Kyriacos Kareklas

@gulbenkian.pt

Integrative Behavioural Biology Group
Gulbenkian Research Institute

Kyriacos Kareklas


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https://researchid.co/k.kareklas

RESEARCH, TEACHING, or OTHER INTERESTS

Ecology, Evolution, Behavior and Systematics, Animal Science and Zoology, Behavioral Neuroscience
18

Scopus Publications

462

Scholar Citations

12

Scholar h-index

14

Scholar i10-index

Scopus Publications

  • Evolutionarily conserved role of oxytocin in zebrafish social reward encoding
    Kyriacos Kareklas, Lisbeth Herrera-Castillo, Gil Levkowitz, Rui F. Oliveira
    Biology Letters, 2025
    Social rewards may have evolved in social species to reinforce adaptive social interactions. Yet, evidence for social rewards is still scarce, and the underlying mechanisms remain unclear. A key candidate to regulate the value of social stimuli is oxytocin due to its role in social affiliation, which is traced to its origins in ray-finned fish—but whether it encodes rewards is uncertain. Using a single-trial conditioned place preference test, we found that wild-type zebrafish increased preference for a neutral unpreferred cue associated with a same-sex sibling, while oxytocin receptor ( oxtr ) mutants did not. These findings demonstrate the necessity of oxtr for social rewards, while the short exposure infers its role in encoding rather than consolidation. Our results provide evidence for an evolutionarily conserved role of oxytocin in social reward encoding given the available evidence for similar effects in rodents.
  • Emotional contagion and prosocial behaviour in fish: An evolutionary and mechanistic approach
    Kyriacos Kareklas, Rui F. Oliveira
    Neuroscience and Biobehavioral Reviews, 2024
  • Oxytocin and Social Isolation: Nonapeptide Regulation of Social Homeostasis
    Kyriacos Kareklas, Rui F. Oliveira
    Masterclass in Neuroendocrinology, 2024
  • Autism-associated gene shank3 is necessary for social contagion in zebrafish
    Kyriacos Kareklas, Magda C. Teles, Elena Dreosti, Rui F. Oliveira
    Molecular Autism, 2023
    Background Animal models enable targeting autism-associated genes, such as the shank3 gene, to assess their impact on behavioural phenotypes. However, this is often limited to simple behaviours relevant for social interaction. Social contagion is a complex phenotype forming the basis of human empathic behaviour and involves attention to the behaviour of others for recognizing and sharing their emotional or affective state. Thus, it is a form of social communication, which constitutes the most common developmental impairment across autism spectrum disorders (ASD). Methods Here we describe the development of a zebrafish model that identifies the neurocognitive mechanisms by which shank3 mutation drives deficits in social contagion. We used a CRISPR-Cas9 technique to generate mutations to the shank3a gene, a zebrafish paralogue found to present greater orthology and functional conservation relative to the human gene. Mutants were first compared to wild types during a two-phase protocol that involves the observation of two conflicting states, distress and neutral, and the later recall and discrimination of others when no longer presenting such differences. Then, the whole-brain expression of different neuroplasticity markers was compared between genotypes and their contribution to cluster-specific phenotypic variation was assessed. Results The shank3 mutation markedly reduced social contagion via deficits in attention contributing to difficulties in recognising affective states. Also, the mutation changed the expression of neuronal plasticity genes. However, only downregulated neuroligins clustered with shank3a expression under a combined synaptogenesis component that contributed specifically to variation in attention. Limitations While zebrafish are extremely useful in identifying the role of shank3 mutations to composite social behaviour, they are unlikely to represent the full complexity of socio-cognitive and communication deficits presented by human ASD pathology. Moreover, zebrafish cannot represent the scaling up of these deficits to higher-order empathic and prosocial phenotypes seen in humans. Conclusions We demonstrate a causal link between the zebrafish orthologue of an ASD-associated gene and the attentional control of affect recognition and consequent social contagion. This models autistic affect-communication pathology in zebrafish and reveals a genetic attention-deficit mechanism, addressing the ongoing debate for such mechanisms accounting for emotion recognition difficulties in autistic individuals.
  • Social and asocial learning in zebrafish are encoded by a shared brain network that is differentially modulated by local activation
    Júlia S. Pinho, Vincent Cunliffe, Kyriacos Kareklas, Giovanni Petri, Rui F. Oliveira
    Communications Biology, 2023
    Group living animals use social and asocial cues to predict the presence of reward or punishment in the environment through associative learning. The degree to which social and asocial learning share the same mechanisms is still a matter of debate. We have used a classical conditioning paradigm in zebrafish, in which a social (fish image) or an asocial (circle image) conditioned stimulus (CS) have been paired with an unconditioned stimulus (US=food), and we have used the expression of the immediate early gene c-fos to map the neural circuits associated with each learning type. Our results show that the learning performance is similar to social and asocial CSs. However, the brain regions activated in each learning type are distinct and a community analysis of brain network data reveals segregated functional submodules, which seem to be associated with different cognitive functions involved in the learning tasks. These results suggest that, despite localized differences in brain activity between social and asocial learning, they share a common learning module and social learning also recruits a specific social stimulus integration module. Therefore, our results support the occurrence of a common general-purpose learning module, that is differentially modulated by localized activation in social and asocial learning.
  • Social zebrafish: Danio rerio as an emerging model in social neuroendocrinology
    Kyriacos Kareklas, Magda C. Teles, Ana Rita Nunes, Rui F. Oliveira
    Journal of Neuroendocrinology, 2023
    The fitness benefits of social life depend on the ability of animals to affiliate with others and form groups, on dominance hierarchies within groups that determine resource distribution, and on cognitive capacities for recognition, learning and information transfer. The evolution of these phenotypes is coupled with that of neuroendocrine mechanisms, but the causal link between the two remains underexplored. Growing evidence from our research group and others demonstrates that the tools available in zebrafish, Danio rerio, can markedly facilitate progress in this field. Here, we review this evidence and provide a synthesis of the state‐of‐the‐art in this model system. We discuss the involvement of generalized motivation and cognitive components, neuroplasticity and functional connectivity across social decision‐making brain areas, and how these are modulated chiefly by the oxytocin‐vasopressin neuroendocrine system, but also by reward‐pathway monoamine signaling and the effects of sex‐hormones and stress physiology.
  • Evolutionarily conserved role of oxytocin in social fear contagion in zebrafish
    Ibukun Akinrinade, Kyriacos Kareklas, Magda C. Teles, Thais K. Reis, Michael Gliksberg, et al.
    Science, 2023
    Emotional contagion is the most ancestral form of empathy. We tested to what extent the proximate mechanisms of emotional contagion are evolutionarily conserved by assessing the role of oxytocin, known to regulate empathic behaviors in mammals, in social fear contagion in zebrafish. Using oxytocin and oxytocin receptor mutants, we show that oxytocin is both necessary and sufficient for observer zebrafish to imitate the distressed behavior of conspecific demonstrators. The brain regions associated with emotional contagion in zebrafish are homologous to those involved in the same process in rodents (e.g., striatum, lateral septum), receiving direct projections from oxytocinergic neurons located in the pre-optic area. Together, our results support an evolutionary conserved role for oxytocin as a key regulator of basic empathic behaviors across vertebrates.
  • Complex strategies: an integrative analysis of contests in Siamese fighting fish
    Kyriacos Kareklas, Hansjoerg P. Kunc, Gareth Arnott
    BMC Zoology, 2022
    Background Animals use contests to attain resources and employ strategic decisions to minimise contest costs. These decisions are defined by behavioural response to resource value and competitive ability, but remain poorly understood. This is because the two factors are typically studied separately. Also, their study relies on overgeneralised assumptions that (i) strategies are fixed, (ii) modulated by the motivation or drive to fight and (iii) used to manage costs proportional to the timing of the loser’s retreat. To address these problems, we adopt an integrative sequential analysis that incorporates competitive ability and resource value factors, to characterise territorial contest decisions in male Siamese fighting fish (Betta splendens). Results Individuals exhibited a chronological organisation of behaviour, engaging opponents first with frontal display, then switching to lateral display before deciding to attack, and reserved retreats for later stages. Using asymmetries in retreats as a proxy for outcome, the likelihood of winning was found to be mostly dependent on display. However, resource and contest conditions affected initiation latency, display, attack and retreat, suggesting that strategic decisions influence all behaviour. Overall, sequential behaviour varied consistently with individual aggressiveness and resource-value factors, and increasingly with information on competitive ability collected during the contest. This enabled shifts in tactics, such as disadvantaged individuals responding first with aggression and later with submission. Motivation to continue fighting, after interruption by startle, was also adjusted to information gathered during the contest and progressively with energetic state. Two clusters of correlated behaviours were identified, cost-mitigation (display and retreat) and escalation (initiation and attack), but changes in motivation were associated only with cost mitigation. Conclusions Our findings contrast dominant assumptions that strategic decisions are fixed, controlled by motivational state and sufficiently described by outcome-dependent measures. We instead demonstrate that strategic decisions are complex, comprising functional changes in assessment, information use and motivational effects, which are not always inter-dependent.
  • Phenotypic architecture of sociality and its associated genetic polymorphisms in zebrafish
    Claúdia Gonçalves, Kyriacos Kareklas, Magda C. Teles, Susana A. M. Varela, João Costa, et al.
    Genes Brain and Behavior, 2022
    Sociality relies on motivational and cognitive components that may have evolved independently, or may have been linked by phenotypic correlations driven by a shared selective pressure for increased social competence. Furthermore, these components may be domain‐specific or of general‐domain across social and non‐social contexts. Here, we used zebrafish to test if the motivational and cognitive components of social behavior are phenotypically linked and if they are domain specific or of general domain. The behavioral phenotyping of zebrafish in social and equivalent non‐social tests shows that the motivational (preference) and cognitive (memory) components of sociality: (1) are independent from each other, hence not supporting the occurrence of a sociality syndrome; and (2) are phenotypically linked to non‐social traits, forming two general behavioral modules, suggesting that sociality traits have been co‐opted from general‐domain motivational and cognitive traits. Moreover, the study of the association between single nucleotide polymorphisms (SNPs) and each behavioral module further supports this view, since several SNPs from a list of candidate “social” genes, are statistically associated with the motivational, but not with the cognitive, behavioral module. Together, these results support the occurrence of general‐domain motivational and cognitive behavioral modules in zebrafish, which have been co‐opted for the social domain.
  • Extrinsic stressors modulate resource evaluations: insights from territoriality under artificial noise
    Kyriacos Kareklas, Hansjoerg P. Kunc, Gareth Arnott
    Frontiers in Zoology, 2021
    Background Competition is considered to rely on the value attributed to resources by animals, but the influence of extrinsic stressors on this value remains unexplored. Although natural or anthropogenic environmental stress often drives decreased competition, assumptions that this relies on resource devaluation are without formal evidence. According to theory, physiological or perceptual effects may influence contest behaviour directly, but motivational changes due to resource value are expected to manifest as behavioural adjustments only in interaction with attainment costs and resource benefits. Thus, we hypothesise that stressor-induced resource devaluations will impose greater effects when attainment costs are high, but not when resource benefits are higher. Noise may elicit such effects because it impacts the acoustic environment and imposes physiological and behavioural costs to animals. Therefore, we manipulated the acoustic environment using playbacks of artificial noise to test our hypotheses in the territorial male Siamese fighting fish, Betta splendens. Results Compared to a no-playback control, noise reduced defense motivation only when territory owners faced comparatively bigger opponents that impose greater injury costs, but not when territories also contained bubble nests that offer reproductive benefits. In turn, nest-size decreases were noted only after contests under noise treatment, but temporal nest-size changes relied on cross-contest variation in noise and comparative opponent size. Thus, the combined effects of noise are conditional on added attainment costs and offset by exceeding resource benefits. Conclusion Our findings provide support for the hypothesised modulation of resource value under extrinsic stress and suggest implications for competition under increasing anthropogenic activity.
  • Increased aggressive motivation towards formidable opponents: evidence of a novel form of mutual assessment
    Kyriacos Kareklas, Rebekah McMurray, Gareth Arnott
    Animal Behaviour, 2019
  • Signal complexity communicates aggressive intent during contests, but the process is disrupted by noise
    Kyriacos Kareklas, James Wilson, Hansjoerg P. Kunc, Gareth Arnott
    Biology Letters, 2019
  • Relationships between personality and lateralization of sensory inputs
    Kyriacos Kareklas, Gareth Arnott, Robert W. Elwood, Richard A. Holland
    Animal Behaviour, 2018
  • Grouping promotes risk-taking in unfamiliar settings
    Kyriacos Kareklas, Robert W. Elwood, Richard A. Holland
    Behavioural Processes, 2018
  • Fish learn collectively, but groups with differing personalities are slower to decide and more likely to split
    Kyriacos Kareklas, Robert W. Elwood, Richard A. Holland
    Biology Open, 2018
  • Personality effects on spatial learning: Comparisons between visual conditions in a weakly electric fish
    Kyriacos Kareklas, Robert W. Elwood, Richard A. Holland
    Ethology, 2017
  • Plasticity varies with boldness in a weaklyelectric fish
    Kyriacos Kareklas, Gareth Arnott, Robert W. Elwood, Richard A. Holland
    Frontiers in Zoology, 2016
  • Water-induced finger wrinkles improve handling of wet objects
    Kyriacos Kareklas, Daniel Nettle, Tom V. Smulders
    Biology Letters, 2013

RECENT SCHOLAR PUBLICATIONS

  • Stress, health and social behavior
    K Kareklas, RF Oliveira
    Elsevier , 2026
    2026
  • Evolutionarily conserved role of oxytocin in zebrafish social reward encoding
    K Kareklas, L Herrera-Castillo, G Levkowitz, RF Oliveira
    Biology Letters 21 (11) , 2025
    2025
  • Nonapeptide evolution and the regulation of social behaviour in teleost fish: from molecules to sociality
    K Kareklas, P Sorigue, RF Oliveira
    Evolutionary and comparative neuroendocrinology, 441-471 , 2025
    2025
    Citations: 2
  • Emotional contagion and prosocial behaviour in fish: An evolutionary and mechanistic approach
    K Kareklas, RF Oliveira
    Neuroscience & Biobehavioral Reviews 163, 105780 , 2024
    2024
    Citations: 17
  • Oxytocin and social isolation: nonapeptide regulation of social homeostasis
    K Kareklas, RF Oliveira
    Neuroendocrinology of behavior and emotions: environmental and social … , 2024
    2024
    Citations: 3
  • Social zebrafish: Danio rerio as an emerging model in social neuroendocrinology
    K Kareklas, MC Teles, AR Nunes, RF Oliveira
    Journal of neuroendocrinology 35 (9), e13280 , 2023
    2023
    Citations: 25
  • Autism-associated gene shank3 is necessary for social contagion in zebrafish
    K Kareklas, MC Teles, E Dreosti, RF Oliveira
    Molecular Autism 14 (1), 23 , 2023
    2023
    Citations: 15
  • Brain Networks of Social and Asocial Learning
    JS Pinho, V Cunliffe, K Kareklas, G Petri, RF Oliveira
    Neuroscience , 2023
    2023
  • Social and asocial learning in zebrafish are encoded by a shared brain network that is differentially modulated by local activation
    JS Pinho, V Cunliffe, K Kareklas, G Petri, RF Oliveira
    Communications Biology 6 (1), 633 , 2023
    2023
    Citations: 21
  • Evolutionarily conserved role of oxytocin in social fear contagion in zebrafish
    I Akinrinade, K Kareklas, MC Teles, TK Reis, M Gliksberg, G Petri, ...
    Science 379 (6638), 1232-1237 , 2023
    2023
    Citations: 103
  • Complex strategies: an integrative analysis of contests in Siamese fighting fish
    K Kareklas, HP Kunc, G Arnott
    BMC zoology 7 (1), 59 , 2022
    2022
    Citations: 2
  • Phenotypic architecture of sociality and its associated genetic polymorphisms in zebrafish
    C Gonçalves, K Kareklas, MC Teles, SAM Varela, J Costa, RB Leite, ...
    Genes, Brain and Behavior 21 (5), e12809 , 2022
    2022
    Citations: 11
  • Oxytocin regulation of social transmission of fear in zebrafish reveals its evolutionary conserved role in emotional contagion
    I Akinrinade, K Kareklas, M Gliksberg, G Petri, G Levkowitz, RF Oliveira
    bioRxiv, 2021.10. 06.463413 , 2021
    2021
    Citations: 1
  • Extrinsic stressors modulate resource evaluations: insights from territoriality under artificial noise
    K Kareklas, HP Kunc, G Arnott
    Frontiers in zoology 18 (1), 12 , 2021
    2021
    Citations: 5
  • Increased aggressive motivation towards formidable opponents: evidence of a novel form of mutual assessment
    K Kareklas, R McMurray, G Arnott
    Animal Behaviour 153, 33-40 , 2019
    2019
    Citations: 15
  • Signal complexity communicates aggressive intent during contests, but the process is disrupted by noise
    K Kareklas, J Wilson, HP Kunc, G Arnott
    Biology letters 15 (4) , 2019
    2019
    Citations: 27
  • Relationships between personality and lateralization of sensory inputs
    K Kareklas, G Arnott, RW Elwood, RA Holland
    Animal Behaviour 141, 127-135 , 2018
    2018
    Citations: 11
  • Fish learn collectively, but groups with differing personalities are slower to decide and more likely to split
    K Kareklas, RW Elwood, RA Holland
    Biology Open 7 (5), bio033613 , 2018
    2018
    Citations: 16
  • Grouping promotes risk-taking in unfamiliar settings
    K Kareklas, RW Elwood, RA Holland
    Behavioural processes 148, 41-45 , 2018
    2018
    Citations: 29
  • Personality effects on spatial learning: comparisons between visual conditions in a weakly electric fish
    K Kareklas, RW Elwood, RA Holland
    Ethology 123 (8), 551-559 , 2017
    2017
    Citations: 44

MOST CITED SCHOLAR PUBLICATIONS

  • Evolutionarily conserved role of oxytocin in social fear contagion in zebrafish
    I Akinrinade, K Kareklas, MC Teles, TK Reis, M Gliksberg, G Petri, ...
    Science 379 (6638), 1232-1237 , 2023
    2023
    Citations: 103
  • Water-induced finger wrinkles improve handling of wet objects
    K Kareklas, D Nettle, TV Smulders
    Biology letters 9 (2), 20120999 , 2013
    2013
    Citations: 79
  • Personality effects on spatial learning: comparisons between visual conditions in a weakly electric fish
    K Kareklas, RW Elwood, RA Holland
    Ethology 123 (8), 551-559 , 2017
    2017
    Citations: 44
  • Plasticity varies with boldness in a weakly-electric fish
    K Kareklas, G Arnott, RW Elwood, RA Holland
    Frontiers in zoology 13 (1), 22 , 2016
    2016
    Citations: 36
  • Grouping promotes risk-taking in unfamiliar settings
    K Kareklas, RW Elwood, RA Holland
    Behavioural processes 148, 41-45 , 2018
    2018
    Citations: 29
  • Signal complexity communicates aggressive intent during contests, but the process is disrupted by noise
    K Kareklas, J Wilson, HP Kunc, G Arnott
    Biology letters 15 (4) , 2019
    2019
    Citations: 27
  • Social zebrafish: Danio rerio as an emerging model in social neuroendocrinology
    K Kareklas, MC Teles, AR Nunes, RF Oliveira
    Journal of neuroendocrinology 35 (9), e13280 , 2023
    2023
    Citations: 25
  • Social and asocial learning in zebrafish are encoded by a shared brain network that is differentially modulated by local activation
    JS Pinho, V Cunliffe, K Kareklas, G Petri, RF Oliveira
    Communications Biology 6 (1), 633 , 2023
    2023
    Citations: 21
  • Emotional contagion and prosocial behaviour in fish: An evolutionary and mechanistic approach
    K Kareklas, RF Oliveira
    Neuroscience & Biobehavioral Reviews 163, 105780 , 2024
    2024
    Citations: 17
  • Fish learn collectively, but groups with differing personalities are slower to decide and more likely to split
    K Kareklas, RW Elwood, RA Holland
    Biology Open 7 (5), bio033613 , 2018
    2018
    Citations: 16
  • Autism-associated gene shank3 is necessary for social contagion in zebrafish
    K Kareklas, MC Teles, E Dreosti, RF Oliveira
    Molecular Autism 14 (1), 23 , 2023
    2023
    Citations: 15
  • Increased aggressive motivation towards formidable opponents: evidence of a novel form of mutual assessment
    K Kareklas, R McMurray, G Arnott
    Animal Behaviour 153, 33-40 , 2019
    2019
    Citations: 15
  • Phenotypic architecture of sociality and its associated genetic polymorphisms in zebrafish
    C Gonçalves, K Kareklas, MC Teles, SAM Varela, J Costa, RB Leite, ...
    Genes, Brain and Behavior 21 (5), e12809 , 2022
    2022
    Citations: 11
  • Relationships between personality and lateralization of sensory inputs
    K Kareklas, G Arnott, RW Elwood, RA Holland
    Animal Behaviour 141, 127-135 , 2018
    2018
    Citations: 11
  • Extrinsic stressors modulate resource evaluations: insights from territoriality under artificial noise
    K Kareklas, HP Kunc, G Arnott
    Frontiers in zoology 18 (1), 12 , 2021
    2021
    Citations: 5
  • Oxytocin and social isolation: nonapeptide regulation of social homeostasis
    K Kareklas, RF Oliveira
    Neuroendocrinology of behavior and emotions: environmental and social … , 2024
    2024
    Citations: 3
  • Nonapeptide evolution and the regulation of social behaviour in teleost fish: from molecules to sociality
    K Kareklas, P Sorigue, RF Oliveira
    Evolutionary and comparative neuroendocrinology, 441-471 , 2025
    2025
    Citations: 2
  • Complex strategies: an integrative analysis of contests in Siamese fighting fish
    K Kareklas, HP Kunc, G Arnott
    BMC zoology 7 (1), 59 , 2022
    2022
    Citations: 2
  • Oxytocin regulation of social transmission of fear in zebrafish reveals its evolutionary conserved role in emotional contagion
    I Akinrinade, K Kareklas, M Gliksberg, G Petri, G Levkowitz, RF Oliveira
    bioRxiv, 2021.10. 06.463413 , 2021
    2021
    Citations: 1
  • Stress, health and social behavior
    K Kareklas, RF Oliveira
    Elsevier , 2026
    2026