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Understanding variation in social organization that lacks a strong phylogenetic signal represents a key focus of research in behavioural ecology. Accordingly, we established a framework that identifies whether a range of ecological and social factors are affecting the social maintenance of taxa across multiple categories of social variation (ranging from large to fine‐scale): 1) forms of sociality, 2) degree of sociality, 3) social plasticity and 4) hierarchy maintenance. Each category of variation can then be assessed in combination to provide an outlook for social maintenance in light of predictor factors. We modelled this framework by quantifying each category over time, space and disturbance regime using multiple species of coral‐dwelling gobies, genus Gobiodon. Gobies are an interesting model system as they vary in social structure, have within‐group cooperation, and form mutualisms with coral hosts, which are vulnerable to climatic disturbances. We found that gobies varied in forms of sociality – from being more solitary or pair‐forming in high disturbance regimes, versus group‐forming in moderate disturbance regimes at some locations. Only low or moderate degrees of sociality were observed in gobies, with location or disturbance regime affecting some species. The size of coral hosts influenced the social plasticity of gobies, which was affected by climatic disturbances. Gobies did not exhibit direct changes to hierarchy maintenance, as location and disturbance regime did not affect their size‐based hierarchies. Lastly, by combining the four categories of variation, we found a high loss of sociality in coral‐dwelling gobies due to environmental disturbances, which likely affects overall goby survival as group‐forming can improve survival and fitness. By using our structured framework, we identified which categories of social variation were influenced by ecological factors like location and disturbance. This framework therefore provides an excellent tool for predicting future responses of animal societies to environmental stressors. [ABSTRACT FROM AUTHOR]

Mutualisms are prevalent in many ecosystems, yet little is known about how symbioses are affected by ecological pressures. Here, we show delayed recovery for 13 coral‐dwelling goby fishes (genus Gobiodon) compared with their host Acropora corals following four consecutive cyclones and heatwaves. While corals became twice as abundant in 3 years postdisturbances, gobies were only half as abundant relative to predisturbances and half of the goby species disappeared. Although gobies primarily occupied one coral species in greater abundance predisturbances, surviving goby species shifted hosts to newly abundant coral species when their previously occupied hosts became rare postdisturbances. As host specialization is key for goby fitness, shifting hosts may have negative fitness consequences for gobies and corals alike and affect their survival in response to environmental changes. Our study is an early sign that mutualistic partners may not recover similarly from multiple disturbances, and that goby host plasticity, while potentially detrimental, may be the only possibility for early recovery. [ABSTRACT FROM AUTHOR]

With the onset and increasing frequency of multiple disturbances, the recovery potential of critical ecosystem-building species and their mutual symbionts is threatened. Similar effects to both hosts and their symbionts following disturbances have been assumed. However, we report unequal declines between hosts and symbionts throughout multiple climate-driven disturbances in reef-building Acropora corals and cryptobenthic coral-dwelling Gobiodon gobies. Communities were surveyed before and after consecutive cyclones (2014, 2015) and heatwaves (2016, 2017). After cyclones, coral diameter and goby group size (i.e., the number of gobies within each coral) decreased similarly by 28–30%. After heatwave-induced bleaching, coral diameter decreased substantially (47%) and gobies mostly inhabited corals singly. Despite several coral species persisting after bleaching, all goby species declined, leaving 78% of corals uninhabited. These findings suggest that gobies, which are important mutual symbionts for corals, are unable to cope with consecutive disturbances. This disproportionate decline could lead to ecosystem-level disruptions through loss of key symbiont services to corals. [ABSTRACT FROM AUTHOR]

Animals forming social groups that include breeders and nonbreeders present evolutionary paradoxes; why do breeders tolerate nonbreeders? And why do nonbreeders tolerate their situation? Both paradoxes are often explained with kin selection. Kin selection is, however, assumed to play little or no role in social group formation of marine organisms with dispersive larval phases. Yet, in some marine organisms, recent evidence suggests small‐scale patterns of relatedness, meaning that this assumption must always be tested. Here, we investigated the genetic relatedness of social groups of the emerald coral goby, Paragobiodon xanthosoma. We genotyped 73 individuals from 16 groups in Kimbe Bay, Papua New Guinea, at 20 microsatellite loci and estimated pairwise relatedness among all individuals. We found that estimated pairwise relatedness among individuals within groups was significantly higher than the pairwise relatedness among individuals from the same reef, and pairwise relatedness among individuals from the same reef was significantly higher than the pairwise relatedness among individuals from different reefs. This spatial signature suggests that there may be very limited dispersal in this species. The slightly positive relatedness within groups creates the potential for weak kin selection, which may help to resolve the paradox of why breeders tolerate subordinates in P. xanthosoma. The other paradox, why nonbreeders tolerate their situation, is better explained by alternative hypotheses such as territory inheritance, and ecological and social constraints. We show that even in marine animals with dispersive larval phases, kin selection needs to be considered to explain the evolution of complex social groups. [ABSTRACT FROM AUTHOR]

Social organization is a key factor influencing a species’ foraging and reproduction, which may ultimately affect their survival and ability to recover from catastrophic disturbance. Severe weather events such as cyclones can have devastating impacts to the physical structure of coral reefs and on the abundance and distribution of its faunal communities. Despite the importance of social organization to a species’ survival, relatively little is known about how major disturbances such as tropical cyclones may affect social structures or how different social strategies affect a species’ ability to cope with disturbance. We sampled group sizes and coral sizes of group-forming and pair-forming species of the Gobiid genus Gobiodon at Lizard Island, Great Barrier Reef, Australia, before and after two successive category 4 tropical cyclones. Group sizes of group-forming species decreased after each cyclone, but showed signs of recovery four months after the first cyclone. A similar increase in group sizes was not evident in group-forming species after the second cyclone. There was no change in mean pair-forming group size after either cyclone. Coral sizes inhabited by both group- and pair-forming species decreased throughout the study, meaning that group-forming species were forced to occupy smaller corals on average than before cyclone activity. This may reduce their capacity to maintain larger group sizes through multiple processes. We discuss these patterns in light of two non-exclusive hypotheses regarding the drivers of sociality in Gobiodon, suggesting that benefits of philopatry with regards to habitat quality may underpin the formation of social groups in this genus. [ABSTRACT FROM AUTHOR]

While habitat is often a limiting resource for group-living animals, we have yet to understand what aspects of habitat are particularly important for the maintenance of sociality. As anthropogenic disturbances rapidly degrade the quality of many habitats, site-associated animals are facing additional stressors that may alter the trade-offs of moving or remaining philopatric. Here we examined how habitat health, size and saturation affect movement decisions of a coral-dwelling goby, the five-lined coral goby, Gobiodon quinquestrigatus , that resides within bleaching-susceptible Acropora coral hosts. To assess effects of habitat health, we translocated individuals far from their home corals into dead corals with the choice of adjacent healthy corals. To assess effects of habitat size and saturation, we manipulated coral sizes and the number of residents in healthy corals. Remarkably, 55% of gobies returned home regardless of treatment, 7% stayed in the new coral, and the rest were not found. Unlike other coral reef fishes, habitat factors did not affect how costs of movement influence group-living decisions in this species. These obligate coral-dwelling fishes preferred to home instead of choosing alternative habitat, which suggests a surprising awareness of their ecological surroundings. However, disregarding alternative high-quality habitat is concerning as it may affect population persistence under conditions of rapid habitat degradation. • Not all social animals make the same movement decisions related to their habitat. • We tested the influence of habitat size, health and saturation on movement of fish. • Gobiodon risk high predation costs to go home instead of choosing adjacent habitat. • Gobiodon are unlike other social coral reef fishes, which prefer adjacent habitat. • Habitat and conspecific familiarity are key in the movement decisions of Gobiodon. [ABSTRACT FROM AUTHOR]