The hands and feet of haplorhine primates (apes and monkeys) have similar intrinsic proportions that tend to correlate with their habitat and mode of locomotion. For example, arboreal quadrupeds (e.g. New World monkeys) have hands and feet with long digits in relation to the palm or sole, and a relatively long first digit enabling a secure grasp on small arboreal supports. Suspensory primates such as gibbons hang below arboreal supports by combinations of forelimbs and hindlimbs, and their extremities have long, curved phalanges. Among terrestrial species, digitigrade quadrupeds (e.g. papionins) have short straight phalanges relative to the metapodials (metacarpals and metatarsals). Remarkably, even humans have similarly proportioned extremities, despite the fact that their hands and feet perform different functions. Human hands and feet are short in relation to the limbs, with short, robust metapodials, short lateral phalanges and a proportionately longer first digit (great toe and thumb). NSF support will allow Campbell Rolian to test whether these skeletal similarities between hands and feet in haplorhines are the result of selection for similar functions, or whether underlying developmental phenomena such as pleiotropy (when one gene locus affects multiple aspects of the phenotype) cause hand and foot bones to be more strongly correlated with each other than with other parts of the skeleton. Pleiotropic effects between hand and foot developmental genetic programs can have potentially conflicting roles in the evolution of digit morphology. When hand and foot digits evolve to perform similar locomotor functions, pleiotropy should facilitate correlated changes in morphology. However, when hand and foot digits evolve to perform separate functions, then pleiotropic effects may constrain the independent evolution of digital shape in the hands and feet. Campbell will collect morphometric data from the bones of the hands and feet of over 500 individuals from 13 taxa, selected to represent the diversity of locomotor behaviors and breadth of evolutionary relatedness among haplorhines. These data will be used to compare patterns of phenotypic covariation within and between species, testing hypotheses about the importance of function vs development in driving the independent evolution of digit morphology in primates. Significance and Broader Impacts: Few studies have addressed empirically how developmental constraints may bias natural selection for morphological divergence. Campbell will address this important question by looking at covariation in haplorhine hands and feet. Using primate limb skeletons as a case study, this project will provide broader insight into the patterns and processes of vertebrate morphological evolution, particularly as they relate to the growing field of evolutionary developmental biology (evo-devo). This project also has important implications for the study of human evolution. For instance, results may provide evidence that human hands and feet did not evolve their intrinsic proportions independently. Such information will be critical for testing long-standing hypotheses about the selective history of manipulative ability and bipedalism in the hominin lineage. Additional broader impacts of the study include providing teaching tools for undergraduate education, and the creation of a valuable digital archive of primate hand and foot skeletons. Through publications in peer reviewed journals and presentations at interdisciplinary conferences, this project will also help integrate graduate training and research in physical anthropology with evolutionary developmental biology.
