A tale of two theories: parent-offspring conflict and reproductive skew

The recent development of reproductive skew (RS) theory shows striking parallels with that of parent-offspring conflict (POC) theory a decade earlier. In particular, the concept of 'battleground' and 'resolution' models in POC theory is equally relevant to RS theory. The battleground of conflict in POC and RS has been defined by different constraints (which I term 'optimization' and 'group stability' constraints, respectively). This distinction is not inherent but arises simply because POC models assume that the fitness benefits of an increasing share of resource show diminishing returns, whereas skew models assume a linear relation between reproductive share and fitness. Incorporating diminishing returns into skew models reveals a simple and almost wholly neglected explanation for reproductive sharing. Models of POC have moved on from simply defining the battleground to consider how conflict within it is resolved. The development of analogous models for RS theory is at a relatively early stage. In particular, more work is needed to understand the manner and extent to which overt aggression can mediate reproductive control. Lessons learned from attempts to test POC theory can help guide tests of RS theory, and provide information on both the nature of the battleground over reproduction and the mechanism by which conflicts are resolved. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.