Negotiation over offspring care - how should parents respond to each other's efforts?

Models of biparental care predict that parents should compensate incompletely for any change in their partner's investment. Experimental tests have, however, yielded results that range from full compensation, through a lack of any reaction, to a matching response. Here we suggest a new, adaptive explanation for such variation. Building on an approach developed by McNamara et al., we incorporate uncertainty regarding brood need or value into a game-theoretical model of biparental negotiation over offspring care. We show that when each parent has only partial information, greater effort invested by one serves as a signal to the other of brood need. This favors a matching response by the focal parent's mate, whereas the impact of increased effort on the marginal value of investment favors a compensatory response. The net outcome depends on the relative strength of these two effects. The greater the variation in brood need compared with parental state, the weaker the predicted level of compensation, and the more likely matching is to occur. Our model also suggests why males and females might respond differently to each other. If there is an informational asymmetry between them, then the parent that is better informed about brood need should work harder, respond more strongly to changes in brood need, be less sensitive to changes in the cost of feeding, and compensate more strongly for changes in partner effort. If the asymmetry is very great, the poorly informed parent may even match changes in its partner's work rate.