| Although most investigations into sexual selection have focused on animals with separate sexes, it can also be an important force in animal hermaphrodites. Hermaphrodites have an additional strategy available to them in the face of sexual selection; they are capable of adjusting the ratio of resources invested in mating in the male role versus the female role depending on current sexual selection forces. Sex allocation complicates sexually selected strategies because any increased investment in one sexual role results in a decreased investment in the other. Typical invertebrate hermaphrodites have internal sperm storage organs, which can lead to sexual selection in the form of sperm competition. Body size, which has been left out of most models of sex allocation in simultaneous hermaphrodites, can affect the amount of resources that an individual has for reproduction as well as the size of sperm storage organs and is, therefore, a logical first place to look for differences in strategies within populations.; Chapter One provides a theoretical model to predict sex allocation in a population of simultaneous hermaphrodites with body size variation. The results of the mathematical model demonstrate that optimal hermaphroditic strategies vary within populations with body size and depend on the traits of the individual, the current mate and the population at large. Opisthobranch sea slugs, which show an astonishing diversity of mating patterns, are used as a model system to investigate the effects of body size on hermaphroditic mating strategies. Chapter Two investigates the effect of body size on mating patterns in the sea slug Alderia modesta through laboratory mating experiments and allozyme paternity analysis. Chapters Three and Four describe the growth, seasonality, spatial patterns, mating patterns and individual movements in a field population of the black sea hare, Aplysia vaccaria . In Chapter Five a field study of mating patterns combined with microsatellite paternity analysis investigates the effect of body size on reproduction in the California sea hare, Aplysia californica. Empirical findings support the prediction that body size is an important determinant of mating strategies, leading to size-assortative mating, size biases in mating roles, and size effects on gamete production. |
