Conflict Resolution in Insect Societies

Abstract

■ Abstract Although best known for cooperation, insect societies also manifest many potential conflicts among individuals. These conflicts involve both direct reproduction by individuals and manipulation of the reproduction of colony members. Here we review five major areas of reproductive conflict in insect societies: (a) sex allocation, (b) queen rearing, (c) male rearing, (d) queen-worker caste fate, and (e) breeding conflicts among totipotent adults. For each area we discuss the basis for conflict (potential conflict), whether conflict is expressed (actual conflict), whose interests prevail (conflict outcome), and the factors that reduce colony-level costs of conflict (conflict resolution), such as factors that cause workers to work rather than to lay eggs. Reproductive conflicts are widespread, sometimes having dramatic effects on the colony. However, three key factors (kinship, coercion, and constraint) typically combine to limit the effects of reproductive conflict and often lead to complete resolution. INTRODUCTIONObservation of an insect society readily reveals cooperation. Workers actively work for the good of the colony as they forage, guard, build, and nurse. Detailed study reinforces this impression. Workers cooperate to forage and defend by means of sophisticated communication signals (56,113). In some species cooperation includes extreme altruism, with defending workers sacrificing their lives as they deploy detachable stings or chemical-filled exploding abdomens to deter intruders (56,113). However, sophisticated cooperation in one area of social life does not preclude conflict in another. Egg laying, brood rearing, and queen-worker caste development, for example, can all be associated with significant conflict. Indeed, potential conflict in insect societies is inevitable because insect societies are almost always families, not clones. Nevertheless, conflict in insect colonies is less obvious 0066-4170/06/0107-0581$20.00 581 Annu. Rev. Entomol. 2006.51:581-608. Downloaded from arjournals.annualreviews.org by University of Massachusetts -Amherst on 10/14/09. For personal use only. 582RATNIEKS FOSTER WENSELEERS than cooperation, which suggests that conflict may often be resolved or weak. What factors enable insect societies to resolve their conflicts? In this review, we discuss the large body of work devoted to this question, which has focused primarily on the eusocial Hymenoptera (bees, ants, and wasps). INCLUSIVE FITNESS THEORY: EXPLANATION FOR BOTH COOPERATION AND CONFLICTInclusive fitness theory (47) provides a general explanation for reproductive division of labor in eusocial insects, with some individuals forgoing direct reproduction to help rear the offspring of other colony members. The intermediate levels of relatedness typically found in insect societies provide a strong incentive for altruism, and kin are also close at hand and can readily be helped by defense or food collection. Ironically, the same theory also led to the realization that insect societies are subject to internal conflic...

Altruism in insect societies and beyond: voluntary or enforced?

“…The killing of worker-laid eggs by the queen (queen policing) is also widespread and is particularly common in species with small colonies [5,18]. If policing does coerce altruism by reducing the opportunity for workers to reproduce, we predict that fewer workers should lay eggs in species with more effective egg policing [7,13].…”

“…As we argue here, in many cases it is not. Over the past few decades, several important coercive behaviours have been discovered in insect societies ( Figure 1) [5], ranging from the killing of worker-laid eggs [6] to preventing larvae from developing into queens via food control [1]. In inclusive fitness terms, such coercion promotes altruism because it reduces the benefit of attempting to reproduce directly relative to the benefit of rearing non-descendant kin [7,8].…”

“…Altruism: an action that, on average, decreases the lifetime direct fitness of an actor and benefits one or more recipients [4]. Coercion: social pressure in the form of the punishment or policing of group members, usually to prevent them from acting selfishly and thereby harming the group or colony as a whole; the words enforcement and sanction have similar meanings [5]. Enforced altruism: altruism, or the level of altruism, favoured by natural selection acting on individuals in social groups with coercion [14].…”

“…Evidence for enforced altruism: egg-laying by workers Although worker policing was first discovered in the honeybee [6], it has since been found in several other ant, bee and wasp species [5,18]. The killing of worker-laid eggs by the queen (queen policing) is also widespread and is particularly common in species with small colonies [5,18].…”

Cuticular Hydrocarbons Provide Reliable Cues of Fertility in the Ant Gnamptogenys striatula

“…150 ectatommine and ponerine species, however, the specialized queen caste is rare or absent, and mated workers or "gamergates" take over the role of the queen in some or all of the colonies (Peeters, 1991). Because all individuals in these species are totipotent, i.e., able to mate and reproduce, there is potential for reproductive conflict (Monnin and Ratnieks, 2001;Ratnieks et al, 2006). One expression of this conflict is dominance behavior, which in most species is critical in establishing and maintaining a reproductive division of labor (Ito, 1993;Liebig et al, 1999;Monnin and Peeters, 1999).…”