Chapter 13 Summary

Social integration entails cooperating, giving aid, and synchronizing activities with other individuals. Because these behaviors usually involve a cost to the donor, they will not evolve unless there is a compensatory benefit. Models of cooperation are based on either indirect genetic benefits via kin selection or greenbeard altruism, or on direct benefits arising from mutualism, synergism, or reciprocity.
Integration signals typically involve requests for aid by the sender and donation of aid by the receiver. Under most cooperation models, the receiver must bestow the aid on a known target individual to benefit, so recognition of the sender is essential. The process of recognition has three components: production of an identifying signal, cue, or label; perception of the signal, which entails comparison of the received signal against a previously acquired template of the target recipient; and some action by the donor based on a threshold decision rule to accept or reject the target. Donors acquire a template of the target through association with a spatial location, familiarity (associative learning of the target individual’s characteristics), phenotype matching, or genetically-linked recognition tags.
Identity signals evolve when a potential recipient of aid or cooperation benefits from making its true identity known to donors. In response, donors evolve fastidious discrimination abilities to identify desirable target recipients when the cost of aiding random individuals is high. Signals in all modalities can be designed to encode individually distinctive signature information by increasing their complexity and the number of variable orthogonal components. Identity signals serve functions in territory defense, parent–offspring communication, pair coordination, family and group cohesion, and status signaling.
Mate recognition spans three levels. Species recognition entails distinguishing conspecific from nonconspecific members of the opposite sex. Species-distinctive signals arise as populations diverge and adapt to local ecological conditions. Sexual selection can also drive speciation and lead to species-specific signals. Mate-quality recognition is the mechanism by which good-quality mates are identified. Many species appear to possess multivariate mate attraction signals, with some less variable static components under stabilizing selection providing species identity information and other more variable dynamic components under directional selection providing mate quality information. Whether receivers use these two components with a hierarchical rule to first select conspecifics and then evaluate quality, or combine them into a one-dimensional preference function and apply an acceptance threshold, remains controversial and probably varies among species. Partner recognition is found in species that form male–female bonds for the purpose of cooperative reproduction. Partners develop distinctive signals that help them to find each other in a crowd of other conspecifics.
Extended male–female partnerships form when males are selected to help females care for offspring. Highly synchronized visual and acoustic mutual displays evolve to facilitate continued mate evaluation; recognition and greeting after a separation; cooperative territory defense; and mate guarding against same-sex rivals. Tactile interactions such as allogrooming and huddling not only serve a hygienic function but also may reduce aggression between pair mates. Sequential displays between breeding pairs help to synchronize male and female hormonal cycles and coordinate reproductive episodes. Pairs may improve the efficiency of their joint parental care efforts by employing negotiation rules to arrive at a final allocation of effort or by communicating and coordinating their trips to the brood with food.
Species with parental care require parent–offspring recognition mechanisms to identify their own offspring and to avoid bestowing costly care on nonoffspring. The mechanism employed depends on the rate of offspring development, type of nest or roost site, family size, degree of sociality, and foraging strategy. When immobile young are raised in a nest, nest location cues are used to identify offspring, but once the offspring become mobile and mingle with those of other parents, one or both parties typically evolve distinctive individual signature signals and refined discrimination abilities. Mutual recognition between parents and offspring evolves when the offspring of many parents are placed in a crËche. When broods are very large and isolated in a nest or burrow, a shared family identity signal is favored over individual identity information.
Parents and offspring disagree to a certain extent over the amount of parental investment to be provided, with offspring preferring more than the parent is optimally selected to give. The best examples of parent–offspring conflict are brood sex ratio conflict between queens and workers in hymenoptera and genomic imprinting in mammals. Two categories of offspring begging models offer potential resolutions to the conflict over offspring provisioning. Honest signaling models view begging as an informative signal of offspring need, which parents use to allocate food delivery. Sibling scramble competition models assume that begging is a strategy of jostling for food brought to the nest by the parent and view begging vigor as an indicator of offspring quality. These two processes mark the endpoints of a continuum from high to low parental power; which one prevails depends on the number of parents, the size of the brood, the style of food delivery, the availability of food, and the age of the offspring.
Multimodal begging signals by dependent offspring to parents usually increase in vigor as a function of offspring hunger. In response to begging for food, parents typically increase their rate of food provisioning. But food is not always selectively delivered to the hungriest offspring in the brood. Instead, it may be given to the largest or strongest sibling. Siblings may negotiate among themselves or collaborate to reduce competitive costs and increase parental care. Parents also signal to their offspring. Directive signals are given to mobile broods to maintain cohesion, identify appropriate food, and warn against predators. Parents in a few species teach their offspring about food handling and environmental hazards.
Mechanisms of group-mate recognition in animals that live in cooperative societies depend on group size and stability. When groups are relatively small and stable in composition, group-mate recognition can be based on associative learning of individual signature traits. Some long-lived species with fission-fusion societies can still manage group interactions based on individual recognition and long-term memory. When groups are large and associated with a nest, as in social insect colonies, recognition is based on an acquired group label or badge. Within social insect colonies with multiple queens or sires, there is an absence of subfamily discrimination, caused by selection for a high tolerance threshold, muting of identity cues, or active scrambling of recognition cues. Large fluid flocks and herds do not require group identification and instead may use status and age badges to mediate associations and aggressive interactions.
Appeasement signals reduce costly aggression within stable groups. Subordinates give submissive signals to suppress attacks by dominants, and dominants give conflict-avoidance displays indicating benign intentions as well as reassurance displays to subordinates. After a conflict, competitors often engage in reconciliation, or other individuals may offer third-party consolation. Allogrooming serves to reduce tension and reaffirm bonds and future cooperation between valued reciprocating group members, in addition to its obvious hygienic function. Greeting ceremonies are common during reunions in fission-fusion societies. Greeting in female primates often entails hugging and kissing, whereas in male primates and dominant female hyenas, the displays are more ritualized and often involve genital touching.
Members of stable mobile groups must reach a consensus in deciding when and where to move next. Such decisions may be made by a large fraction of the group (democratic) using a quorum-sensing mechanism to assess when a majority threshold has been reached. Alternatively, a small fraction of the group (oligarchic) or a single leader (despotic) may make the decisions, which other group members must accept despite potential conflicts of interest. Once groups are on the move, they employ visual cues or acoustic contact signals to maintain group cohesion.
Cooperative breeding systems range from egalitarian mutual care of a joint brood to skewed rearing of a single individual’s offspring by nonreproductive helpers. Egalitarian systems show evidence of competition during egg laying, but thereafter employ a variety of signals to coordinate territory and nest defense, parental care, and provisioning of the young. In skewed systems, helpers are closely related to the breeder, and selection favors suppression of conflict and highly efficient organization. Large colonies of eusocial insects employ division of labor based on age to allocate worker effort to different tasks. Worker activities are controlled not by central commands but by a self-organizing system of simple rules and individual decision making based on a large number of cues plus a few signals.