Fighting Assessment Triggers Rapid Changes in Activity of the Brain Social Decision-Making Network of Cichlid Fish

Behavioral transcriptomic effects of triploidy and probiotic therapy (Bifidobacterium, Lactobacillus, and Lactococcus mixture) on juvenile Chinook salmon (Oncorhynchus tshawytscha)

Aquaculturists use polyploid fish to maximize production albeit with some unintended consequences including compromised behaviors and physiological function. Given benefits of probiotic therapies (e.g., improved immune response, growth, and metabolism), we explored probiotic supplementation (mixture of Bifidobacterium, Lactobacillus, and Lactococcus), to overcome drawbacks. We first examined fish gut bacterial community composition using 16S metabarcoding (via principal coordinate analyses and PERMANOVA) and determined probiotics significantly impacted gut bacteria composition (p = 0.001). Secondly, we examined how a genomic disruptor (triploidy) and diet supplements (probiotics) impact gene transcription and behavioral profiles of hatchery-reared Chinook salmon (Oncorhynchus tshawytscha). Juveniles from four treatment groups (diploid-regular feed, diploid-probiotic feed, triploid-regular feed, and triploid-probiotic feed; n = 360) underwent behavioral assays to test activity, exploration, neophobia, predator evasion, aggression/sociality, behavioral sensitivity, and flexibility. In these fish, transcriptional profiles for genes associated with neural functions (neurogenesis/synaptic plasticity) and biomarkers for stress response and development (growth/appetite) were (i) examined across treatments and (ii) used to describe behavioral phenotypes via principal component analyses and general linear mixed models. Triploids exhibited a more active behavioral profile (p = 0.002), and those on a regular diet had greater Neuropeptide Y transcription (p = 0.02). A growth gene (early growth response protein 1, p = 0.02) and long-term neural development genes (neurogenic differentiation factor, p = 0.003 and synaptysomal-associated protein 25-a, p = 0.005) impacted activity and reactionary profiles, respectively. Overall, our probiotic treatment did not compensate for triploidy. Our research highlights novel applications of behavioral transcriptomics for identifying candidate genes and dynamic, mechanistic associations with complex behavioral repertoires.

Neural mechanism underlying depressive-like state associated with social status loss

Downward social mobility is a well-known mental risk factor for depression, but its neural mechanism remains elusive. Here, by forcing mice to lose against their subordinates in a non-violent social contest, we lower their social ranks stably and induce depressive-like behaviors. These rank-decline-associated depressive-like behaviors can be reversed by regaining social status. In vivo fiber photometry and single-unit electrophysiological recording show that forced loss, but not natural loss, generates negative reward prediction error (RPE). Through the lateral hypothalamus, the RPE strongly activates the brain's anti-reward center, the lateral habenula (LHb). LHb activation inhibits the medial prefrontal cortex (mPFC) that controls social competitiveness and reinforces retreats in contests. These results reveal the core neural mechanisms mutually promoting social status loss and depressive behaviors. The intertwined neuronal signaling controlling mPFC and LHb activities provides a mechanistic foundation for the crosstalk between social mobility and psychological disorder, unveiling a promising target for intervention.

Impact of intraspecific variation in teleost fishes: aggression, dominance status and stress physiology

Dominance-based social hierarchies are common among teleost fishes. The rank of an animal greatly affects its behaviour, physiology and development. The outcome of fights for social dominance is affected by heritable factors and previous social experience. Divergent stress-coping styles have been demonstrated in a large number of teleosts, and fish displaying a proactive coping style have an advantage in fights for social dominance. Coping style has heritable components, but it appears to be largely determined by environmental factors, especially social experience. Agonistic behaviour is controlled by the brain's social decision-making network, and its monoaminergic systems play important roles in modifying the activity of this neuronal network. In this Review, we discuss the development of dominance hierarchies, how social rank is signalled through visual and chemical cues, and the neurobiological mechanisms controlling or correlating with agonistic behaviour. We also consider the effects of social interactions on the welfare of fish reared in captivity.

Role of Habenula in Social and Reproductive Behaviors in Fish: Comparison With Mammals

Social behaviors such as mating, parenting, fighting, and avoiding are essential functions as a communication tool in social animals, and are critical for the survival of individuals and species. Social behaviors are controlled by a complex circuitry that comprises several key social brain regions, which is called the social behavior network (SBN). The SBN further integrates social information with external and internal factors to select appropriate behavioral responses to social circumstances, called social decision-making. The social decision-making network (SDMN) and SBN are structurally, neurochemically and functionally conserved in vertebrates. The social decision-making process is also closely influenced by emotional assessment. The habenula has recently been recognized as a crucial center for emotion-associated adaptation behaviors. Here we review the potential role of the habenula in social function with a special emphasis on fish studies. Further, based on evolutional, molecular, morphological, and behavioral perspectives, we discuss the crucial role of the habenula in the vertebrate SDMN.

Activation of noradrenergic locus coeruleus and social behavior network nuclei varies with duration of male midshipman advertisement calls

Vocal courtship is vital to the reproductive success of many vertebrates and is therefore a highly-motivated behavioral state. Catecholamines have been shown to play an essential role in the expression and maintenance of motivated vocal behavior, such as the coordination of vocal-motor output in songbirds. However, it is not well-understood if this relationship applies to anamniote vocal species. Using the plainfin midshipman fish model, we tested whether specific catecholaminergic (i.e., dopaminergic and noradrenergic) nuclei and nodes of the social behavior network (SBN) are differentially activated in vocally courting (humming) versus non-humming males. Herein, we demonstrate that tyrosine hydroxylase immunoreactive (TH-ir) neuron number in the noradrenergic locus coeruleus (LC) and induction of cFos (an immediate early gene product and proxy for neural activation) in the preoptic area differentiated humming from non-humming males. Furthermore, we found relationships between activation of the LC and SBN nuclei with the total amount of time that males spent humming, further reinforcing a role for these specific brain regions in the production of motivated reproductive-related vocalizations. Finally, we found that patterns of functional connectivity between catecholaminergic nuclei and nodes of the SBN differed between humming and non-humming males, supporting the notion that adaptive behaviors (such as the expression of advertisement hums) emerge from the interactions between various catecholaminergic nuclei and the SBN.

Fish self-awareness: limits of current knowledge and theoretical expectations

Animal self-awareness is divided into three levels: bodily, social, and introspective self-awareness. Research has focused mainly on the introspection of so-called higher organisms such as mammals. Herein, we turn our attention to fish and provide opinions on their self-awareness based on a review of the scientific literature. Our specific aims are to discuss whether fish (A) could have a neural substrate supporting self-awareness and whether they display signs of (B) social and (C) introspective self-awareness. The present knowledge does not exclude the possibility that fish could have a simple neocortex or other structures that support certain higher cognitive processes, as the function of the primate cerebral cortex can be replaced by other neurological structures. Fish are known to display winner, loser, and audience effects, which could be interpreted as signs of social self-awareness. The audience effect may be explained not only by ethological cost and benefit theory but also by the concept of public self-awareness, which comes from human studies. The behavioural and neural manifestations of depression may be induced in fish under social subordination and may be viewed as certain awareness of a social status. The current findings on fish introspective self-awareness have been debated in the scientific community and, therefore, demand replication to provide more evidence. Further research is needed to verify the outlined ideas; however, the current knowledge indicates that fish are capable of certain higher cognitive processes, which raises questions and implications regarding ethics and welfare in fish-related research and husbandry.

Neural substrates involved in the cognitive information processing in teleost fish

Over the last few decades, it has been shown that fish, comprising the largest group of vertebrates and in many respects one of the least well studied, possess many cognitive abilities comparable to those of birds and mammals. Despite a plethora of behavioural studies assessing cognition abilities and an abundance of neuroanatomical studies, only few studies have aimed to or in fact identified the neural substrates involved in the processing of cognitive information. In this review, an overview of the currently available studies addressing the joint research topics of cognitive behaviour and neuroscience in teleosts (and elasmobranchs wherever possible) is provided, primarily focusing on two fundamentally different but complementary approaches, i.e. ablation studies and Immediate Early Gene (IEG) analyses. More recently, the latter technique has become one of the most promising methods to visualize neuronal populations activated in specific brain areas, both during a variety of cognitive as well as non-cognition-related tasks. While IEG studies may be more elegant and potentially easier to conduct, only lesion studies can help researchers find out what information animals can learn or recall prior to and following ablation of a particular brain area.

Social interactions upregulate hemolymph tryptophan and tyrosine levels in the male lobster cockroach

In the present study, we found that tryptophan (TRP) and tyrosine (TYR) levels are increased in hemolymph of male Nauphoeta cinerea after social contact with either male or female conspecifics. Hemolymph was collected from individual males before and after the social interactions, and samples were analyzed by HPLC-ECD; analyte identities were confirmed by UPLC/MS. After a male-male first encounter fight, hemolymph TRP and TYR levels were significantly increased in dominants compared with the levels before the encounter. Conversely, TRP and TYR in subordinates were maintained at levels similar to those before the encounter. While after-fight TRP and TYR levels were significantly higher in dominants than subordinates, no significant differences were found in the contestants before the fight. Moreover, contact with an isolated male antenna was sufficient to stimulate attack behavior and increase hemolymph TRP and TYR titers to levels similar to those seen in dominants. After a male-female interaction, two distinct outcomes could be observed. Either hemolymph TRP and TYR levels were increased in successfully mated males, or TRP and TYR levels were unchanged in males that only exhibited premating wing-raising behavior but failed in mating. After contacting the antenna of a socially naïve male with an isolated female antenna, three patterns of behavior and related amino acid response were observed: 1) only premating wing-raising behavior with significant increase of TRP and TYR levels, 2) only attack behavior with significant increase of TRP and TYR levels, and 3) mixed wing-raising and attack behaviors with no significant changes in TRP and TYR levels. The present results show a robust response of hemolymph TRP and TYR to social contact. In light of previously characterized responses in pheromone and juvenile hormone levels, these amine responses suggest that the physiological response of N. cinerea to social contact is multi-dimensional.

Altered neuronal activity in the visual processing region of eye-fluke-infected fish

Fish, like most vertebrates, are dependent on vision to varying degrees for a variety of behaviours such as predator avoidance and foraging. Disruption of this key sensory system therefore should have some impact on the ability of fish to execute these tasks. Eye-flukes, such as Tylodelphys darbyi, often infect fish where they are known to inflict varying degrees of visual impairment. In New Zealand, T. darbyi infects the eyes of Gobiomorphus cotidianus, a freshwater fish, where it resides in the vitreous chamber between the lens and retina. Here, we investigate whether the presence of the parasite in the eye has an impact on neuronal information transfer using the c-Fos gene as a proxy for neuron activation. We hypothesized that the parasite would reduce visual information entering the eye and therefore result in lower c-Fos expression. Interestingly, however, c-Fos expression increased with T. darbyi intensity when fish were exposed to flashes of light. Our results suggest a mechanism for parasite-induced visual disruption when no obvious pathology is caused by infection. The more T. darbyi present the more visual stimuli the fish is presented with, and as such may experience difficulties in distinguishing various features of its external environment.

An updated field guide for snark hunting: Comparative contributions to behavioral neuroendocrinology in the era of model organisms

Studying neuroendocrine behavioral regulatory mechanisms in a variety of species across vertebrate groups is critical for determining how they work in natural contexts, how they evolved, and ultimately what can be generalized from them, potentially even to humans. All of the above are difficult, at best, if work within our field is exclusively done in traditional laboratory organisms. The importance of comparative approaches for understanding the relationships between hormones and behavior has been recognized and advocated for since our field's inception through a series of papers centered upon a poetic metaphor of Snarks and Boojums, all of which have articulated the benefits that come from studying a diverse range of species and the risks associated with a narrow focus on "model organisms." This mini-review follows in the footsteps of those powerful arguments, highlighting some of the comparative work since the latest interactions of the metaphor that has shaped how we think about three major conceptual frameworks within our field, two of them formalized - the Organization/Activation Model of sexual differentiation and the Social Brain Network - and one, context-dependency, that is generally associated with virtually all modern understandings of how hormones affect behavior. Comparative approaches are broadly defined as those in which the study of mechanism is placed within natural and/or evolutionary contexts, whether they directly compare different species or not. Studies are discussed in relation to how they have either extended or challenged generalities associated with the frameworks, how they have shaped subsequent work in model organisms to further elucidate neuroendocrine behavioral regulatory mechanisms, and how they have stimulated work to determine if and when similar mechanisms influence behavior in our own species.