The main research interest of the lab is the integrative study of social behavior that combines the study of proximate causes (gene modules, hormones, neural circuits, cognitive processes) and ultimate effects (evolutionary consequences).
In particular we are interested in understanding how brain and behavior can be shaped by the social environment, and how the cognitive, neural and genetic mechanisms underlying plasticity in the expression of social behavior have evolved. Current research interests are centered on three main research topics:
1. Evolution of social cognition and of its neuromolecular mechanisms
Animals living in social groups have to adjust the expression of their social behavior to constant changes in the social environment. Therefore, it is expected that the acquisition and processing of social information have posed a major selective pressure in social species, and that specific cognitive modules might have evolved to deal with the social domain. Thus, we are particularly interested in identifying the cognitive building blocks of social competence (i.e. the ability to adjust the expression of social behavior to changes in the social environment) and to test if there are specific cognitive adaptations to the social environment, or if social information is acquired and processed using general domain mechanisms. Moreover, we are also interested to test if social competence is an organismal performance trait that impacts the Darwinian fitness and may itself be subject to selection. Our approach to these questions involves a combination of artificial selection experiments with neuroethological techniques using zebrafish a model organism, which aim to unveil the neuromolecular mechanisms of social cognition and how they evolve in response to selection.
2. Genomic and epigenomic mechanisms of social plasticity
The occurrence of social plasticity poses two key questions:
(a) What are the mechanisms animals use for sensing and responding adaptively to specific cues in the social environment that trigger plastic responses?
(b) How can the same genome produce different social phenotypes in response to cues in the social environment?
We are currently investigating the role of immediate early genes (IEGs: c-fos, egr-1) as translators of social information into biological information that regulate transitions between neurogenomic states (i.e. gene expression profiles which correspond to the expression of a given behavioural/phenotypic state), and what are the key cues in the social environment that trigger their response. We are also investigating how social experience drives IEG mediated changes in neurogenomic states, and how these states can be stabilized by epigenomic changes. We are using both zebrafish and a cichlid fish to test these ideas, taking advantage of the genomic resources available for these species.
3. Neuroendocrinology of social interactions and of social plasticity
The neural mechanisms underlying plasticity in the expression of social behavior may rely in either structural or functional changes on the underlying neural circuits. In the former case social experience may induce changes in the wiring, or other structural dimensions of relevant circuits; in the latter case, the properties of the same underlying circuit may be changed by experience. In order to address these questions we are interested in characterizing the brain network underlying social behavior and in understanding how social experience changes its structure (e.g. socially driven adult neurogenesis) and function (e.g. socially driven neuromodulation). In particular we are interested in the role of steroid hormones and nonapeptides (AVT and oxytocin/isotocin) as social-sensitive neuromodulators involved in the plasticity of social behavior at two different levels of variation:
(a) behavioral flexibility – transient and reversible/labile changes in social behavior driven by social experience and social context; and
(b) developmental social plasticity – irreversible switches between discrete behavioral phenotypes expressed by the same genotype, driven by developmental processes in response to environmental cues.
We are using cichlid fish (Mozambique tilapia) and a blenniid fish (peacock blenny) with sequential alternative reproductive tactics to address these questions. We also conduct some studies on human subjects to test specific hypotheses within the framework described above.
4. Fish cognition and welfare
Since we keep and manipulate many fish in our lab and since we study fish behavior and cognition we became interested in using our knowledge on these subjects to help to improve fish husbandry and handling procedures towards better research and animal welfare. In this respect we have mainly focused on two topics:
(a) cognitive appraisal – We are testing the idea that fish may use cognitive appraisal to create a representation of their environment. If this is the case then cognitive bias may occur and some individuals may perceive the same stimulus has more positive or as more negative (i.e. optimists/pessimists, respectively). In this scenario inter-individual differences in cognitive bias may parallel in inter-individual variation in stress responses and susceptibility to disease which may have a profound impact on husbandry procedures and on research results, if not taken into account.
(b) asking fish what they want – We are developing behavioural paradigms that allow us to “ask” fish about their environmental preferences, such that one can make more informed decisions about housing conditions and procedures. We are also testing if fish preferences are always adaptive (i.e. if in artificial environments where choices not present in the wild become available fish do not express fitness-costly preferences).
ONGOING RESEARCH GRANTS
1. COPEWELL: A new integrative framework for the study of fish welfare based on the concepts of allostasis, appraisal and coping styles (EU-FP7 collaborative project FP7-KBBE-2010-4)
COPEWELL aims to provide a better understanding of the underpinning mechanisms and basic knowledge about the physiology, biology, and behaviour of fishes and to give a deeper understanding of the basic mechanisms involved in coping styles. We will use an innovative hypothesis-driven multidisciplinary approach that aims to explore the links between brain function, behaviour and adaptive plasticity (WPs 1 and 2). Underlying mechanisms will be addressed by localising key elements of the stress-responsive serotonergic and learning and memory systems in the telencephalon, and for the first time also analyse rates of brain cell proliferation, neurogenesis, and expression of genes controlling other aspects of brain function, as learning and memory, in fish expressing different coping styles. The project will also focus on the understanding of how animals experience their world, based on appraisal theory and experimental studies of appraisal mechanisms in farmed fish, and not simply on the description of animal behaviour or stress responses (WP2 Appraisal). COPEWELL will further study the ontogeny of brain function and neuroendocrine stress responses in the call species Atlantic salmon (Salmo salar), European sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata), and will provide new insights on the interrelations between different relevant husbandry practices, plasticity of brain function and stress response during early ontogeny. COPEWELL will explore potential consequences of early life stress experiences on the welfare and quality of juvenile fish, substantiate the concept of allostatic stress regulation in fish and determine thresholds between eustress that are considered positive for welfare and distress that can have severe negative consequences for fish welfare as: “it will attempt to discriminate between normal adaptive stress responses and situations of potential consequence to animal welfare, in relation to different relevant husbandry practices and rearing methods” (WP3Allostasis and WP4 Ontogeny). The expected impact the COPEWELL project is to deepen our knowledge on the development of the brain function, behaviour and stress response in relation to the different husbandry practises and rearing methods. It will also serve to define how short or long episodes of stress during the early life affect the welfare and quality of juveniles and adult fish (WPs 3 & 4). It will significantly contribute in providing and extending the knowledge basis for the development of tools such as new individual-based indicators for a better assessment of fish welfare, e.g. by identifying and verifying non-invasive indicators of coping styles. Perhaps most important, COPEWELL will provide a new framework, based on evolutionary principles and an understanding of subjective experience of welfare as an evolved survival mechanism, making welfare available for scientific inquiry.
2. Molecular mechanisms and evolutionary implications of social plasticity (FCT grant EXCL/BIA-ANM/0549/2012)
According to classic evolutionary theory nonheritable phenotypic variation would seem to be irrelevant to evolutionary change, since adaptation by natural selection rather depends on heritable phenotypic variation produced by genetic variation. However, when the rate of genetic evolutionary change is outpaced by changes in the environment the need for adaptive change without genetic mutation emerges. In this scenario, the evolution of phenotypic plasticity is favored according to which environmental cues sensed by the organism lead the same genotype to produce different phenotypes depending on environmental conditions (i.e. reaction norm). Thus, despite the fact that the contribution of nonheritable phenotypic variation to evolutionary change appears to be a paradox, the evolution of mechanisms that generate it can be a common evolutionary phenomenon. Different traits show different evolutionary changes in plasticity, both in terms of the time lag to respond to the environmental cue and of the magnitude of the response. Among animals, behavioral traits exhibit both more rapid and stronger plasticity than morphological traits, which makes behavioral plasticity a key adaptive response to changing environmental conditions. At the proximate level behavioral plasticity depends on the development of a central nervous system which allows for rapid and integrated organismal responses in order to maintain homeostasis (or allostasis). Many of these responses are simple reflexes and fixed action patterns elicited by a stimulus in the environment, when it determinately predicts an appropriate response. However, when environmental complexity and ambiguity increases, the capacity to adaptively modify behavior, as a function of experience (learning) and context, is needed. One of the most ambiguous components of the environment is the social domain, since it is made of other behavioral agents with an inherent level of unpredictability of their actions, with whom the individual needs to interact. Hence, the ability of animals to regulate the expression of social behavior, as to adapt their behavioral output to specific situations in a complex and variable social world, is expected to depend on the evolution of plastic responses. These allow the same genotype to produce different behavioral phenotypes (social plasticity), rather than to genetically determine rules controlling fixed responses. Thus, social plasticity should be viewed as a key ecological performance trait that impacts Darwinian fitness.
Here we propose an integrative framework for understanding the proximate mechanisms and ultimate consequences of social plasticity. According to this framework, social plasticity is achieved by rewiring or by biochemically switching nodes of the neural network underlying social behavior in response to perceived social information. Therefore, at the molecular level, it depends on the social regulation of gene expression, so that different neurogenomic states correspond to different behavioral responses and the switches between states are orchestrated by signaling pathways that interface the social environment and the genotype. At the evolutionary scale social plasticity can be seen as an adaptive trait that can be under positive selection when changes in the environment outpace the rate of genetic evolutionary change. However, when social plasticity is too costly or incomplete, behavioral consistency (behavioral syndromes) can emerge by directional selection which recruits gene modules corresponding to favored behavioral states in that environment.
In this project we will address the following questions (Q):
Q1. What are the mechanisms animals use for sensing and responding adaptively to specific environmental cues that trigger plastic responses?
Q2. How can the same genome produce different social phenotypes in response to cues provided by the ecological and social environment?
Q3. Is plasticity itself subject to selection and might therefore evolve?
The choice of fish as study models is justified by the fact that teleosts are the most diverse and plastic taxa among vertebrates. Following Krogh’s principle, we have chosen what we considered to be the species of choice to most conveniently study each of these questions (Q1: zebrafish, tilapia; Q2: peacock blenny; Q3: zebrafish).
As a result of this project we expect to show how knowledge of the proximate mechanisms underlying social plasticity is crucial to understanding its costs, limits and evolutionary consequences, therefore highlighting the fact that proximate mechanisms of nonheritable phenotypic variation contribute to the dynamics of selection.
3. Comparative social cognition: zebrafish as a neurobehavioural model (FCT grant PTDC/PSI-PCO/118776/2010)
The complexity of the social system is considered to be a major selective force in brain evolution. This major impact of the social realm on the nervous system seems to be due to the need that social living animals have to continuously adjust the expression of their social behavior to a changing social environment. For doing this they need not only to respond to sensory information about the social world, but also to emotional cues from conspecifics and to social context. Thus, some kind of general appraisal mechanism that allows organisms to evaluate the valence and salience of stimuli in order to determine the appropriate affective state and behavioral output (e.g. approach vs. withdrawal) must have evolved. Furthermore, opportunities to use public sources of information (i.e. social learning), at lower costs than trough asocial private sources (i.e. trial-and-error learning), is also ubiquitous in social environments. Therefore, cognitive appraisal of socially relevant information that elicits functional affective states and social learning seem to be cognitive abilities that must have been prompted by social complexity, and that may have had an impact on the evolution of nervous systems. In contrast to this rationale most research in this area has focused on comparative work in humans and non-human primates, and to some extent in rodents and corvids, on what are considered to be highly complex cognitive abilities (i.e. not explainable by associative learning rules, that therefore would implicate the occurrence of Human-like mental processes; e.g. theory of mind, imitation). This path of research has been prompted by an ongoing debate in contemporary psychology between associative and rational explanations of animal behavior. We propose that a more profitable way to address the evolution of social cognition is to identify what are the elementary cognitive processes particularly needed for the development of social skills, to assess if they have differentiated neural modules in the nervous system, and then to search for their presence in different animal groups. In this project we propose to address two basic aspects of social cognition, cognitive appraisal of social information and social learning, using the zebrafish as a model of a social teleost fish. In recent years, zebrafish (Danio rerio) has emerged as a major model organism in biomedical research and a large number of neuroanatomic and genomic tools became available for this species. The use of a fish species has also the added value of establishing these cognitive processes in the most divergent phylogenetic vertebrate branch from that of mammals (for whom most data on social cognition is available).
The broader goals of the project are: 1. Establish the occurrence of cognitive appraisal in zebrafish and identify the brain areas involved in the evaluation of valence and salience of social stimuli. The following dimensions of appraisal, and their neural representation, will be investigated: intrinsic valence of the stimuli, familiarity, predictability, violation of expectations and perception of control. 2. Assess the occurrence of social learning in zebrafish and characterize the underlying neural mechanisms. A major difference between social and asocial learning is that prediction error that is usually considered a learning signal is not directly available in the former. Thus, a comparison of the underlying neural mechanisms of these two learning modes is particularly relevant. Three different forms of social learning will be investigated: eavesdropping, observational conditioning and copying. 3. Genetically dissect the neural circuits involved in social cognition (identified in previous points) to manipulate cognitive appraisal and social learning mechanisms. Taking advantage of the large number of GAL4-UAS enhancer trap lines available that have restricted expression in different brain areas (e.g. dorsomedial telencephalon = amygdala; dorsolateral telencephalon = hippocampus), once the area of interest has been identified gain and loss of function can be triggered genetically, and its impact on social cognition tasks assessed. Immediate-early genes (IEG) will be used to map brain activation in the tasks described above, since IEGs constitute the first gene expression response to the stimulation of a neuron, by a variety of natural experiences from the exposure to sensory stimuli to the production of species typical behavior. Therefore, the accumulation of IEG mRNA or protein is widely used as a marker of functional neural activity. The research proposed here will help to develop a neurobehavioural comparative framework to search for common elementary modules of social cognition within vertebrates, and it will also further support the use of zebrafish as a vertebrate model organism for translational research in social and affective neuroscience.
4. NEURAL MECHANISMS OF COGNITIVE BIAS IN ZEBRAFISH (BIAL Foundation grant # 64/12)
In this project we aim to uncover the genetic pathways and neural circuits involved in cognitive appraisal and in the response to stressors, using zebrafish (Danio rerio) as a model organism. The broader goals of the project are:
1) To develop a behavioural assay to test cognitive bias in zebrafish, and to characterize the behavioural and neuroendocrine profiles of “optimistic” and “pessimistic” individuals. Immediate early genes (IEG) will be used to map brain activation, since they constitute the first gene expression response to the stimulation of a neuron. Therefore, the accumulation of IEG mRNA or protein will be used as a marker of functional neural activity.
2) To assess if cognitive bias (e.g. pessimistic bias) is mediating the inter-individual variation in the susceptibility to the detrimental effects of stress, using behavioural, systemic (stress axis activity and adult neurogenesis) and cellular (telomere dynamics) read-outs.
3) To manipulate genetically the neural circuits involved in the cognitive appraisal of stressors (identified in 1) and check its effects on the activation of the stress response. Taking advantage of the large number of GAL4-UAS enhancer trap lines available in zebrafish that have restricted expression in different brain areas (e.g. dorsomedial telencephalon = amygdala; dorsolateral telencephalon = hippocampus), once the area of interest has been identified gain and loss of function can be triggered genetically, and its impact on the stress response assessed.
Although this project is focused on basic biological mechanisms of stress, its outcomes have the potential to have a significant impact in stress management and open the way for the use of zebrafish as a stress model organism in translational biomedical research.