Sexually selected weapons can wear out, decreasing their effectiveness in combat.

Sexual selection has resulted in some of the most elaborate traits seen in animals, many of which are used as weapons. These weapons can be incredibly diverse, even within species. Such morphological variation has largely been attributed to the environment in which individuals are reared and their genetics. However, variation in weapon form could also be the result of a weapon wearing out from usage. This mechanism has received relatively little attention. In this study, we demonstrate that sexually selected weapons can wear out from repeated use, providing experimental evidence that weapon usage can contribute to the diversity of weapon shapes observed within species. In a second experiment, we demonstrate that having a worn-out weapon decreases an individual's fighting ability. This finding illustrates that the shape of a weapon can have an important role in determining contest outcomes. Overall, these results suggest that individuals are limited in the number of times they can effectively use their weapons, which may be one factor (among others) influencing how frequently an animal engages in a fight.

Expansion and Functional Diversification of Long-Wavelength-Sensitive Opsin in Anabantoid Fishes.

Gene duplication is one of the most important sources of novel genotypic diversity and the subsequent evolution of phenotypic diversity. Determining the evolutionary history and functional changes of duplicated genes is crucial for a comprehensive understanding of adaptive evolution. The evolutionary history of visual opsin genes is very dynamic, with repeated duplication events followed by sub- or neofunctionalization. While duplication of the green-sensitive opsins rh2 is common in teleost fish, fewer cases of multiple duplication events of the red-sensitive opsin lws are known. In this study, we investigate the visual opsin gene repertoire of the anabantoid fishes, focusing on the five lws opsin genes found in the genus Betta. We determine the evolutionary history of the lws opsin gene by taking advantage of whole-genome sequences of nine anabantoid species, including the newly assembled genome of Betta imbellis. Our results show that at least two independent duplications of lws occurred in the Betta lineage. The analysis of amino acid sequences of the lws paralogs of Betta revealed high levels of diversification in four of the seven transmembrane regions of the lws protein. Amino acid substitutions at two key-tuning sites are predicted to lead to differentiation of absorption maxima (λmax) between the paralogs within Betta. Finally, eye transcriptomics of B. splendens at different developmental stages revealed expression shifts between paralogs for all cone opsin classes. The lws genes are expressed according to their relative position in the lws opsin cluster throughout ontogeny. We conclude that temporal collinearity of lws expression might have facilitated subfunctionalization of lws in Betta and teleost opsins in general.

Associations of the immune system in aggression traits and the role of microglia as mediators.

There is an important relationship between the immune system and aggressive behavior. Aggressive encounters acutely increase the levels of proinflammatory cytokines, and there are positive correlations between aggressive traits and peripheral proinflammatory cytokines. Endotoxin lipopolysaccharide (LPS) treatment, which results in peripheral immune activation, decreases aggressive behavior as one of the sickness behavioral symptoms. In contrast, certain brain infections and chronic interferon treatment are associated with increased aggression. Indeed, the effects of proinflammatory cytokines on the brain in aggressive behavior are bidirectional, depending on the type and dose of cytokine, target brain region, and type of aggression. Some studies have suggested that microglial activation and neuroinflammation influence intermale aggression in rodent models. In addition, pathological conditions as well as physiological levels of cytokines produced by microglia play an important role in social and aggressive behavior in adult animals. Furthermore, microglial function in early development is necessary for the establishment of the social brain and the expression of juvenile social behaviors, including play fighting. Overall, this review discusses the important link between the immune system and aggressive traits and the role of microglia as mediators of this link.

Study on the fire extinguishing effect of compressed nitrogen foam on 280 Ah lithium iron phosphate battery.

This study conducted experimental analyses on a 280 Ah single lithium iron phosphate battery using an independently constructed experimental platform to assess the efficacy of compressed nitrogen foam in extinguishing lithium-ion battery fires. Based on theoretical analysis, the fire-extinguishing effects of compressed nitrogen foam at different outlet pressures from foam mixture tanks were analyzed, examining factors such as battery surface temperature, flame temperature, and thermal weight loss. The results indicate that the compressed nitrogen foam can extinguish the open flame of the battery in 14 s at 0.7 MPa, with the battery's surface temperature dropping by approximately 11 % before and after the application of the extinguishing agent. Compared with other commonly used extinguishing agents, the compressed nitrogen foam demonstrates superior extinguishing efficiency, but its cooling efficiency is somewhat lower. At pressures ranging from 0.4 to 0.6 MPa, the foam displays prolonged drainage time and sustained cooling effects, rendering it more suitable for lithium-ion battery fire scenarios. To address the issue of reduced cooling performance during later stages of fire suppression by compressed nitrogen foam, an intermittent injection approach has been proposed to effectively preserve its cooling efficacy.

Fighting behavior, conflict perceptions, and firearm access among U.S. adolescents in a pediatric emergency department.

OBJECTIVE: Prior evidence demonstrates that both firearm access and fighting can predict future violence and injury in adolescents. We aimed to examine associations between firearm access with fighting behavior and conflict perception in a sample of adolescents in an urban emergency department (ED) setting. METHODS: In 2023, we conducted a secondary analysis of 13,610 adolescent encounters in the ED of a U.S. children's hospital from 2013 to 2020, using a universally applied, self-administered computerized behavioral health survey. We compared patient characteristics by reported firearm access and fighting behavior using chi-squared tests. Generalized estimating equations (GEE) were used to investigate associations between 1) fighting behavior and firearm access, and 2) between fighting behavior and respondent preference to and reporting of fighting incident to law enforcement after adjusting for race and ethnicity, age, and gender. RESULTS: Approximately one-quarter of the sample reported past year fighting. Youth who reported fighting were more likely to report firearm access (AOR = 1.66, 95%CI = [1.49-1.86]). This association strengthened among youth who perceived continued conflict after a fight (AOR = 2.05, 95%CI = [1.73-2.43]). Youth who perceived continued conflict following a fight were more likely to report (AOR = 1.97, 95%CI = [1.65-2.36]) or want to report (AOR = 2.63, 95%CI = [1.81-3.81]) the fight to law enforcement. CONCLUSIONS: Those perceiving continued conflict after a fight were more likely to report access to firearms and endorse retaliation; however, they were more likely to want to report the fight to law enforcement. These findings highlight the potential for more comprehensive ED risk assessment to reduce retaliation and reinjury for adolescents reporting fighting behavior.

Comparative analysis of immunological changes following realgar and arsenic trioxide treatments in a murine model of myelodysplastic syndrome.

BACKGROUND: Myelodysplastic syndrome (MDS) is a prevalent hematological neoplastic disorder in clinics and its immunopathogenesis has garnered growing interest. Oral and intravenous arsenic agents have long been used to treat hematological malignancies. The main component of oral arsenic is realgar (arsenic disulfide), while arsenic trioxide is the main component of intravenous arsenic. METHODS: This study aimed to assess the effects of ATO and Realgar on the enhancement of peripheral blood, drug safety, and T cell immune status in the NUP98-HOXD13 (NHD13) mice model of MDS, specifically in the peripheral blood, spleen, and liver. RESULTS: The study findings indicate that realgar and arsenic trioxide (ATO) can improve peripheral hemogram in mice, whereas realgar promotes higher peripheral blood cell production than ATO. Furthermore, the clinical administration method and dose did not cause significant toxicity or side effects and thus can be considered safe. Coexistence and interconversion of hyperimmune function and immunosuppression in mice were also observed in this study. In addition, there were interactions between immune cells in the peripheral blood, spleen, and liver to regulate the immune balance of the body and activate immunity via T-cell activation. CONCLUSION: In summary, oral and intravenous arsenic agents are beneficial in improving peripheral hemogram and immunity in mice.

All-in-one bio-derived poly(L-lactic acid)-based composite with fire-resistance and smoke-suppression performance.

The flammability of bio-derived poly(L-lactic acid) (PLA) greatly limits its application and eco-friendly multifunctional fire-fighting PLA-based composites are highly desired. In this work, a fully bio-based modified CS (C-CS) and commercially available eco-friendly ammonium polyphosphate (APP) were used as a synergistic flame retardant agent (C-CS/APP) to investigate its effects on fire-proofing performance and diverse properties of the PLA. The PLA/5%C-CS/5%APP composite exhibited excellent fire-resistant performance with anti-droplet, smoke-suppression and self-extinguishing property, and its limited oxygen index enhanced by 37 % (compared with neat PLA). This composite reached the highest V-0 fire safety rating, and its peak of heat release rate and total smoke production reduced by 26.5 % and 68.3 %, respectively. In addition, the char residue yield after the cone calorimeter test increased by 46 times in the composite, indicating an outstanding char-forming capacity. The condensed phase flame retardancy played a crucial role on the fire-fighting of this composite, that is, significantly enhanced char residue (as a physical barrier) blocked the heat exchange and O2 entry, and further suppressed the combustion reaction. Additionally, the PLA-based composite showed outstanding UV-absorption property, good anti-bacterial effect, and increased hydrophilicity and crystallizability.

Addressing Combative Behaviour in Spanish Bulls by Measuring Hormonal Indicators.

The fighting bull is characterised by its natural aggressiveness, but the physiological mechanisms that underlie its aggressive behaviour are poorly studied. This study determines the hormonal component of aggressiveness in fighting bulls by analysing their behaviour during a fight and correlating it to their serotonin, dopamine and testosterone levels. We also determine whether aggressive behaviour can be estimated in calves. Using 195 animals, samples were obtained when the animals were calves and after 5 years. Aggressiveness scores were obtained by an observational method during bullfights, and serotonin, dopamine and testosterone levels were determined in all animals using validated enzyme immunoassay kits. The results revealed a strong correlation of serotonin and dopamine levels with aggressiveness scores in bulls during fights, but no correlation was found with respect to testosterone. These correlations led to established cut-off point and linear regression curves to obtain expected aggressiveness scores for calves at shoeing. There were no significant differences between the expected scores obtained in calves and the observed scores in bulls. Therefore, this study demonstrates that hormone determination in calves may be a great indicator of combativeness in bulls and can reliably be used in the selection of fighting bulls.

Recent development and fighting strategies for lincosamide antibiotic resistance.

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

The evolution of social play in songbirds, parrots and cockatoos - emotional or highly complex cognitive behaviour or both?

Social play has been described in many animals. However, much of this social behaviour among birds, particularly in adults, is still relatively unexplored in terms of the environmental, psychological, and social dynamics of play. This paper provides an overview of what we know about adult social play in birds and addresses areas in which subtleties and distinctions, such as in play initiation and social organisation and its relationship to expressions of play, are considered in detail. The paper considers emotional, social, innovative, and cognitive aspects of play, then the environmental conditions and affiliative bonds, suggesting a surprisingly complex framework of criteria awaiting further research. Adult social play has so far been studied in only a small number of avian species, exclusively in those with a particularly large brain relative to body size without necessarily addressing brain functions and lateralization. When lateralization of brain function is considered, it can further illuminate a possibly significant relevance of play behaviour to the evolution of cognition, to management of emotions, and the development of sociality.

Partially divided caging reduces overall aggression and anxiety which may indicate improved welfare in group housed male C57BL/6J mice.

Deciding which environmental enrichment is used in mouse caging is often subjective, with cost frequently prevailing over welfare benefits, including aggression and anxiety. While many devices introduced to encourage natural behaviors and reduce aggression show mixed results, we have previously demonstrated significant reductions in aggressive behavior between group-housed male mice housed in partially divided caging. To further assess behavior, we have raised male C57BL/6J mice in either partially divided caging or in standard caging with no divider. Animal behavior was tested on rotarod, open field, novel object recognition, elevated plus maze, and Y maze. Body weights were taken weekly beginning at weaning and bite wounds were counted weekly beginning at 133 days old. Aggressive behavior was recorded weekly beginning at 133 days old. Results indicated significantly less anxiety in the elevated-plus maze, statistically fewer bite wounds, and a statistically significant decrease in aggressive behaviors of mice in partially divided caging compared to mice in standard cages. We conclude that reductions in anxiety, aggressive behavior, and bite wounds may indicate improved overall welfare for non-sibling, group housed male mice.

Temporal Trends of Physical Fights and Physical Attacks Among Adolescents Aged 12-15 years From 30 Countries From Africa, Asia, and the Americas.

PURPOSE: There is a scarcity of literature on temporal trends in physical fighting and physical attacks among the global adolescent population. Therefore, we aimed to examine these trends in a nationally representative sample of school-going adolescents aged 12-15 years from 30 countries in Africa, Asia, and the Americas, for which temporal trends of physical fighting and physical attacks are largely unknown. METHODS: Cross-sectional data from the Global School-based Student Health Survey 2003-2017 were analyzed. Self-reported data on past 12-month physical fights and physical attacks were collected. For each survey, the prevalence and 95% confidence interval of physical fights and physical attacks were calculated. Linear regression models were used to examine crude linear trends. RESULTS: Data on 190,493 students aged 12-15 years were analyzed [mean (standard deviation) age 13.7 (1.0) years; 48.9% boys]. The mean prevalence of past 12-month physical fight and physical attack was 36.5% and 37.2%, respectively. Significant decreasing trends in physical fights were observed in 16/30 countries, while significant increasing trends were found in 2/30 countries. For physical attacks, significant decreasing and increasing trends were observed in 13/26 and 1/26 countries, respectively. The remaining countries showed stable trends. DISCUSSION: It is encouraging that decreasing trends in physical fighting and physical attacks were observed across a large number of countries. However, stable trends were also common, while increasing trends also existed, suggesting that global efforts to address adolescent violence are still required.

Complete genome sequence of a novel papillomavirus in Siamese fighting fish (Betta splendens) from Trinidad and Tobago.

Here, we announce the complete genome of a previously undescribed papillomavirus from a betta fish, Betta splendens. The genome is 5,671 bp with a GC content of 38.2%. Variants were detected in public databases. This genome is most similar to papillomaviruses that infect sea bass (52.9 % nucleotide identity).

O ensino de lutas/artes marciais como uma prática de educação libertadora: entremeando círculos de cultura, situações-problema e jogos / The teaching of fights/martial arts as a liberating education practice: interspersing crop circles, situational issues, and games / La enseñanza de lucha/artes marciales como práctica de educación liberadora: intercalando círculos en las cosechas, problemas situacionales y juegos

RESUMO A inserção das Lutas/Artes Marciais no campo escolar tem sido tema frequente no campo da Educação Física. As obras de Paulo Freire emergem como possibilidade para atuação pedagógica nesse tema. Realizou-se uma pesquisa-formação qualitativa, com observação, análise e reflexão sobre a experiência com três turmas de Ensino Médio de uma escola pública do município de Lavras (Brasil), somando-se 44 horas/aula. Recorreu-se a um diário de bordo para registro. Os resultados apontaram para uma vasta bagagem cultural dos estudantes sobre o assunto. Concluiu-se que o ensino de práticas como essa, numa perspectiva de educação libertadora, pode contribuir com a formação de sujeitos autônomos, com visões ampliadas de mundo.

ABSTRACT The insertion of Fights/Martial Arts in the school field has been a frequent theme in the field of Physical Education. Paulo Freire's works emerge as a possibility for pedagogical action in this theme. A qualitative research was carried out, with observation, analysis and reflection on the experience with three high school classes from a public school in the municipality of Lavras (Brazil), adding up to 44 hours/class. A logbook was used for recording. The results pointed to a vast cultural baggage of students on the subject. It was concluded that the teaching of practices like this, in a perspective of liberating education, can contribute to the formation of autonomous subjects, with expanded views of the world.

RESUMEN La inserción de las Luchas/Artes Marciales en el ámbito escolar ha sido un tema frecuente en el campo de la Educación Física. Las obras de Paulo Freire emergen como una posibilidad de acción pedagógica en esta temática. Se realizó una investigación cualitativa, con observación, análisis y reflexión sobre la experiencia con tres clases de secundaria de una escuela pública del municipio de Lavras (Brasil), sumando 44 horas/clase. Para el registro se utilizó un cuaderno de bitácora. Los resultados apuntaron a un vasto bagaje cultural de los estudiantes sobre el tema. Se concluyó que la enseñanza de prácticas como ésta, en una perspectiva de educación liberadora, puede contribuir a la formación de sujetos autónomos, con visiones ampliadas del mundo.

Martial arts, combat sports, and mental health in adults: A systematic review.

Martial arts (MA) and combat sports (CS) are physical activities that may be associated with health-related outcomes. The aim of this systematic review was to synthesize and evaluate the available evidence on the relationship between MA and CS training and mental health of adult practitioners (≥18 years). CochraneLibrary, EBSCOhost, Web-of-Science, and Scopus databases were searched up to September 2022 for measures of self-related constructs, ill-being and well-being, cognition and brain structure/function, in adult MA/CS practitioners. Seventy cross-sectional and two longitudinal studies were retained and submitted to risk of bias assessments through an adapted version of the Cochrane Collaboration's Tool. Associations between MA/CS practice and self-related constructs were inconclusive for both consistency and strength of evidence. Limited evidence of significant associations emerged for sub-domains of ill-being (i.e., externalizing and internalizing emotion regulation), and well-being. In regard to cognitive and brain structural/functional variables, evidence of positive association with MA/CS practice was consistent with respect to perceptual and inhibition abilities but limited with respect to attention and memory. Evidence on negative associations of boxing with changes of brain structure integrity due to concussions was also inconclusive. Functional imaging techniques could shed light onto brain activation mechanisms underlying complex cognitive performance. In relation to moderators, mixed results were found for activity exposure, expertise, level of competitive engagement (which often covary with the length of training) and sex and type of MA/CS. The MA/CS' multifaceted nature may produce different, sometimes conflicting outcomes on mental health. Studies on MA/CS represent a flourishing research area needing extensive improvement in theoretical and practical approaches.

Male spiny frogs enter the underwater battlefield with loose skin exhibiting enhanced penetration of capillaries into the epidermis.

The skin has multiple functions, and capillaries can penetrate the epidermis to shorten the diffusion path while allowing maintenance of overall epidermal thickness for nonrespiratory roles. However, a method for quantifying the capillary penetration extent is lacking. Such a method may facilitate making comparisons and detecting associations, potentially making the extent a useful variable in biological studies. We quantified the extent as the ratio of the average minimum thickness of epidermis overlying each capillary to the average epidermal thickness along a skin section and then explored its performance in the Emei mustache toad, Leptobrachium boringii, a species in which breeding males with loose skin call and fight each other with maxillary spines underwater. The ratio showed informative associations with other variables, such as perfused capillary density. It displayed small intragroup variation and could be more sensitive than other variables in revealing structural differences in the skin. The ratio estimates were lowest and were correlated with epidermal and stratum compactum thicknesses in breeding males, i.e., a covariation but not reinforcement against stabbing, constituting early evidence consistent with the increased extensibility of loose skin conferring a defensive advantage during combat in amphibians. In addition, our results lead to the hypothesis that high hemoglobin density along subepidermal capillaries favors the maintenance of low blood partial oxygen pressure and hence increases cutaneous oxygen uptake. We also provide evidence supporting the new idea that the cooccurrence of loose skin and underwater calling found in some frogs can be explained by the latter benefiting from a large functional respiratory surface area. Awareness of the usefulness of the ratio may promote its application and the quantification of the penetration. Regarding exchange surface design, these findings for L. boringii imply a case in which looseness increases surface area as well as prevents damage.

Investigation on preventive inerting approach of coal spontaneous combustion in gob considering adsorption effect.

Coal spontaneous combustion in the gob poses a significant threat to coal mining operations. Designing optimal process parameters for nitrogen injection to prevent and control fires efficiently is crucial. To achieve this, a multi-field coupling equation was established, considering the adsorption of coal to gas. The model's accuracy was verified on-site, and the effects of nitrogen injection at different locations and flow rates were simulated. The optimal injection parameters were determined by analyzing temperature and inerting time. The results showed that the coal spontaneous combustion hazardous zone in the gob tested on-site was consistent with the simulation from the perspective of physisorption. Nitrogen injection had three stages: gas expansion, rapid oxygen dilution, and complete inerting. The nitrogen injection effect presented a nonlinear change in injection location and flow rate. The optimal nitrogen injection location for the Tingnan Coal Mine in Shaanxi was determined to be 90 m behind the working face on the inlet side, with an optimal flow rate of 800 m3/min. This study focused on gas adsorption and offered valuable insights for creating high-efficiency fire-fighting techniques that involve inserting in the gob.

Trade-offs between immunity and competitive ability in fighting ant males.

BACKGROUND: Fighting disease while fighting rivals exposes males to constraints and trade-offs during male-male competition. We here tested how both the stage and intensity of infection with the fungal pathogen Metarhizium robertsii interfere with fighting success in Cardiocondyla obscurior ant males. Males of this species have evolved long lifespans during which they can gain many matings with the young queens of the colony, if successful in male-male competition. Since male fights occur inside the colony, the outcome of male-male competition can further be biased by interference of the colony's worker force. RESULTS: We found that severe, but not yet mild, infection strongly impaired male fighting success. In late-stage infection, this could be attributed to worker aggression directed towards the infected rather than the healthy male and an already very high male morbidity even in the absence of fighting. Shortly after pathogen exposure, however, male mortality was particularly increased during combat. Since these males mounted a strong immune response, their reduced fighting success suggests a trade-off between immune investment and competitive ability already early in the infection. Even if the males themselves showed no difference in the number of attacks they raised against their healthy rivals across infection stages and levels, severely infected males were thus losing in male-male competition from an early stage of infection on. CONCLUSIONS: Males of the ant C. obscurior have a well-developed immune system that raises a strong immune response very fast after fungal exposure. This allows them to cope with mild pathogen exposures without compromising their success in male-male competition, and hence to gain multiple mating opportunities with the emerging virgin queens of the colony. Under severe infection, however, they are weak fighters and rarely survive a combat already at early infection when raising an immune response, as well as at progressed infection, when they are morbid and preferentially targeted by worker aggression. Workers thereby remove males that pose a future disease threat by biasing male-male competition. Our study thus reveals a novel social immunity mechanism how social insect workers protect the colony against disease risk.

Is it for real? Structural differences between play and real fighting in adult chimpanzees (Pan troglodytes).

In primates, as well as in other mammals, play fighting (PF) is a complex form of playful activity that is structurally similar to real fighting (RF) and may also be used in a competitive way. Here, we verify the structural key differences that can distinguish PF from RF in adult chimpanzees (Pan troglodytes). We collected 962 h of video recording on 30 adult individuals belonging to four chimpanzee groups (Mona Chimpanzee Sanctuary, Spain; La Vallée des Singes and ZooParc de Beauval, France). We applied different indices-two of which were borrowed from the ecological measures of biodiversity-to test for structural differences between PF (345 sessions) and RF (461 sessions) in the levels of behavior repetition (Repeatability of Same Behavior Index, RSBI), distribution uniformity (Pielou Index, J), variability (Shannon Index, H') and, symmetry (i.e., reciprocal exchange of offensive/defensive behaviors; Asymmetry Index, AI). Moreover, we compared the session duration between PF and RF. We found that duration and RSBI were higher in PF than RF while AI was higher in RF than PF. No difference was found between J and H'. Interestingly, both females and males maintained similar ranking positions (determined via Normalized David's scores) in RF and PF. Our study indicates that session duration, behavior repetition, and symmetry can be distinctive structural key features of PF whereas dominance role-reversal, behavior variability, and distribution uniformity were not. PF in adult chimpanzees may have elements of serious contexts (e.g., absence of role-reversal as in RF) which is in line with the view that play is a blended, multifunctional behavior deriving from the re-combination of different behavioral systems. Our findings highlight the need to investigate play structure and manifestation in a nuanced way to better understand the actual motivation that underlies what appears to be play.

Nicotine reduces social dominance and neutralizes experience-dependent effects during social conflicts in zebrafish (Danio rerio).

Nicotine, a psychoactive pollutant, binds to nicotinic acetylcholine receptors and disrupts the cholinergic modulation and reward systems of the brain, leading to attention deficit, memory loss, and addiction. However, whether nicotine affects social behaviors remains unknown. We assessed the effects of nicotine on the fighting behavior of zebrafish. Adult zebrafish treated with 5 µM nicotine were used in dyadic fighting tests with size-matched control siblings. The results indicate that nicotine treatment not only significantly reduced the likelihood of winning but also impaired the winner-loser effects (winner and loser fish did not show higher winning and losing tendencies in the second fight, respectively, after treatment.) Nicotine led to a considerable increase in c-fos-positive signals in the interpeduncular nucleus (IPN) of the brain, indicating that nicotine induces neural activity in the habenula (Hb)-IPN circuit. We used transgenic fish in which the Hb-IPN circuit was silenced to verify whether nicotine impaired the winner-loser effect through the Hb-IPN pathway. Nicotine-treated fish in which the medial part of the dorsal Hb was silenced did not have a higher winning rate, and nicotine-treated fish in which the lateral part of the dorsal Hb was silenced did not have a higher loss rate. This finding suggests that nicotine impairs the winner-loser effect by modulating the Hb-IPN circuit. Therefore, in these zebrafish, nicotine exposure impaired social dominance and neutralized experience-dependent effects in social conflicts, and it may thereby disturb the social hierarchy and population stability of such fish.