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.

A systematic review and meta-analysis of unimodal and multimodal predation risk assessment in birds

Despite a wealth of studies documenting prey responses to perceived predation risk, researchers have only recently begun to consider how prey integrate information from multiple cues in their assessment of risk. We conduct a systematic review and meta-analysis of studies that experimentally manipulated perceived predation risk in birds and evaluate support for three alternative models of cue integration: redundancy/equivalence, enhancement, and antagonism. One key insight from our analysis is that the current theory, generally applied to study cue integration in animals, is incomplete. These theories specify the effects of increasing information level on mean, but not variance, in responses. In contrast, we show that providing multiple complementary cues of predation risk simultaneously does not affect mean response. Instead, as information richness increases, populations appear to assess risk more accurately, resulting in lower among-population variance in response to manipulations of perceived predation risk. We show that this may arise via a statistical process called maximum-likelihood estimation (MLE) integration. Our meta-analysis illustrates how explicit consideration of variance in responses can yield important biological insights.

Interplay of cooperative breeding and predation risk on egg allocation and reproductive output

Predation risk can influence behavior, reproductive investment, and, ultimately, individuals' fitness. In high-risk environments, females often reduce allocation to reproduction, which can affect offspring phenotype and breeding success. In cooperative breeders, helpers contribute to feed the offspring, and groups often live and forage together. Helpers can, therefore, improve reproductive success, but also influence breeders' condition, stress levels and predation risk. Yet, whether helper presence can buffer the effects of predation risk on maternal reproductive allocation remains unstudied. Here, we used the cooperatively breeding sociable weaver Philetairus socius to test the interactive effects of predation risk and breeding group size on maternal allocation to clutch size, egg mass, yolk mass, and yolk corticosterone. We increased perceived predation risk before egg laying using playbacks of the adults' main predator, gabar goshawk (Micronisus gabar). We also tested the interactive effects of group size and prenatal predator playbacks on offspring hatching and fledging probability. Predator-exposed females laid eggs with 4% lighter yolks, but predator-calls' exposure did not clearly affect clutch size, egg mass, or egg corticosterone levels. Playback-treatment effects on yolk mass were independent of group size, suggesting that helpers' presence did not mitigate predation risk effects on maternal allocation. Although predator-induced reductions in yolk mass may decrease nutrient availability to offspring, potentially affecting their survival, playback-treatment effects on hatching and fledging success were not evident. The interplay between helper presence and predator effects on maternal reproductive investment is still an overlooked area of life history and physiological evolutionary trade-offs that requires further studies.

Effects of competition and predation operating at individual and population levels: an overview of results from a long-term field experiment

After an overview of the discussion about the existence of intra- and interspecific competition that illustrates the contradictory opinions I conclude that long-term field experiments are needed for firm conclusions. I discuss in some detail the role of two factors that limit population size of secondary cavity nesting birds e.g. territorial behavior and adequate cavities. This is followed by an overview of experimental long-term field studies in Belgium showing that intra- and interspecific competition in a great tit-blue tit system exists. By using nestbox configurations with high densities of nestboxes that differ in the diameter of their entrance hole in replicate study plots it is possible to manipulate the breeding densities of great tit Parus major and blue tit Cyanistes caeruleus independently, thereby varying the intensity of intra- and interspecific competition between these two coexisting species. When blue tit densities are experimentally increased local recruitment of great tits increases, and adult great tit post-breeding dispersal to other study plots decreases, implying that great tits use blue tit density to evaluate habitat quality and that high blue tit density results in heterospecific attraction. The reverse is not true. An experimental increase in great tit density leading to an increase in interspecific competition in a plot where blue tit density was already high leads to a decrease in blue tit nestling mass (illustrating interspecific competition for food), but to a gradual increase in blue tit body size. Both are primarily caused by an increase in the body size of immigrants (caused by intraspecific competition for protected roosting holes) in contrast to the control plot, where neither is observed. I also summarize behavioral, ecological and possible evolutionary effects of sparrowhawks on blue tits after sparrowhawks settled in an isolated study plot halfway through the study: adult survival substantially decreased for both sexes, but more for females that laid large clutches, leading to selection for females that laid a smaller clutch. This led to a change in the reproduction/survival life-history trade-off. Adult winter weights and nestling weights decreased, and the heaviest fledglings were selected against. Furthermore the frequency of polygyny increased. The long-term experiments also document the role of the use of public information and that species that compete can be attracted to sites in which competitor density is high.

Born without a Silver Spoon: A Review of the Causes and Consequences of Adversity during Early Life

A huge amount of research attention has focused on the evolution of life histories, but most research focuses on dominant individuals that acquire a disproportionate level of reproductive success, while the life histories and reproductive tactics of subordinate individuals have received less attention. Here, we review the links between early life adversity and performance during adulthood in birds, and highlight instances in which subordinate individuals outperform dominant conspecifics. Subordinate individuals are those from broods raised under high risk of predation, with low availability of food, and/or with many parasites. Meanwhile, the broods of many species hatch or are born asynchronously and mitigation of the asynchrony is generally lacking from variation in maternal effects such as egg size and hormone deposition or genetic effects such as offspring sex or parentage. Subordinate individuals employ patterns of differential growth to attempt to mitigate the adversity they experience during early life, yet they overwhelmingly fail to overcome their initial handicap. In terms of surviving through to adulthood, subordinate individuals employ other "suboptimal" tactics, such as adaptively timing foraging behaviors to avoid dominant individuals. During adulthood, meanwhile, subordinate individuals rely on "suboptimal" tactics, such as adaptive dispersal behaviors and competing for partners at optimal times, because they represent the best options available to them to acquire copulations whenever possible. We conclude that there is a gap in knowledge for direct links between early life adversity and subordination during adulthood, meaning that further research should test for links. There are instances, however, where subordinate individuals employ "suboptimal" tactics that allow them to outperform dominant conspecifics during adulthood.

Female red-winged blackbirds (Agelaius phoeniceus) do not alter nest site selection, maternal programming, or hormone-mediated maternal effects in response to perceived nest predation or brood parasitism risk

Predation or brood parasitism risks can change the behaviors and reproductive decisions in many parental animals. For oviparous species, mothers can mitigate their reproductive success in at least three ways: (1) by avoiding nest sites with high predation or parasitism risks, (2) through hormonal maternal effects that developmentally prime offspring for survival in risky environments, or (3) by investing less in reproduction when predation or parasitism risks are high. Here, we tested if perceived predation and parasitism risks can induce any of these behavioral or physiological responses by exposing female red-winged blackbirds (Agelaius phoeniceus) to playbacks of two major nest threats, a predator (Cooper's hawk, Accipiter cooperii) and an obligate brood parasite (brown-headed cowbird; Molothrus ater), as well as two controls (harmless Eastern meadowlark, Sturnella magna; and silence). We found that female blackbirds did not avoid nesting at sites treated with predator or brood parasite playbacks, nor were females more likely to abandon nesting attempts at these sites. Egg size and yolk hormone profiles, which are common proxies for maternal investment in oviparous species, were statistically similar across treatment sites. Instead, we found intraclutch variation in yolk steroid hormone profiles: concentrations of three progestogens (pregnanedione, 17α-hydroxypregnenolone, and deoxycorticosterone) and two androgens (testosterone and androstenedione) were higher in third-laid than first-laid eggs. Our study largely confirms previous findings of consistent intraclutch yolk hormone variation in this species, in birds in general, and in other oviparous lineages, but uniquely reports on several yolk steroid hormones largely overlooked in the literature on hormone-mediated maternal effects.

Growth in marine mammals: a review of growth patterns, composition and energy investment

Growth of structural mass and energy reserves influences individual survival, reproductive success, population and species life history. Metrics of structural growth and energy storage of individuals are often used to assess population health and reproductive potential, which can inform conservation. However, the energetic costs of tissue deposition for structural growth and energy stores and their prioritization within bioenergetic budgets are poorly documented. This is particularly true across marine mammal species as resources are accumulated at sea, limiting the ability to measure energy allocation and prioritization. We reviewed the literature on marine mammal growth to summarize growth patterns, explore their tissue compositions, assess the energetic costs of depositing these tissues and explore the tradeoffs associated with growth. Generally, marine mammals exhibit logarithmic growth. This means that the energetic costs related to growth and tissue deposition are high for early postnatal animals, but small compared to the total energy budget as animals get older. Growth patterns can also change in response to resource availability, habitat and other energy demands, such that they can serve as an indicator of individual and population health. Composition of tissues remained consistent with respect to protein and water content across species; however, there was a high degree of variability in the lipid content of both muscle (0.1-74.3%) and blubber (0.4-97.9%) due to the use of lipids as energy storage. We found that relatively few well-studied species dominate the literature, leaving data gaps for entire taxa, such as beaked whales. The purpose of this review was to identify such gaps, to inform future research priorities and to improve our understanding of how marine mammals grow and the associated energetic costs.

Larval and/or Adult Exposure to Intraguild Predator Harmonia axyridis Alters Reproductive Allocation Decisions and Offspring Growth in Menochilus sexmaculatus

Maternal effects can reduce offspring susceptibility to predators by altering resource allocation to young and reproducing larger offspring. While the perception of predation risk can vary according to a prey's life stage, it is unclear whether maternally experienced intraguild predation (IGP) risk during different life stages influences the maternal effects of predatory insects. We investigated the influence of exposure to intraguild predators (Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)) during the larval and/or adult stages on reproductive decisions and offspring growth in Menochilus sexmaculatus (Fabricius). Independent of the life stage, when M. sexmaculatus females experienced IGP risk, their body weight and fecundity decreased, but the proportion of trophic eggs produced increased. However, egg mass, egg clutch number, and egg clutch size were not influenced by the treatment. Next, when offspring encountered H. axyridis, mothers experiencing IGP risk during the larval and/or adult stages could increase their offspring's weight. Moreover, offspring in IGP environments reached a similar size as those with no-IGP environments when mothers experienced IGP risk during the larval and/or adult stages. Overall, M. sexmaculatus larval and/or adult exposure to IGP risk had no influence on egg size, but increased offspring body size when faced with H. axyridis. Additionally, mothers experiencing IGP risk during different life stages showed increased production of trophic eggs. Because IGP is frequently observed on M. sexmaculatus and favours relatively larger individuals, different stages of M. sexmaculatus express threat-sensitively to IGP risk; inducing maternal effects can be an adaptive survival strategy to defend against H. axyridis.

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.

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.

Postpartum maternal exposure to predator odor alters offspring antipredator behavior, basal HPA axis activity and immunoglobulin levels in adult Brandt's voles

Predation risk can program offspring behavior, physiology, and fitness through maternal effect, but most studies have mainly focused on this effect during pregnancy; little is known about the effect of postpartum predation risk on offspring's phenotype. Here, we compared the antipredator behaviors of adult offspring (approximately 90 days old) produced by female Brandt's voles (Lasiopodomys brandtii) exposed to one of three treatments: cat odor (CO), rabbit odor (RO), and distilled water (DW) for 60 min daily from postpartum day 1-18. Basal levels of plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT), hypothalamic corticotrophin releasing hormone (CRH), as well as spleen immunoglobulins (IgA, IgM, and IgG) were also measured. Our data showed that the offspring of CO-exposed mothers displayed less head-out behavior to acute 15-min CO exposure, and female offspring showed more freezing behavior. CO offspring showed significantly lower basal ACTH and CORT levels than the RO and DW offspring. Additionally, female but not male CO offspring had higher hypothalamic CRH expression and spleen IgG levels than controls, showing a sex-specific effect. These findings demonstrate that postpartum maternal predator risk exposure promotes a passive-avoidant response to these cues in adult offspring, showing a cross-generational maternal effect of postpartum predation risk. Further, these changes may be associated with alterations in the hypothalamic-pituitary-adrenal axis and immune function.

Pre- and Postnatal Predator Cues Shape Offspring Anti-predatory Behavior Similarly in the Bank Vole

Prey animals can assess the risks predators present in different ways. For example, direct cues produced by predators can be used, but also signals produced by prey conspecifics that have engaged in non-lethal predator-prey interactions. These non-lethal interactions can thereby affect the physiology, behavior, and survival of prey individuals, and may affect offspring performance through maternal effects. We investigated how timing of exposure to predation-related cues during early development affects offspring behavior after weaning. Females in the laboratory were exposed during pregnancy or lactation to one of three odor treatments: (1) predator odor (PO) originating from their most common predator, the least weasel, (2) odor produced by predator-exposed conspecifics, which we call conspecific alarm cue (CAC), or (3) control odor (C). We monitored postnatal pup growth, and we quantified foraging and exploratory behaviors of 4-week-old pups following exposure of their mothers to each of the three odour treatments. Exposure to odors associated with predation risk during development affected the offspring behavior, but the timing of exposure, i.e., pre- vs. postnatally, had only a weak effect. The two non-control odors led to different behavioral changes: an attraction to CAC and an avoidance of PO. Additionally, pup growth was affected by an interaction between litter size and maternal treatment, again regardless of timing. Pups from the CAC maternal treatment grew faster in larger litters; pups from the PO maternal treatment tended to grow faster in smaller litters. Thus, in rodents, offspring growth and behavior are seemingly influenced differently by the type of predation risk perceived by their mothers.

Maternal and personal information mediates the use of social cues about predation risk

Organisms can gain information about predation risks from their parents, their own personal experience, and their conspecifics and adjust their behavior to alleviate these risks. These different sources of information can, however, provide conflicting information due to spatial and temporal variation of the environment. This raises the question of how these cues are integrated to produce adaptive antipredator behavior. We investigated how common lizards (Zootoca vivipara) adjust the use of conspecific cues about predation risk depending on whether the information is maternally or personally acquired. We experimentally manipulated the presence of predator scent in gestating mothers and their offspring in a full-crossed design. We then tested the consequences for social information use by monitoring offspring social response to conspecifics previously exposed to predator cues or not. Lizards were more attracted to the scent of conspecifics having experienced predation cues when they had themselves no personal information about predation risk. In contrast, they were more repulsed by conspecific scent when they had personally obtained information about predation risk. However, the addition of maternal information about predation risk canceled out this interactive effect between personal and social information: lizards were slightly more attracted to conspecific scent when these two sources of information about predation risk were in agreement. A chemical analysis of lizard scent revealed that exposure to predator cues modified the chemical composition of lizard scents, a change that might underlie lizards’ use of social information. Our results highlight the importance of considering multiple sources of information while studying antipredator defenses.

Nestling Physiology Is Independent of Somatic Development in a Common Raptor, the American Kestrel (Falco sparverius)

AbstractAlthough many studies have documented the developmental trajectory of somatic traits in birds, few measure physiological traits, and even fewer document individual variation in developmental trajectory across ecological context. Hematological traits underlying aerobic capacity can be predictive of nestling survival, fledgling flight ability, and ultimately recruitment. This study aimed to assess individual variation in the developmental trajectory of two physiological traits that underlie aerobic capacity, hematocrit and hemoglobin concentration, in relation to somatic development and ecological context. Our study species, the American kestrel (Falco sparverius), is sexually dimorphic and therefore likely to show sexual variation in developmental trajectory and nestling maturity. We used lay date, year, brood size, nestling sex ratio, and parental nest visit rate to assess ecological context. Although somatic traits showed similar trajectories across nestlings, developmental trajectory for hematocrit and hemoglobin concentration showed individual variation not previously documented. This individual variation in developmental change, or trajectory, for physiological traits could not be explained by somatic development, sex, parental nest visit rate, lay date, year, brood size, or nestling sex ratio. However, we did find higher final hemoglobin concentration in 2018 and in nests with earlier lay dates. These findings demonstrate the importance of assessing physiological traits that capture aspects of individual quality distinct from somatic traits. Future studies are needed to understand the causes of individual variation in developmental trajectory, which cannot be explained by the ecological variables presented here, and the potential fitness consequences of this variation.

Interactions Between Maternal, Paternal, Developmental, and Immediate Environmental Effects on Anti-predator Behavior of the Snail Physa acuta

Transgenerational plasticity, which occurs when the environment experienced by parents changes the phenotype of offspring, is widespread in animal and plant species. Both maternal and paternal environments can underlie transgenerational plasticity, but experimental studies unraveling how their effects interact together and with the personal (both developmental and immediate) environments are still rare. Yet unraveling these interactions is fundamental to understanding how offspring integrate past and present environmental cues to produce adaptive phenotype. Using the hermaphroditic and freshwater snail Physa acuta, we tested how predator cues experienced by offspring, mothers and fathers interact to shape offspring anti-predator behavior. We raised a first generation of snails in the laboratory with or without chemical predator cues and realized full-factorial crosses to disentangle maternal and paternal cues. We then raised the second generation of snails with or without predator cues and assessed, when adults, their escape behavior in two immediate environments (with or without predator cues) and activity in the immediate environment without predator cues. We found that personal, maternal, and paternal predator cues interacted to shape offspring escape behavior and activity. Firstly, for escape behavior, snails integrated the cues from developmental and parental environments only when exposed to predator cues in their immediate environment, suggesting that personal immediate experience must corroborate the risky parental environment to reveal transgenerational plasticity. For activity, this same hypothesis helps explain why no clear pattern of transgenerational plasticity was revealed, as activity was only measured without predator cues in the immediate environment. Secondly, a single maternal exposure to predator cues decreased offspring escape behavior while a single paternal exposure had no effect, surprisingly demonstrating sex-specific transgenerational plasticity for a simultaneous hermaphroditic species. Thirdly, when both mother and father were exposed, paternal cues were integrated by offspring according to their own developmental environment. The paternal exposure then mitigated the reduction in escape behavior due to the maternal exposure only when offspring developed in control condition. Overall, our study highlighted complex patterns of sex-specific transgenerational plasticity resulting from non-additive interactions between parental, developmental and immediate experiences.

Developmental transitions in body color in chacma baboon infants: Implications to estimate age and developmental pace

OBJECTIVES

In many primates, one of the most noticeable morphological developmental traits is the transition from natal fur and skin color to adult coloration. Studying the chronology and average age at such color transitions can be an easy and noninvasive method to (a) estimate the age of infants whose dates of birth were not observed, and (b) detect interindividual differences in the pace of development for infants with known birth dates.

MATERIALS AND METHODS

Using a combination of photographs and field observations from 73 infant chacma baboons (Papio ursinus) of known ages, we (a) scored the skin color of six different body parts from pink to gray, as well as the color of the fur from black to gray; (b) validated our method of age estimation using photographic and field observations on an independent subset of 22 infants with known date of birth; and (c) investigated ecological, social, and individual determinants of age-related variation in skin and fur color.

RESULTS

Our results show that transitions in skin color can be used to age infant chacma baboons less than 7 months old with accuracy (median number of days between actual and estimated age = 10, range = 0-86). We also reveal that food availability during the mother's pregnancy, but not during lactation, affects infant color-for-age and therefore acts as a predictor of developmental pace.

DISCUSSION

This study highlights the potential of monitoring within- and between-infant variation in color to estimate age when age is unknown, and developmental pace when age is known.

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.

The development of flight behaviours in birds

Flight is a unique adaptation at the core of many behaviours in most bird species, whether it be foraging, migration or breeding. Birds have developed a wide diversity of flight modes (e.g. flapping, gliding, soaring, hovering) which involves very specialized behaviours. A key issue when studying flight behaviours is to understand how they develop through all the ontogenetic stages of birds, from the embryo to the flying adult. This question typically involves classical debates on animal behaviour about the importance of maturation and experience. Here, we review the literature available on the development of flight behaviours in birds. First, we focus on the early period when young birds are not yet capable of flight. We discuss examples and show how endogenous processes (e.g. wing flapping in the nest, flight development timing) and environmental factors (e.g. maternal stress, nutritional stress) can influence the development of flight behaviours. Then, we review several examples showing the different processes involved in the development of flight in flight-capable juveniles (e.g. practice, trial and error learning, social learning). Despite the lack of experimental studies investigating this specific question at different developmental stages, we show that several patterns can be identified, and we anticipate that the development of new tracking techniques will allow us to study this question more thoroughly in more bird species.

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.

Maternal predator-exposure affects offspring size at birth but not telomere length in a live-bearing fish

The perception of predation risk could affect prey phenotype both within and between generations (via parental effects). The response to predation risk could involve modifications in physiology, morphology, and behavior and can ultimately affect long-term fitness. Among the possible modifications mediated by the exposure to predation risk, telomere length could be a proxy for investigating the response to predation risk both within and between generations, as telomeres can be significantly affected by environmental stress. Maternal exposure to the perception of predation risk can affect a variety of offspring traits but the effect on offspring telomere length has never been experimentally tested. Using a live-bearing fish, the guppy (Poecilia reticulata), we tested if the perceived risk of predation could affect the telomere length of adult females directly and that of their offspring with a balanced experimental setup that allowed us to control for both maternal and paternal contribution. We exposed female guppies to the perception of predation risk during gestation using a combination of both visual and chemical cues and we then measured female telomere length after the exposure period. Maternal effects mediated by the exposure to predation risk were measured on offspring telomere length and body size at birth. Contrary to our predictions, we did not find a significant effect of predation-exposure neither on female nor on offspring telomere length, but females exposed to predation risk produced smaller offspring at birth. We discuss the possible explanations for our findings and advocate for further research on telomere dynamics in ectotherms.

Transitions in paternal social status predict patterns of offspring growth and metabolic transcription

One type of parental effect occurs when changes in parental phenotype or environment trigger changes to offspring phenotype. Such nongenetic parental effects can be precisely triggered in response to an environmental cue in time-locked fashion, or in other cases, persist for multiple generations after the cue has been removed, suggesting multiple timescales of action. For parental effects to serve as reliable signals of current environmental conditions, they should be reversible, such that when cues change, offspring phenotypes change in accordance. Social hierarchy is a prevalent feature of the environment, and current parental social status could signal the environment in which offspring will be born. Here, we sought to address parental effects of social status and their timescale of action in mice. We show that territorial competition in seminatural environments affects offspring growth. Although dominant males are not heavier than nondominant or control males, they produce faster growing offspring, particularly sons. The timing, effect-size, and sex-specificity of this association are modulated by maternal social experience. We show that a change in paternal social status is sufficient to modulate offspring weight: from one breeding cycle to the next, status-ascending males produce heavier sons than before, and status-descending males produce lighter sons than before. Current paternal status is also highly predictive of liver transcription in sons, including molecular pathways controlling oxidative phosphorylation and iron metabolism. These results are consistent with a parental effect of social experience, although alternative explanations are considered. In summary, changes in paternal social status are associated with changes in offspring growth and metabolism.

Premature birth stunts early growth and is a possible driver of stress-induced maternal effects in the guppy Poecilia reticulata

We tested the effects of gestational stress, principally in the form of alarm cue extracted from the skin of conspecifics, on reproduction in female guppies (Poecilia reticulata) and the growth and behaviour of their offspring. Offspring from mothers exposed to alarm cue exhibited stunted growth in the first few days post-partum, which appeared to be mediated by shortening of the gestation period, the length of which directly correlated with growth rate within the first 6 days post-partum. Mature offspring did not differ in behaviour or stress responses compared with controls and so the effects of maternal predation stress did not appear to persist into adulthood. A different form of gestational stress, dietary restriction, did not significantly affect offspring growth, though brood size was reduced, suggesting that the effects of predation stress were not mediated by differences in resource demand or consumption.

Growth rate and locomotor performance tradeoff is not universal in birds

Though a tradeoff between growth rate and locomotor performance has been proposed, empirical data on this relationship are still limited. Here we statistically analyze the associations of growth rate and flight ability in birds by assessing how growth rate is correlated with three wing parameters of birds: flight muscle ratio, wing aspect ratio, and wing loading. We find that fast-growing birds tended to have higher flight muscle ratios and higher wing loadings than slow-growing birds, which suggests that fast-growing birds may have better takeoff performance, but lower efficiency in maneuvering flight. Accordingly, our findings suggest that the relationship between growth rate and flight ability is more complex than a simple tradeoff. Since the hindlimbs also contribute greatly to the locomotion of birds, future investigations on the relationship between growth rate and hindlimb performance will provide more insights into the evolution of birds.

Flexible responses to stage-specific offspring threats

When caring for their young, parents must compensate for threats to offspring survival in a manner that maximizes their lifetime reproductive success. In birds, parents respond to offspring threats by altering reproductive strategies throughout the breeding attempt. Because altered reproductive strategies are costly, when threats to offspring are limited, parents should exhibit a limited response. However, it is unclear if response to offspring threat is the result of an integrated set of correlated changes throughout the breeding attempt or if responses are a flexible set of dissociable changes that are stage-specific. We test these hypotheses in a system where house wrens (Troglodytes aedon) compete for nesting cavities with Carolina chickadees (Poecile carolinensis) by usurping and destroying their nests during the early stage of the breeding attempt (the egg stage). Due to the specificity of the house wren threat, we can test whether parental responses to an offspring threat show flexibility and stage specificity or if parental strategies are an integrated and persistent response. We monitored nests in a natural population to compare life history traits of chickadees nesting in boxes that were in the presence of house wrens to chickadees nesting in boxes that did not overlap with house wrens. Carolina chickadees that nested near house wrens laid significantly smaller clutch sizes (early change in reproductive strategy) but did not alter nestling provisioning or nestling stage length (late change in reproductive strategy), suggesting that chickadees respond in a flexible and stage-specific manner to the threat of house wrens. By responding only when a threat is highest, parents minimize the cost of antithreat responses. Our study suggests that parents can respond in subtle and nuanced ways to offspring threats in the environment and specifically alter reproductive behaviors at the appropriate stage.

Differences in perceived predation risk associated with variation in relative size of extra-pair and within-pair offspring

Extra-pair paternity (EPP) is a widespread phenomenon in birds. Researchers have long hypothesized that EPP must confer a fitness advantage to extra-pair offspring (EPO), but empirical support for this hypothesis is definitively mixed. This could be because genetic benefits of EPP only exist in a subset of environmental contexts to which a population is exposed. From 2013 to 2015, we manipulated perceived predator density in a population of tree swallows (Tachycineta bicolor) breeding in New York to see whether fitness outcomes of extra-pair and within-pair offspring (WPO) varied with predation risk. In nests that had been exposed to predators, EPO were larger, longer-winged and heavier than WPO. In nonpredator nests, WPO tended to be larger, longer-winged and heavier than EPO, though the effect was nonsignificant. We found no differences in age, morphology or stress physiology between extra-pair and within-pair sires from the same nest, suggesting that additive genetic benefits cannot fully explain the differences in nestling size that we observed. The lack of an effect of predator exposure on survival or glucocorticoid stress physiology of EPO and WPO further suggests that observed size differences do not reflect more general variation in intrinsic genetic quality. Instead, we suggest that size differences may have arisen through differential investment into EPO and WPO by females, perhaps because EPO and WPO represent different reproductive strategies, with each type of nestling conferring a fitness advantage in specific ecological contexts.

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.

Predation risk affects egg mass but not egg steroid hormone concentrations in yellow-legged gulls

Predators have both direct, consumptive effects on their prey and non-lethal effects on physiology and behavior, including reproductive decisions, with cascading effects on prey ecology and evolution. Here, we experimentally tested such non-lethal effects of exposure to increased predation risk on clutch size, egg mass, and the concentration of yolk steroid hormones in the yellow-legged gull Larus michahellis. We simulated increased predation risk by displaying stuffed predators (adult fox Vulpes vulpes, and adult buzzard Buteo buteo) to breeding adults before egg laying. The concentration of corticosterone, which has been shown to increase under exposure to maternal predation risk in other species, and of testosterone did not differ between eggs from mothers exposed to the predators and eggs from control mothers (i.e., eggs exposed to a novel object of similar size and position to the stuffed predators). The concentration of the two hormones negatively covaried. Clutch size did not vary according to experimental treatment, whereas egg mass was markedly larger in clutches from nests exposed to predators than in clutches from control nests. By increasing egg mass, mothers may reduce the risk of cooling of the eggs when incubation is impeded by predators, boost energy reserves, reduce post-natal detectability caused by food solicitation, and/or enhance development at hatching, thus increasing the chances of offspring survival. In general, our results are inconsistent with most of the few previous studies on similar non-lethal predator effects and suggest that such effects may vary among species according to ecological conditions, social behavior, and developmental mode.

Higher Nest Predation Favors Rapid Fledging at the Cost of Plumage Quality in Nestling Birds

High predation risk can favor rapid offspring development at the expense of offspring quality. Impacts of rapid development on phenotypic quality should be most readily expressed in traits that minimize fitness costs. We hypothesize that ephemeral traits that are replaced or repaired after a short period of life might express trade-offs in quality as a result of rapid development more strongly than traits used throughout life. We explored this idea for plumage quality in nestling body feathers, an ephemeral trait. We found a strong trade-off whereby nestlings that spend less time in the nest produced lower-quality plumage with less dense barbs relative to adults across 123 temperate and tropical species. For a subset of these species ( n=67 ), we found that variation in the risk of nest predation explained additional variation in plumage quality beyond development time. Ultimately, the fitness costs of a poor-quality ephemeral trait, such as nestling body feathers, may be outweighed by the fitness benefits of shorter development times that reduce predation risk. At the same time, reduced resource allocation to traits with small fitness costs, such as ephemeral traits, may ameliorate resource constraints from rapid development on traits with larger fitness impacts.

Developmental stress reduces body condition across avian life-history stages: A comparison of quantitative magnetic resonance data and condition indices

Animals exposed to stressful developmental conditions can experience sustained physiological, behavioral, and fitness effects. While extensive research shows how developmental stress affects development, few studies have examined the effects on body composition. To test the effects of developmental stress on nestling and adult body composition, we dosed nestling zebra finches (Taeniopygia guttata) with either a corticosterone (CORT) or control treatment. We calculated condition indices (scaled mass, residual mass, and ratio indices) from morphometric measurements and used quantitative magnetic resonance (QMR) to assess body composition during early development and adulthood. We compared these three traditionally-used condition indices to QMR-derived body composition measurements, to test how well they predict relative fat mass. Our results show that developmental stress decreases body mass, and has a dose-dependent effect on tarsus length in nestling birds. Furthermore, stress treatment during the nestling period had long-lasting effects on adult body mass, lean mass and tarsus length. None of the three condition indices were good indicators of relative fat mass in nestlings, but all indices were closely associated with relative fat mass in adults. The scaled mass index was more closely associated with relative fat mass than the other condition indices, when calculated from wing chord length in nestlings. In adults however, the residual mass index and the ratio index were better indicators of relative body fat than the scaled mass index, when calculated from tarsus length. Our data demonstrate the short and long-term impact of developmental stress on birds, and highlight important age-related factors to consider when using condition indices.

Prenatal influences on temperament development: The role of environmental epigenetics

This review summarizes current knowledge and outlines future directions relevant to questions concerning environmental epigenetics and the processes that contribute to temperament development. Links between prenatal adversity, epigenetic programming, and early manifestations of temperament are important in their own right, also informing our understanding of biological foundations for social-emotional development. In addition, infant temperament attributes represent key etiological factors in the onset of developmental psychopathology, and studies elucidating their prenatal foundations expand our understanding of developmental origins of health and disease. Prenatal adversity can take many forms, and this overview is focused on the environmental effects of stress, toxicants, substance use/psychotropic medication, and nutrition. Dysregulation associated with attention-deficit/hyperactivity-disruptive disorders was noted in the context of maternal substance use and toxicant exposures during gestation, as well as stress. Although these links can be made based on the existing literature, currently few studies directly connect environmental influences, epigenetic programming, and changes in brain development/behavior. The chain of events starting with environmental inputs and resulting in alterations to gene expression, physiology, and behavior of the organism is driven by epigenetics. Epigenetics provides the molecular mechanism of how environmental factors impact development and subsequent health and disease, including early brain and temperament development.

Error management theory and the adaptive significance of transgenerational maternal-stress effects on offspring phenotype

It is well established that circulating maternal stress hormones (glucocorticoids, GCs) can alter offspring phenotype. There is also a growing body of empirical work, within ecology and evolution, indicating that maternal GCs link the environment experienced by the mother during gestation with changes in offspring phenotype. These changes are considered to be adaptive if the maternal environment matches the offspring's environment and maladaptive if it does not. While these ideas are conceptually sound, we lack a testable framework that can be used to investigate the fitness costs and benefits of altered offspring phenotypes across relevant future environments. We present error management theory as the foundation for a framework that can be used to assess the adaptive potential of maternal stress hormones on offspring phenotype across relevant postnatal scenarios. To encourage rigorous testing of our framework, we provide field-testable hypotheses regarding the potential adaptive role of maternal stress across a diverse array of taxa and life histories, as well as suggestions regarding how our framework might provide insight into past, present, and future research. This perspective provides an informed lens through which to design and interpret experiments on the effects of maternal stress, provides a framework for predicting and testing variation in maternal stress across and within taxa, and also highlights how rapid environmental change that induces maternal stress may lead to evolutionary traps.

Integrating Ecological and Evolutionary Context in the Study of Maternal Stress

Maternal stress can prenatally influence offspring phenotypes and there are an increasing number of ecological studies that are bringing to bear biomedical findings to natural systems. This is resulting in a shift from the perspective that maternal stress is unanimously costly, to one in which maternal stress may be beneficial to offspring. However, this adaptive perspective is in its infancy with much progress to still be made in understanding the role of maternal stress in natural systems. Our aim is to emphasize the importance of the ecological and evolutionary context within which adaptive hypotheses of maternal stress can be evaluated. We present five primary research areas where we think future research can make substantial progress: (1) understanding maternal and offspring control mechanisms that modulate exposure between maternal stress and subsequent offspring phenotype response; (2) understanding the dynamic nature of the interaction between mothers and their environment; (3) integrating offspring phenotypic responses and measuring both maternal and offspring fitness outcomes under real-life (either free-living or semi-natural) conditions; (4) empirically testing these fitness outcomes across relevant spatial and temporal environmental contexts (both pre- and post-natal environments); (5) examining the role of maternal stress effects in human-altered environments-i.e., do they limit or enhance fitness. To make progress, it is critical to understand the role of maternal stress in an ecological context and to do that, we must integrate across physiology, behavior, genetics, and evolution.

Parental and embryonic experiences with predation risk affect prey offspring behaviour and performance

Because phenotypic plasticity can operate both within and between generations, phenotypic outcomes are often shaped by a complex history of environmental signals. For example, parental and embryonic experiences with predation risk can both independently and interactively influence prey offspring traits early in their life. Parental and embryonic risk experiences can also independently shape offspring phenotypes throughout an offspring's ontogeny, but the persistence of their interactive effects throughout offspring ontogeny is unknown. We examined the effects of parental and embryonic experiences with predation risk on the response of 1-year-old prey (the carnivorous snail, Nucella lapillus) offspring to current predation risk. We found that parental and embryonic risk experiences had largely independent effects on offspring performance and that these effects were context dependent. Parental experience with risk had strong impacts on multiple offspring traits in the presence of current risk that generally improved offspring performance under risk, but embryonic risk experience had relatively weaker effects and only operated in the absence of current risk to reduce offspring growth. These results illustrate that past environmental experiences can dynamically shape organism phenotypes across ontogeny and that attention to these effects is key to a better understanding of predator/prey dynamics in natural systems.

Synergistic effects of parental and embryonic exposure to predation risk on prey offspring size at emergence

Cues signaling predation risk can strongly influence prey phenotypes both within and between generations. Parental and embryonic effects have been shown to operate independently in response to predation risk, but how they interact to shape offspring life history traits remains largely unknown. Here, we conducted experiments to examine the synergistic impacts of parental and embryonic experiences with predation risk on offspring size at emergence in the snail, Nucella lapillus, which is an ecologically important intermediate consumer on rocky intertidal shores. We found that when embryos were exposed to predation risk, the offspring of risk-experienced parents emerged larger than those of parents that had no risk experience. This response was not the result of increased development time, greater resource availability, or fewer emerging offspring, but may have occurred because both parental and embryonic experiences with risk increased growth efficiency, perhaps by reducing embryonic respiration rates under risk. Our results highlight the potential for organisms to be influenced by a complex history of environmental signals with important consequences for individual fitness and predator-prey interactions.

Flight performance in the altricial zebra finch: Developmental effects and reproductive consequences

The environmental conditions animals experience during development can have sustained effects on morphology, physiology, and behavior. Exposure to elevated levels of stress hormones (glucocorticoids, GCs) during development is one such condition that can have long‐term effects on animal phenotype. Many of the phenotypic effects of GC exposure during development (developmental stress) appear negative. However, there is increasing evidence that developmental stress can induce adaptive phenotypic changes. This hypothesis can be tested by examining the effect of developmental stress on fitness‐related traits. In birds, flight performance is an ideal metric to assess the fitness consequences of developmental stress. As fledglings, mastering takeoff is crucial to avoid bodily damage and escape predation. As adults, takeoff can contribute to mating and foraging success as well as escape and, thus, can affect both reproductive success and survival. We examined the effects of developmental stress on flight performance across life‐history stages in zebra finches (Taeniopygia guttata). Specifically, we examined the effects of oral administration of corticosterone (CORT, the dominant avian glucocorticoid) during development on ground‐reaction forces and velocity during takeoff. Additionally, we tested for associations between flight performance and reproductive success in adult male zebra finches. Developmental stress had no effect on flight performance at all ages. In contrast, brood size (an unmanipulated variable) had sustained, negative effects on takeoff performance across life‐history stages with birds from small broods performing better than birds from large broods. Flight performance at 100 days posthatching predicted future reproductive success in males; the best fliers had significantly higher reproductive success. Our results demonstrate that some environmental factors experienced during development (e.g. clutch size) have stronger, more sustained effects than others (e.g. GC exposure). Additionally, our data provide the first link between flight performance and a direct measure of reproductive success.

Predator encounters have spatially extensive impacts on parental behaviour in a breeding bird community

Predation risk has negative indirect effects on prey fitness, partly mediated through changes in behaviour. Evidence that individuals gather social information from other members of the population suggests that events in a community may impact the behaviour of distant individuals. However, spatially wide-ranging impacts on individual behaviour caused by a predator encounter elsewhere in a community have not been documented before. We investigated the effect of a predator encounter (hawk model presented at a focal nest) on the parental behaviour of pied flycatchers (Ficedula hypoleuca), both at the focal nest and at nearby nests different distances from the predator encounter. We show that nest visitation of both focal pairs and nearby pairs were affected, up to 3 h and 1 h, respectively. Parents also appeared to compensate initial disrupted feeding by later increasing nest visitation rates. This is the first evidence showing that the behaviour of nearby pairs was affected away from an immediate source of risk. Our results indicate that the impacts of short-term predator encounters may immediately extend spatially to the broader community, affecting the behaviour of distant individuals. Information about predators is probably quickly spread by cues such as intra- and heterospecific alarm calls, in communities of different taxa.

Offspring reaction norms shaped by parental environment: interaction between within- and trans-generational plasticity of inducible defenses

BACKGROUND

Within-generational plasticity (WGP) and transgenerational plasticity (TGP) are mechanisms allowing rapid adaptive responses to fluctuating environments without genetic change. These forms of plasticity have often been viewed as independent processes. Recent evidence suggests that WGP is altered by the environmental conditions experienced by previous generations (i.e., TGP). In the context of inducible defenses, one of the most studied cases of plasticity, the WGP x TGP interaction has been poorly investigated.

RESULTS

We provide evidence that TGP can alter the reaction norms of inducible defenses in a freshwater snail. The WGP x TGP interaction patterns are trait-specific and lead to decreased slope of reaction norms (behaviour and shell thickness). Offspring from induced parents showed a higher predator avoidance behaviour and a thicker shell than snails from non-induced parents in no predator-cue environment while they reached similar defenses in predator-cue environment. The WGP x TGP interaction further lead to a switch from a plastic towards a constitutive expression of defenses for shell dimensions (flat reaction norm).

CONCLUSIONS

WGP-alteration by TGP may shape the adaptive responses to environmental change and then has a substantial importance to understand the evolution of plasticity.

Acute embryonic exposure to corticosterone alters physiology, behaviour and growth in nestlings of a wild passerine

Maternally-derived glucocorticoids can modify the normal development of young animals. To date, little is known about maternal effects that are mediated by acute embryonic exposure to glucocorticoids. In birds, elevated maternal transmission of corticosterone (CORT) to egg albumen is mainly dependent on acute stress. In this study, we increased CORT levels in the egg albumen of a wild passerine, the great tit (Parus major), breeding in favourable deciduous and less suitable coniferous habitat. Subsequently we measured the somatic growth, baseline and acute glucocorticoid responses, immunity and behaviour of prenatally manipulated offspring with respect to control siblings. We found that prenatally CORT-exposed nestlings had lower baseline CORT levels, a more rapid decline in CORT during recovery from a standardized stressor, and a reduced heterophil/lymphocyte ratio compared with controls. Although stress-induced total CORT levels remained unchanged, free CORT levels were significantly lower and the levels of corticosteroid binding globulins (CBG) significantly higher in experimental offspring. Prenatally CORT-exposed offspring begged longer after hatching than controls. Stress-induced behavioural activity of fledglings did not differ between treatments, while its association with baseline CORT levels was significant in the control group only. The body mass and tarsus length of fledglings was positively affected by manipulation in unfavourable coniferous habitat only. We conclude that maternal effects related to elevated levels of albumen CORT modify diverse aspects of offspring phenotype and potentially increase offspring performance in resource poor environments. Moreover, our results indicate that maternal glucocorticoids may suppress the effect of hormones on behavioural responses.

The importance of trans-generational effects in Lepidoptera

The importance of trans-generational effects in shaping an individuals’ phenotype and fitness, and consequently even impacting population dynamics is increasingly apparent. Most of the research on trans-generational effects still focuses on plants, mammals, and birds. In the past few years, however, increasing number of studies, especially on maternal effects, have highlighted their importance also in many insect systems. Lepidoptera, specifically butterflies, have been used as model systems for studying the role of phenotypic plasticity within generations. As ectotherms, they are highly sensitive to environmental variation, and indeed many butterflies show adaptive phenotypic plasticity in response to environmental conditions. Here, we synthesize what is known about trans-generational effects in Lepidoptera, compile evidence for different environmental cues that are important drivers of trans-generational effects, and point out which offspring traits are mainly impacted. Finally, we emphasize directions for future research that are needed for better understanding of the adaptive nature of trans-generational effects in Lepidoptera in particular, but potentially also in other organisms.