DISSERTATION RESEARCH: Evolution and Development of Polyphenism in the Beetle Onthophagus taurus

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In most species of animals there is a fairly constant relationship in the relative sizes of body parts for all individuals. In some species, however, it is the normal condition that some fraction of individuals is disproportionately shaped when compared to others in the same species. These differences in the size, and also shape, of body parts occurs in a wide variety of organisms and could be controlled by genetic, developmental or ecological factors. This research will examine the importance of such factors in the rapid evolution of body shape in the beetle Onthophagus taurus. Male O. taurus that exceed a critical body size develop a pair of spectacular horns on their heads, while those smaller than this threshold remain hornless. Several recently established O. taurus populations have diverged dramatically in this critical threshold body size. This project combines ecological and morpholgical approaches with studies on the developmental mechanisms that control growth and proportionality of body parts. Evolutionary changes of mechanisms controlling development may play a pivotal role in speciation and the origin of biodiversity. This project will provide important insights into how environmental conditions can foster modifications of developmental control mechanisms in natural populations. Such knowledge is crucial for evaluating the role of developmental processes in the origin of morphological diversity.