Abstract
Coercion is an important but underrated component in the evolution of cooperative behaviour. According to the pay-to-stay hypothesis of cooperative breeding, subordinates trade alloparental care for the concession to stay in the group. Punishment of idle subordinates is a key prediction of this hypothesis, which has received some experimental scrutiny. However, previous studies neither allowed separating between punishment and effects of disruption of social dynamics, nor did they differentiate between different helping behaviours that may reflect either mutualistic or reciprocal interaction dynamics. In the cooperative breeder Neolamprologus pulcher, we experimentally engineered the ability of subordinates to contribute to alloparental care by manipulating two different helping behaviours independently from one another in a full factorial design. We recorded the treatment effects on breeder aggression, subordinate helping efforts and submissive displays. We found two divergent regulatory mechanisms of cooperation, dependent on behavioural function. Experimental impediment of territory maintenance of subordinates triggered punishment by dominants, whereas prevented defence against egg predators released a compensatory response of subordinates without any enforcement, suggesting pre-emptive appeasement. These effects occurred independently of one another. Apparently, in the complex negotiation process among members of cooperative groups, behaviours fulfilling different functions may be regulated by divergent interaction mechanisms.
Highlights
Cooperation theory deals with the central paradox that interactions may involve altruism, which ostensibly cannot evolve by natural royalsocietypublishing.org/journal/rsos R
Four solutions have been proposed to resolve this paradox [2]. (i) Kin-selection theory [3,4] 2 explains cases where cooperating partners have common fitness interests due to shared genes, as exemplified by eusocial organisms. (ii) In mutualistic interactions such as in group hunting predators, individuals may benefit each other as a by-product of purely selfish traits [5,6]. (iii) Alternatively, cooperative behaviour may be demanded from individuals through enforcement by more powerful social partners [5,7,8]. (iv) evolutionarily stable levels of cooperation can result from reciprocal exchanges among cooperating partners [9,10]
Our data show that dominant breeders adjust their level of aggression towards subordinates depending on how much the latter invest into territory maintenance
Summary
Cooperation theory deals with the central paradox that interactions may involve altruism, which ostensibly cannot evolve by natural royalsocietypublishing.org/journal/rsos R. (iv) evolutionarily stable levels of cooperation can result from reciprocal exchanges among cooperating partners [9,10]. (iii) Alternatively, cooperative behaviour may be demanded from individuals through enforcement by more powerful social partners [5,7,8]. These four evolutionary mechanisms are not mutually exclusive. The subordinate, on the other hand, may have outside options and threaten to end the cooperative interaction altogether, thereby putting a limit on what dominants can demand without reciprocating [13,14]. In social cichlids and paper wasps, for example, subordinates provide less help if they are given options to switch to a different group [15,16,17]
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