Introduction

It is now almost three decades since sperm competition was defined in terms of competition between the ejaculates of two or more males for a given set of eggs (Parker 1970). That article reviewed the evidence in insects and suggested a variety of ways in which the selective pressure of sperm competition may shape a range of adaptations across behavioural, physiological and morphological levels. Sperm competition is now accepted as a discipline in its own right, and currently attracts considerable interest. In addition to a host of papers, there exist four books on the subject (Smith 1984; Birkhead & Møller 1992, 1998; Baker & Bellis 1995) and others are in preparation.

Interest has focused on both empirical and theoretical aspects of sperm competition, and our own contribution has mainly related to the formulation of a prospective theoretical basis. We wish in this chapter to summarise the current theoretical models and their predictions on one specific aspect of this work: the economics of sperm allocation by males in relation to the information available to them. We stress that our concept of ‘information’ is a broad one. We include information in the form of cues correlating with the risk or intensity of sperm competition, perceived by a given male at the time of mating, and also include ‘information’ in the sense of a ‘self-knowledge’ (an adaptive response in relation to a given male's personal circumstances or state). In order to do this we compare predicted sperm allocation patterns in the absence of information with those predicted under specific information regimes.