Solitary Individuals Research Articles

Carlgren’s hesitation allayed: redescription and systematics of Heteranthus verruculatus Klunzinger, 1877 (Cnidaria, Actiniaria), with a redefinition of Heteranthidae Carlgren, 1900

Abstract Species boundaries delineating tropical sea anemones (Cnidaria, Actiniaria) of the zooxanthellate genus, Heteranthus Klunzinger, 1877, are unclear. There are currently two valid Heteranthus species: type species Heteranthus verruculatus Klunzinger, 1877, first reported from Koseir, Egypt, and H. insignis Carlgren, 1943, from Poulo Condore, Vietnam. In describing the latter from a single, poorly preserved specimen, zoologist Oskar Carlgren expressed apprehension with traits he had used to establish this species. Carlgren’s doubts persisted later in writing when he found a similar-looking sea anemone from the Great Barrier Reef. Crucial details to positively identify either species have since remained limited. Here, we re-diagnosed Heteranthus and re-described its type species based on observations of specimens we have obtained from Singapore and Pulau Ambon (Indonesia), and of museum material collected elsewhere across the Indo-West Pacific region (n > 180). Supported by molecular phylogenetic evidence, the family Heteranthidae Carlgren, 1900 was reinstated and re-diagnosed. Heteranthus verruculatus is encountered in the lower intertidal region amongst seagrass, in rocky crevices, or coral rubble. It occurs as solitary individuals or in clonal clusters, well-camouflaged against the substratum. Individuals were observed to frequently propagate by longitudinal fission, resulting in a varied appearance. Type material of H. verruculatus and H. insignis were re-examined and as we found no differences between them, the two were synonymised. We inferred that Carlgren probably misinterpreted cnidae and histological data in defining H. insignis as a distinct species. This revision clarifies the taxonomy and geographic range of H. verruculatus, an Indo-West Pacific species that is found from the Red Sea to subtropical Australia and Hawaii.

Evolution of multicellular life cycles under costly fragmentation.

A fascinating wealth of life cycles is observed in biology, from unicellularity to the concerted fragmentation of multicellular units. However, the understanding of factors driving their evolution is still limited. We show that costs of fragmentation have a major impact on the evolution of life cycles due to their influence on the growth rates of the associated populations. We model a group structured population of undifferentiated cells, where cell clusters reproduce by fragmentation. Fragmentation events are associated with a cost expressed by either a fragmentation delay, an additional risk, or a cell loss. The introduction of such fragmentation costs vastly increases the set of possible life cycles. Based on these findings, we suggest that the evolution of life cycles involving splitting into multiple offspring can be directly associated with the fragmentation cost. Moreover, the impact of this cost alone is strong enough to drive the emergence of multicellular units that eventually split into many single cells, even under scenarios that strongly disfavour collectives compared to solitary individuals.

The impacts of domestic dogs (Canis familiaris) on wildlife in two Brazilian hotspots and implications for conservation

Exotic species are major threats to biodiversity worldwide. Domestic dogs (Canis familiaris) are among the most common invasive predators in the world, interacting with wildlife in many ways. We present ecological data based on camera traps and occasional observations of free–roaming domestic dogs from localities within the Brazilian Atlantic forest and Cerrado hotspots. Canis familiaris was the second most abundant mammal species, and the most abundant carnivore. Dogs chased, killed, and/or competed with at least 26 native species. They consumed none of the killed animals, which together with the predominant records of solitary individuals acting during the daytime indicates they are mainly free–roaming dogs relying on humans for food and shelter. The high numbers of dogs and the wide range of prey suggest wildlife could be greatly impacted by domestic dogs, especially in areas that are highly threatened by anthropogenic activities, such as biodiversity hotspots. We highlight possible measures (such as the eradication or removal of dogs from natural areas) that could help to reduce the environmental damage caused by domestic dogs in the region.

Microhabitats choice in intertidal gastropods is species-, temperature- and habitat-specific.

Understanding how behavioural adaptations can limit thermal stress for intertidal gastropods will be crucial for climate models. Some behavioural adaptations are already known to limit desiccation and thermal stresses as shell-lifting, shell-standing, towering, aggregation of conspecifics or habitat selection. Here we used the IRT (i.e. infrared thermography) to investigate the thermal heterogeneity of a rocky platform, with four different macrohabitats (i.e. bare rock, rock with barnacles, mussels and mussels incrusted by barnacles) over four thermally contrasted months. We investigated the body temperature of Littorina littorea and Patella vulgata found on this platform and the temperature of their microhabitat (i.e. the substratum within one body length around of each individual). We also considered the aggregation behaviour of each species and assessed the percentage of thermal microhabitat choice (i.e choice for a microhabitat with a temperature different than the surrounding substrate). We did not find any aggregation of L. littorea on the rocky platform during the four studied months. In contrast, P. vulgata were found in aggregates in all the studied periods and within each habitat, but there was no difference in body temperature between aggregated and solitary individuals. These two gastropods species were preferentially found on rock covered by barnacles in the four studied months. The presence of a thermal microhabitat choice in L. littorea and P. vulgata is habitat-dependent and also season-dependent. In June, July and November the choice was for a microhabitat with temperatures lower than the temperatures of the surrounding substrate whereas in December, individuals choose microhabitats with higher temperatures than the temperatures of their substratum. Taken together, these results suggest that gastropods species are able to explore their environment to find sustainable thermal macrohabitats and microhabitats and adapt this behaviour in function of the conditions of temperatures.

Lone males: Solitary and group-living male howler monkey (Alouatta palliata) behavioral ecology in a Costa Rican rainforest.

Many group-living primate species have evolved the capacity for some individuals to live alone for part of their lives, but this solitary life stage has rarely been the subject of focused research. The mantled howler monkey (Alouatta palliata) is a social primate species with bisexual dispersal that lives in mixed-sex groups with low male-to-female sex ratios. Consequently, males often spend a long period of their lives as solitary individuals. This study compares the tree use, feeding, and long-distance vocalization behavior of solitary and group-living mantled howler monkey males living within a fragmented rainforest in Costa Rica, La Suerte Biological Research Station. Based on differences in competitive ability between solitary and group-living males, we predicted that lone males would be found in significantly smaller feeding and resting trees, consume more low-quality foods, and produce shorter howling bouts made at lower rates than group-living males. We collected data on tree use and feeding during 30-min focal samples on male focal animals, recording data at 2-min intervals. We measured the trees in which the monkeys fed and rested for two or more intervals, and recorded the plant parts consumed. We recorded howling behavior using all-occurrences sampling. Lone males used significantly smaller feeding and resting trees, consumed more low-quality foods, and howled at lower rates but had longer howling bouts triggered by anthropogenic noise more than group-living males. Our results demonstrate that lone males differ in their behavioral ecology compared to group-living males, thus improving understanding of the solitary male life stage in primates.

Locust Bacterial Symbionts: An Update.

Simple SummaryLocust plagues have been devastating vegetation and agriculture since ancient times. The tendency of locusts to form huge swarms and migrate long distances is a hallmark of the locust phenomenon. The ecological and economic importance of locust plagues has attracted much research into different aspects of the natural history of these insects. One of the many investigated aspects of the locust phenomenon is that of their interaction with the bacteria they harbor in and on their body. These locust-associated bacteria have been shown to affect certain physiological traits (such as immunity and swarm cohesion), as well as possibly affecting and being affected by different factors in the locust biology. Here, we review the current understanding of the locust–bacteria interaction. We focus on identifying the bacterial strains and their locations within the insects; the role of the bacteria and their importance to their host’s life; the mechanism of transmitting important bacteria across locust generations; and more. Finally, we offer some new perspectives and research directions that could broaden our understanding of the locust-associated bacteria and their role in locust outbreaks.As one of the world’s most infamous agricultural pests, locusts have been subjected to many in-depth studies. Their ability at one end of their behavioral spectrum to live as solitary individuals under specific conditions, and at the other end of the spectrum to form swarms of biblical scale, has placed them at the focus of vast research efforts. One important aspect of locust ecology is that of their interactions with the bacteria that reside in and on them. Although this aspect of locust ecology has been little studied relative to the mainstream locust research, these bacteria have been shown both to affect locust immunity and to participate in maintaining swarm integrity through the secretion of attractant volatiles. The interaction between locusts and their bacteria seems, however, to be bi-directional, with the bacteria themselves, as recently shown, being influenced by their host’s swarming tendencies. This seems to be a consequence of the bacterial composition in the locust’s gut, reproductive organs, and integument undergoing change with the change in their host’s behavior. In this review we describe the current state of knowledge of the locust–bacteria interactions (data exists mainly for the desert and the migratory locusts), as well as highlighting some newly-gained understanding; and offer perspectives for future research.

Gregariousness affects performance and defensive reactions in swallowtail caterpillars

1. Group living in caterpillars may enhance individual performance due to sharing of costs associated with individual tasks when dealing with biotic or abiotic ecological factors.2. In the gregarious caterpillar Battus polydamas archidamas (Papilionidae) egg clusters and caterpillar groups vary in size. We hypothesized that individual survival would be higher in larger groups and that group living would enhance individual performance: shorter development time and/or reduced frequency of (presumably costly) defensive reactions in larvae and larger adult size. We also tested whether the group size conferring the highest survival to laboratory‐reared caterpillars matched the most frequent egg clutch size in the field.3. We collected egg clutches in the field and reared caterpillars in groups of 1, 6, 10, and 14 individuals. We quantified larval survival and stage duration as well as adult mass under laboratory conditions, excluding natural enemies. We also recorded the frequency of larval defensive reactions (thrashing and osmeterium display) against a tactile stimulus of first‐instar larvae.4. Group living enhanced caterpillar survival, particularly during the first instars, when caterpillars are 100% gregarious. Groups of intermediate size reduced larval development time but group living did not affect adult mass. Individual caterpillars in groups showed defensive reactions less frequently than solitary individuals, revealing a cost‐saving feature of gregariousness for this swallowtail species. The most frequent clutch size in the field (9–10 eggs) did not match the larval group with highest survival (14 individuals), but did match the group with shortest development time.

Breeding patterns of female prairie voles (Microtus ochrogaster) displaying alternative reproductive tactics.

Individuals of either sex may display alternative behaviors to obtain copulations, but few studies have examined the breeding patterns of females and males in populations where individuals of both sexes exhibit alternative reproductive tactics (ARTs). In prairie voles (Microtus ochrogaster), most adults are territorial, residing at a single nest site either as male-female pairs or as solitary individuals. However, some adults adopt nonterritorial, wandering tactics. During two field seasons monitoring prairie vole populations maintained in seminatural enclosures, we found evidence that females exhibiting different ARTs bred differentially with resident and wandering males. Females residing at a nest with a male bred significantly more often with a paired resident male, primarily their social partner, and significantly less often with male wanderers compared to single resident females or wandering females. These patterns were not due to chance, because paired resident females produced offspring with paired resident males significantly more than expected based on the relative abundance of these males in the population, whereas single resident females produced offspring with male wanderers significantly more than expected based on the proportion of male wanderers in the population. We did not find any evidence that multiple paternity was greater in the litters of single resident females and wanderer females even though these females lacked a male social partner to limit mating access by multiple males. This suggests that mate guarding by a female's male social partner was not the primary determinant of multiple paternity in the litters of females exhibiting different reproductive tactics. However, male ART did affect the likelihood of multiple paternity. Females that produced offspring with single resident or wanderer males had an increased likelihood of multiple paternity relative to females producing offspring with paired resident males. The results of this study show that female and male ARTs can affect breeding patterns.

DholeCuon alpinusin Satchari National Park: on the first verifiable evidence from northeast Bangladesh

AbstractThe distribution range of the globally Endangered dholeCuon alpinusoverlaps mixed evergreen mid-hill forests of northeastern Bangladesh but lacks any authentic documentation. With the first evidence from this region, we observed the activity pattern of dhole, of its prey and of human activities in Satchari National Park, a part of a larger northeastern forested area, Raghunandan Hill Reserve Forest – the northernmost fringe of the Baramura Hills of India. We obtained 32 photos of solitary individuals on eight different events from six out of 587 camera trap days. Naïve occupancy estimate for dhole was 0.41 with a detection probability of 0.65. We identified two individuals, and reported five predation events. We encountered a moderately high temporal overlap of dhole activity with that of barking deer (∆̂1= 0.65, CI = 0.42–0.83), human activity (0.63, 0.38–0.89), and livestock movement (0.59, 0.38–0.89). Given that dhole is a diurnal hyper-carnivore, illegal logging and tourism pressure appeared as major disturbances to the species' existence in the park. Habitats of northeastern protected forests, their adjacency with hill ranges of Tripura, and dhole being a habitat generalist, we conjecture its presence in the entire region and recommend thorough camera-trapping efforts.

Flocking in complex environments-Attention trade-offs in collective information processing.

The ability of biological and artificial collectives to outperform solitary individuals in a wide variety of tasks depends crucially on the efficient processing of social and environmental information at the level of the collective. Here, we model collective behavior in complex environments with many potentially distracting cues. Counter-intuitively, large-scale coordination in such environments can be maximized by strongly limiting the cognitive capacity of individuals, where due to self-organized dynamics the collective self-isolates from disrupting information. We observe a fundamental trade-off between coordination and collective responsiveness to environmental cues. Our results offer important insights into possible evolutionary trade-offs in collective behavior in biology and suggests novel principles for design of artificial swarms exploiting attentional bottlenecks.

Individual, but not population asymmetries, are modulated by social environment and genotype in Drosophila melanogaster

Theory predicts that social interactions can induce an alignment of behavioral asymmetries between individuals (i.e., population-level lateralization), but evidence for this effect is mixed. To understand how interaction with other individuals affects behavioral asymmetries, we systematically manipulated the social environment of Drosophila melanogaster, testing individual flies and dyads (female-male, female-female and male-male pairs). In these social contexts we measured individual and population asymmetries in individual behaviors (circling asymmetry, wing use) and dyadic behaviors (relative position and orientation between two flies) in five different genotypes. We reasoned that if coordination between individuals drives alignment of behavioral asymmetries, greater alignment at the population-level should be observed in social contexts compared to solitary individuals. We observed that the presence of other individuals influenced the behavior and position of flies but had unexpected effects on individual and population asymmetries: individual-level asymmetries were strong and modulated by the social context but population-level asymmetries were mild or absent. Moreover, the strength of individual-level asymmetries differed between strains, but this was not the case for population-level asymmetries. These findings suggest that the degree of social interaction found in Drosophila is insufficient to drive population-level behavioral asymmetries.

Imagining Ro: On the social life of islets and the politics of islandography

This article engages the challenge of island history as caught in between national historiography and local life stories. It focuses on Ro, a Greek islet bordering Turkey that has been imagined and idealized as a space of national resistance and resilience. The article unpacks the grand national narrative that has been developed with regard to the heroic life story of a solitary woman living on the island. It utilizes local counter-narratives as well as the life stories of other solitary individuals who have periodically lived on the island. To that extent, the article aims, on the one hand, to sensitize as to the politics of islandography and, on the other, to highlight the importance of social history in challenging hegemonic or colonial narratives as well as reimagining island space.

Растительные сукцессии на отвалах угольных шахт в лесостепи Тульской области

The paper describes vegetation successions that can be observed on waste piles of Moscow lignite basin. Characterization of succession are performed with geobotanical descriptions that were made at non-recultivated waste pile, levelled dump and phytomeliorated waste pile. ^lonization of coal waste piles by plants corresponds to primary succession that proceeds in specific edaphic conditions. Term and trajectory of this process on waste piles of Moscow lignite basin in the Tula oblast differ at various object types. The rate of revegetation is slowest at slopes of waste piles and levelled spoils, where only solitary individuals of ruderal species can occur. At levelled spoils’ surfaces and self-developing deluvial-proluvial foreslopes (which is forming at waste pile foot) pioneer plant groups, simple structured phytocoenoses and complex structured phytoco-enoses are discovered. Most common tree species in simple structured and complex structured communities is Betula pendula. Under the toxic flow influence herbaceous layer at deluvial-proluvial foreslopes and in certain parts of levelled spoil consists mainly of Calamagrostis epigeios, Equisetum spp., Convolvulus arvensis. Out of toxic flow influence at levelled spoil forb meadows with large proportion of legumes (Trifolium hybridum, Lotus corniculatus, Melilotus albus etc.) occur. Succession stages changing is not rapid and revegetation processes takes decades; the phytomelioration of Moscow lignite basin waste piles in the Tula oblast can speed this process up by overcoming the delayed pioneer plant groups stage. The pattern of plant succession trajectories on waste piles of Moscow lignite basin in forest-steppe landscapes of the north part of the Central Russian Upland was developed.

Reproductive skew in cooperative breeding: Environmental variability, antagonistic selection, choice, and control.

A multitude of factors may determine reproductive skew among cooperative breeders. One explanation, derived from inclusive fitness theory, is that groups can partition reproduction such that subordinates do at least as well as noncooperative solitary individuals. The majority of recent data, however, fails to support this prediction; possibly because inclusive fitness models cannot easily incorporate multiple factors simultaneously to predict skew. Notable omissions are antagonistic selection (across generations, genes will be in both dominant and subordinate bodies), constraints on the number of sites suitable for successful reproduction, choice in which group an individual might join, and within‐group control or suppression of competition. All of these factors and more are explored through agent‐based evolutionary simulations. The results suggest the primary drivers for the initial evolution of cooperative breeding may be a combination of limited suitable sites, choice across those sites, and parental manipulation of offspring into helping roles. Antagonistic selection may be important when subordinates are more frequent than dominants. Kinship matters, but its main effect may be in offspring being available for manipulation while unrelated individuals are not. The greater flexibility of evolutionary simulations allows the incorporation of species‐specific life histories and ecological constraints to better predict sociobiology.

Revealing hidden density-dependent phenotypic plasticity in sedentary grasshoppers in the genus Schistocerca Stål (Orthoptera: Acrididae: Cyrtacanthacridinae)

Comparative quantification of reaction norms across closely related species in a clade is rare, but such a study can reveal valuable insights into understanding how reaction norms evolve along phylogeny. The grasshopper genus Schistocerca Stål (Orthoptera: Acrididae: Cyrtacanthacridinae) is an ideal group to study the evolution of density-dependent phenotypic plasticity because it includes both swarming locusts and non-swarming sedentary grasshoppers, which show varying degrees of plastic reaction norms in many traits. The swarming locusts exhibit locust phase polyphenism in which cryptically colored and solitary individuals can transform into conspicuously colored and highly gregarious individuals in response to increases in population density. The sedentary grasshoppers do not swarm in nature, and thus it has been assumed that they have little or no expression of plastic reaction norms in many traits, except for color, which has been shown to be a phylogenetically conserved trait. In this study, we have quantified density-dependent reaction norms in behavior, color, body size, and morphometric ratio in the nymphs of four sedentary species within Schistocerca by conducting explicit rearing experiments to induce potential phenotypic changes in response to isolation and crowding. In contrast to our previous assumption, we find that all four species show a certain level of density-dependent plastic reaction norms, which implies that these sedentary species have hidden reaction norms that can only be induced experimentally, some components of which must be phylogenetically conserved. Furthermore, we demonstrate that rearing density differentially affects the expression of reaction norms in different species, suggesting that different reaction norms must have followed independent evolutionary trajectories.

Characterization and Expression of Genes Encoding Superoxide Dismutase in the Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae).

Superoxide dismutase (SOD) is an antioxidant metalloenzyme that catalyzes the dismutation of the superoxide anion O2- to O2 and H2O2. Many studies have focused on the role of SOD in response to abiotic stress, but its role during biotic stress, such as changes in organismal population density, has rarely been investigated. The oriental armyworm, Mythimna separata, is an economically important pest that exhibits phenotypic changes in response to population density. Solitary and gregarious phases occur at low and high population density, respectively. To examine the role of SODs in response to population density stress, we cloned two genes encoding SOD, MsCuZnSOD and MsMnSOD, and compared their expression in solitary and gregarious phases of M. separata. The MsCuZnSOD and MsMnSOD ORFs were 480 and 651 bp and encoded predicted protein products of 159 and 216 amino acids, respectively. The two SODs contained motifs that are typical of orthologous proteins. Real-time PCR indicated that the two SOD genes were expressed throughout developmental stages and were significantly upregulated in more mature stages of gregarious M. separata. Expression of the two SOD genes in various tissues of sixth-instar larvae was higher in gregarious versus solitary insects. Furthermore, expression of the SOD genes was significantly upregulated in response to crowding in solitary individuals, but suppressed in gregarious insects subjected to isolation. Collectively, these results suggest that population density may be key factor in the induction of SOD genes in M. separata.

Seawater acidification and temperature modulate anti-predator defenses in two co-existing Mytilus species

The effects of short-term (7 days) experimental ocean acidification (−0.4 pH units) and warming (+5 °C) on anti-predator defenses of two sympatric Mytilus species from China, M. coruscus and M. edulis, in the presence and absence of predator cues were investigated. Results suggested species-specific independent negative effects of acidification and warming on the number and weight of byssal threads, the force of thread attachment, and total thread plaque area. Similar negative effects were observed for clustering behaviour, with acidification and warming independently increasing the number of solitary individuals and decreasing the percentage of mussels in clusters. Acidification effects on byssus were strongly exacerbated when predators were present. Ultimately, this study suggests that short-term exposure to experimental warming and acidification can negatively impact anti-predator defense strategies in mussels with potential ramifications for predator-prey interactions and ecological functioning in systems where mussel beds play a key ecological role.

Baseline activity and shoal type determine antipredator behaviors in bluegill from a southern Ontario lake

Shoaling is an evolved behavior in fishes that has several adaptive advantages, including allowing individuals to avoid predation through risk dilution. However, factors such as size disparity and the presence of heterospecifics may influence the behavior of individual fish within shoals following exposure to elevated predation risk. Using bluegill Lepomis macrochirus as a model species, we measured changes in area use, shoaling index, and movement of a focal individual in isolation, in single-species shoals with two conspecifics, or in mixed-species shoals with two congeneric pumpkinseed L. gibbosus. The experimental shoals were exposed to one of three chemical cues selected to present graded levels of risk: lakewater controls (lowest risk), Northern pike Esox lucius predator odor (kairomones; intermediate risk), or conspecific chemical alarm cues (highest risk). Within the individual bluegill, we found that the multivariate response of area use and post-stimulus activity (line crosses) of the focal fish was significantly influenced by pre-stimulus activity, but not by cue type or fish size. As univariate responses, post-stimulus activity varied positively with pre-stimulus activity. Post-stimulus activity was greater in single-species shoals compared to mixed-species shoals, and again varied positively with pre-stimulus activity. Contrary to predictions, bluegill did not demonstrate graded antipredator responses to the chemical cues. Our findings suggest that prey fish may alter their risk-aversive behaviors in response to chemical stimuli based on shoal composition and provide further insight into the role of intra-prey guild interactions in response to predators in co-occurring prey species. When faced with predation, individuals in groups may experience lower levels of risk than solitary individuals. Using bluegill as a model organism, we examined how antipredator behaviors, in response to chemical cues indicating different levels of risk, varied between focal individuals as singletons and in single- and mixed-species shoals. Contrary to our prediction of graded stepwise responses indicative of differing levels of risk posed by the cues, we found that individuals with greater baseline activity levels demonstrated weaker antipredator responses independent of cue type, while fish in single-species shoals had higher post-stimulus activity levels than fish in mixed-species shoals. Our results suggest that studies examining changes in antipredator and shoaling behaviors will benefit from including ecologically relevant scenarios involving sympatric prey guild members.

Predators attacking virtual prey reveal the costs and benefits of leadership

A long-standing assumption in social behavior is that leadership incurs costs as well as benefits, and this tradeoff can result in diversified social roles in groups. The major cost of leadership in moving animal groups is assumed to be predation, with individuals leading from the front of groups being targeted more often by predators. Nevertheless, empirical evidence for this is limited, and experimental tests are entirely lacking. To avoid confounding effects associated with observational studies, we presented a simulation of virtual prey to real fish predators to directly assess the predation cost of leadership. Prey leading others are at greater risk than those in the middle of groups, confirming that any benefits of leading may be offset by predation costs. Importantly, however, followers confer a net safety benefit to leaders, as prey leading others were less likely to be attacked compared with solitary prey. We also find that the predators preferentially attacked when solitary individuals were more frequent, but this effect was relatively weak compared with the preference for attacking solitary prey during an attack. Using virtual prey, where the appearance and behavior of the prey can be manipulated and controlled exactly, we reveal a hierarchy of risk from solitary to leading to following social strategies. Our results suggest that goal-orientated individuals (i.e., potential leaders) are under selective pressure to maintain group cohesion, favoring effective leadership rather than group fragmentation. Our results have significant implications for understanding the evolution and maintenance of different social roles in groups.

Changes in sociality of butterflyfishes linked to population declines and coral loss

Degradation and loss of reef habitat is one of the foremost threats to coral reef fishes, especially for highly specialised species with specific reliance on live corals. Aside from affecting the carrying capacity of local environments, declines in the quality and quantity of critical reef habitats may lead to changes in behaviour, condition and fitness of individual fishes. This study explores changes in the sociality (specifically, the proportion of individuals observed in pairs) for coral reef butterflyfishes over a 15-yr period, in the northern Great Barrier Reef. During the study period where there were significant disturbances that reduced coral cover, there were also sustained declines in abundance of many butterflyfishes. Across five species of pairing butterflyfishes (Chaetodon baronessa, C. lunulatus, C. citrinellus, C. auriga and C. vagabundus), the overall proportion of individuals in pairs varied among the three surveys (2002, 2009, and 2017) and was positively correlated with live coral cover. This pattern was most apparent for, and largely driven by changes in sociality of, C. baronessa. Declines in incidence of pairing may suggest that pairing is untenable as prey becomes limiting, or elevated rates of adult mortality increasingly disrupt patterns of sociality. Disruptions to sociality, and thereby reproductive systems, may add to population declines and greatly constrain subsequent recovery and resilience of populations. For other more generalist or non-coral feeders, the relative incidence of pairing actually increased due to disproportionate declines in abundance of solitary individuals.