Background: Acquiring high resolution quantitative behavioural data underwater often involves installation of costly infrastructure, or capture and manipulation of animals. Aquatic movement ecology can therefore be limited in taxonomic range and ecological coverage. Methods: Here we present a novel deep-learning based, multi-individual tracking approach, which incorporates Structure-from-Motion in order to determine the 3D location, body position and the visual environment of every recorded individual. The application is based on low-cost cameras and does not require the animals to be confined, manipulated, or handled in any way. Results: Using this approach, single individuals, small heterospecific groups and schools of fish were tracked in freshwater and marine environments of varying complexity. Positional tracking errors as low as 1.09 ± 0.47 cm (RSME) in underwater areas up to 500 m 2 were recorded. Conclusions: This cost-effective and open-source framework allows the analysis of animal behaviour in aquatic systems at an unprecedented resolution. Implementing this versatile approach, quantitative behavioural analysis can be employed in a wide range of natural contexts, vastly expanding our potential for examining non-model systems and species.
Dominant individuals are often most influential in their social groups, affecting movement, opinion, and performance across species and contexts. Yet, behavioral traits like aggression, intimidation, and coercion, which are associated with and in many cases define dominance, can be socially aversive. The traits that make dominant individuals influential in one context may therefore reduce their influence in other contexts. Here, we examine this association between dominance and influence using the cichlid fish Astatotilapia burtoni, comparing the influence of dominant and subordinate males during normal social interactions and in a more complex group consensus association task. We find that phenotypically dominant males are aggressive, socially central, and that these males have a strong influence over normal group movement, whereas subordinate males are passive, socially peripheral, and have little influence over normal movement. However, subordinate males have the greatest influence in generating group consensus during the association task. Dominant males are spatially distant and have lower signal-to-noise ratios of informative behavior in the association task, potentially interfering with their ability to generate group consensus. In contrast, subordinate males are physically close to other group members, have a high signal-to-noise ratio of informative behavior, and equivalent visual connectedness to their group as dominant males. The behavioral traits that define effective social influence are thus highly context specific and can be dissociated with social dominance. Thus, processes of hierarchical ascension in which the most aggressive, competitive, or coercive individuals rise to positions of dominance may be counterproductive in contexts where group performance is prioritized.
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In many species, cultures, and contexts, social dominance reflects the ability to exert influence over the behavior of others. Yet the behavioral attributes of those in dominant positions, and the behaviors of actually influential individuals may not be the same, and the behavioral attributes that generate influence in one social context may reduce influence in others. The question of what makes an effective leader is therefore not straightforward, and has many answers depending on the context in which leadership and influence is to be manifested. Most importantly, social dominance cannot always be assumed to be equivalent with social influence. Here we examine whether socially dominant males in the cichlid fish Astatotilapia burtoni are more effective in exerting social influence than socially subordinate males. Using machine-vision based automated tracking of behavior, we find that dominant males in this species display behavioral traits that typify leadership across taxonomic systems -they are aggressive, occupy central social network positions, and lead group movements, whereas subordinate males are passive, socially peripheral, and have little influence over typical group movement. However, in a more complex group-consensus task the influence of dominant males breaks down, and subordinate males become more effective agents of social change. In a more sophisticated group consensus task involving a visual association task, the behavioral attributes that define male dominance -aggression, rapid movement, and increased physical distance to othersinterfere with the ability of dominant males to generate group to consensus. Dominant males occupy more spatially distant positions, and had lower signal-to-noise ratio of informative behavior in the association task, while subordinate males are typically is close physical association with their group members, have high signal-to-noise behaviors in the association task, and equal visual connectivity to other group members as dominant males. The attributes that define effective social influence are therefore highly context-specific in this species. These results demonstrate that in this and many other species including humans, behavioral traits that are typical of socially dominant individuals may be the same that reduce their social influence in other contexts.
A key aspect of understanding social interactions in marine animals is determining whether individuals freely interact in fission-fusion groups, or have spatially structured interactions, for example territories or home ranges. Territoriality can influence access to mates, food resources, or shelter sites, and may also impact conservation efforts, as the delineation of marine protected areas relies on knowledge of home ranges and movement patterns. However, accurately determining distribution and movement is challenging for many marine species, especially small and medium species, which cannot carry beacons or tags to automatically measure movement, and are also difficult for human observers to accurately follow. Yet these smaller species comprise the bulk of near-shore assemblages, and are essential conservation targets. As such, novel solutions for monitoring movement and behavior are required. Here we use a combination of tracking and environmental reconstruction to explore territoriality, aggression, and navigation in a small marine fish, explicitly applying this technique to questions of sociality in the marine environment. We use the Mediterranean Rainbow Wrasse, Coris julis, as a test case, but this approach can be extended to many other species and contexts. In contrast with previous reports for this species, we find that during our observation period, female C. julis occupy consistent territories over sand patches, and that they defend these territories against same-sex conspecifics. Displacement experiments revealed two further important social behavioral traits – first that displaced individuals were able to navigate back to their territory, avoiding almost all other female territories as they returned. Second that when displaced fish approached the territories of others, residents of these territories were often aggressive to the non-neighboring fish, in contrast with our observations of low aggression counts toward their natural neighbors. Resident fish therefore appear to show differing levels of aggressiveness depending on their social relationship with same-sex conspecifics. Overall, these results suggest a sophisticated degree of social behavior in this marine wrasse, dependent on social and structural environment, but which can only effectively be revealed by state-of-the-art tracking and environment reconstruction techniques.
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