Divergence of developmental trajectories is triggered interactively by early social and ecological experience in a cooperative breeder

Social Complexity During Early Development has Long-Term Effects on Neuroplasticity in the Social Decision-Making Network

In social species, early social experience shapes the development of appropriate social behaviours during conspecific interactions referred to as social competence. However, the underlying neuronal mechanisms responsible for the acquisition of social competence are largely unknown. A key candidate to influence social competence is neuroplasticity, which functions to restructure neural networks in response to novel experiences or alterations of the environment. One important mediator of this restructuring is the neurotrophin BDNF, which is well conserved among vertebrates. We studied the highly social fish Neolamprologus pulcher, in which the impact of early social experience on social competence has been previously shown. We investigated experimentally how variation in the early social environment impacts markers of neuroplasticity by analysing the relative expression of the bdnf gene and its receptors p75NTR and TrkB across nodes of the social decision-making network. In fish raised in larger groups, bdnf and TrkB were upregulated in the anterior tuberal nucleus, compared to fish raised in smaller groups, while TrkB was downregulated and bdnf was upregulated in the lateral part of the dorsal telencephalon. In the preoptic area (POA), all three genes were upregulated in fish raised in large groups, suggesting that early social experiences might lead to changes of the neuronal connectivity in the POA. Our results highlight the importance of early social experience in programming the constitutive expression of neuroplasticity markers, suggesting that the effects of early social experience on social competence might be due to changes in neuroplasticity.

Helping niches may trigger the development of task specialization and division of labour

Multimember societies often exhibit Division of labour (DoL), where different individuals perform distinct tasks such as brood care, food acquisition and defence. While demand for tasks exists at the group level, assigning them to specific members poses an organizational challenge. I propose the 'Helping Niche Specialization hypothesis' (HeNS hypothesis), which suggests that cues indicating societal demand for tasks along with the current distribution of help, influence individual biases towards specific task preferences. This process may begin during early ontogeny, even before helping behaviours are actively performed. I first introduce the concept of the 'helping niche', a special form of the social niche. Next, I outline procedures central to the HeNS hypothesis, which represent a stepwise process: (i) societal and environmental cues bias individuals towards task preferences, which may arise already during early life, (ii) experience with preferred tasks reinforces these biases, (iii) learning-by-doing enhances task performance, and/or (iv) reduced response thresholds make task execution more likely, leading to (v) differentiation and specialization. Furthermore, I discuss the costs and benefits of specialization, how helping niches may emerge during development, the environmental conditions that favour them, and alternative pathways to DoL.This article is part of the theme issue 'Division of labour as key driver of social evolution'.

Does the stress axis mediate behavioural flexibility in a social cichlid, Neolamprologus pulcher?

Behavioural flexibility plays a major role in the way animals cope with novel situations, and physiological stress responses are adaptive and highly efficient mechanisms to cope with unpredictable events. Previous studies investigating the role of stress responses in mediating behavioural flexibility were mostly done in laboratory rodents using stressors and cognitive challenges unrelated to the ecology of the species. To better understand how stress mediates behavioural flexibility in a natural context, direct manipulations of the stress response and cognitive tests in ecologically relevant contexts are needed. To this aim, we pharmacologically blocked glucocorticoid receptors (GR) in adult Neolamprologus pulcher using a minimally invasive application of a GR antagonist. GR blockade prevents the recovery after a stressful event, which we predicted to impair behavioural flexibility. After the application of the GR antagonist, we repeatedly exposed fish to a predator and tested their behavioural flexibility using a detour task, i.e. fish had to find a new, longer route to the shelter when the shortest route was blocked. While the latencies to find the shelter were not different between treatments, GR blocked fish showed more failed attempts during the detour tasks than control fish. Furthermore, weak performance during the detour tasks was accompanied by an increase of fear related behaviours. This suggests that blocking GR changed the perception of fear and resulted in an impaired behavioural flexibility. Therefore, our results support a potential link between the capacity to recover from stressors and behavioural flexibility in N. pulcher with potential consequences for an effective and adaptive coping with changing environments.

Assessment and the regulation of adaptive phenotypic plasticity

Organisms can react to environmental variation by altering their phenotype, and such phenotypic plasticity is often adaptive. This plasticity contributes to the diversity of phenotypes across the tree of life. Generally, the production of these phenotypes must be preceded by assessment, where the individual acquires information about its environment and phenotype relative to that environment, and then determines if and how to respond with an alternative phenotype. The role of assessment in adaptive plasticity is, therefore, crucial. In this Review, we (1) highlight the need for explicitly considering the role of assessment in plasticity; (2) present two different models for how assessment and the facultative production of phenotypes are related; and (3) describe an overarching framework for how assessment evolves. In doing so, we articulate avenues of future work and suggest that explicitly considering the role of assessment in the evolution of plasticity is key to explaining how and when plasticity occurs. Moreover, we emphasize the need to understand the role of assessment in adaptive versus maladaptive plasticity, which is an issue that will become increasingly important in a rapidly changing world.

Submissive behaviour is affected by group size in a social fish

For social groups to form and be stable over time, animals must develop strategies to cope with conflict among group members. Animals may behave submissively either by fleeing from an aggressor, or by signalling submission. The use of these two submissive responses may vary depending on the social and ecological context. Group size is a key aspect of social context for group living animals, as individuals in smaller groups may respond to aggression differently than those from larger groups. Here, we examine the relationship between group size and submissive behaviour in a cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher). We found that subordinate fish showed similar levels of submission signals in response to dominant aggression in larger and smaller groups, however, subordinates from larger groups were less likely to flee from dominant aggression than those in smaller groups. Subordinates in larger groups also showed more digging behaviour which may be also used to avoid conflict with the dominant group members. Our data show that social context affects submissive behaviour in a cooperatively breeding fish.

Early social complexity influences social behaviour but not social trajectories in a cooperatively breeding cichlid fish

Social competence-defined as the ability to optimize social behaviour according to available social information-can be influenced by the social environment experienced in early life. In cooperatively breeding vertebrates, the current group size influences behavioural phenotypes, but it is not known whether the group size experienced in early life influences behavioural phenotypes generally or social competence specifically. We tested whether being reared in large versus small groups for the first two months of life affects social behaviours, and associated life-history traits, in the cooperatively breeding cichlid Neolamprologus pulcher between the ages of four and twelve months. As we predicted, fish raised in larger and more complex groups showed higher social competence later in life. This was shown in several ways: they exhibited more, and earlier, submissive behaviour in response to aggression from a dominant conspecific, and-in comparison to fish raised in small groups-they exhibited more flexibility in the expression of submissive behaviour. By contrast, there was no evidence that early social complexity, as captured by the group size, affects aggression or exploration behaviour nor did it influence the propensity to disperse or show helping behaviour. Our results emphasize the importance of early-life social complexity for the development of social competence.

Egg-mediated maternal effects in a cooperatively breeding cichlid fish

Mothers can influence offspring phenotype through egg-mediated maternal effects, which can be influenced by cues mothers obtain from their environment during offspring production. Developing embryos use these components but have mechanisms to alter maternal signals. Here we aimed to understand the role of mothers and embryos in how maternal effects might shape offspring social phenotype. In the cooperatively breeding fish Neolamprologus pulcher different social phenotypes develop in large and small social groups differing in predation risk and social complexity. We manipulated the maternal social environment of N. pulcher females during egg laying by allocating them either to a small or a large social group. We compared egg mass and clutch size and the concentration of corticosteroid metabolites between social environments, and between fertilized and unfertilized eggs to investigate how embryos deal with maternal signalling. Mothers in small groups produced larger clutches but neither laid smaller eggs nor bestowed eggs differently with corticosteroids. Fertilized eggs scored lower on a principal component representing three corticosteroid metabolites, namely 11-deoxycortisol, cortisone, and 11-deoxycorticosterone. We did not detect egg-mediated maternal effects induced by the maternal social environment. We discuss that divergent social phenotypes induced by different group sizes may be triggered by own offspring experience.

Conformity and differentiation are two sides of the same coin

Variation between individuals is a key component of selection and hence evolutionary change. Social interactions are important drivers of variation, potentially making behaviour more similar (i.e., conform) or divergent (i.e., differentiate) between individuals. While documented across a wide range of animals, behaviours and contexts, conformity and differentiation are typically considered separately. Here, we argue that rather than independent concepts, they can be integrated onto a single scale that considers how social interactions drive changes in interindividual variance within groups: conformity reduces variance within groups while differentiation increases it. We discuss the advantages of placing conformity and differentiation at different ends of a single scale, allowing for a deeper understanding of the relationship between social interactions and interindividual variation.

Leveraging big data to uncover the eco-evolutionary factors shaping behavioural development

Mapping the eco-evolutionary factors shaping the development of animals' behavioural phenotypes remains a great challenge. Recent advances in 'big behavioural data' research-the high-resolution tracking of individuals and the harnessing of that data with powerful analytical tools-have vastly improved our ability to measure and model developing behavioural phenotypes. Applied to the study of behavioural ontogeny, the unfolding of whole behavioural repertoires can be mapped in unprecedented detail with relative ease. This overcomes long-standing experimental bottlenecks and heralds a surge of studies that more finely define and explore behavioural-experiential trajectories across development. In this review, we first provide a brief guide to state-of-the-art approaches that allow the collection and analysis of high-resolution behavioural data across development. We then outline how such approaches can be used to address key issues regarding the ecological and evolutionary factors shaping behavioural development: developmental feedbacks between behaviour and underlying states, early life effects and behavioural transitions, and information integration across development.

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

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

Dopamine modulates social behaviour in cooperatively breeding fish

Dopamine is part of the reward system triggering the social decision-making network in the brain. It has hence great potential importance in the regulation of social behaviour, but its significance in the control of behaviour in highly social animals is currently limited. We studied the role of the dopaminergic system in social decision-making in the cooperatively breeding cichlid fish, Neolamprologus pulcher, by blocking or stimulating the dopaminergic D1-like and D2-like receptors. We first tested the effects of different dosages and timing of administration on subordinate group members' social behaviour within the group in an unchallenging environment. In a second experiment we pharmacologically manipulated D1-like and D2-like receptors while experimentally challenging N. pulcher groups by presenting an egg predator, and by increasing the need for territory maintenance through digging out sand from the shelter. Our results show that the D1-like and D2-like receptor pathways are differently involved in the modulation of aggressive, submissive and affiliative behaviours. Interestingly, the environmental context seems particularly crucial regarding the role of the D2-like receptors in behavioural regulation of social encounters among group members, indicating a potential pathway in agonistic and cooperative interactions in a pay-to-stay scenario. We discuss the importance of environmental information in mediating the role of dopamine for the modulation of social behaviour.

Stress axis programming generates long-term effects on cognitive abilities in a cooperative breeder

The ability to flexibly adjust behaviour to social and non-social challenges is important for successfully navigating variable environments. Social competence, i.e. adaptive behavioural flexibility in the social domain, allows individuals to optimize their expression of social behaviour. Behavioural flexibility outside the social domain aids in coping with ecological challenges. However, it is unknown if social and non-social behavioural flexibility share common underlying cognitive mechanisms. Support for such shared mechanism would be provided if the same neural mechanisms in the brain affected social and non-social behavioural flexibility similarly. We used individuals of the cooperatively breeding fish Neolamprologus pulcher that had undergone early-life programming of the hypothalamic-pituitary-interrenal axis by exposure to (i) cortisol, (ii) the glucocorticoid receptor antagonist mifepristone, or (iii) control treatments, and where effects of stress-axis programming on social flexibility occurred. One year after the treatments, adults learned a colour discrimination task and subsequently, a reversal-learning task testing for behavioural flexibility. Early-life mifepristone treatment marginally enhanced learning performance, whereas cortisol treatment significantly reduced behavioural flexibility. Thus, early-life cortisol treatment reduced both social and non-social behavioural flexibility, suggesting a shared cognitive basis of behavioural flexibility. Further our findings imply that early-life stress programming affects the ability of organisms to flexibly cope with environmental stressors.

Acoustic and visual adaptations to predation risk: a predator affects communication in vocal female fish

Predation is an important ecological constraint that influences communication in animals. Fish respond to predators by adjusting their visual signaling behavior, but the responses in calling behavior in the presence of a visually detected predator are largely unknown. We hypothesize that fish will reduce visual and acoustic signaling including sound levels and avoid escalating fights in the presence of a predator. To test this we investigated dyadic contests in female croaking gouramis (Trichopsis vittata, Osphronemidae) in the presence and absence of a predator (Astronotus ocellatus, Cichlidae) in an adjoining tank. Agonistic behavior in T. vittata consists of lateral (visual) displays, antiparallel circling, and production of croaking sounds and may escalate to frontal displays. We analyzed the number and duration of lateral display bouts, the number, duration, sound pressure level, and dominant frequency of croaking sounds as well as contest outcomes. The number and duration of lateral displays decreased significantly in predator when compared with no-predator trials. Total number of sounds per contest dropped in parallel but no significant changes were observed in sound characteristics. In the presence of a predator, dyadic contests were decided or terminated during lateral displays and never escalated to frontal displays. The gouramis showed approaching behavior toward the predator between lateral displays. This is the first study supporting the hypothesis that predators reduce visual and acoustic signaling in a vocal fish. Sound properties, in contrast, did not change. Decreased signaling and the lack of escalating contests reduce the fish's conspicuousness and thus predation threat.

OUP accepted manuscript

Organisms interact with their environments in various ways. We present a conceptual framework that distinguishes three mechanisms of organism–environment interaction. We call these NC³ mechanisms: niche construction, in which individuals make changes to the environment; niche choice, in which individuals select an environment; and niche conformance, in which individuals adjust their phenotypes in response to the environment. Each of these individual-level mechanisms affects an individual's phenotype–environment match, its fitness, and its individualized niche, defined in terms of the environmental conditions under which the individual can survive and reproduce. Our framework identifies how individuals alter the selective regimes that they and other organisms experience. It also places clear emphasis on individual differences and construes niche construction and other processes as evolved mechanisms. The NC³ mechanism framework therefore helps to integrate population-level and individual-level research.

Sociability as a personality trait in animals: methods, causes and consequences

Within animal populations there is variation among individuals in their tendency to be social, where more sociable individuals associate more with other individuals. Consistent inter-individual variation in 'sociability' is considered one of the major axes of personality variation in animals along with aggressiveness, activity, exploration and boldness. Not only is variation in sociability important in terms of animal personalities, but it holds particular significance for, and can be informed by, two other topics of major interest: social networks and collective behaviour. Further, knowledge of what generates inter-individual variation in social behaviour also holds applied implications, such as understanding disorders of social behaviour in humans. In turn, research using non-human animals in the genetics, neuroscience and physiology of these disorders can inform our understanding of sociability. For the first time, this review brings together insights across these areas of research, across animal taxa from primates to invertebrates, and across studies from both the laboratory and field. We show there are mixed results in whether and how sociability correlates with other major behavioural traits. Whether and in what direction these correlations are observed may differ with individual traits such as sex and body condition, as well as ecological conditions. A large body of evidence provides the proximate mechanisms for why individuals vary in their social tendency. Evidence exists for the importance of genes and their expression, chemical messengers, social interactions and the environment in determining an individual's social tendency, although the specifics vary with species and other variables such as age, and interactions amongst these proximate factors. Less well understood is how evolution can maintain consistent variation in social tendencies within populations. Shifts in the benefits and costs of social tendencies over time, as well as the social niche hypothesis, are currently the best supported theories for how variation in sociability can evolve and be maintained in populations. Increased exposure to infectious diseases is the best documented cost of a greater social tendency, and benefits include greater access to socially transmitted information. We also highlight that direct evidence for more sociable individuals being safer from predators is lacking. Variation in sociability is likely to have broad ecological consequences, but beyond its importance in the spread of infectious diseases, direct evidence is limited to a few examples related to dispersal and invasive species biology. Overall, our knowledge of inter-individual variation in sociability is highly skewed towards the proximate mechanisms. Our review also demonstrates, however, that considering research from social networks and collective behaviour greatly enriches our understanding of sociability, highlighting the need for greater integration of these approaches into future animal personality research to address the imbalance in our understanding of sociability as a personality trait.

Early social deprivation shapes neuronal programming of the social decision-making network in a cooperatively breeding fish

The early social environment an animal experiences may have pervasive effects on its behaviour. The social decision-making network (SDMN), consisting of interconnected brain nuclei from the forebrain and midbrain, is involved in the regulation of behaviours during social interactions. In species with advanced sociality such as cooperative breeders, offspring are exposed to a large number and a great diversity of social interactions every day of their early life. This diverse social environment may have life-long consequences on the development of several neurophysiological systems within the SDMN, although these effects are largely unknown. We studied these life-long effects in a cooperatively breeding fish, Neolamprologus pulcher, focusing on the expression of genes involved in the monoaminergic and stress response systems in the SDMN. N. pulcher fry were raised until an age of 2 months either with their parents, subordinate helpers and same-clutch siblings (+F), or with same-clutch siblings only (-F). Analysis of the expression of glucocorticoid receptor, mineralocorticoid receptor, corticotropin releasing factor, dopamine receptors 1 and 2, serotonin transporter and DNA methyltransferase 1 genes showed that early social experiences altered the neurogenomic profile of the preoptic area. Moreover, the dopamine receptor 1 gene was up-regulated in the preoptic area of -F fish compared to +F fish. -F fish also showed up-regulation of GR1 expression in the dorsal medial telencephalon (functional equivalent to the basolateral amygdala), and in the dorsolateral telencephalon (functional equivalent to the hippocampus). Our results suggest that early social environment has life-long effects on the development of several neurophysiological systems within the SDMN.

Injury alters motivational trade-offs in calves during the healing period

Injury can produce long-lasting motivational changes that may alter decisions made under risk. Our objective was to determine whether a routine painful husbandry procedure, hot-iron disbudding, affects how calves trade off risk avoidance against a competing motivation (i.e., feeding), and whether this response depends on time since injury. We used a startle test to evaluate this trade-off in calves disbudded 0 or 21 days previously and non-injured control calves. For 3 days, calves were individually habituated to the testing arena in which they received a 0.5 L milk meal via a rubber teat. On the 4^th day, upon approaching the milk reward, the calf was startled by a sudden noise. We assessed the duration and magnitude of the calf’s startle response, their latency to return to the milk bottle, and duration spent suckling after startling. No treatment differences were observed in the duration and magnitude of the startle response or in the probability of returning to the bottle after startling. However, among those who did return, disbudded calves spent longer suckling, indicating they accepted more risk in order to feed compared to controls. In addition, calves with 21-day-old injuries tended to return to the bottle faster compared to newly disbudded calves and controls. We suggest that hot-iron disbudding increases calves’ motivation to suckle, as they were more likely to prioritize this behaviour over risk avoidance compared to control calves. This effect was most evident 21 days after disbudding, indicating that injury can produce long-term changes in motivational state.

The serotonin 1A receptor modulates the social behaviour within groups of a cooperatively-breeding cichlid

The neurotransmitter serotonin (5-HT) reduces aggressive behaviour in a number of vertebrates, and the 5-HT_1A receptor is known to be involved in this regulation. However, the role of this receptor in the modulation of sociopositive behaviour remains largely unknown. Here we investigated the role of the 5-HT_1A receptor in the regulation of aggressive, submissive and affiliative behaviour in the cooperatively-breeding cichlid Neolamprologus pulcher. In two experiments, we performed intramuscular injections of a 5-HT_1A agonist (8-OH-DPAT) and antagonist (Way-100635) followed by recordings of social behaviour of injected fish within their social groups. We determined the concentrations and post-injection times when the drugs had the greatest effect on social behaviour. We recorded spontaneous social behaviour in both experiments. In the second experiment we also recorded behaviour after social groups received a territorial challenge by live presentations of either conspecifics or egg predators. The 5-HT_1A agonist caused an increase in aggression and a decrease in submission and affiliation, whereas the antagonist had the opposite effects. Thus, the 5-HT_1A receptor plays an important regulatory role not only for aggressive but also sociopositive behaviour.

Dietary-based developmental plasticity affects juvenile survival in an aquatic detritivore

Developmental plasticity is ubiquitous in natural populations, but the underlying causes and fitness consequences are poorly understood. For consumers, nutritional variation of juvenile diets is probably associated with plasticity in developmental rates, but little is known about how diet quality can affect phenotypic trajectories in ways that might influence survival to maturity and lifetime reproductive output. Here, we tested how the diet quality of a freshwater detritivorous isopod (Asellus aquaticus), in terms of elemental ratios of diet (i.e. carbon : nitrogen : phosphorus; C : N : P), can affect (i) developmental rates of body size and pigmentation and (ii) variation in juvenile survival. We reared 1047 individuals, in a full-sib split-family design (29 families), on either a high- (low C : P, C : N) or low-quality (high C : P, C : N) diet, and quantified developmental trajectories of body size and pigmentation for every individual over 12 weeks. Our diet contrast caused strong divergence in the developmental rates of pigmentation but not growth, culminating in a distribution of adult pigmentation spanning the broad range of phenotypes observed both within and among natural populations. Under low-quality diet, we found highest survival at intermediate growth and pigmentation rates. By contrast, survival under high-quality diet survival increased continuously with pigmentation rate, with longest lifespans at intermediate growth rates and high pigmentation rates. Building on previous work which suggests that visual predation mediates the evolution of cryptic pigmentation in A. aquaticus, our study shows how diet quality and composition can generate substantial phenotypic variation by affecting rates of growth and pigmentation during development in the absence of predation.

Early social experience has life-long effects on baseline but not stress-induced cortisol levels in a cooperatively breeding fish

In cooperatively breeding cichlid fish, the early social environment has lifelong effects on the offspring's behaviour, life-history trajectories and brain gene expression. Here, we asked whether the presence or absence of parents and subordinate helpers during early life also shapes fluctuating levels of cortisol, the major stress hormone in the cichlid Neolamprologus pulcher. To non-invasively characterize baseline and stress-induced cortisol levels, we adapted the 'static' holding-water method often used to collect waterborne steroid hormones in aquatic organisms by including a flow-through system allowing for repeated sampling without handling of the experimental subjects. We used 8-year-old N. pulcher either raised with (+F) or without (-F) parents and helpers in early life. We found that N. pulcher have a peak of their circadian cortisol cycle in the early morning, and that they habituated to the experimental procedure after four days. Therefore, we sampled the experimental fish in the afternoon after four days of habituation. -F fish had significantly lower baseline cortisol levels, whereas stress-induced cortisol levels did not differ between treatments. Thus, we show that the early social environment has life-long effects on aspects of the physiological stress system of the Hypothalamic-Pituitary-Interrenal (HPI) axis. We discuss how these differences in physiological state may have contributed to the specialization in different social and life-history trajectories of this species.

Context-dependent consequences of color biases in a social fish

Colorful visual signals can provide receivers with valuable information about food, danger, and the quality of social partners. However, the value of the information that color provides varies depending on the situation, and color may even act as a sensory trap where signals that evolved under one context are exploited in another. Despite some elegant early work on color as a sensory trap, few empirical studies have examined how color biases may vary depending on context and under which situations biases can be overridden. Here, using Neolamprologus pulcher, a highly social cichlid fish from Lake Tanganyika, we conducted a series of experiments to determine color biases and investigate the effects of these biases under different contexts. We found that N. pulcher interacted the most with yellow items and the least with blue items. These biases were maintained during a foraging-based associative learning assay, with fish trained using yellow stimuli performing better than those trained using blue stimuli. However, these differences in learning performance did not extend to reversal learning; fish were equally capable of forming new associations regardless of the color they were initially trained on. Finally, in a social choice assay, N. pulcher did not display a stronger preference for conspecifics whose yellow facial markings had been artificially enhanced. Together, these findings suggest that the influence of color biases varies under different contexts and supports the situational dependency of color functions.

Head up displays are a submission signal in the group-living daffodil cichlid

Dominance hierarchies can reduce conflict within social groups and agonistic signals can help to establish and maintain these hierarchies. Behaviours produced by subordinates in response to aggression are often assumed to function as signals of submission, however, these behaviours may serve other purposes, for example, defence or escape. For a behaviour to act as a submission signal, the receiver must respond by reducing their likelihood of further aggression towards the signaller. In the current study, we examine the receiver response to a putative signal of submission, the head up display, within established social groups of the cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher). We found that when subordinate signallers produce the head up display in response to aggression from the breeder male, he exhibited a longer latency to behave aggressively towards that individual again. We also report that head up displays are rarely produced without being elicited by aggression, and the number of head up displays correlates with the amount of aggression received. Our results demonstrate that the head up display is used as a signal of submission in the daffodil cichlid and provide insight into intragroup communication in an emerging model system for the study of social behaviour.

Early social and ecological experience triggers divergent reproductive investment strategies in a cooperative breeder

Unlike eusocial systems, which are characterized by reproductive division of labour, cooperative breeders were predicted not to exhibit any reproductive specialization early in life. Nevertheless, also cooperative breeders face a major life-history decision between dispersal and independent breeding vs staying as helper on the natal territory, which might affect their reproductive strategies. In the cooperatively-breeding cichlid Neolamprologus pulcher early-life social and predator experiences induce two behavioural types differing in later-life social and dispersal behaviour. We performed a long-term breeding experiment to test whether the two early-life behavioural types differ in their reproductive investment. We found that the early-dispersing type laid fewer and smaller eggs, and thus invested overall less in reproduction, compared to the philopatric type. Thus N. pulcher had specialised already shortly after birth for a dispersal and reproductive strategy, which is in sharp contrast to the proposition that reproductively totipotent cooperative breeders should avoid reproductive specialization before adulthood.

Early-life manipulation of cortisol and its receptor alters stress axis programming and social competence

In many vertebrate species, early social experience generates long-term effects on later life social behaviour. These effects are accompanied by persistent modifications in the expression of genes implicated in the stress axis. It is unknown, however, whether stress axis programming can affect the development of social competence, and if so, by which mechanism(s). Here, we used pharmacological manipulations to persistently reprogramme the hypothalamic-pituitary-interrenal axis of juvenile cooperatively breeding cichlids, Neolamprologus pulcher. During the first two months of life, juveniles were repeatedly treated with cortisol, mifepristone or control treatments. Three months after the last manipulation, we tested for treatment effects on (i) social competence, (ii) the expression of genes coding for corticotropin-releasing factor ( crf), glucocorticoid receptor ( gr1) and mineralocorticoid receptor ( mr) in the telencephalon and hypothalamus and (iii) cortisol levels. Social competence in a social challenge was reduced in cortisol-treated juveniles, which is in accordance with previous work applying early-life manipulations using different social experiences. During early life, both cortisol and mifepristone treatments induced a persistent downregulation of crf and upregulation of mr in the telencephalon. We suggest that these persistent changes in stress gene expression may represent an effective physiological mechanism for coping with stress. This article is part of the theme issue 'Developing differences: early-life effects and evolutionary medicine'.

Simulating more realistic predation threat using attack playbacks

Use of virtual proxies of live animals are rapidly gaining ground in studies of animal behaviour. Such proxies help to reduce the number of live experimental animals needed to stimulate the behaviour of experimental individuals and to increase standardisation. However, using too simplistic proxies may fail to induce a desired effect and/or lead to quick habituation. For instance, in a predation context, prey often employ multimodal cues to detect predators or use specific aspects of predator behaviour to assess threat. In a live interaction, predator and prey often show behaviours directed towards each other, which are absent in virtual proxies. Here we compared the effectiveness of chemical and visual predator cues in the cooperatively breeding cichlid Neolamprologus pulcher, a species in which predation pressure has been the evolutionary driver of its sociality. We created playbacks of predators simulating an attack and tested their effectiveness in comparison to a playback showing regular activity and to a live predator. We further compared the effectiveness of predator odour and conspecific skin extracts on behaviours directed towards a predator playback. Regular playbacks of calmly swimming predators were less effective than live predators in stimulating a focal individual's aggression and attention. However, playbacks mimicking an attacking predator induced responses much like a live predator. Chemical cues did not affect predator directed behaviour.

Genomics of Developmental Plasticity in Animals

Developmental plasticity refers to the property by which the same genotype produces distinct phenotypes depending on the environmental conditions under which development takes place. By allowing organisms to produce phenotypes adjusted to the conditions that adults will experience, developmental plasticity can provide the means to cope with environmental heterogeneity. Developmental plasticity can be adaptive and its evolution can be shaped by natural selection. It has also been suggested that developmental plasticity can facilitate adaptation and promote diversification. Here, we summarize current knowledge on the evolution of plasticity and on the impact of plasticity on adaptive evolution, and we identify recent advances and important open questions about the genomics of developmental plasticity in animals. We give special attention to studies using transcriptomics to identify genes whose expression changes across developmental environments and studies using genetic mapping to identify loci that contribute to variation in plasticity and can fuel its evolution.

Heritabilities, social environment effects and genetic correlations of social behaviours in a cooperatively breeding vertebrate

Social animals interact frequently with conspecifics, and their behaviour is influenced by social context, environmental cues and the behaviours of interaction partners, allowing for adaptive, flexible adjustments to social encounters. This flexibility can be limited by part of the behavioural variation being genetically determined. Furthermore, behaviours can be genetically correlated, potentially constraining independent evolution. Understanding social behaviour thus requires carefully disentangling genetic, environmental, maternal and social sources of variations as well as the correlation structure between behaviours. Here, we assessed heritability, maternal, common environment and social effects of eight social behaviours in Neolamprologus pulcher, a cooperatively breeding cichlid. We bred wild-caught fish in a paternal half-sibling design and scored ability to defend a resource against conspecifics, to integrate into a group and the propensity to help defending the group territory ("helping behaviour"). We assessed genetic, social and phenotypic correlations within clusters of behaviours predicted to be functionally related, namely "competition," "aggression," "aggression-sociability," "integration" and "integration-help." Helping behaviour and two affiliative behaviours were heritable, whereas there was little evidence for a genetic basis in all other traits. Phenotypic social effects explained part of the variation in a sociable and a submissive behaviour, but there were no maternal or common environment effects. Genetic and phenotypic correlation within clusters was mostly positive. A group's social environment influenced covariances of social behaviours. Genetic correlations were similar in magnitude but usually exceeding the phenotypic ones, indicating that conclusions about the evolution of social behaviours in this species could be provisionally drawn from phenotypic data in cases where data for genetic analyses are unobtainable.

Seasonal plasticity in anti-predatory strategies: Matching of color and color preference for effective crypsis

Effective anti-predatory strategies typically require matching appearance and behavior in prey, and there are many compelling examples of behavioral repertoires that enhance the effectiveness of morphological defenses. When protective adult morphology is induced by developmental environmental conditions predictive of future predation risk, adult behavior should be adjusted accordingly to maximize predator avoidance. While behavior is typically strongly affected by the adult environment, developmental plasticity in adult behavior-mediated by the same pre-adult environmental cues that affect morphology-could ensure an effective match between anti-predatory morphology and behavior. The coordination of environmentally induced responses may be especially important in populations exposed to predictable environmental fluctuations (e.g., seasonality). Here, we studied early and late life environmental effects on a suite of traits expected to work together for effective crypsis. We focused on wing color and background color preference in Bicyclus anynana, a model of developmental plasticity that relies on crypsis as a seasonal strategy for predator avoidance. Using a full-factorial design, we disentangled effects of developmental and adult ambient temperature on both appearance and behavior. We showed that developmental conditions affect both adult color and color preference, with temperatures that simulate natural dry season conditions leading to browner butterflies with a perching preference for brown backgrounds. This effect was stronger in females, especially when butterflies were tested at lower ambient temperatures. In contrast to the expectation that motionlessness enhances crypsis, we found no support for our hypothesis that the browner dry-season butterflies would be less active. We argue that the integration of developmental plasticity for morphological and behavioral traits might improve the effectiveness of seasonal anti-predatory strategies.

Why and how the early-life environment affects development of coping behaviours

Understanding the ways in which individuals cope with threats, respond to challenges, make use of opportunities and mediate the harmful effects of their surroundings is important for predicting their ability to function in a rapidly changing world. Perhaps one of the most essential drivers of coping behaviour of adults is the environment experienced during their early-life development. Although the study of coping, defined as behaviours displayed in response to environmental challenges, has a long and rich research history in biology, recent literature has repeatedly pointed out that the processes through which coping behaviours develop in individuals are still largely unknown. In this review, we make a move towards integrating ultimate and proximate lines of coping behaviour research. After broadly defining coping behaviours (1), we review why, from an evolutionary perspective, the development of coping has become tightly linked to the early-life environment (2), which relevant developmental processes are most important in creating coping behaviours adjusted to the early-life environment (3), which influences have been shown to impact those developmental processes (4) and what the adaptive significance of intergenerational transmission of coping behaviours is, in the context of behavioural adaptations to a fast changing world (5). Important concepts such as effects of parents, habitat, nutrition, social group and stress are discussed using examples from empirical studies on mammals, fish, birds and other animals. In the discussion, we address important problems that arise when studying the development of coping behaviours and suggest solutions.

Evolutionary conserved neural signature of early life stress affects animal social competence

In vertebrates, the early social environment can persistently influence behaviour and social competence later in life. However, the molecular mechanisms underlying variation in animal social competence are largely unknown. In rats, high-quality maternal care causes an upregulation of hippocampal glucocorticoid receptors (gr) and reduces offspring stress responsiveness. This identifies gr regulation as a candidate mechanism for maintaining variation in animal social competence. We tested this hypothesis in a highly social cichlid fish, Neolamprologus pulcher, reared with or without caring parents. We find that the molecular pathway translating early social experience into later-life alterations of the stress axis is homologous across vertebrates: fish reared with parents expressed the glucocorticoid receptor gr1 more in the telencephalon. Furthermore, expression levels of the transcription factor egr-1 (early growth response 1) were associated with gr1 expression in the telencephalon and hypothalamus. When blocking glucocorticoid receptors (GR) with an antagonist, mifepristone (RU486), parent-reared individuals showed more socially appropriate, submissive behaviour when intruding on a larger conspecific's territory. Remarkably, mifepristone-treated fish were less attacked by territory owners and had a higher likelihood of territory takeover. Our results indicate that early social-environment effects on stress axis programming are mediated by an evolutionary conserved molecular pathway, which is causally involved in environmentally induced variation of animal social competence.