Wiley, R. H., and K. N. Rabenold.   1984.   The evolution of cooperative breeding by delayed reciprocity and queuing for favorable social positions.   Evolution 38:   609-621.


The evolution of cooperative breeding, in which nonbreeding members of a group help to raise the breeding members' young, can result from one or more of three possible advantages for helpers: (1) immediate, direct advantages, such as immediate improvement in survival; (2) indirect advantages from kin selection; and (3) delayed, direct advantages for helpers that join a queue for eventual succession to an advantageous reproductive position.

The conditions under which either of the first two kinds of selection can provide a sufficient explanation for the evolution of cooperative breeding are relatively well understood. We have now developed quantitative conditions under which the third sort of selection can provide a sufficient explanation.

More than one of these sources of selection are likely to influence the evolution of cooperative breeding in any particular case. Nevertheless, we need quantitative conditions under which each provides a sufficient explanation in order to understand how the three sorts of selection could complement each other.

Delayed advantages provide a sufficient explanation for helping if joining a queue for a favorable reproductive position and helping to raise the breeding individuals' subsequent young increase the spread of an individual's genes. A complete explanation thus requires conditions (1) for the evolution of delayed breeding, (2) for the curtailment of cheating among helpers, and (3) for the evolutionary stability of queuing behavior.

Delayed breeding can evolve when the eventual reproductive advantages compensate quantitatively for the delay in the onset of reproduction. For a population of stripe-backed wrens in Venezuela, this condition for the evolution of helping is satisfied for males of all ages and for females to age 4.

When helpers contribute to the increased fecundity of breeding members of groups, queuing for succession to breeding status in a group amounts to a special case of delayed reciprocity. The young that an individual helps to raise become the individual's helpers when it succeeds to breeding status in the group. In this special case of reciprocity, cheating by failing to help cannot spread, provided (1) demographic conditions favoring delayed reproduction and queuing for breeding remain the same for successive cohorts and (2) individuals queue for breeding positions.

The evolution of this form of delayed reciprocity thus requires that queuing behavior satisfy the conditions for an evolutionarily stable strategy. Of several possibilities, the one most likely to explain evolutionarily stable queuing in stripe-backed wrens appears to be mutualistic cooperation among acquainted individuals.