In a groundbreaking study emerging from the University of Otago’s Department of Anatomy, researchers have uncovered the astonishingly swift manifestation of dominant behavior in the New Zealand spotty, or paketi, a remarkable species of sex-changing fish endemic to the region. This discovery reveals that social hierarchy shifts within these fish do not merely evolve over days or weeks but can occur in a matter of minutes following the removal of a dominant individual. This rapid behavioral adjustment underscores the extraordinary plasticity of social dynamics and neural mechanisms in sex-changing fishes, offering fresh insights into the complex interplay between environmental cues and physiological transformations.
The New Zealand spotty, or paketi, is a protogynous hermaphrodite, meaning individuals typically begin life as females and later transition to males in response to social stimuli, primarily related to dominance hierarchies within their communities. This transition not only involves profound changes in reproductive physiology but also significant behavioral modifications. The recent study, published in the prestigious journal Proceedings of the Royal Society B, delves into the nuanced behavioral shifts that precede the well-characterized physical and gonadal changes during sex transformation.
Led by PhD candidate Haylee Quertermous, the research employed controlled experimental designs to observe social dynamics in real-time. By systematically removing dominant males from established groups and closely monitoring the behavior of second-ranked females, the team documented aggressive behaviors emerging within minutes. These included rapid “rushes” — sudden, swift approaches toward subordinate fish — and physical contacts such as nips aimed typically at the tail and fins of less dominant individuals. This aggressive assertion shortly after the dominant individual’s removal signals an immediate reorganization of the social hierarchy.
.adsslot_OwIiEtpLq0{width:728px !important;height:90px !important;}
@media(max-width:1199px){ .adsslot_OwIiEtpLq0{width:468px !important;height:60px !important;}
}
@media(max-width:767px){ .adsslot_OwIiEtpLq0{width:320px !important;height:50px !important;}
}
ADVERTISEMENT
Remarkably, the researchers highlight that while the complete process of sex change in paketi spans several weeks, the initiation of dominant behavior occurs almost instantaneously. In many experimental tanks, subordinate fish began displaying dominance-associated aggression within minutes, far sooner than the previously assumed hour-long threshold for observable behavioral changes. This rapid onset challenges former conceptions of hermaphroditic sex change as a predominantly gradual process and emphasizes that behavior can act as the swiftest indicator of social reorganization.
Importantly, the dominant behaviors exhibited by these fish do not merely mirror stereotypical male or female activities based on traditional sexual dimorphism. Unlike clownfish, which transition from male to female with associated shifts in behavior, paketi modify social conduct concomitant with their sex change in a way that complexifies binary gender behavioral models in fishes. The study suggests that dominance, rather than strict sex-based roles, drives many social interactions within spotty groups, reflecting a sophisticated form of social adaptability.
The team further confirmed that body size critically influences hierarchical positions, with larger individuals generally occupying dominant ranks. This stems from the linear nature of the dominance hierarchy in paketi, where size is a primary determinant of rank and, consequently, of the likelihood of impending sex change. When disruptions occur within this structured order, less dominant but sufficiently large individuals promptly assume higher positions and begin exhibiting behaviors consistent with dominance, setting the stage for physiological changes that culminate in sex transformation.
Beyond behavioral observations, the study broke new ground by examining the neural correlates underpinning these social shifts. Employing neurobiological analyses, researchers identified significant modulation within the fish’s social decision-making network (SDMN) — a well-conserved brain circuit across vertebrates that integrates external social cues and internal physiological states to guide behavior. Fish ascending in rank exhibited pronounced changes in neural activity within this network compared to their lower-ranked counterparts, emphasizing the SDMN’s crucial role in mediating rapid behavioral transitions.
Dr. Kaj Kamstra, who spearheaded the neurobiological components of the research, articulated the broader implications of these findings. He emphasized that the study sheds light on how social environments dynamically shape brain function and behavior, highlighting an evolutionary advantage of neural flexibility. Such plasticity enables organisms like the paketi to adapt to sudden social upheavals with minimal latency, thereby improving survival and reproductive success in changing social landscapes.
The intricate connection between behavior, brain functionality, and physiology demonstrated by this research enriches our understanding of social dynamics across species. The rapid restructuring of hierarchies and the associated neural changes mirror adaptive mechanisms that might be conserved in a wide array of animals, including mammals. This positions the paketi as a compelling model system for exploring evolutionary biology, behavioral ecology, and neuroethology, with potential analogies relevant to human social behavior.
These insights also carry pragmatic ramifications for fisheries science and aquaculture. Numerous commercially important fish, such as New Zealand’s blue cod, exhibit sex-changing traits influenced by social hierarchies akin to those observed in paketi. Understanding the neural and behavioral triggers of sex change could inform sustainable management practices and improve breeding protocols, ultimately enhancing productivity and ecological stability in commercial fisheries that rely on sex-changing species.
Moreover, the study’s findings challenge entrenched perspectives on sex and gender in animal behavior, revealing a fluid continuum governed by social contexts rather than fixed categories. This revelation prompts a reconsideration of sex-associated behavioral paradigms in ecological and evolutionary studies, urging scientists to incorporate the nuanced interplay between environment, brain, and behavior into their frameworks.
In conclusion, the research conducted by the University of Otago’s team marks a significant milestone in deciphering the rapid dynamics of social hierarchy formation and sex change in the New Zealand spotty. By documenting behavioral transformations within minutes and linking these changes to neural adaptations, the study opens new avenues for exploring the evolutionary mechanisms underlying social flexibility. These findings not only advance basic science but also hold promise for applied fields such as fisheries management and conservation biology, underscoring the intricate bonds connecting behavior, brain, and environment in the natural world.
Subject of Research: Animals
Article Title: Behavioural and neural correlates of social hierarchy formation in a sex-changing fish
News Publication Date: 14-May-2025
Web References: http://dx.doi.org/10.1098/rspb.2024.2097
Image Credits: Gemmell Lab, University of Otago
Keywords: Evolutionary biology, Ecological adaptation, Ecological speciation, Sociobiology, Behavioral ecology, Evolutionary ecology, Evolutionary genetics, Evolution
Tags: behavioral plasticity in marine lifeenvironmental cues and fish behaviorHaylee Quertermous research findingsneural mechanisms in fish dominanceNew Zealand spotty dominance hierarchyphysiological changes during sex transformationProceedings of the Royal Society B fish studyprotogynous hermaphroditism in fishrapid behavioral adaptation in fishsex-changing fish behaviorsocial dynamics in aquatic speciesUniversity of Otago fish research