The evolution of larval competition strategies in Callosobruchus maculatus and C. analis.

Callosobruchus maculatus and C. analis present an interesting problem to the evolutionary ecologist. The larvae of both species complete their development within the seeds of various legumes such as black-eyed beans. However, the two species compete over the resources within the bean in very different ways. C. maculatus larvae compete in a scramble process; the larvae avoid each other within the bean and several adults can emerge from a single bean. In contrast the larva of C. analis compete actively within the bean, seeking each other out and fighting until only one larva is left alive. As a consequence, only a single C. analis adult will emerge from each bean, no matter how many larvae were initially present. In this thesis I try to determine the types of selective forces that can cause two species to evolve such different competition strategies when competing over similar resources.
In Chapter 3 it is suggested that differences in the cost of exploitation competition suffered by the two species could explain why they originally evolved different larval competition strategies, but that these differences are not enough to maintain the strategies under current conditions. It is suggested that historical constraints may have limited C. analis to using an ancestral contest competition strategy that is maladaptive on the large hosts which this species currently uses.
In chapter 4 the effect of host size on the cost of exploitation competition is investigated further. As expected, the cost of exploitation competition increases as bean size decreases.
In chapter 5 the cost of fighting is measured for C. analis larvae. Although the fitness of a larva that fights over a bean and wins is affected by having fought, the magnitude of the effect is small, and probably of little evolutionary consequence.
In chapter 6 a game theory model is presented that investigates the effect of asymmetries in fighting and passive competitive ability on the evolution of competition strategies. The results suggest that such asymmetries will increase the possibility that aggressive competition strategies will evolve and could also explain the conditional strategies used by some strains of C. maculatus.
In chapter 7 a genetic model is presented that investigates the effects of population structure on the evolution of competition strategies. The results of the model suggest that the patchy population structure, typical of stored product pests such as Callosobruchus beetles, can favour the evolution of scramble competition strategies.
Finally the factors that may affect the competition strategy that a species evolves ~e discussed in more general terms.