The multidimensional consequences of the juvenile environment: towards an integrative view of the adult phenotype

Multiple behavioral mechanisms shape development in a highly social cichlid fish

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

Using Acoustic Data Repositories to Study Vocal Responses to Playback in a Neotropical Songbird

Birds may alter song structure in response to territorial challenges to convey information about aggressive intent or fighting ability. Professional and amateur ornithologists upload daily many birdsong recordings into acoustic data repositories, usually scoring whether songs were recorded in response to a conspecific playback or produced spontaneously. We analyzed recordings from these repositories to evaluate if song traits of Rufous-browed Peppershrikes (Cyclarhis gujanensis) vary between playback-elicited songs and spontaneous songs. For each recording after playback, we chose one spatially closer spontaneous recording to avoid geographic bias. Birds recorded after playback produced slightly longer songs than birds that were singing spontaneously. This result was accounted for by increases in the amount of sound and silence within a song after the playback instead of changes in the mean number or duration of elements. Playback did not alter song frequency parameters (bandwidth, minimum, mean, and maximum frequencies) or song rate. These results indicate that song duration might mediate aggressive interactions in Rufous-browed Peppershrikes. Even considering limitations such as unknown playback stimulus identity and possible pseudoreplication, acoustic data repositories give a unique yet unexplored opportunity to gather insights into the evolution of song flexibility during aggressive encounters.

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

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

Delayed early life effects in the threespine stickleback

Early life conditions can have a decisive influence on viability later in life. However, the influence of embryo density within a nest or body cavity on subsequent viability has received little attention within an ecological setting. This is surprising given that embryos often compete for limited resources, such as nutrients and oxygen, and this could influence their viability later in life through carry-over and compensatory effects. We show that the density of fertilized eggs within the nests of threespine stickleback males (Gasterosteus aculeatus) influences their viability after hatching. Embryos from larger broods hatch earlier and at a smaller size than those from smaller broods, which reduces their survival until the age of four weeks. This indicates a trade-off between the number and viability of offspring that males can raise to the hatching stage, which could explain the high incidence of partial egg cannibalism in nest-brooding fishes-as a strategy to improve the survival of remaining offspring. These results highlight the importance of considering conditions at the embryonic stage when evaluating the impact of early life conditions on viability and the adaptive value of reproductive decisions.

Why study plasticity in multiple traits? New hypotheses for how phenotypically plastic traits interact during development and selection

Organisms can often respond adaptively to a change in their environment through phenotypic plasticity in multiple traits, a phenomenon termed as multivariate plasticity. These different plastic responses could interact and affect each other's development as well as selection on each other, but the causes and consequences of these interactions have received relatively little attention. Here, we propose a new conceptual framework for understanding how different plastic responses can affect each other's development and why organisms should have multiple plastic responses. A plastic change in one trait could alter the phenotype of a second plastic trait by changing either the cue received by the organism (cue-mediated effect) or the response to that cue (response-mediated effect). Multivariate plasticity could benefit the organism either because the plastic responses work better when expressed together (synergy) or because each response is more effective under different environmental circumstances (complementarity). We illustrate these hypotheses with case studies, focusing on interactions between behavior and morphology, plastic traits that differ in their reversibility. Future empirical and theoretical research should investigate the consequences of these interactions for additional factors important for the evolution of plasticity, such as the limits and costs of plasticity.

Condition- and context-dependent alternative reproductive tactic in Drosophila prolongata

Species with intense male–male competition for access to females often show alternative reproductive tactics (ARTs) where males of lower competitive ability adopt a sneaky behavior to gain access to mates. These ARTs are usually associated with intrasexual dimorphisms, in that males with distinct morphologies show different tactics. In some cases, however, males adopt different tactics without being dimorphic. Male Drosophila prolongata exhibit continuous variation in body size and shape, with enlarged forelegs that they use in male-male contests and in courtship, including stimulation of the female’s abdomen. During this “leg vibration,” however, nearby males can intercept the courted female and mate without their own courtship. Here, we studied the causes and consequences of these different mating tactics in competitive mating trials between males varying in their size and shape. We found that male mating tactics were condition-dependent. Whereas large, high-condition males were more likely to show leg vibration in their courtship, smaller, lower-condition males were more likely to intercept. However, the number of offspring produced was independent of male condition and reproductive tactic. We discuss possible scenarios for the evolution and maintenance of the ARTs and some future directions for the study of ARTs in this species and in general.

Context-dependent carryover effects of hypoxia and warming in a coastal ecosystem engineer

Organisms are increasingly likely to be exposed to multiple stressors repeatedly across ontogeny as climate change and other anthropogenic stressors intensify. Early life stages can be particularly sensitive to environmental stress, such that experiences early in life can "carry over" to have long-term effects on organism fitness. Despite the potential importance of these within-generation carryover effects, we have little understanding of how they vary across ecological contexts, particularly when organisms are re-exposed to the same stressors later in life. In coastal marine systems, anthropogenic nutrients and warming water temperatures are reducing average dissolved oxygen (DO) concentrations while also increasing the severity of naturally occurring daily fluctuations in DO. Combined effects of warming and diel-cycling DO can strongly affect the fitness and survival of coastal organisms, including the eastern oyster (Crassostrea virginica), a critical ecosystem engineer and fishery species. However, whether early life exposure to hypoxia and warming affects oysters' subsequent response to these stressors is unknown. Using a multiphase laboratory experiment, we explored how early life exposure to diel-cycling hypoxia and warming affected oyster growth when oysters were exposed to these same stressors 8 weeks later. We found strong, interactive effects of early life exposure to diel-cycling hypoxia and warming on oyster tissue : shell growth, and these effects were context-dependent, only manifesting when oysters were exposed to these stressors again two months later. This change in energy allocation based on early life stress exposure may have important impacts on oyster fitness. Exposure to hypoxia and warming also influenced oyster tissue and shell growth, but only later in life. Our results show that organisms' responses to current stress can be strongly shaped by their previous stress exposure, and that context-dependent carryover effects may influence the fitness, production, and restoration of species of management concern, particularly for sessile species such as oysters.

Effects of maternal exposure to a bacterial antigen and altered post-hatching rearing conditions on avian offspring behaviour

Abstract

The early-life environment plays a crucial role in shaping morphological, physiological, and behavioural traits, with potential long-term consequences for fitness. Indeed, a set of factors experienced by offspring during prenatal and early post-natal development has been recognised to affect behavioural trait expression in later life. Several studies have shown that in birds, nutritional and social rearing conditions and maternal and/or neonatal immunisations may profoundly determine the development and establishment of behaviour in offspring. To our knowledge, no research has examined whether and how the interaction between immune-mediated maternal effects and post-hatching rearing conditions affects offspring behaviour. Here, we studied the effects of maternal exposure to a bacterial antigen and altered brood size on docility, breathing rate, and aggression in the offspring of great tit, Parus major. We used a 2 × 2 design to investigate the interactive effects of maternal immunisation and brood size manipulation on offspring behavioural development. We found no such interactive effect on offspring behaviour, although we observed it regarding to offspring body mass and tarsus length. Maternal immunisation itself did not affect offspring behaviour. However, we demonstrated that the offspring breathing rate and level of aggression were affected by brood size manipulation. Both breathing rate and aggression in offspring reared in enlarged broods were lower than those in offspring reared in non-manipulated broods. Our study did not confirm earlier reports that immune-mediated maternal effects modulate offspring behavioural development, but we showed that brood size during rearing might indeed be a factor that affects offspring behaviour.

Significance statement

The early environment experienced by offspring constitutes a significant source of developmental plasticity, which may profoundly affect the establishment of their behavioural traits. Food availability, social conditions, and maternal or offspring infection are crucial factors shaping various behavioural traits in birds. However, there remains a lack of studies emphasising the potential interactive effects of early-life conditions on behavioural trait development in natural bird populations. Here, to our knowledge for the first time, we experimentally examined how maternal immunisation and altered post-hatching rearing conditions interact to determine the behaviour of fledged offspring. We found that maternal treatment and brood size manipulation interactively affected offspring body mass and tarsus length, but this interaction had no effect on offspring behaviour. Our findings suggest that different mechanisms may underlie the development of morphological and behavioural traits.

Evaluating endoplasmic reticulum stress and unfolded protein response through the lens of ecology and evolution

Considerable progress has been made in understanding the physiological basis for variation in the life-history patterns of animals, particularly with regard to the roles of oxidative stress and hormonal regulation. However, an underappreciated and understudied area that could play a role in mediating inter- and intraspecific variation of life history is endoplasmic reticulum (ER) stress, and the resulting unfolded protein response (UPR^ER ). ER stress response and the UPR^ER maintain proteostasis in cells by reducing the intracellular load of secretory proteins and enhancing protein folding capacity or initiating apoptosis in cells that cannot recover. Proper modulation of the ER stress response and execution of the UPR^ER allow animals to respond to intracellular and extracellular stressors and adapt to constantly changing environments. ER stress responses are heritable and there is considerable individual variation in UPR^ER phenotype in animals, suggesting that ER stress and UPR^ER phenotype can be subjected to natural selection. The variation in UPR^ER phenotype presumably reflects the way animals respond to ER stress and environmental challenges. Most of what we know about ER stress and the UPR^ER in animals has either come from biomedical studies using cell culture or from experiments involving conventional laboratory or agriculturally important models that exhibit limited genetic diversity. Furthermore, these studies involve the assessment of experimentally induced qualitative changes in gene expression as opposed to the quantitative variations that occur in naturally existing populations. Almost all of these studies were conducted in controlled settings that are often quite different from the conditions animals experience in nature. Herein, we review studies that investigated ER stress and the UPR^ER in relation to key life-history traits including growth and development, reproduction, bioenergetics and physical performance, and ageing and senescence. We then ask if these studies can inform us about the role of ER stress and the UPR^ER in mediating the aforementioned life-history traits in free-living animals. We propose that there is a need to conduct experiments pertaining to ER stress and the UPR^ER in ecologically relevant settings, to characterize variation in ER stress and the UPR^ER in free-living animals, and to relate the observed variation to key life-history traits. We urge others to integrate multiple physiological systems and investigate how interactions between ER stress and oxidative stress shape life-history trade-offs in free-living animals.

Early-life relationships matter: Social position during early life predicts fitness among female spotted hyenas

How social development in early-life affects fitness remains poorly understood. Though there is growing evidence that early-life relationships can affect fitness, little research has investigated how social positions develop or whether there are particularly important periods for social position development in an animal's life history. In long-lived species in particular, understanding the lasting consequences of early-life social environments requires detailed, long-term datasets. Here we used a 25-year dataset to test whether social positions held during early development predicted adult fitness. Specifically, we quantified social position using three social network metrics: degree, strength and betweenness. We determined the social position of each individual in three types of networks during each of three stages of ontogeny to test whether they predict annual reproductive success (ARS) or longevity among adult female spotted hyenas Crocuta crocuta. The social positions occupied by juvenile hyenas did predict their fitness, but the effects of social position on fitness measures differed between stages of early development. Network metrics when individuals were young adults better predicted ARS, but network metrics for younger animals, particularly when youngsters were confined to the communal den, better predicted longevity than did metrics assessed during other stages of development. Our study shows how multiple types of social bonds formed during multiple stages of social development predict lifetime fitness outcomes. We suggest that social bonds formed during specific phases of development may be more important than others when considering fitness outcomes.

On the evolution of carry-over effects

The environment experienced early in life often affects the traits that are developed after an individual has transitioned into new life stages and environments. Because the phenotypes induced by earlier environments are then screened by later ones, these 'carry-over effects' influence fitness outcomes across the entire life cycle. While the last two decades have witnessed an explosion of studies documenting the occurrence of carry-over effects, little attention has been given to how they adapt and diversify. To aid future research in this area, we present a framework for the evolution of carry-over effects. Carry-over effects can evolve in two ways. First, the expression of traits later in life may become more or less dependent on the developmental processes of earlier stages (e.g., 'adaptive decoupling'). Genetic correlations between life stages then either strengthen or weaken. Alternatively, those influential developmental processes that begin early in life may become more or less sensitive to that earlier environment. Here, plasticity changes in all the traits that share those developmental pathways across the whole life cycle. Adaptive evolution of a carry-over effect is governed by selection on the induced phenotypes in the later stage, and also by selection on any developmentally linked traits in the earlier life stage. When these selective pressures conflict, the evolution of the carry-over effect will be biased towards maximizing performance in the life stage with stronger selection. Because life stages often contribute unequally to total fitness, the strength of selection in any one stage depends on: (a) the relationship between the traits and the stage-specific fitness components (e.g., juvenile survival, adult mating success), and (b) the reproductive value of the life stage. Considering the evolution of carry-over effects reveals several intriguing features of the evolution of life histories and phenotypic plasticity more generally. For instance, carry-over effects that manifest as maladaptive plasticity in one life stage may represent an adaptive strategy for maximizing fitness in stages with stronger selection. Additionally, adaptation to novel environments encountered early in the life cycle may be faster in the presence of carry-over effects that influence sexually selected traits.

Links between personality, early natal nutrition and survival of a threatened bird

There is growing recognition that variation in animal personality traits can influence survival and reproduction rates, and consequently may be important for wildlife population dynamics. Despite this, the integration of personality research into conservation has remained uncommon. Alongside the establishment of personality as an important source of individual variation has come an increasing interest in factors affecting the development of personality. Recent work indicates the early environment, including natal nutrition, may play a stronger role in the development of personality than previously thought. In this study, we investigated the importance of three personality metrics (activity, boldness and acclimation time) for estimating survival of a threatened species, the hihi (Notiomystis cincta), and evaluated the influence of early natal nutrition on those metrics. Our results showed that boldness (as measured from a one-off cage test) had a positive effect on the probability of juvenile hihi surviving to adulthood. There was also a tendency for juveniles that received carotenoid supplementation in the nest to be bolder than those that did not, suggesting that the early environment had some influence on the expression of boldness in juvenile hihi. Linking the development of personality traits with ultimate effects on vital rates may benefit conservation management, as it could enable developmentally targeted management interventions. To our knowledge, this study is the first to identify potential linkages between early natal nutrition, personality and fitness in a wild-living population. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.

We Are What We Eat: A Stoichiometric and Ecometabolomic Study of Caterpillars Feeding on Two Pine Subspecies of Pinus sylvestris

Many studies have addressed several plant-insect interaction topics at nutritional, molecular, physiological, and evolutionary levels. However, it is still unknown how flexible the metabolism and the nutritional content of specialist insect herbivores feeding on different closely related plants can be. We performed elemental, stoichiometric, and metabolomics analyses on leaves of two coexisting Pinus sylvestris subspecies and on their main insect herbivore; the caterpillar of the processionary moth (Thaumetopoea pityocampa). Caterpillars feeding on different pine subspecies had distinct overall metabolome structure, accounting for over 10% of the total variability. Although plants and insects have very divergent metabolomes, caterpillars showed certain resemblance to their plant-host metabolome. In addition, few plant-related secondary metabolites were found accumulated in caterpillar tissues which could potentially be used for self-defense. Caterpillars feeding on N and P richer needles had lower N and P tissue concentration and higher C:N and C:P ratios, suggesting that nutrient transfer is not necessarily linear through trophic levels and other plant-metabolic factors could be interfering. This exploratory study showed that little chemical differences between plant food sources can impact the overall metabolome of specialist insect herbivores. Significant nutritional shifts in herbivore tissues could lead to larger changes of the trophic web structure.

The role of complex cues in social and reproductive plasticity

Phenotypic plasticity can be a key determinant of fitness. The degree to which the expression of plasticity is adaptive relies upon the accuracy with which information about the state of the environment is integrated. This step might be particularly beneficial when environments, e.g. the social and sexual context, change rapidly. Fluctuating temporal dynamics could increase the difficulty of determining the appropriate level of expression of a plastic response. In this review, we suggest that new insights into plastic responses to the social and sexual environment (social and reproductive plasticity) may be gained by examining the role of complex cues (those comprising multiple, distinct sensory components). Such cues can enable individuals to more accurately monitor their environment in order to respond adaptively to it across the whole life course. We briefly review the hypotheses for the evolution of complex cues and then adapt these ideas to the context of social and sexual plasticity. We propose that the ability to perceive complex cues can facilitate plasticity, increase the associated fitness benefits and decrease the risk of costly 'mismatches' between phenotype and environment by (i) increasing the robustness of information gained from highly variable environments, (ii) fine-tuning responses by using multiple strands of information and (iii) reducing time lags in adaptive responses. We conclude by outlining areas for future research that will help to determine the interplay between complex cues and plasticity.

Immune deployment increases larval vulnerability to predators and inhibits adult life-history traits in a dragonfly

While deploying immune defences early in ontogeny can trade-off with the production and maintenance of other important traits across the entire life cycle, it remains largely unexplored how features of the environment shape the magnitude or presence of these lifetime costs. Greater predation risk during the juvenile stage may particularly influence such costs by (1) magnifying the survival costs that arise from any handicap of juvenile avoidance traits and/or (2) intensifying allocation trade-offs with important adult traits. Here, we tested for predator-dependent costs of immune deployment within and across life stages using the dragonfly, Pachydiplax longipennis. We first examined how larval immune deployment affected two traits associated with larval vulnerability to predators: escape distance and foraging under predation risk. Larvae that were induced to mount an immune response had shorter escape distances but lower foraging activity in the presence of predator cues. We also induced immune responses in larvae and reared them through emergence in mesocosms that differed in the presence of large predatory dragonfly larvae (Aeshnidae spp.). Immune-challenged larvae had later emergence overall and lower survival in pools with predators. Immune-challenged males were also smaller at emergence and developed less sexually selected melanin wing coloration, but these effects were independent of predator treatment. Overall, these results highlight how mounting an immune defence early in ontogeny can have substantial ecological and physiological costs that manifest both within and across life stages.

Trade-offs between larval survival and adult ornament development depend on predator regime in a territorial dragonfly

Trade-offs between juvenile survival and the development of sexually selected traits can cause ontogenetic conflict between life stages that constrains adaptive evolution. However, the potential for ecological interactions to alter the presence or strength of these trade-offs remains largely unexplored. Antagonistic selection over the accumulation and storage of resources could be one common cause of environment-specific trade-offs between life stages: higher condition may simultaneously enhance adult ornament development and increase juvenile vulnerability to predators. We tested this hypothesis in an ornamented dragonfly (Pachydiplax longipennis). Higher larval body condition indeed enhanced the initial development of its intrasexually selected wing coloration, but was opposed by viability selection in the presence of large aeshnid predators. In contrast, viability selection did not oppose larval body condition in pools when aeshnids were absent, and was not affected when we manipulated cannibalism risk. Trade-offs between larval survival and ornament development, mediated through the conflicting effects of body condition, therefore occurred only under high predation risk. We additionally characterized how body condition influences several traits associated with predator avoidance. Although body condition did not affect burst distance, it did increase larval abdomen size, potentially making larvae easier targets for aeshnid predators. As high body condition similarly increases vulnerability to predators in many other animals, predator-mediated costs of juvenile resource accumulation could be a common, environment-specific limitation on the elaboration of sexually selected traits.

Maternal predator odour exposure programs metabolic responses in adult offspring

A cardinal feature of the reaction to stress is the promotion of energy mobilization, enabling appropriate behavioural responses. Predator odours are naturalistic and ecologically relevant stressors present over evolutionary timescales. In this study, we asked whether maternal predator odour exposure could program long-term energy mobilization in C57BL/6 mice offspring. To test this hypothesis, we measured rates of oxygen consumption in prenatally predator odour exposed mice in adulthood while controlling for levels of locomotor activity at baseline and under stress. Circulating thyroid hormone levels and the transcript abundance of key regulators of the hypothalamic-pituitary-thyroid axis within the periventricular nucleus (PVN) of the hypothalamus and in the liver, including carriers and receptors and thyrotropin-releasing hormone, were measured as endocrine mediators facilitating energy availability. Prenatally predator odour exposed mice of both sexes mobilized more energy during lower energy demand periods of the day and under stressful conditions. Further, prenatally predator odour exposed mice displayed modifications of their hypothalamic-pituitary-thyroid axis through increased circulating thyroxine and thyroid hormone receptor α within the PVN and decreased transthyretin in the liver. Overall, these results suggest that maternal exposure to predator odour is sufficient to increase long-term energy mobilization in adult offspring.

Environmental Adaptations, Ecological Filtering, and Dispersal Central to Insect Invasions

Insect invasions, the establishment and spread of nonnative insects in new regions, can have extensive economic and environmental consequences. Increased global connectivity accelerates rates of introductions, while climate change may decrease the barriers to invader species' spread. We follow an individual-level insect- and arachnid-centered perspective to assess how the process of invasion is influenced by phenotypic heterogeneity associated with dispersal and stress resistance, and their coupling, across the multiple steps of the invasion process. We also provide an overview and synthesis on the importance of environmental filters during the entire invasion process for the facilitation or inhibition of invasive insect population spread. Finally, we highlight important research gaps and the relevance and applicability of ongoing natural range expansions in the context of climate change to gain essential mechanistic insights into insect invasions.

Comparative Analyses of Phenotypic Trait Covariation within and among Populations

Many morphological, behavioral, physiological, and life-history traits covary across the biological scales of individuals, populations, and species. However, the processes that cause traits to covary also change over these scales, challenging our ability to use patterns of trait covariance to infer process. Trait relationships are also widely assumed to have generic functional relationships with similar evolutionary potentials, and even though many different trait relationships are now identified, there is little appreciation that these may influence trait covariation and evolution in unique ways. We use a trait-performance-fitness framework to classify and organize trait relationships into three general classes, address which ones more likely generate trait covariation among individuals in a population, and review how selection shapes phenotypic covariation. We generate predictions about how trait covariance changes within and among populations as a result of trait relationships and in response to selection and consider how these can be tested with comparative data. Careful comparisons of covariation patterns can narrow the set of hypothesized processes that cause trait covariation when the form of the trait relationship and how it responds to selection yield clear predictions about patterns of trait covariation. We discuss the opportunities and limitations of comparative approaches to evaluate hypotheses about the evolutionary causes and consequences of trait covariation and highlight the importance of evaluating patterns within populations replicated in the same and in different selective environments. Explicit hypotheses about trait relationships are key to generating effective predictions about phenotype and its evolution using covariance data.

Water Stress Affects Development Time but Not Takeoff Performance in the Butterfly Pararge aegeria

Most organisms are limited in the amount and type of resources they are able to extract from the environment. The juvenile environment is particularly important in this regard, as conditions over ontogeny can influence the adult phenotype. Whole-organism performance traits, such as locomotion, are susceptible to such environmental effects, yet the specific biotic and abiotic factors driving performance plasticity have received little attention. We tested whether speckled wood Pararge aegeria L. butterflies reared under conditions of water stress exhibited poorer flight morphology and performance than control individuals. Despite large differences in mortality between treatments, we found no effects of water stress treatment on takeoff performance and only minor treatment effects on flight morphology. However, butterflies reared on water-stressed diets exhibited both significantly greater mortality and longer development times than did control individuals. Pararge aegeria larvae may compensate for this stress by prolonging development, resulting in similar realized performance capacities at least in takeoff performance in surviving adult butterflies; other measures of flight performance remain to be considered. Alternatively, the adult phenotype may be insulated from environmental effects at the larval stage in these insects.

Ancestry trumps experience: Transgenerational but not early life stress affects the adult physiological stress response

Exposure to stressors can affect an organism's physiology and behavior as well as that of its descendants (e.g. through maternal effects, epigenetics, and/or selection). We examined the relative influence of early life vs. transgenerational stress exposure on adult stress physiology in a species that has populations with and without ancestral exposure to an invasive predator. We raised offspring of eastern fence lizards (Sceloporus undulatus) from sites historically invaded (high stress) or uninvaded (low stress) by predatory fire ants (Solenopsis invicta) and determined how this different transgenerational exposure to stress interacted with the effects of early life stress exposure to influence the physiological stress response in adulthood. Offspring from these high- and low-stress populations were exposed weekly to either sub-lethal attack by fire ants (an ecologically relevant stressor), topical treatment with a physiologically-appropriate dose of the stress-relevant hormone, corticosterone (CORT), or a control treatment from 2 to 43weeks of age. Several months after treatments ended, we quantified plasma CORT concentrations at baseline and following restraint, exposure to fire ants, and adrenocorticotropic hormone (ACTH) injection. Exposure to fire ants or CORT during early life did not affect lizard stress physiology in adulthood. However, offspring of lizards from populations that had experienced multiple generations of fire ant-invasion exhibited more robust adult CORT responses to restraint and ACTH-injection compared to offspring from uninvaded populations. Together, these results indicate that transgenerational stress history may be at least as important, if not more important, than early life stress in affecting adult physiological stress responses.

Australian black field crickets show changes in neural gene expression associated with socially-induced morphological, life-history, and behavioral plasticity

BACKGROUND

Ecological and evolutionary model organisms have provided extensive insight into the ecological triggers, adaptive benefits, and evolution of life-history driven developmental plasticity. Despite this, we still have a poor understanding of the underlying genetic changes that occur during shifts towards different developmental trajectories. The goal of this study is to determine whether we can identify underlying gene expression patterns that can describe the different life-history trajectories individuals follow in response to social cues of competition. To do this, we use the Australian black field cricket (Teleogryllus commodus), a species with sex-specific developmental trajectories moderated by the density and quality of calls heard during immaturity. In this study, we manipulated the social information males and females could hear by rearing individuals in either calling or silent treatments. We next used RNA-Seq to develop a reference transcriptome to study changes in brain gene expression at two points prior to sexual maturation.

RESULTS

We show accelerated development in both sexes when exposed to calling; changes were also seen in growth, lifespan, and reproductive effort. Functional relationships between genes and phenotypes were apparent from ontological enrichment analysis. We demonstrate that increased investment towards traits such as growth and reproductive effort were often associated with the expression of a greater number of genes with similar effect, thus providing a suite of candidate genes for future research in this and other invertebrate organisms.

CONCLUSIONS

Our results provide interesting insight into the genomic underpinnings of developmental plasticity and highlight the potential of a genomic exploration of other evolutionary theories such as condition dependence and sex-specific developmental strategies.

Eco-evo-devo of the lemur syndrome: did adaptive behavioral plasticity get canalized in a large primate radiation?

BACKGROUND

Comprehensive explanations of behavioral adaptations rarely invoke all levels famously admonished by Niko Tinbergen. The role of developmental processes and plasticity, in particular, has often been neglected. In this paper, we combine ecological, physiological and developmental perspectives in developing a hypothesis to account for the evolution of 'the lemur syndrome', a combination of reduced sexual dimorphism, even adult sex ratios, female dominance and mild genital masculinization characterizing group-living species in two families of Malagasy primates.

RESULTS

We review the different components of the lemur syndrome and compare it with similar adaptations reported for other mammals. We find support for the assertion that the lemur syndrome represents a unique set of integrated behavioral, demographic and morphological traits. We combine existing hypotheses about underlying adaptive function and proximate causation by adding a potential developmental mechanism linking maternal stress and filial masculinization, and outline an evolutionary scenario for its canalization.

CONCLUSIONS

We propose a new hypothesis linking ecological, physiological, developmental and evolutionary processes to adumbrate a comprehensive explanation for the evolution of the lemur syndrome, whose assumptions and predictions can guide diverse future research on lemurs. This hypothesis should also encourage students of other behavioral phenomena to consider the potential role of developmental plasticity in evolutionary innovation.

Introducing biological realism into the study of developmental plasticity in behaviour

There is increasing attention for integrating mechanistic and functional approaches to the study of (behavioural) development. As environments are mostly unstable, it is now often assumed that genetic parental information is in many cases not sufficient for offspring to become optimally adapted to the environment and that early environmental cues, either indirectly via the parents or from direct experience, are necessary to prepare them for a specific environment later in life. To study whether these early developmental processes are adaptive and through which mechanism, not only the early environmental cues but also how they impinge on the later-life environmental context has therefore to be taken into account when measuring the animal's performance. We first discuss at the conceptual level six ways in which interactions between influences of different time windows during development may act (consolidation, cumulative information gathering and priming, compensation, buffering, matching and mismatching, context dependent trait expression). In addition we discuss how different environmental factors during the same time window may interact in shaping the phenotype during development. Next we discuss the pros and cons of several experimental designs for testing these interaction effects, highlighting the necessity for full, reciprocal designs and the importance of adjusting the nature and time of manipulation to the animal's adaptive capacity. We then review support for the interaction effects from both theoretical models and animal experiments in different taxa. This demonstrates indeed the existence of interactions at multiple levels, including different environmental factors, different time windows and between generations. As a consequence, development is a life-long, environment-dependent process and therefore manipulating only the early environment without taking interaction effects with other and later environmental influences into account may lead to wrong conclusions and may also explain inconsistent results in the literature.

Context-Dependent Plastic Response during Egg-Laying in a Widespread Newt Species

Previous research on predator-induced phenotypic plasticity mostly focused on responses in morphology, developmental time and/or behaviour during early life stages, but the potential significance of anticipatory parental responses has been investigated less often. In this study I examined behavioural and maternal responses of gravid female smooth newts, Lissotriton vulgaris, in the presence of chemical cues originating from invertebrate predators, Acilius sulcatus water beetles and Aeshna cyanea dragonfly larvae. More specifically, I tested the extent of oviposition preference, plasticity in egg-wrapping behaviour and plasticity in egg size when females had the possibility to lay eggs at oviposition sites with and without predator cues during overnight trials. I found that individuals did not avoid laying eggs in the environment with predator cues; however, individuals that deposited eggs into both environments adjusted the size of the laid eggs to the perceived environment. Females deposited larger eggs earlier in the season but egg size decreased with time in the absence of predator cues, whereas individuals laid eggs of average size throughout the investigated reproductive period when such cues were present. Also, egg size was found to be positively related to hatching success. Individuals did not adjust their wrapping behaviour to the presence of predator cues, but females differed in the extent of egg-wrapping between ponds. Females’ body mass and tail depth were also different between ponds, whereas their body size was positively associated with egg size. According to these results, female smooth newts have the potential to exhibit activational plasticity and invest differently into eggs depending on temporal and environmental factors. Such an anticipatory response may contribute to the success of this caudate species under a wide range of predator regimes at its natural breeding habitats.

Anthropogenic host plant expansion leads a nettle-feeding butterfly out of the forest: consequences for larval survival and developmental plasticity in adult morphology

Recent anthropogenic eutrophication has meant that host plants of nettle-feeding insects became quasi-omnipresent in fertile regions of Western Europe. However, host plant resource quality – in terms of microclimate and nutritional value – may vary considerably between the ‘original’ forest habitat and ‘recent’ agricultural habitat. Here, we compared development in both environmental settings using a split-brood design, so as to explore to what extent larval survival and adult morphology in the nettle-feeding butterfly Aglais urticae are influenced by the anthropogenic environment. Nettles along field margins had higher C/N ratios and provided warmer microclimates to larvae. Larvae developed 20% faster and tended to improve their survival rates, on the agricultural land compared to woodland. Our split-brood approach indicated plastic responses within families, but also family effects in the phenotypic responses. Adult males and females had darker wing pigmentation in the drier and warmer agricultural environment, which contrasts with the thermal melanism hypothesis. Developmental plasticity in response to this microclimatically different and more variable habitat was associated with a broader phenotypic parameter space for the species. Both habitat expansion and developmental plasticity are likely contributors to the ecological and evolutionary success of these nettle-feeding insects in anthropogenic environments under high nitrogen load.

The life history of whole-organism performance

For almost 40 years, studies of whole-organism performance have formed a cornerstone of evolutionary physiology. Although its utility as a heuristic guide is beyond question, and we have learned much about morphological evolution from its application, the ecomorphological paradigm has frequently been applied to performance evolution in ways that range from unsatisfactory to inappropriate. More importantly, the standard ecomorphological paradigm does not account for tradeoffs among performance and other traits, nor between performance traits that are mediated by resource allocation. A revised paradigm that includes such tradeoffs, and the possible ways that performance and fitness-enhancing traits might affect each other, could potentially revivify the study of phenotypic evolution and make important inroads into understanding the relationships between morphology and performance and between performance and Darwinian fitness. We describe such a paradigm, and discuss the various ways that performance and key life-history traits might interact with and affect each other. We emphasize both the proximate mechanisms potentially linking such traits, and the likely ultimate factors driving those linkages, as well as the evolutionary implications for the overall, multivariate phenotype. Finally, we highlight several research directions that will shed light on the evolution and ecology of whole-organism performance and related life-history traits.

Genomics: moving behavioural ecology beyond the phenotypic gambit

Researchers studying the adaptive significance of behaviour typically assume that genetic mechanisms will not inhibit evolutionary trajectories, an assumption commonly known as the 'phenotypic gambit'. Although the phenotypic gambit continues to be a useful heuristic for behavioural ecology, here we discuss how genomic methods provide new tools and conceptual approaches that are relevant to behavioural ecology. We first describe how the concept of a genetic toolkit for behaviour can allow behavioural ecologists to synthesize both genomic and ecological information when assessing behavioural adaptation. Then we show how gene expression profiles can be viewed as complex phenotypic measurements, used to (1) predict behaviour, (2) evaluate phenotypic plasticity and (3) devise methods to manipulate behaviour in order to test adaptive hypotheses. We propose that advances in genomics and bioinformatics may allow researchers to overcome some of the logistical obstacles that motivated the inception of the phenotypic gambit. Behavioural ecology and genomics are mutually informative, providing potential synergy that could lead to powerful advances in the field of animal behaviour.