The Genetic Evolutionary History of the Mammalian Skeleton
An interdisciplinary approach
We are interested in the genetic basis of mammalian skeletal variation and evolution with a focus on primates. This requires a two-pronged approach that integrates quantitative genetics with paleontology.
Quantitative genetic analyses of dental variation on the pedigreed populations of baboons and mice enable us to model statistically how genetic, non-genetic, and covariate effects contribute to the overall population variation in traits such as tooth size, enamel thickness, and extra cusps. QTL analyses are used to identify chromosomal regions that may contain genes that determine some of this variation.
These genetic data can be integrated with the fossil record to study morphological (phenotypic) evolution from a genotypic perspective. The rich African fossil record documenting the last 10 million years of Old World monkey evolution reveals when--and in what order--dental morphological changes occurred. Our research on the modern baboons provides insight into the genetics that underpin the anatomical variation, allowing us to reconstruct the genetic evolutionary history of the primate dentition through interpretation of the fossil record. The integration of paleontological, genetic, and neontological information will consequently allow the evolution of the dentition to be reconstructed at a larger scale through the consideration of changes in selective pressures involving ecological and/or dietary shifts. By studying multiple mammalian taxa (mice and baboons), we are able to test the pervasiveness of these genetic architectures (and thereby, whether or not they may also characterize other extant and extinct taxa).
Our laboratory research is directly complemented by active field paleontology research programs in Kenya, Tanzania and Ethiopia, and by comparative studies on modern and fossil primates in North American and African museums.
Field Paleontology
Our primary field project is the Tanzanian International Paleoanthropological Research Project. TIPRP is co-directed by Drs. Hlusko and Jackson Njau (National Natural History Museum, Arusha, Tanzania). Tanzania remains relatively unexplored in terms of human evolutionary research. All of the known sites that have yielded remains of our ancestors are located in the north, such as Olduvai Gorge and Laetoli. We studied recently released NASA satellite imagery and geological maps and found potentially fossiliferous sediments in areas that have not yet been explored for their paleoanthropological potential. Our goal is to inventory and document previously unknown localities.
Quantitative Genetics
Baboons: In collaboration with scientists at the Southwest Foundation for Biomedical Research in San Antonio, Texas, we are investigating the genetic mechanisms underlying baboon dental variation. These analyses enable us to estimate heritability of and genetic covariance between dental traits based on the known familial relationships of more than 3,000 baboons in this colony. Additionally, genetic linkage analysis are performed in order to search for regions of the genome that possibly contain genes that underlie this variation. These quantitative genetic analyses are designed to complement and inform studies of baboon evolution and dental development.
Mice: We are also undertaking quantitative genetic analyses of skeletal and dental variation in mice in order to compare the genetic architectures of various phenotypes between these two fairly diverse taxa. The study sample is an outbred population of mice collected and bred by Richard Sage. The collection was skeletonized and is now housed in the Museum of Vertebrate Zoology. Analyses are just in the inital stages, but we are already finding similarities between them.