Acoustic communication in zebra finches signals when mates will take turns with parental duties

It is well known that reproductive performance improves with age in birds. Many hypotheses, involving factors such as differential survival, delayed breeding, breeding experience, foraging ability and reproductive effort, have been proposed to explain this pattern. Although these hypotheses are not mutually exclusive, they can be classified in three major groups relating to progressive appearance or disappearance of phenotypes, age-related improvements of competence, and optimization of reproductive effort. However, a closer examination of the literature reveals that only few studies have rigorously tested the hypotheses. Future work should focus on carefully designed tests that critically investigate the hypotheses.

Evolutionary game theory is concerned with the evolutionarily stable outcomes of the process of natural selection. The theory is especially relevant when the fitness of an organism depends on the behaviour of other members of its population. Here we focus on the interaction between two organisms that have a conflict of interest. The standard approach to such two-player games is to assume that each player chooses a single action and that the evolutionarily stable action of each player is the best given the action of its opponent. We argue that, instead, most two-player games should be modelled as involving a series of interactions in which opponents negotiate the final outcome. Thus we should be concerned with evolutionarily stable negotiation rules rather than evolutionarily stable actions. The evolutionarily stable negotiation rule of each player is the best rule given the rule of its opponent. As we show, the action chosen as a result of the negotiation is not the best action given the action of the opponent. This conclusion necessitates a fundamental change in the way that evolutionary games are modelled.