Aggressive Interactions Research Articles

Neural response to aggressive and positive interactions in violent offenders and nonviolent individuals.

BackgroundDue to its severe negative consequences, human violence has been targeted by a vast number of studies. Yet, neurobiological mechanisms underlying violence are still widely unclear and it seems necessary to aim for high ecological validity to learn about mechanisms contributing to violence in real life.MethodsThe present functional magnetic resonance imaging (fMRI) study investigated the neurofunction of individuals with a history of violent offenses compared with that of controls using a laboratory paradigm requesting individuals to empathically engage in videos depicting provocative aggressive and positive social interactions from a first‐person perspective.ResultsThe contrast of aggressive vs. positive scenarios revealed midbrain activation patterns associated with caudal periaqueductal gray (PAG) in violent offenders; In controls, the rostral PAG was involved. Additionally, only in controls, this contrast revealed an involvement of the amygdaloidal complex. Moreover, in violent offenders the contrast of positive vs. aggressive situations revealed an involvement of areas in the insula, post‐central gyrus and anterior cingulate cortex.ConclusionsOur results support findings on the differential role of PAG subdivisions in response to threat and point to altered processing of positive social interactions in violent offenders. They further support the notion that changes in PAG recruitment might contribute to violent individuals “taking action” instead of freezing in case of threatening situations.

Bottlenose dolphins (Tursiops truncatus) aggressive behavior towards other cetacean species in the western Mediterranean

Aggressive behavior of bottlenose dolphins (Tursiops truncatus) towards conspecifics is widely described, but they have also often been reported attacking and killing harbour porpoises (Phocoena phocoena) around the world. However, very few reports exist of aggressive interactions between bottlenose dolphins and other cetacean species. Here, we provide the first evidence that bottlenose dolphins in the western Mediterranean exhibit aggressive behavior towards both striped dolphins (Stenella coeruleoalba) and Risso’s dolphins (Grampus griseus). Necropsies and visual examination of stranded striped (14) and Risso’s (2) dolphins showed numerous lesions (external rake marks and different bone fractures or internal organ damage by blunt trauma). Indicatively, these lessons matched the inter-tooth distance and features of bottlenose dolphins. In all instances, these traumatic interactions were presumed to be the leading cause of the death. We discuss how habitat changes, dietary shifts, and/or human colonization of marine areas may be promoting these interactions.

Plumage colour saturation predicts long-term, cross-seasonal social dominance in a mutually ornamented bird

Dominance hierarchies are known to reduce agonistic interactions between individuals and may be influenced by differences in phenotypes such as body size, personality or cognition. Colour ornamentation, especially with melanin-based colours, can also be a badge of status signalling social dominance, but status signalling with carotenoid-based colours is little understood. Here we studied whether different phenotypes, including individual differences in carotenoid-based colour ornamentation, body size, personality-, cognition- and stress-related traits, predict social dominance in the highly social and mutually ornamented common waxbill, Estrilda astrild . We monitored aggressive interactions of waxbills living in seminatural conditions, in a large mesocosm, using data from a radiofrequency identification system in the nonbreeding and breeding seasons over 2 consecutive years. We found the position of individual waxbills in the dominance hierarchy repeatable across seasons and years. Furthermore, the steepness of the dominance hierarchy was greater in the breeding seasons, perhaps because of increased competition over mates or breeding resources. Contrary to previous work with waxbills in birdcages, here body size did not predict social dominance, perhaps because in our more natural setting aggressive encounters were mostly airborne, where large body size may not confer a fighting advantage and may even reduce manoeuvrability. Sex, reactive-to-proactive personality differences and traits related to cognition or stress did not predict social dominance either. Finally, red colour saturation, but not the size of the red patch, strongly predicted social dominance and may thus act as a badge of status. This is one of the few studies testing whether size or saturation of carotenoid-based plumage coloration indicates social dominance and suggests that saturation may more often signal dominance. • Waxbills have mildly steep but stable social hierarchies across years and seasons. • Saturation of carotenoid-based red plumage colour indicates social dominance. • Size of red plumage areas does not correlate with social dominance. • Sex, personality, cognition and size were not related to social dominance.

Neural Correlates of Decisions in Quasi-Realistic, Affective Social Interactions in Individuals With Violence-Related Socialization.

Appropriate social behavior in aggressive-provocative interactions is a prerequisite for a peaceful life. In previous research, the dysfunctions of the control of aggression were suggested to be modulated by enhanced bottom-up (sub-cortically driven) and reduced top-down (iso-cortical frontal) processing capability. In the present study, two groups of individuals with enhanced (EG) and normal (NG) experiences of violent acts during their socialization made binary behavioral decisions in quasi-realistic social interactions. These interactions were presented in short video clips taken from a first-person perspective. The video clips showed social interaction scenarios oriented on realistic everyday life situations. The behavioral data supported the distinct affective qualities of three categories of social interactions. These categories were labeled as aggressive–provocative, social–positive, and neutral–social interactions. Functional neuroimaging data showed extended activation patterns and higher signal intensity for the NG compared to the EG in the lateral inferior frontal brain regions for the aggressive provocative interactions. Furthermore, the peri-aqueductal gray (PAG) produced enhanced activations for the affective interaction scenarios (i.e., aggressive-provocative and social-positive) in both groups and as a trend with the medium effect size for the neutral interactions in the EG. As the individuals in the EG did not show open aggression during the functional MRIA (fMRI) investigation, we concluded that they applied individual self-control strategies to regulate their aggressive impulses immediately. These strategies appeared to be top-down regulated through the dorsal frontal brain areas. The predominant recruitment of the heteromodal cortices during the neural processing of complex social interactions pointed to the important role of the learning history of individuals and their socialization with differing levels of violent experiences as crucial modulators in convicts. Our data suggest that building or strengthening the association between prototypical social contexts (e.g., aggressive-provocative interactions) and appropriate behaviors as a response to it provides a promising approach to successfully re-socialize people with a delinquent history.

Water temperature modulates social behavior of ornamental cichlid (Pterophyllum scalare) in an artificial system

ABSTRACT Environmental changes can cause physiological alterations in fish, which may affect some behavioral patterns. We evaluated the effects of water temperature on the aggressive behavior of male freshwater angelfish, Pterophyllum scalare. We subjected pairs to three water temperature conditions: low (23.8 ± 0.8°C), medium (27.9 ± 1.2°C), and high (31.7 ± 1.0°C), with eight repetitions each. We assessed latency to fighting, aggressive interaction frequency, and territorial defense. In low and high temperatures there was a reduction in aggressive behavior exhibitions in comparison to medium temperatures (P < 0.05). As a result, water temperature can influence aggressive motivation and territorial establishment, given that temperatures closer to species optima (27.9 ± 1.2°C) can favor social contests for an Amazonian ornamental cichlid species, P. scalare.

7 Behavioral Indicators of Post-weaning Stress Susceptibility in Cross-fostered Pigs

Abstract Cross-fostering is a common swine husbandry practice; however, little research has focused on the effects of foster stress on piglets post-weaning. This study evaluated the effect of cross-fostering on behavioral indicators of post-weaning stress susceptibility. Litters (n = 40) were allocated to 1 of 2 treatments: control (CON) and foster. Three piglets (FOS) from each CON litter were randomly selected and moved to a foster litter 12–24 h post-farrowing, where they were nursed along resident (RES) piglets until weaning (approximately 18 d of age). At 21- and 28-d post-weaning, a male and female piglet from each treatment (FOS, RES, CON) underwent 1 of 2 behavior tests: social isolation and social confrontation. Both tests were conducted in an isolated 1.22 × 1.22 m novel pen. For social isolation, escape attempts, movement between floor quadrants (i.e. locomotion), defecation, and urination events were counted. For social confrontation, the latency to first aggressive interaction and the number of aggressive interactions were quantified. All data were analyzed using the GLIMMIX procedure in SAS. The CON piglets moved between quadrants more frequently than RES piglets (P = 0.02), while FOS piglets moved between quadrants intermediate to (but not different from) CON and RES piglets (P = 0.44 and 0.12, respectively). Females moved between quadrants more frequently than males (P &amp;lt; 0.0001). The latency to first aggressive interaction was shorter in FOS piglets compared to CON piglets (P = 0.048). There was a treatment by sex interaction (P &amp;lt; 0.01) for number of aggressive interactions, with CON and RES females having more aggressive interactions than their male counterparts (P = 0.04 for both) while FOS females had fewer aggressive interactions than FOS males (P = 0.007). No additional differences were detected (all P &amp;gt; 0.05). Overall, these results provide little evidence that FOS piglets exhibit an increase in behavioral stress susceptibility post-weaning. However, future work should expand upon and clarify the social confrontation findings.

Networks never rest: An investigation of network evolution in three species of animals

Despite considerable advancement in the study of network evolution, three basic limitations are common to the data collected: (1) examining a small number of networks, (2) not observing networks from scratch, (3) not collecting time-stamped, continuous records of all interactions among all members of groups. Here, we avoid these limitations by observing all aggressive interactions leading to network formation from the moment of introduction among all members of 45 groups of four individuals each in three species of animals: chickens, cichlid fish, and mice. We apply several recently developed methods for the visualization and analysis of network evolution to these unique datasets. We discover, first, that network evolution is a remarkably dynamic process across all three species: networks do not evolve to specific structures and then remain in those configurations. Instead, we find dynamic stability in which many groups continually return to a general class of structures. Second, we find considerable similarity across species in the pathways that the groups take through different possible network configurations as they evolve. Third, we show that transitive component triads are more stable than intransitive ones. Fourth, we track the evolution of individual ranks within groups and discover that many individuals do not have stable positions. Finally, we discuss fundamental questions that our findings raise for the study of networks in both animals and humans.

Aggressive interactions and consistency of dominance hierarchies of the native and nonnative cichlid fishes of the Balsas basin.

Dominance hierarchies are generally established based on the levels of aggressiveness that animals present. Frequently, animals fight to establish a dominance hierarchy and obtain a disputed resource. The Mexican mojarra Cichlasoma istlanum is a native species of the Balsas river basin and coexists there with four nonnative cichlids: tilapia Oreochromis sp., convict cichlid Amatitlania nigrofasciata, spotcheek cichlid Thorichthys maculipinnis, and green terror Andinoacara rivulatus. These five cichlid species compete for spaces for reproduction, feeding, and shelter and frequently engage in aggressive interactions to obtain these resources. We quantified dominance indices to evaluate the hierarchical structure of dominance among these five cichlids and the duration of aggressive behaviors of the Mexican mojarra during experimental contests between the native species and each of the four nonnative species. The Mexican mojarra was consistently dominant over the other four cichlid species, performing a larger number of aggressive behaviors and investing more time in attacking than the nonnative cichlids, which resulted in a higher hierarchical position. Our results show that the native fish, Mexican mojarra, established dominance over all four nonnative cichlid fish of the Balsas basin. Thus, the establishment of nonnative cichlid species in the Balsas basin is likely associated with factors other than behavioral dominance.

Sexual performance and survival of males of Ceratitis capitata VIENNA 8 (Diptera: Tephritidae) inoculated with a commercial formulation of Beauveria bassiana

AbstractThe Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is a polyphagous pest that feeds upon more than 300 host plants, including fruits and vegetables. To eradicate this pest, the Mexican program (Programa Moscamed) targeting fruit flies applied a novel approach that works with the sterile insect technique (SIT) by inoculating sterile flies with fungal spores of a commercial formulation of Beauveria bassiana (Balsamo) Vuillemin. Dissemination occurs through contact with the sterile insect with wild populations. However, the fungus is known to reduce the homeostatic condition of the vector (sexual and aggressive interactions) to the point that it affects physical contact with the receptor. The objective was to evaluate the effect of B. bassiana on the sexual performance and survival of sterile males of the C. capitata strain VIENNA 8. Mating competition, induction of sterility, production of the sexual pheromone and survival were compared between inoculated and non‐inoculated sterile males. The parameters evaluated were fundamental to evaluate the success in the SIT. The results of the study indicated that the inoculated males with B. bassiana showed a gradual decrease in sexual performance (mating, induction of sterility and production of the sexual pheromone) and survival after treatment. We conclude that for SIT release programs, the effectiveness of targeted males is up to 5 days post‐inoculation. The implications of this biological control method in SIT are discussed.

Behavioural and energetic consequences of competition among three overwintering swan (Cygnus spp.) species

BackgroundWinter numbers of the northwest European population of Bewick’s Swans (Cygnus columbianus bewickii) declined recently by c. 40%. During the same period, numbers of two sympatric and ecologically-similar congeners, the Mute Swan (Cygnus olor) and Whooper Swan (Cygnus cygnus) showed increases or stability. It has been suggested that these opposing population trends could have a causal relationship, as Mute and Whooper Swans are larger and competitively dominant to Bewick’s Swans in foraging situations. If so, effects of competition of Mute and Whooper Swans on Bewick’s Swans should be detectable as measurable impacts on behaviour and energetics.MethodsHere, we studied the diurnal behaviour and energetics of 1083 focal adults and first-winter juveniles (“cygnets”) of the three swan species on their winter grounds in eastern England. We analysed video recordings to derive time-activity budgets and these, together with estimates of energy gain and expenditure, were analysed to determine whether individual Bewick’s Swans altered the time spent on key behaviours when sharing feeding habitat with other swan species, and any consequences for their energy expenditure and net energy gain.ResultsAll three swan species spent a small proportion of their total time (0.011) on aggressive interactions, and these were predominantly intraspecific (≥ 0.714). Mixed-effects models indicated that sharing feeding habitat with higher densities of Mute and Whooper Swans increased the likelihood of engaging in aggression for cygnet Bewick’s Swans, but not for adults. Higher levels of interspecific competition decreased the time spent by Bewick’s Swan cygnets on foraging, whilst adults showed the opposite pattern. When among low densities of conspecifics (< c. 200 individuals/km2), individual Bewick’s Swans spent more time on vigilance in the presence of higher densities of Mute and Whooper Swans, whilst individuals within higher density Bewick’s Swan flocks showed the opposite pattern. Crucially, we found no evidence that greater numbers of interspecific competitors affected the net energy gain of either adult or cygnet Bewick’s Swans.ConclusionsWe found no evidence that Bewick’s Swan net energy gain was affected by sharing agricultural feeding habitat with larger congeners during winter. This was despite some impacts on the aggression, foraging and vigilance behaviours of Bewick’s Swans, especially among cygnets. It is unlikely therefore that competition between Bewick’s Swans and either Mute or Whooper Swans at arable sites in winter has contributed to the observed decline in Bewick’s Swan numbers. Further research is needed, however, to test for competition in other parts of the flyway, including migratory stopover sites and breeding areas.

Is individual temperament related to behaviors in a social context for a Neotropical parakeet species?

The relations of temperament dimensions obtained in tests traditionally used to assess interindividual differences with long-term behaviors and social rank of animals are poorly understood. Here, our aims were: (a) to investigate the relationships between temperament dimensions obtained through behavioral tests and the social rank of white-eyed parakeets (Psittacara leucophthalmus), and (b) to evaluate the relationships between temperament dimensions with social and non-social behaviors in group-housing captivity. Three temperament tests were applied for each parakeet singly: reaction to an unknown person, novel object, and reaction to potential predator tests. Bird’s behaviors during the tests were recorded, generating 13 behavioral variables to which a factor analysis was applied to extract the main dimensions of parakeets’ temperament. Social rank was obtained through the observation of aggressive social interactions for animals kept in groups of four individuals, recording the winner and loser of each event. To extract the dominance hierarchy, we used the Elo-rating and David’s index of dominance (as higher values are more dominant). Pearson’s correlation coefficients were used to investigate the relationships between temperament dimensions with social rank and parakeets’ behaviors in group-housing captivity obtained with the two methods. Individual differences in parakeets in three main temperament dimensions were described (‘vigilance’, ‘boldness’, and ‘responsiveness to humans’). David’s score was significantly correlated with ‘boldness’ (r = 0.63), and a trend was found for Elo-rating (r = 0.54). For the ‘vigilance’ dimension, dominant parakeets based on David’s score (r = 0.53) and Elo-rating (r = 0.55) tended to be more vigilant. Temperament was also related to the behavioral categories in group-housing captivity. Bold parakeets spent more time in preening (r = 0.56), had a higher frequency of negative social interactions (r = 0.64), and tended to spend less time interacting with the environment (r = −0.51). Vigilant parakeets had a lower frequency of positive social interactions (r = −0.55) and spent a lower percentage of time in locomotion (r = −0.55). In conclusion, the temperament dimensions obtained for parakeets through behavioral tests were related to their social rank and the behaviors in group-housing captivity. For captive social psittacids, such as those in rescue centers, temperament could prove useful in decisions about choosing individuals to be housed together, because temperament allows inferences about the dominance of the individuals, avoiding unnecessary disputes and injuries inside the aviaries.

Anthropogenic noise, song, and territorial aggression in southern house wrens

Anthropogenic noise constrains the transmission of birdsong and alters the behavior of receivers. Many birds adjust their acoustic signals to minimize the interference of anthropogenic noise on signal transmission. Birds may also change their acoustic signals to exchange information during aggressive interactions. However, it is unclear how birds deal with a potential trade‐off between adjusting their acoustic signals to better transmit in noisy environments versus mediating aggressive interactions. Additionally, we do not know how urbanization and anthropogenic noise alters the territorial behavior of receivers. We investigated the interplay among song, territorial aggression, urbanization, and anthropogenic noise, in males of the southern house wren Troglodytes aedon musculus, using recordings of spontaneous songs (non‐aggressive context) and a playback experiment simulating a male territorial intrusion (aggressive context). We found that urban wrens behaved more aggressively in response to the intruder by singing more and spent more time closer to the intruder than rural wrens regardless of noise. Males produced songs with lower minimum frequency and trills with wider frequency bandwidth and higher vocal performance under acute (playback) than relaxed (post‐playback) aggressive encounters. These results suggest that males use songs to communicate aggressive intent or fighting ability. Urban wrens produced higher‐pitched songs and trills than rural wrens irrespective of aggressive context. Urban wrens in the noisiest territories also produced the highest‐pitched trills but only in the non‐aggressive context. Rural wrens in the noisiest territories tended to produce the longest songs (non‐aggressive context) or produced the shortest songs (aggressive context). Results suggest that urbanization affects territorial and vocal behaviors in southern house wrens. Males in this species seem to primarily adjust acoustic signals in response to the territorial intruder rather than noise.

Effects of stocking density on a typical crab-clam polyculture system: Behavioral mechanisms of predation and competition in swimming crab (Portunus trituberculatus)

Stocking density determines the performance of polyculture. However, the underlying mechanisms of how density affects the behavior of aquaculture animal are still unclear, especially the predation and competition. Here we selected a typical polyculture system containing predator swimming crabs (Portunus trituberculatus) and prey Manila clams (Ruditapes philippinarum), and examined the influence of stocking density on crab predation, competition, and their interactions. Specifically, we calculated the predation rate, and quantified the foraging behavior and encounter behavior between crabs. Results show that, with increasing stocking density, the predation rate significantly decreased as a result of aggressive interactions between crabs (e.g., fighting and threatening). Increased crab density promoted their competition, which was manifested as an increase in the proportion of time spent on aggression. However, the probability of aggressive behavior upon encounter was reduced to avoid time loss and the risk of injury during aggression. Nevertheless, the prolonged aggressive behavior negatively affected the foraging efficiency, as indicated by an increase in the proportion of handling time and a decrease in the probability of consumption upon capture. While the crabs attempted to compensate for the reduced foraging efficiency by significantly increasing the probability of capture upon encounter, the impacts of aggressive interactions outweighed their coping capacity, rendering a reduction in observed predation rates. The revealing of behavioral mechanisms not only provides an improved understanding of how the stocking density affects the behavior of crabs, but also helps to optimize the management of crab-clam polyculture.

Synthetic Olfactory Agonist Use in the Farrowing House to Reduce Sow Distress and Improve Piglet Survival.

Simple SummaryWithin intensive livestock industries, it is important to pursue the continual improvement of animal welfare. The farrowing crate design in most piggeries is currently the best way to optimize piglet welfare and reduce piglet mortality caused by being crushed by the sow. However, some studies have shown that restriction in a farrowing crate exacerbates sow distress at specific times during farrowing at lactation, which may compromise piglet survival. Therefore, there is a need to investigate strategies that may alleviate the stress experienced by the sow due to being confined. A synthetic olfactory agonist, a commercial product that mimics naturally occurring pheromones, previously reduced aggressive interactions in sows. Therefore, this product was investigated to determine its effectiveness at reducing sow stress and improving piglet survival during birth and lactation. We found no effect on the sow’s stress hormone levels between treatments in response to a stressor. However, first-litter sows experienced a decreased farrowing duration, but this did not extend to improvements in piglet pre-weaning survival. This synthetic olfactory agonist does not appear to be a suitable tool to reduce sow distress around birth or improve piglet pre-weaning survival.The aim of the study was to investigate if the application of a synthetic olfactory agonist (SOA) would reduce indicators of stress in sows, in response to a stressor prior to parturition, and if it would improve farrowing house performance of sows and their piglets. Two studies were conducted: an intensive study with 47 sows, either having their first or second litter (Control n = 24; SOA n = 23); and a commercial validation study with 418 sows, either having their first litter or have had multiple litters (Control n = 210; SOA n = 208). Within the intensive study, sows were housed with or without a synthetic olfactory agonist suspended in the creep area of the farrowing crate, whereas within the commercial validation study, sows were housed with or without a synthetic olfactory agonist suspended over the adjoining creep area of two farrowing crates. Within the intensive study, despite a discernible increase in cortisol concentration in response to a stressor (snout rope test), cortisol response was not different between treatments (p > 0.05). Farrowing duration in first-litter sows exposed to the SOA was decreased (p < 0.001) whilst there was no impact on farrowing duration in second litter sows. Piglets were not attracted by the SOA to increase their utilisation of the creep area and spent more time in proximity to the sow (p < 0.05). Within the commercial validation study, no impacts were seen on piglet production measures (p > 0.05). Largely the use of an SOA within the farrowing house did not impact the sow or her piglets in either the intensive study or commercial validation study. Based on these current results, the use of SOA within the farrowing house is not supported.

Human Decision-Making as a Key Factor in the Risk of Wolf-Dog Interactions during Outdoor Activities.

Simple SummaryThe aim of the study was to determine the nature and causes of direct contact between a wolf and domestic dog during different forms of human recreation. The results are crucial for reducing human–nature conflicts and for education. Thanks to this study, we conclude that humans are responsible for reducing the risk of direct contact between these two canine species. The risk of interaction between wolves and a dog that is with a human depends on the distance between the dog and its owner, the number of wolves, and the size of the dog. Hunting with a dog poses a seven times greater risk of interaction with wolves compared to recreational walking.As a result of species protection in Poland, wolves now appear in places that are attractive for human recreation, increasing their exposure to dogs. This creates a risk of spontaneous direct interactions between these two canine species. Aggressive interactions between the gray wolf and the domestic dog lead to human–large predator conflicts. This study examined wolf–dog interactions using data collected in an online questionnaire and included questions related to factors that might influence the likelihood of interactions between these canines. One of the most important factors affecting the likelihood of interaction between a dog and a wolf was the distance between the dog and the human. The number of wolves was also important—the more wolves, the more likely they were to interact with dogs. The risk of interaction also significantly increases with decreasing distance to human settlements. There were also statistical differences in terms of the type of outdoor activity being engaged in. Hunting was seven times more likely to result in a wolf–dog interaction than normal walk. We postulate that the choices made by the human (dog control and type of recreation) caring for the dog are an important factor that can reduce the risk of direct contact between dogs and wolves.

Resource limitation, intra‐group aggression and brain neuropeptide expression in a social wasp

Abstract Nourishment can have profound effects on social behaviour, including aggressive interactions between individuals. The prevailing theoretical and empirical understanding is that when nutritional resources are limited, inter‐individual competition and aggression will increase. Alternatively, studies from some group‐living species suggest limited nutrition can lead to increased cooperation, including by a reduction in inter‐individual aggression. Thus, a general model for understanding how and why nutritional resource limitation affects aggressive behaviour remains elusive. We suggest that the link between nourishment and future reproductive potential may be a key missing element of models that predict how nutritional resource availability affects inter‐individual aggression in social animals. We investigated how nourishment influenced intra‐colony aggression and its molecular correlates in colonies of the social paper wasp Polistes fuscatus, which contain workers that maintain flexible reproductive potential as adults. We subjected colonies to either a high or low feeding treatment, and examined subsequent effects on behaviour, nutritional/reproductive physiology and brain gene expression. We found that nutritional restriction reduced aggressive interactions. Thus, resource limitation was linked to reduced intra‐group conflict. Thus, individual worker paper wasps appear to have the capacity to adjust their behaviour (e.g. reduced aggression) in response to nutritional stress; this suggests they may invest nutritional resources in the colony when resources are limiting, and in the self (and possible future reproduction) when resources are abundant. Differential brain gene expression results implicate two well‐known neuropeptides associated with aggression and/or nutrient signalling across taxa, Tachykinin and Neuropeptide F, as possible mediators of nutritionally dependent intra‐colony aggression. This adds to a growing understanding that deeply conserved genes associated with core, conserved behaviours such as feeding and aggression in solitary insects can play a role in the regulation of social plasticity in more highly social species. A free Plain Language Summary can be found within the Supporting Information of this article.

Temporal Patterns in Interactions Across Same- and Mixed-Sex Wild Zebrafish Dyads.

Animals communicate with each other through a variety of behavioral interactions, many of which are often complex due to the interplay of several ecological factors. Observations on dyadic interactions can help throw light on the more complex interactions observed among group living organisms and can help in understanding mechanisms of behaviors related to mating strategies, dominance hierarchies, and decision-making. This study focused on the assessment of several generally observed interactions among dyads of different sexes (female-female, male-male, and male-female) in wild zebrafish (Danio rerio). Temporal dynamics of these interactive behaviors were observed in 45 dyads across 3 time intervals of the day. We used generalized linear mixed models to investigate the effect of time, sex of dyad, and their interaction on specific behaviors. While the frequency of occurrence of some behaviors showed clear variation across time intervals of the day, these were further found to depend on the composition of the dyad. Contrary to previous reports, we found that same-sex dyads are equally aggressive and aggressive interactions did not vary temporally. Mating-associated interactions, as expected, were significantly higher in mixed-sex dyads and declined significantly from early morning to afternoon. Interestingly, we also found some mating-associated interactions in same-sex dyads. A fine line exists between social and mating-associated interactions in many organisms and so we speculate that these interactions could also be social interactions and not mating-related behavior. Our findings shed light on complex interactive behaviors among zebrafish, that are likely to be affected by time as well as sex composition of interacting individuals and thus has important implications for groups varying in sex ratios in the wild.

Report of an extra-pair copulation in the Rufous Hornero, Furnarius rufus (Aves: Furnariidae)

In the last decade, studies in bird breeding biology have shown that infidelity is prevalent in socially monogamous species. Here, we describe an extra-pair copulation (EPC) event in the Rufous Hornero (Furnarius rufus), a socially monogamous bird with year-round territoriality and low levels of extra-pair paternity. Before the EPC, a within-pair copulation (WPC) occurred inside the pair’s territory. The WPC occurred on the ground and between a banded male (ca. 6 years-old) and an unbanded female. Ten minutes later this breeding pair invaded a neighboring territory, presumably to forage. The territorial male was chased back to its territory by an unbanded male neighbor after being detected. The male neighbor was paired with an unbanded female that did not participate in the aggressive interaction. When flying back to its territory the male neighbor copulated with the territorial female on the ground (ie. EPC). The territorial male flew, vocalized, and perched above the male neighbor, interrupting the EPC. The aggressive interaction then ceased as each pair resumed foraging in their respective territories. These observations suggest that Rufous Horneros can use EPC to obtain immediate benefits (food access in a neighbor’s territory). Moreover, WPC may be detected by neighbors and physical mate guarding and/or frequent WPC may be necessary to prevent EPC in the Rufous Hornero.

Pervasive low‐frequency vocal modulation during territorial contests in Eurasian Scops Owls (Otus scops)

In several animal species, including birds, individuals are known to produce low‐frequency vocalizations during aggressive interactions with conspecifics. In this study, I investigated territorial interactions between male Eurasian Scops Owls Otus scops that occupied territories in a densely packed area. The single‐note hoot of the Scops Owl is generally thought to be highly repeatable; however, extensive recording of male–male interactions identified previously unrecognized variation in the structure of hoots. Male Scops Owls gave hoots at a frequency lower than usual when engaging in short‐distance contests with neighbouring males. Within‐subject analysis revealed that the caller’s average hoot frequency was positively correlated with the distance from its rival. During contests, males gradually reduced their hoot frequency as they approached one another, perhaps reflecting changes in the degree of escalation. Furthermore, there is evidence that male Scops Owls have voluntary control of their hoot frequency also on a very short time scale. Males gave deeper hoots immediately after the rival initiated countersinging, and returned to their usual frequency range at the end of the interaction. This study confirms in part the findings of other authors’ experimental work, where male owls adjusted their vocal frequency when challenged by an opponent. However, that study suggested that vocal frequency would encode information about the caller’s bodyweight. In contrast, the results of the present study cannot exclude the hypothesis that the hoot of the Scops Owl is a variable, conventional signal that reflects the willingness to escalate the conflict. The reliability of the signal could be maintained by the risk of retaliation by the opponent, usually located a few metres from the caller.

Novel species interactions and environmental conditions reduce foraging competency at the temperate range edge of a range-extending coral reef fish

Poleward range extensions of coral reef species can reshuffle temperate communities by generating competitive interactions that did not exist previously. However, novel environmental conditions and locally adapted native temperate species may slow tropical invasions by reducing the ability of invaders to access local resources (e.g. food and shelter). We test this hypothesis on wild marine fish in a climate warming hotspot using a field experiment encompassing artificial prey release. We evaluated seven behaviours associated with foraging and aggressive interactions in a common range-extending coral reef fish (Abudefduf vaigiensis) and a co-shoaling temperate fish (Microcanthus strigatus) along a latitudinal temperature gradient (730 km) in SE Australia. We found that the coral reef fish had reduced foraging performance (i.e. slower prey perception, slower prey inspection, decreased prey intake, increased distance to prey) in their novel temperate range than in their subtropical range. Furthermore, higher abundance of temperate fishes was associated with increased retreat behaviour by coral reef fish (i.e. withdrawal from foraging on released prey), independent of latitude. Where their ranges overlapped, temperate fish showed higher foraging and aggression than coral reef fish. Our findings suggest that lower foraging performance of tropical fish at their leading range edge is driven by the combined effect of environmental factors (e.g. lower seawater temperature and/or unfamiliarity with novel conditions in their extended temperate ranges) and biological factors (e.g. increased abundance and larger body sizes of local temperate fishes). Whilst a future increase in ocean warming is expected to alleviate current foraging limitations in coral reef fishes at leading range edges, under current warming native temperate fishes at their trailing edges appear able to slow the range extension of coral reef fishes into temperate ecosystems by limiting their access to resources.