures of Anxiety and Fearfulness in Different Strains of Laying Hens

Maternal stress can affect the offspring of birds, possibly due to hormone deposition in the egg. Additionally, phenotypic diversity resulting from domestication and selection for productivity has created a variety of poultry lines that may cope with stress differently. In this study, we investigated the effects of maternal stress on the behavior of different strains of laying hens and the role of corticosterone as its mediator. For this, fertilized eggs of five genetic lines-two brown (Brown 1 and 2), two white (White 1 and 2), and one pure line White Leghorn-were reared identically as four flocks of 27 birds (24F: 3M) per strain. Each strain was equally separated into two groups: Maternal Stress ("MS"), where hens were subjected to a series of daily acute psychological stressors for 8 days before egg collection, and "Control," which received routine husbandry. Fertile eggs from both treatments were collected at three different ages forming different offspring groups that were treated as replicates; additional eggs from Control were injected either with corticosterone diluted in a vehicle solution ("CORT") or just "Vehicle." Eggs from each replicate were incubated and hatched, and offspring (N = 1,919) were brooded under identical conditions. To measure the effects of maternal stress on anxiety and fear-like behavior, offspring were subjected to a social isolation test (SI) between 5 and 10 days of age and a tonic immobility test (TI) at 9 weeks of age. Compared to Control, MS decreased the number of distress vocalizations emitted by White 2 in SI. No effects of MS were observed in TI, and no effects of CORT were observed in any tests. Overall, brown lines vocalized more in SI and remained in TI for a longer duration than white strains, suggesting genetic differences in fear behavior. Females vocalized more than males in TI and showed a trend toward significance for the same trait in SI. Overall, results suggest that the effects of maternal stress on fearfulness are not directly mediated by corticosterone. Moreover, it highlights behavioral differences across various strains of laying hens, suggesting that fear responses are highly dependent on genotype.

Seasonal changes in yolk hormone concentrations carry-over to offspring traits

Yolk hormones are substances which transmit non-genetic factors from the mother to the next generation. The systematic changes of yolk hormone concentrations within asynchronously hatching clutches have been interpreted as a means to adaptively shape the offspring's phenotype. However, in synchronously hatching clutches the role of yolk hormones is less understood. We investigated whether seasonal changes between eggs in the yolk hormones testosterone (Testo), progesterone (Prog) and corticosterone (Cort) also occur in the grey partridge, a synchronously hatching precocial species without direct food competition between siblings. Specifically we asked whether yolk hormone concentrations systematically vary with season and whether they affect the offspring's hatching mass, mass gain, circulating baseline and stress-induced Cort. Additionally, we investigated the effect of genetic background and food availability on yolk hormone concentrations by subjecting grey partridge hens of two strains (wild and domesticated) to two different feeding regimes (predictable vs. unpredictable feeding) during egg laying. We hypothesized that egg hormone concentrations change over the season, but breeding in captivity over many generations and ad libitum food access could have resulted in domestication effects which abolished potential seasonal effects. Results showed that progressing season had a strong positive effect on yolk Prog and yolk Testo, but not on yolk Cort. Feeding regimes and strain had no effect on yolk hormones. Offspring mass and mass gain increased and baseline Cort decreased with progressing season. In addition, yolk Testo correlated positively with offspring mass gain and negatively with baseline Cort, while yolk Prog had a positive correlation with baseline Cort. Strain and feeding regimes of the mother had no effect on offspring traits. In conclusion, grey partridge chicks hatching late in the season might benefit from the increased concentrations of the growth-stimulating yolk Testo and by this catch-up in development. Hence, yolk hormone concentration could adaptively shape the offspring phenotype in a precocial species.

Effects of prenatal stress and genetics on embryonic survival and offspring growth of laying hens

Early-life exposure to stressors can shape the phenotype of the offspring resulting in changes that may affect their prehatch and posthatch development. This can be modeled indirectly through maternal exposure to stressors (natural model) or by offspring exposure to stress hormones (pharmacological model). In this study, both models were used to investigate the effects of genetic line on hatchability, late embryonic mortality, sex ratio, and body weight until 17 wk of age. To form the parent stock, fertilized eggs of 4 commercial genetic lines — two brown (brown 1 and 2), two white (white 1 and 2), and a pure line White Leghorn — were incubated, hatched, and housed identically in 4 flocks of 27 birds (24 females and 3 males) per strain. Each strain was equally separated into 2 groups: “maternal stress,” where hens were subjected to a series of acute psychological stressors (e.g., physical restraint, transportation) for 8 D before egg collection, and “control,” where hens received routine husbandry. At 3 maternal ages, fertile eggs from both treatments were collected, and additional eggs from the control group were injected with corticosterone (10 ng/mL egg content) (“CORT”). A “vehicle” treatment was included to account for effects of egg manipulation. Each maternal age comprised a replicate over time. Eggs were incubated and hatched, and the offspring (N = 1,919) were brooded until 17 wk under identical conditions. The results show that prenatal stress interacted with strain to decrease embryonic survival and growth. Among all strains, brown 2 was consistently the most affected line in both prehatch and posthatch development. Our study shows that embryonic survival and offspring growth are mostly affected by the pharmacological model and that strain differences may increase susceptibility to prenatal stress. Moreover, it suggests that the natural stressor model may be useful for quantifying the response of the mother to stressors, whereas the pharmacological model may be useful for quantifying the response of the embryo to increased levels of corticosterone.

Human behaviour at the origin of maternal effects on offspring behaviour in laying hens (Gallus gallus domesticus)

Regular visual presence of humans is known to reduce chickens' human-generated stress responses. Here we questioned whether, more than mere visual presence, human behaviour affects laying hen behaviour and subsequently their offspring's behaviour. We hypothesized that human behaviour triggers maternal effects via variations in yolk hormone levels. For five consecutive weeks, two groups of hens were exposed to the same durations of human presence (30 min twice a day, five days a week) but the behaviour of the human differed between groups. The first group (H+) was exposed to predictable arrival of the experimenter, slow movements combined with static presence, stroking during handling and human voice. Whereas the second group of hens (H-) was exposed to unpredictable arrival of the experimenter which remained silent, in motion, and did not provide stroking during handling. At the end of the treatment, we evaluated egg quality and offspring behaviour. We found that avoidance of the experimenter by H+ hens but not by H- hens decreased significantly. Fertility rates and concentrations of yolk progesterone and estradiol in H+ hens' eggs were higher than in H- hens' eggs. Fear of humans, neophobia or the capacity to solve a detour task did not differ significantly between H+ and H- chicks. Social discrimination tests showed that H+ chicks but not H- chicks typically preferred a familiar conspecific to a stranger. These results show that, with the same duration in the presence of the birds, humans through their behaviour engender variations in fertility rates, yolk hormone levels and transgenerational effects on social skills. Rarely explored, our data suggest that maternal effects influence filial imprinting. These data have broad implications for laboratory, commercial systems and conservatory programs where the inevitable presence of humans could trigger maternal effects on offspring phenotype.

Maternal and Embryonic Stress Influence Offspring Behavior in the Cuttlefish Sepia officinalis

Stress experienced during prenatal development-either applied to reproducing females (maternal stress), directly to developing offspring (embryonic stress) or in combination-is associated with a range of post-natal behavioral effects in numerous organisms. We conducted an experiment to discern if maternal and embryonic stressors affect the behavior of hatchlings of the cuttlefish Sepia officinalis, a species with features that allow for the examination of these stress types in isolation. Separating the impact of stress transmitted through the mother vs. stress experienced by the embryo itself will help clarify the behavioral findings in viviparous species for which it is impossible to disentangle these effects. We also compared the effect of a naturally-occurring (predator cue) and an "artificial" (bright, randomly-occurring LED light) embryonic stressor. This allowed us to test the hypothesis that a threat commonly faced by a species (natural threat) would be met with a genetically-programmed and adaptive response while a novel one would confound innate defense mechanisms and lead to maladaptive effects. We found that the maternal stressor was associated with significant differences in body patterning and activity patterns. By contrast, embryonic exposure to stressors increased the proportion of individuals that pursued prey. From these results, it appears that in cuttlefish, maternal and embryonic stressors affect different post-natal behavior in offspring. In addition, the effect of the artificial stressor suggests that organisms can sometimes react adaptively to a stressor even if it is not one that has been encountered during the evolutionary history of the species.

Transgenerational transmission of a stress-coping phenotype programmed by early-life stress in the Japanese quail

An interesting aspect of developmental programming is the existence of transgenerational effects that influence offspring characteristics and performance later in life. These transgenerational effects have been hypothesized to allow individuals to cope better with predictable environmental fluctuations and thus facilitate adaptation to changing environments. Here, we test for the first time how early-life stress drives developmental programming and transgenerational effects of maternal exposure to early-life stress on several phenotypic traits in their offspring in a functionally relevant context using a fully factorial design. We manipulated pre- and/or post-natal stress in both Japanese quail mothers and offspring and examined the consequences for several stress-related traits in the offspring generation. We show that pre-natal stress experienced by the mother did not simply affect offspring phenotype but resulted in the inheritance of the same stress-coping traits in the offspring across all phenotypic levels that we investigated, shaping neuroendocrine, physiological and behavioural traits. This may serve mothers to better prepare their offspring to cope with later environments where the same stressors are experienced.

Artificially Increased Yolk Hormone Levels and Neophobia in Domestic Chicks

In birds there is compelling evidence that the development and expression of behavior is affected by maternal factors, particularly via variation in yolk hormone concentrations of maternal origin. In the present study we tested whether variation in yolk hormone levels lead to variation in the expression of neophobia in young domestic chicks. Understanding how the prenatal environment could predispose chicks to express fear-related behaviors is essential in order to propose preventive actions and improve animal welfare. We simulated the consequences of a maternal stress by experimentally enhancing yolk progesterone, testosterone and estradiol concentrations in hen eggs prior to incubation. The chicks from these hormone-treated eggs (H) and from sham embryos (C) that received the vehicle-only were exposed to novel food, novel object and novel environment tests. H chicks approached a novel object significantly faster and were significantly more active in a novel environment than controls, suggesting less fearfulness. Conversely, no effect of the treatment was found in food neophobia tests. Our study highlights a developmental influence of yolk hormones on a specific aspect of neophobia. The results suggest that increased yolk hormone levels modulate specifically the probability of exploring novel environments or novel objects in the environment.

Early experiences matter: a review of the effects of prenatal environment on offspring characteristics in poultry

Early life experiences can be important in determining offspring phenotypes and may influence interaction with the environment and hence health, welfare, and productivity. The prenatal environment of poultry can be divided into the pre-lay environment and the egg storage/incubation environment, both of which can affect offspring outcomes. The ability to separate maternal and egg/incubation effects makes birds well suited to this type of research. There are many factors, including feeding and nutrition, environmental conditions, husbandry practices, housing system, social environment, infectious environment, and maternal health status, that can influence both the health and performance and behavior and cognition of the offspring. There are some aspects of the environments that can be changed to produce beneficial effects in the offspring, like addition of certain additives to feed or short changes in incubation temperatures, while other aspects should be avoided to reduce negative effects, such as unpredictable feeding and lighting regimens. Measures of offspring characteristics may prove to be a useful method of assessing parent stock welfare if known stressors result in predictable offspring outcomes. This has the advantage of assessing the parent environment without interfering with the animals and possibly affecting their responses and could lead to improved welfare for the animals.

Yolk hormones influence in ovo chemosensory learning, growth, and feeding behavior in domestic chicks

In this study, we assessed whether prenatal exposure to elevated yolk steroid hormones can influence in ovo chemosensory learning and the behavior of domestic chicks. We simulated a maternal environmental challenge by experimentally enhancing yolk progesterone, testosterone, and estradiol concentrations in hen eggs prior to incubation. The embryos from these hormones-treated eggs (HO) as well as sham embryos (O) that had received the vehicle-only were exposed to the odor of fish oil (menhaden) between embryonic Days 11 and 20. An additional group of control embryos (C) was not exposed to the odor. All chicks were tested following hatching for their feeding preferences between foods that were or were not odorized with the menhaden odor. In the 3-min choice tests, the behavior of O chicks differed significantly according to the type of food whereas C and HO chicks showed no preference between odorized and non-odorized food. Our result suggests weaker response in HO chicks. In addition, HO chicks showed impaired growth and reduced intake of an unfamiliar food on the 24-h time scale compared to controls. Our data suggest that embryonic exposure to increased yolk hormone levels can alter growth, chemosensory learning, and the development of feeding behaviors.

Sex-specific differences in offspring personalities across the laying order in magpies Pica pica

Maternal effects provide an important mechanism for mothers to create variation in offspring personality, and to potentially influence offspring life history strategies e.g. creating more/less dispersive phenotypes. However, within-clutch maternal effects often vary and hence there is potential for within-clutch variation in personality. We studied the effects of hatching order on explorative and neophobic behaviour of the magpies Pica pica in relation to sex using novel environment and novel object experiments. Hatching order did affect explorative behaviour in magpie, but did so in opposite directions for either sex. First-hatched females were more explorative and had a tendency to be less neophobic, whereas in males, the reverse was true. Our results suggest that hormonal as well as post-natal environmental mechanisms could be underpinning this pattern. Future research is needed to fully understand the importance of both in creating different offspring personalities. This article is part of a Special Issue entitled: insert SI title.

Parents and early life environment affect behavioral development of laying hen chickens

Severe feather pecking (SFP) in commercial laying hens is a maladaptive behavior which is associated with anxiety traits. Many experimental studies have shown that stress in the parents can affect anxiety in the offspring, but until now these effects have been neglected in addressing the problem of SFP in commercially kept laying hens. We therefore studied whether parental stock (PS) affected the development of SFP and anxiety in their offspring. We used flocks from a brown and white genetic hybrid because genetic background can affect SFP and anxiety. As SFP can also be influenced by housing conditions on the rearing farm, we included effects of housing system and litter availability in the analysis. Forty-seven rearing flocks, originating from ten PS flocks were followed. Behavioral and physiological parameters related to anxiety and SFP were studied in the PS at 40 weeks of age and in the rearing flocks at one, five, ten and fifteen weeks of age. We found that PS had an effect on SFP at one week of age and on anxiety at one and five weeks of age. In the white hybrid, but not in the brown hybrid, high levels of maternal corticosterone, maternal feather damage and maternal whole-blood serotonin levels showed positive relations with offsprings' SFP at one week and offsprings' anxiety at one and five weeks of age. Disruption and limitation of litter supply at an early age on the rearing farms increased SFP, feather damage and fearfulness. These effects were most prominent in the brown hybrid. It appeared that hens from a brown hybrid are more affected by environmental conditions, while hens from a white hybrid were more strongly affected by parental effects. These results are important for designing measures to prevent the development of SFP, which may require a different approach in brown and white flocks.

Long-life partners or sex friends? Impact of parental pair bond on offspring personality

Previous investigations reported that some traits of parental relationships, including pair-bond duration or mate behavioural compatibility, influence subsequent offspring fitness by acting on their behaviour, growth and thus their early survival. We hypothesized that the development of a pair-bond between sexual partners would have a prenatal influence. This study investigated the impact of two pairing managements on the egg characteristics and development of offspring of Japanese quail (Coturnix c. japonica). Thirty males and 30 females were paired either continuously (C) (mates together all the time) or non-continuously (NC) (pairs met only three times a week for five minutes). Separation-reunion tests evaluated parental pair bond. Egg yolk testosterone and androstenedione levels were evaluated, and the somatic and behavioural development of C and NC chicks was assessed. Our results revealed that members of C pairs were attached to their mates and, although no significant differences in androgen levels could be evidenced between egg sets, a higher proportion of C pairs' eggs were fertilized and their chicks appeared less emotive and more social. Our results revealed that parental relationship can modulate the behavioural development of their offspring, probably via non-genetic effects, and this could play a major role in the emergence of inter-individual variability.

Epigenetics and phenotypic variability: some interesting insights from birds

Little is known about epigenetic mechanisms in birds with the exception of the phenomenon of dosage compensation of sex chromosomes, although such mechanisms could be involved in the phenotypic variability of birds, as in several livestock species. This paper reviews the literature on epigenetic mechanisms that could contribute significantly to trait variability in birds, and compares the results to the existing knowledge of epigenetic mechanisms in mammals. The main issues addressed in this paper are: (1) Does genomic imprinting exist in birds? (2) How does the embryonic environment influence the adult phenotype in avian species? (3) Does the embryonic environment have an impact on phenotypic variability across several successive generations? The potential for epigenetic studies to improve the performance of individual animals through the implementation of limited changes in breeding conditions or the addition of new parameters in selection models is still an open question.

Confronting Intrasexual Rivals

The current research sheds light on a physiological mechanism potentially underlying confrontational responses to infidelity. Findings suggest that responses to infidelity threats in adulthood are shaped by hormonally mediated masculinization of the brain in utero. 2D:4D digit ratio (widely regarded as an index of prenatal testosterone exposure) moderated behavioral and endocrinological responses to infidelity threat. After an infidelity prime (but not a control prime), lower (more masculine) 2D:4D was associated with a greater tendency to approach attractive same-sex targets (intrasexual rivals) and with heightened increases in circulating testosterone, a hormone related to a variety of aggressive and confrontational behaviors.

Moderate heat challenge increased yolk steroid hormones and shaped offspring growth and behavior in chickens

Background

Environmental challenges might affect the maternal organism and indirectly affect the later ontogeny of the progeny. We investigated the cross-generation impact of a moderate heat challenge in chickens. We hypothesized that a warm temperature–within the thermotolerance range- would affect the hormonal environment provided to embryos by mothers, and in turn, affect the morphology and behavioral phenotype of offspring.

Methodology/Principal Findings

Laying hens were raised under a standard thermal condition at 21°C (controls) or 30°C (experimental) for 5 consecutive weeks. A significant increase was observed in the internal temperature of hens exposed to the warm treatment; however plasma corticosterone levels remained unaffected. The laying rate was not affected, but experimental hens laid lighter eggs than the controls during the treatment. As expected, the maternal thermal environment affected yolk hormone contents. Eggs laid by the experimental hens showed significantly higher concentrations of yolk progesterone, testosterone, and estradiol. All chicks were raised under standard thermal conditions. The quality of hatchlings, growth, feeding behavior and emotional reactivity of chicks were analyzed. Offspring of experimental hens (C30 chicks) were lighter but obtained better morphological quality scores at hatching than the controls (C21 chicks). C30 chicks expressed lesser distress calls when exposed to a novel food. Unlike C21 chicks, C30 chicks expressed no preference for energetic food.

Conclusion/Significance

Our findings suggest that moderate heat challenge triggers maternal effects and modulate the developmental trajectory of offspring in a way that may be adaptive. This suggests that the impact of heat challenges on captive or wild populations might have a cross-generation effect.

Maternal predator-exposure has lifelong consequences for offspring learning in threespined sticklebacks

Learning is an important form of phenotypic plasticity that allows organisms to adjust their behaviour to the environment. An individual's learning performance can be affected by its mother's environment. For example, mothers exposed to stressors, such as restraint and forced swimming, often produce offspring with impaired learning performance. However, it is unclear whether there are maternal effects on offspring learning when mothers are exposed to ecologically relevant stressors, such as predation risk. Here, we examined whether maternal predator-exposure affects adult offsprings' learning of a discrimination task in threespined sticklebacks (Gasterosteus aculeatus). Mothers were either repeatedly chased by a model predator (predator-exposed) or not (unexposed) while producing eggs. Performance of adult offspring from predator-exposed and unexposed mothers was assessed in a discrimination task that paired a particular coloured chamber with a food reward. Following training, all offspring learned the colour-association, but offspring of predator-exposed mothers located the food reward more slowly than offspring of unexposed mothers. This pattern was not driven by initial differences in exploratory behaviour. These results demonstrate that an ecologically relevant stressor (predation risk) can induce maternal effects on offspring learning, and perhaps behavioural plasticity more generally, that last into adulthood.

Trans-generational effects of prenatal stress in quail

The prenatal environment is a source of phenotypic variability influencing the animal's characteristics. Prenatal stress affects not only the development of offspring, but also that of the following generation. Such effects have been best documented in mammals but can also be observed in birds, suggesting common processes across phylogenetic orders. We found previously that Japanese quail females stressed during laying produced offspring with higher fearfulness, probably related to modulation of testosterone levels in their eggs. Here, we evaluated long-term effects of prenatal stress by analysing reproductive traits of these F(1) offspring and, then, the development of their subsequent (F(2)) offspring. The sexual behaviour of F(1) prenatally stressed (F1PS) males was impaired. F1PS females' eggs contained less yolk and more albumen, and higher yolk testosterone and progesterone levels than did F(1) prenatal control females. The fearfulness of F(2) prenatally stressed quail was greater than that of F(2) prenatal control quail. These F(2) behavioural differences paralleled those evidenced by their parents, suggesting trans-generational transmission of prenatal stress effects, probably mediated by egg compositions of F1PS females.

A place to hide in the home-cage decreases yolk androgen levels and offspring emotional reactivity in Japanese quail

An animal's emotional responses are the result of its cognitive appraisal of a situation. This appraisal is notably influenced by the possibility of an individual to exert control over an aversive event. Although the fact that environment controllability decreases emotional responses in animals is well established, far less is known about its potential trans-generational effects. As the levels of avian yolk hormones can vary according to the mother's environment, we hypothesized that housing environment of mothers would modulate the quality of her eggs and in turn her offspring's behaviour. Two groups of female Japanese quail were constituted: a group that had access to a place to hide in their home-cage (Hd, n = 20) and a group that had nowhere to hide (NoHd, n = 20) when stressed. Both groups were submitted to daily human disturbances for a twenty-day-period. Hd females produced eggs with both less testosterone and androstenedione than did NoHd females. The emotional and social reactivity of Hd females' offspring were lower and their growth was slower than those of NoHd females' offspring. Our results show that a minor difference in housing environment had substantial effects on eggs and offspring. The presence of a shelter probably helped quail to cope with daily human disturbances, producing less reactive offspring. This transgenerational effect caused by an opportunity to hide could lead to applications in care of laboratory animals, conservation biology and animal welfare.