The major objective of the proposed research is to develop an understanding of the evolutionary origins of morphological differences among tamarin species (genus Saguinus). Tamarins are a highly diverse group of New World Monkeys inhabiting Amazonia and the north coast of South America into Panama. They display a wide range of cranial morphologies. Using previously gathered information on patterns of inheritance of skull form and the phylogenetic relationships among the species, the researchers will test a series of hypotheses concerning the evolutionary origin of morphological differences in this group. The studies will serve as a model for analyzing morphological diversity in primate radiations. First, they will test the hypothesis that cranial variability arose by random evolutionary processes, such as genetic drift or randomly varying natural selection. If this hypothesis is not rejected, it is possible that the diversity observed did not arise by special adaptation to specific environments. Next they will use a well-resolved phylogenetic tree to create a series of phylogenetically-independent contrasts among sister groups. They will describe each of these contrasts using a two-group discriminant function standardized with an estimate of the within-species genetic covariance matrix. Each of these discriminant functions represents the pattern of differences in natural selection required to produce the observed morphological differences between related groups of tamarins. The results will be interpreted using the principles of functional morphology. Specific a priori hypotheses, such as selection on overall size as a source of evolutionary morphological divergence, will also be tested.
