Timing of presentation of an audience: aggressive priming and audience effects in male displays of Siamese fighting fish (Betta splendens)

Studies of animal communication often underestimate the presence of individuals other than the signaller-receiver dyad. Signalling interactions often occur in the presence of non-participating individuals (audiences); the effect of these individuals upon the dynamics of interactions has been called the audience effect. Recent studies of fighting fish Betta splendens have shown that the presence of a male audience can increase aggression during interactions. However, in many of these studies males were allowed to see the audience prior to the interaction, thus such pre-exposure may have facilitated aggressive behaviour (aggressive priming). Here we present results of two experiments designed to examine the relative importance of priming and audience effects on the dynamics of aggressive interactions. Males that were pre-exposed showed higher levels of aggression during subsequent interactions regardless of the presence or absence of an audience. When only one of the interactants had been pre-exposed to the audience, the non-exposed male showed similar increases in aggressive behaviour, i.e. matching the level of aggression showed by his opponent. Taken together these results suggest that aggressive priming may have resulted in an over-estimation of the audience effect in previous studies. The results still highlight the importance of social environment in determining the dynamics and outcomes of aggressive contests.     

A community context for aggression? Multi‐species audience effects on territorial aggression in two species of Paridae

1. Territorial aggression in birds is widely observed and is commonly linked to sex, age, body size, physiology, seasonal cues, food resource, urbanization, and a variety of social contexts including conspecific audience effects. However, little is known about the heterospecific audience effects on territorial aggression.
2. Here, we address an emerging idea that heterospecific audience effects may be pervasive influences in the social lives of free‐living birds. We tested the hypothesis that the composition, number, and relative body size of heterospecific audiences observing an aggressive contest will influence the response probability and intensity of aggression displayed.
3. We subjected two Paridae species, tufted titmouse (TUTI, Baeolophus bicolor) and Carolina chickadee (CACH, Poecile carolinensis), to playbacks of aggressive calls during a breeding season in north‐central Florida. At widely spaced playback sites (N = 134) in woodland habitats, we characterized the makeup of heterospecific audiences, aggression type (intra vs. interspecific territoriality), local population density, and various environmental factors (tree density, wind speed, and noise level) that are likely to influence territorial aggression.
4. We found that the presence of heterospecific audiences increased TUTI aggression levels and that both parids were more likely to respond to playback stimuli when their audiences had higher heterospecific diversity (more heterospecific individuals and species). We also found TUTI were more likely to respond when CACH were present but not vice versa.
5. In conclusion, we found evidence that heterospecific audiences significantly influenced the metrics of territorial aggression of free‐living animals and we suggest that the definition of audience effects on the behavior of free‐living animals be expanded to incorporate heterospecific audiences.

     

Heaven it's my wife! Male canaries conceal extra-pair courtships but increase aggressions when their mate watches

Many animals live in a communication network, an environment where individuals can obtain information about competitors or potential mates by observing interactions between conspecifics. In such an environment, interactants might benefit by changing their signalling behaviour in the presence of an audience. This audience effect seems widespread among species, has been observed during various types of interaction (e.g. intra-sexual vs. inter-sexual interaction) and varies according to the social context (e.g. gender, hierarchical or mating status of the audience). However, the way individuals might adapt their signalling behaviour to a combination of these factors remains poorly understood. To address this question, we studied how the presence of an audience affects the behaviour of male domestic canaries Serinus canaria during two types of interactions: (i) an extra-pair interaction and (ii) a male-male competition for food. Males were observed under three conditions: (a) in the absence of audience, (b) in the presence of their mate or (c) of a familiar female. Our results show that male domestic canaries minutely adapt their courting and agonistic behaviours to a combination of: (i) the type of interaction (extra-pair interaction/male-male competition), (ii) the social context (mate, familiar female or nobody in audience) and (iii) the behaviours of both the audience and the interactant. These results highlight the ability of animals to subtly adapt their behaviour to the social environment. This also raises questions about the cognitive foundations and evolution of these processes especially considering that canaries are known neither for having high cognitive abilities nor for being a typical example for the social intelligence hypothesis.     

Sickness behaviour acting as an evolutionary trap? Male house finches preferentially feed near diseased conspecifics

Host behaviour towards infectious conspecifics is a crucial yet overlooked component of pathogen dynamics. Selection is expected to favour individuals who can recognize and avoid infected conspecifics in order to reduce their own risk of infection. However, evidence is scarce and limited to species employing chemical cues. Here, we experimentally examine whether healthy captive house finches (Carpodacus mexicanus) preferentially forage near a same-sex, healthy conspecific versus one infected with the directly transmissible pathogen Mycoplasma gallisepticum (MG), which causes lethargy and visible conjunctivitis. Interestingly, male house finches strongly preferred feeding near diseased conspecifics, while females showed no preference. This sex difference appeared to be the result of lower aggression rates in diseased males, but not in females. The reduced aggression of diseased males may act as an ‘evolutionary trap’ by presenting a historically beneficial behavioural cue in the context of a new environment, which now includes a recently emerged, potentially fatal pathogen. Since MG can be directly transmitted during feeding, healthy males may inadvertently increase their risk of contracting MG. This behaviour is likely to significantly contribute to the continued persistence of MG epidemics in wild populations.     

The ethology of Labroides dimidiatus (cuv. & val.) (Labridae,Pisces) on Aldabra

A small group of Labroides dimidiatus were studied over a period of 4 months in the shallow reef environment of Aldabra. It was found necessary to redefine the concept of a cleaning station. Different sizes of Labroides occupied different types of area and it was found the smallest individuals do not have fixed ranges, but move about beneath available crevices. Larger individuals occupied more open situations and the adults usually lived in pairs. The areas occupied appeared to reflect the fishes' ability to maintain position against strong water movements and tidal currents. Labroides dimidiatus shows territorial, intraspecific aggression and model presentation experiments indicate that body pigmentation acts as the releaser for this aggression. This aggression serves as a dispersal mechanism for young fish. Interspecific aggression occurred against fish with similar body markings to Labroides or which constituted a threat. The cleaning behaviour was studied and it was found that different species of host fish are cleaned in a highly specific manner, and certain hosts are preferred to others. There is evidence that this may be learned as a result of early experience with the host fish. Measurements are made of the cleaning intensity in the area. Some host fish were shown to be attracted to the cleaning range and may adopt invitation postures in the absence of the cleaner. The results are discussed in relation to the recent literature on Labroides dimidiatus and their importance to reef fish populations.     

Contexts and predictability of aggression in chimpanzees

Reasons for aggression may be deduced from the situations preceding aggressive behaviour. This we may call the retrospective approach. In addition to results from this conventional procedure the present paper investigates the predictability of aggressive behaviour. In this so-called anticipatory approach, particular non-agonistic events were used as predictors of aggression. These events had in common that they were intuitively judged to be unpleasant for one of the chimpanzees. This individual was observed during the next 10 min in order to establish if its inclination to exhibit aggression had increased shortly after that seemingly frustrating event. The studies reported here were carried out on a colony of 20 semi-free-living chimpanzees Pan troglodytes in Arnhem Zoo. The data show that: (1) half of all aggressive actions arose in agonistic context: thus aggression was contagious; (2) adult males performed apparent spontaneous aggression remarkably often: this result is suggested to reflect dominance-rivalry among males; (3) aggressive behaviour was predictable on the basis of intuition, but attempts to account for the observer's intuitive knowledge were not entirely successful.     

Coping with social tension: Sex differences in the effect of food provision to small rhesus monkey groups

In previous research, male chimpanzees (Pan troglodytes) were found to be more ‘conciliatory’ than females, in that after aggressive incidents males more often engaged in socially positive contact with former opponents. The first part of the present paper presents similar results for a large breeding troop of rhesus monkeys (Macaca mulatta). To investigate further the possible sex difference in postconflict behaviour, a series of experiments was carried out on small isosexual groups of young rhesus monkeys, three male and three female groups. Food competition was created by providing either a single apple piece (Monopoly test) or a handful of small pieces (Equality test). Observations lasted for 30 min, and behaviour in tests without food provisioning was also recorded. The predicted response to food was an increase in aggression followed by restorative behaviour, such as grooming. In Equality tests both sexes showed similar responses, i.e. increased aggression and decreased grooming and cohesiveness. In Monopoly tests, however, their responses differed. After the aggression increase, which occurred in all groups, males showed a significant increase in grooming and cohesiveness, whereas females showed the (non-significant) opposite trend. Another sex difference was that changes in grooming and aggression frequencies were related to the rank order in female groups, but not in male groups. Since there was no evidence for a direct causal connection between grooming and aggression, a new model is introduced which links grooming behaviour to the type of food provision rather than to the social disturbance by aggression. According to this model inequality in food distribution causes social tensions. Males actively try to reduce these tensions, whereas females do not. Some alternative explanations are also discussed.     

Using video playback to study the effect of an audience on male mating behavior in the Sailfin molly (Poecilia latipinna)

Sexual conflict in poeciliid fishes is well-documented, particularly male sexual harassment and its effects on females. For instance, male attempts to force copulations influence female feeding, energy allocation, and preference for shoaling partners. However, there has been little research conducted to determine how the social environment shapes the occurrence and intensity of sexual harassment. In this study we ask whether an audience male influences the sexual behaviors of a focal male, the correlated feeding time reduction of female Poecilia latipinna, and if the size of the audience male (larger or smaller than the focal male) influences these behaviors. We presented a video of a male, either smaller or larger than the focal male, or an empty tank (control) to a female interacting with a male or female partner and measured feeding times and sexual behaviors. We found that male sexual behaviors increased in the presence of an audience male, especially if the audience male was larger than the focal male. Females fed more in the presence of a partner female than in the presence of a male, which was independent of the audience (i.e., video treatment). Focal female aggression towards the partner female increased with the size of the audience male. The present study shows that an audience male has multiple interacting influences on both male and female behavior.     

Vigilance and social organization in two species of primates

Animals that live in groups may accrue anti-predator benefits by virtue of their association with other individuals. While a number of factors (e.g. habitat quality, group geometry, dominance rank) have been shown to affect the relationship between group living and individual rates of visual vigilance, sociality and vigilance have not been studied specifically in terms of the two competing demands they impose upon an individual's visual time. Two captive groups each of tamarins, Saguinus labiatus, and squirrel monkeys, Saimiri sciureus, were used in three related experiments to determine whether they looked at the social or non-social environment while they engated in a simulated foraging task. The tamarins, whose social behaviour is quite pacific and cooperative relative to the more hierarchical squirrel monkeys, looked at the non-social environment when they visually interrupted their foraging. Squirrel monkeys, however, looked more often at group mates. Detection of predators is probably more likely when an individual directs its attention not to conspecifics, but to the environment. Hence, social organizations in which individuals must pay social attention in order to monitor threats and avoid aggression may reduce individual rates of vigilance for predators. Failure to consider various targets of attention may well overestimate vigilance for predators by including other sorts of attentional phenomena in the measurement of vigilance.     

Aggression in harlequin frogs: male-male competition and a possible conflict of interest between the sexes

Long-term field observations and experimental manipulations were made on a population of harlequin frogs, Atelopus varius, in Costa Rica to document seasonality of intra- and intersexual aggression, determine the function of aggression, and identify the factors that influence success in aggressive encounters. Both males and females defended portions of their home range and exhibited site fidelity. Males were more aggressive towards other males during the pre-breeding and breeding seasons, whereas females were more aggressive towards other females during the post-breeding season. For up to several months prior to oviposition, males attempted to amplex (clasp) females without courtship behaviour, while females chased males from their territories and attempted to dislodge males that amplexed them. In staged encounters the winner was usually the apparent resident, regardless of body size. Frogs from a high-density population were more aggressive than individuals from a low-density population. Subadult males were as aggressive and as likely to win encounters as adult males. The function of aggression seemed to be related to the bizarre reproductives behaviour observed in these frogs. There seemed to be male-male competition for mates, as the operational sex ratio strongly favoured males, oviposition was asynchronous, and amplexus lasted for at least several weeks. Female-female aggression may have been related to defence of foraging or shelter sites, but aggression towards males was likely to be an attempt to thwart unwanted amplexus.     

Territorial aggression can be sensitive to the status of heterospecific intruders

Territorial animals are known to be able to differentiate between intruding individuals posing a low or high threat and adjust their aggressive response accordingly. However, plastic territorial aggression based on recognising individuals with different attributes is typically assumed to be relevant only in the context of conspecific interactions. In this study, we investigated territorial aggression of neotropical cichlid fish in their natural habitat to assess whether responses to different types of individuals of another species can also be plastic. We show that arrow cichlids (Amphilophus zaliosus) adjusted their territorial aggression regarding the status of heterospecific intruders: breeding individuals of Amphilophus astorquii received a lower level of aggression than non-breeders. The same pattern was also found for the two different types of A. astorquii individuals intruding into conspecific territories. These results suggest that heterospecific individuals should not be ignored when considering selection pressures shaping plasticity of aggressive behaviour in territorial animals.     

Maternal yolk androgens stimulate territorial behaviour in black-headed gull chicks

Avian eggs contain substantial amounts of maternal androgens. The concentrations of these yolk androgens are affected by the maternal environment, such as the level of social competition, parasite exposure or food conditions. Since yolk androgens have been shown to affect a wide array of offspring traits, they may adjust the chicks to the expected post-hatching environment, but experimental evidence is still scarce. We investigate in colonial breeding black-headed gulls whether high concentrations of yolk androgens, such as those found in environments with high numbers of social interactions, facilitate aggressiveness and territorial behaviour of the chicks. Black-headed gulls are highly suitable for this, as the semi-precocial chicks defend the natal territory and food against intruders. We manipulated yolk androgen concentrations and investigated their role in both within-nest and between-nest aggression. We found that chicks hatching from androgen-treated eggs defended the natal territory more often than their nest mates from control eggs, without increasing sibling aggression. This suggests that variation in yolk androgen concentrations in relation to the social environment of the mother may indeed allow adjustment of the offspring''s behaviour to the expected frequency of territorial interactions with conspecifics post-hatching.     

Coho Salmon (Oncorhynchus kisutch) Prefer and Are Less Aggressive in Darker Environments

Fish are capable of excellent vision and can be profoundly influenced by the visual properties of their environment. Ambient colours have been found to affect growth, survival, aggression and reproduction, but the effect of background darkness (i.e., the darkness vs. lightness of the background) on preference and aggression has not been evaluated systematically. One-hundred Coho salmon (Oncorhynchus kisutch), a species that is increasing in popularity in aquaculture, were randomly assigned to 10 tanks. Using a Latin-square design, every tank was bisected to allow fish in each tank to choose between all the following colour choices (8 choices in total): black vs. white, light grey, dark grey, and a mixed dark grey/black pattern, as well as industry-standard blue vs. white, light grey, dark grey, and black. Fish showed a strong preference for black backgrounds over all other options (p < 0.01). Across tests, preference strength increased with background darkness (p < 0.0001). Moreover, having darker backgrounds in the environment resulted in less aggressive behaviour throughout the tank (p < 0.0001). These results provide the first evidence that darker tanks are preferred by and decrease aggression in salmonids, which points to the welfare benefits of housing farmed salmon in enclosures containing dark backgrounds.     

Synergistic effects of temperature,diet and colony size on the competitive ability of two ant species

Multiple biotic and abiotic factors influence species coexistence and co‐occurrence patterns. In a competitive environment, for example, temperature and diet variation may modify both foraging behaviour and aggression, thereby changing competitive interactions and species co‐occurrence patterns. In New Zealand, two endemic ant species (Prolasius advenus and Monomorium antarcticum) often form allopatric distributions; though also periodically do co‐occur in the same habitat. Here, we performed a long‐term laboratory experiment in an attempt to understand how diet, colony size and environmental conditions may influence these co‐occurrence patterns. The consequences of temperature and diet variation differed between P. advenus and M. antarcticum. Colonies of P. advenus exhibited increased aggression and foraging activities at higher temperatures. In addition, P. advenus colonies augmented their foraging activities when deprived of a carbohydrate‐rich food source. Conversely, small M. antarcticum colonies exhibited higher aggression than when in large colonies, and increased their foraging activities at lower temperatures. The modulation of aggression and foraging behaviour may influence the likelihood of small P. advenus and M. antarcticum colonies persisting in the long term. Our results are compatible with the hypothesis that the environment is likely to be a strong filter for the negative co‐occurrence patterns we observe between P. advenus and M. antarcticum in New Zealand. Furthermore, this study provides a mechanistic explanation for potential impacts of climate warming on community structure. Environmental modification of aggression and foraging behaviour could potentially alter competitive interactions and influence community assembly.     

Inbred and furious: negative association between aggression and genetic diversity in highly inbred fish

Aggressive behaviour plays an important role in securing resources, defending against predators and shaping social interactions. Although aggression can have positive effects on growth and reproductive success, it is also energetically costly and may increase injury and compromise survival. Individual genetic diversity has been positively associated with aggression, but the cause for such an association is not clear, and it might be related to the ability to recognize kin. To disentangle the relationships between genetic diversity, kinship and aggression, we quantified aggressive behaviour in a wild, self‐fertilizing fish (Kryptolebias marmoratus) with naturally variable degrees of genetic diversity, relatedness and familiarity. We found that in contrast to captive fish, levels of aggression among wild K. marmoratus are positively associated with individual homozygosity, but not with relatedness or familiarity. We suggest that the higher aggression shown by homozygous fish could be related to better kin discrimination and may be facilitated by hermaphrodite competition for scarce males, given the fitness advantages provided by outcrossing in terms of parasite resistance. It seems likely that the relationship between aggression and genetic diversity is largely influenced by both the environment and population history.     

Who's Watching Me: Female Siamese Fighting Fish Alter Their Interactions in Response to an Audience

It is well established that interactions between conspecifics are often influenced by the presence of passive bystanders. Individuals have been found to alter their behavior in a variety of contexts, from foraging to aggression, based on the presence, sex, or identity of an audience. This audience effect may influence not only the nature of a signaling event but also the evolution of signal structure as signals may have to convey information across a distance. Additionally, audience individuals may use information obtained by watching in later encounters with these individuals, which may act as a selection pressure on communication. Communication networks in Siamese fighting fish, Betta splendens, are particularly well studied, with audience effects influencing both male–male interactions and male–female interactions. However, the effects of an audience on female–female interactions have not been examined in this species or any other. This study examined the interactions of pairs of females in three different audience conditions (male, female, and no audience). The results suggest that female–female interactions are affected by the presence of an audience as interactant‐directed gill flaring, the most commonly performed behavior, was performed more with an audience present. Additionally, the sex of the audience seemed to be influential, reflected by a difference in the frequency of interactant‐directed behaviors when a female vs. a male audience was present. This study is one of the first to demonstrate that females modify their behavior as a result of being watched and stresses the importance of examining audience effects in a variety of social contexts.     

Brood-directed parental aggression and early brood loss in the coral reef fish, Acanthochromis polyacanthus (Pomacentridae)

Brood-directed parental aggression, in which parents attack and even kill their own young, is described for the coral reef fish Acanthochromis polyacanthus. This behaviour involves both parents, occurs on days 7–16 post-hatching, and is characteristic of all broods produced early in the spawning season. Such parental aggression appears to underlie widespread early brood loss in the species, i.e. disappearance of young before they reach an age at which they are viable in the absence of parental defence. Simultaneously, there is also a high frequency of sudden increases in the sizes of some tended broods. The data suggest that some brood-tending parents are forcibly expelling their broods from parental territories, and fostering them on to adults still tending broods. By expelling their young and re-spawning, pairs may realize a 7% increase in annual fecundity over pairs that do not expel their young, despite a low survival rate of expelled young.     

Female aggression predicts mode of paternity acquisition in a social lizard

Individual differences in behaviour are ubiquitous in nature. Despite the likely role of selection in maintaining these differences, there are few demonstrations of their fitness consequences in wild populations and, consequently, the mechanisms that link behavioural variation to variation in fitness are poorly understood. Specifically, the consequences of consistent individual differences in behaviour for the evolution of social and mating strategies have rarely been considered. We examined the functional links between variation in female aggression and her social and mating strategies in a wild population of the social lizard Egernia whitii. We show that female Egernia exhibit temporally consistent aggressive phenotypes, which are unrelated to body size, territory size or social density. A female''s aggressive phenotype, however, has strong links to her mode of paternity acquisition (within- versus extra-pair paternity), with more aggressive females having more offspring sired by extra-pair males than less aggressive females. We discuss the potential mechanisms by which female aggression could underpin mating strategies, such as the pursuit/acceptance of extra-pair copulations. We propose that a deeper understanding of the evolution and maintenance of social and mating systems may result from an explicit focus on individual-level female behavioural phenotypes and their relationship with key reproductive strategies.     

Evidence of social niche construction: persistent and repeated social interactions generate stronger personalities in a social spider

While there are now a number of theoretical models predicting how consistent individual differences in behaviour may be generated and maintained, so far, there are few empirical tests. The social niche specialization hypothesis predicts that repeated social interactions among individuals may generate among-individual differences and reinforce within-individual consistency through positive feedback mechanisms. Here, we test this hypothesis using groups of the social spider Stegodyphus mimosarum that differ in their level of familiarity. In support of the social niche specialization hypothesis, individuals in groups of spiders that were more familiar with each other showed greater repeatable among-individual variation in behaviour. Additionally, individuals that were more familiar with each other exhibited lower within-individual variation in behaviour, providing one of the first examples of how the social environment can influence behavioural consistency. Our study demonstrates the potential for the social environment to generate and reinforce consistent individual differences in behaviour and provides a potentially general mechanism to explain this type of behavioural variation in animals with stable social groups.     

Cross-fostering Does Not Influence the Mate Preferences and Territorial Behaviour of Males in Lake Victoria Cichlids

The ability to recognise conspecifics in contexts of mate choice and territorial defence may have large effects on an individual's fitness. Understanding the development of assortative behaviour may shed light on how species assortative behaviour evolves and how it may influence reproductive isolation. This is the case not only for female mate preferences, but also for male mate preferences and male territorial behaviour. Here we test with a cross-fostering experiment whether early learning influences male mate preferences and male–male aggression biases in two closely related, sympatrically occurring cichlid species Pundamilia pundamilia and Pundamilia nyererei from Lake Victoria. Males that had been fostered, either by a conspecific female or by a heterospecific female, were tested for their aggression bias, as well as for their mate preferences, in two-way choice tests. Males cross-fostered with conspecific and heterospecific foster mothers selectively directed their aggression towards conspecific intruders. The cross-fostering treatment also did not affect male mate preferences. These results are in striking contrast with the finding that females of these species show a sexual preference for males of the foster species.