Clutch size, fecundity and parent-offspring conflict

Abstract

Selection often acts in different ways on genes expressed in parents and offspring leading to parent—offspring conflict. The effect of parent—offspring conflict on the evolution of reproductive strategies is explored. Models are constructed using kin-selection techniques and it is argued that these are frequently more useful than techniques from classical population genetics. Parent and offspring optima are compared in models of (1) the trade-off between the number and size of offspring, (2) clutch size and (3) the evolution of reproductive effort with age structure. Parent—offspring conflict over clutch size is examined in more detail. Models of sibling competition are reviewed and it is suggested that the reduction in parental fitness caused by sibling competition may lead to selection on clutch size. The possibility that the parent may be selected to produce a hierarchy of sizes of young in order to reduce sibling conflict is investigated. The preliminary results give little support for this hypothesis. An extreme form of sibling conflict, siblicide, is also discussed. In some cases, the kin-selection approach fails in the analysis of siblicide and classical population genetic models are required. The paper concludes that parent—offspring conflict is a potentially significant, and often overlooked, factor influencing the evolution of reproductive strategies. Birds in their little nests agree And ’tis a shameful sight, When children of one family Fall out, and chide, and fight Isaac Watts,Love between Brothers & Sisters, 1721. Birds in their little nests agree With Chinamen, but not with me. Hilaire Belloc,On Food.