The evolution of oviposition behaviour in the bruchid Callosobruchus maculatus.

Callosobruchus beetles lay their eggs on beans and peas, where the larvae spend all of their pre-reproductive lives. Because survival and fecundity of offspring declines as larval competition increases, the decisions made by an ovipositing female have profound effects on her fitness. Natural selection will therefore favour females that distribute their eggs optimally. The present study uses this assumption to identify the key selection pressures acting on the evolution of clutch size in the bruchid Callosobruchus maculatus.
Chapter 1 provides background information on the study species, discusses the problems elaborated on in following chapters and describes some of the methods used.
In Chapter 2, functional models for oviposition behaviour are described in which assumptions about the major constraints on clutch size vary. It is concluded that whilst some models can be distinguished using qualitative criteria alone, others can only be separated after making quantitative predictions.
Chapter 3 tests some of these quantitative predictions and concludes that time is probably the major constraint on clutch size given that several other females will also lay on the same oviposition sites. However, temporal variation in clutch size, especially with respect to the female's phenotype, suggests that the number of eggs available to females may also constrain clutch size.
Chapter 4 examines the cues and rules used by ovipositing females to discriminate between seeds that differ in egg-load or weight. It concludes that females use the surface area of a seed as a cue to its weight and that a common mechanism may be used to distinguish between seeds that differ in egg-load or weight.
Chapter 5 examines possible physiological constraints on clutch size. The rate of egg maturation and the egg-storing capacity (ESC) of the female may be important constraints when seeds are encountered at high rates.
In Chapter 6, these physiological constraints are incorporated into mechanistic models for clutch size determination. In these models, clutch size is determined by the interaction between external cues, such as those identified in Chapter 4, and external cues, implicated in Chapter 5. Models that include physiological parameters explain significantly more of the variance in clutch size than models that include only external cues. Egg-complement relative to ESC appears to be an important factor determining clutch size in this species.
Chapter 7 discusses some of the general conclusions of the study.