When should signals of submission be given?-A game theory model

Complex strategies: an integrative analysis of contests in Siamese fighting fish

Background

Animals use contests to attain resources and employ strategic decisions to minimise contest costs. These decisions are defined by behavioural response to resource value and competitive ability, but remain poorly understood. This is because the two factors are typically studied separately. Also, their study relies on overgeneralised assumptions that (i) strategies are fixed, (ii) modulated by the motivation or drive to fight and (iii) used to manage costs proportional to the timing of the loser’s retreat. To address these problems, we adopt an integrative sequential analysis that incorporates competitive ability and resource value factors, to characterise territorial contest decisions in male Siamese fighting fish (Betta splendens).

Results

Individuals exhibited a chronological organisation of behaviour, engaging opponents first with frontal display, then switching to lateral display before deciding to attack, and reserved retreats for later stages. Using asymmetries in retreats as a proxy for outcome, the likelihood of winning was found to be mostly dependent on display. However, resource and contest conditions affected initiation latency, display, attack and retreat, suggesting that strategic decisions influence all behaviour. Overall, sequential behaviour varied consistently with individual aggressiveness and resource-value factors, and increasingly with information on competitive ability collected during the contest. This enabled shifts in tactics, such as disadvantaged individuals responding first with aggression and later with submission. Motivation to continue fighting, after interruption by startle, was also adjusted to information gathered during the contest and progressively with energetic state. Two clusters of correlated behaviours were identified, cost-mitigation (display and retreat) and escalation (initiation and attack), but changes in motivation were associated only with cost mitigation.

Conclusions

Our findings contrast dominant assumptions that strategic decisions are fixed, controlled by motivational state and sufficiently described by outcome-dependent measures. We instead demonstrate that strategic decisions are complex, comprising functional changes in assessment, information use and motivational effects, which are not always inter-dependent.

Subordinate submissive responses are predicted by dominant behaviour in a cooperatively breeding fish

In complex social groups, animals rely on communication to facilitate priority access to resources and minimise the costs of conflict. Animals typically have more aggression signals than submission signals. However, some social species do show multiple submission signals, and the context in which these different signals are used is often not well understood. In the current study, we assessed agonistic interactions within groups of the cooperatively breeding daffodil cichlid fish (Neolamprologus pulcher) to investigate the relationship between the aggressive behaviours of the dominant breeding pair, and the submissive responses of the highest ranked subordinate within the group. Daffodil cichlids may respond to aggression by fleeing or by the production of either a tail quiver display or a head up display. Among the two submission signals, the tail quiver display was used more frequently in response to a threat display, while head up displays were produced approximately equally in response to both threat displays and overt aggression. An exaggerated version of the head up display was given more often in response to overt aggression, suggesting a graded submissive response both within and between the two submission signals. Within fish, the frequency of head up displays, but not tail quiver displays, correlated positively with the frequency of threat displays received. The current study helps us to better understand the use of submission signals in a highly social vertebrate and sheds light on submission as an understudied aspect of communication.

Submission signals in animal groups

Aggression is costly, and animals have evolved tactics to mitigate these costs. Submission signals are an underappreciated example of such adaptations. Here we review submissive behaviour, with an emphasis on non-primates. We highlight the design of submission signals and how such signals can reduce costs. Animal societies necessitate frequent social interactions, which can increase the probability of conflict. Where maintaining group proximity is essential, animals cannot avoid aggression by fleeing. Mutual interest between group members may also select for efficient conflict avoidance and resolution mechanisms. As a result, submission signals may be especially well developed among group living species, helping social animals to overcome potential costs of recurring conflict that could otherwise counter the benefits of group living. Therefore, submission signalling can be a crucial aspect of social living and is deserving of specific attention within the broader context of social evolution and communication.

Head up displays are a submission signal in the group-living daffodil cichlid

Dominance hierarchies can reduce conflict within social groups and agonistic signals can help to establish and maintain these hierarchies. Behaviours produced by subordinates in response to aggression are often assumed to function as signals of submission, however, these behaviours may serve other purposes, for example, defence or escape. For a behaviour to act as a submission signal, the receiver must respond by reducing their likelihood of further aggression towards the signaller. In the current study, we examine the receiver response to a putative signal of submission, the head up display, within established social groups of the cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher). We found that when subordinate signallers produce the head up display in response to aggression from the breeder male, he exhibited a longer latency to behave aggressively towards that individual again. We also report that head up displays are rarely produced without being elicited by aggression, and the number of head up displays correlates with the amount of aggression received. Our results demonstrate that the head up display is used as a signal of submission in the daffodil cichlid and provide insight into intragroup communication in an emerging model system for the study of social behaviour.

Characterization of cell proliferation throughout the brain of the African cichlid fish Astatotilapia burtoni and its regulation by social status

New cells are added in the brains of all adult vertebrates, but fishes have some of the greatest potential for neurogenesis and gliogenesis among all taxa, partly due to their indeterminate growth. Little is known, however, about how social interactions influence cell proliferation in the brain of these fishes that comprise the largest group of vertebrates. We used 5-bromo-2'-deoxyuridine (BrdU) to identify and localize proliferation zones in the telencephalon, diencephalon, mesencephalon, and rhombencephalon that were primarily associated with ventricular surfaces in the brain of the African cichlid fish Astatotilapia burtoni. Cell migration was evident in some regions by 1 day post injection, and many newborn cells coexpressed the neuronal marker HuC/D at 30 days, suggesting they had differentiated into neurons. To test the hypothesis that social status and perception of an opportunity to rise in rank influenced cell proliferation, we compared numbers of BrdU-labeled cells in multiple brain nuclei among fish of different social status. Socially suppressed subordinate males had the lowest numbers of proliferating cells in all brain regions examined, but males that were given an opportunity to rise in status had higher cell proliferation rates within 1 day, suggesting rapid upregulation of brain mitotic activity associated with this social transition. Furthermore, socially isolated dominant males had similar numbers of BrdU-labeled cells compared with dominant males that were housed in a socially rich environment, suggesting that isolation has little effect on proliferation and that reduced proliferation in subordinates is a result of the social subordination. These results suggest that A. burtoni will be a useful model to analyze the mechanisms of socially induced neurogenesis in vertebrates.

Cognitive systems for revenge and forgiveness

Minimizing the costs that others impose upon oneself and upon those in whom one has a fitness stake, such as kin and allies, is a key adaptive problem for many organisms. Our ancestors regularly faced such adaptive problems (including homicide, bodily harm, theft, mate poaching, cuckoldry, reputational damage, sexual aggression, and the infliction of these costs on one's offspring, mates, coalition partners, or friends). One solution to this problem is to impose retaliatory costs on an aggressor so that the aggressor and other observers will lower their estimates of the net benefits to be gained from exploiting the retaliator in the future. We posit that humans have an evolved cognitive system that implements this strategy – deterrence – which we conceptualize as a revenge system. The revenge system produces a second adaptive problem: losing downstream gains from the individual on whom retaliatory costs have been imposed. We posit, consequently, a subsidiary computational system designed to restore particular relationships after cost-imposing interactions by inhibiting revenge and motivating behaviors that signal benevolence for the harmdoer. The operation of these systems depends on estimating the risk of future exploitation by the harmdoer and the expected future value of the relationship with the harmdoer. We review empirical evidence regarding the operation of these systems, discuss the causes of cultural and individual differences in their outputs, and sketch their computational architecture.