Faculty Bibliography

It has been argued that the periodicity (in days) between dental enamel growth lines known as striae of Retzius reflects an autonomic biorhythm regulating metabolism and life history. Therefore, quantifying variation in Retzius periodicity (RP) has been recently used as a tool to provide life history and metabolic information among humans, primates, and other mammals. For example, body size is a major driving factor in life history evolution, and correlates strongly with RP in anthropoid primates but not lemurs. Varying datasets disagree as to whether this particular relationship among anthropoid species extends within species, particularly within modern humans. Moreover, little is known regarding the impact that geography has had on life history evolution among modern human populations. Altitude is one unexamined factor that may have influenced this evolution, as high-altitude human populations exhibit multiple adaptations to their relatively hypoxic environment, and low oxygen availability has obvious consequences for overall metabolic output. Therefore, this study uses RP variation to compare a coastal (low altitude) and Andean (high altitude) sample of Pre-Columbian South Americans. We have two major objectives: 1) determine if RP is correlated with body mass within this previously unsampled group, and more importantly; 2) determine if RP differs between coastal and Andean populations, a possible consequence of life history adaptations to altitude. To answer our questions, we gathered teeth from 10 individuals, 5 each from low and high altitude archaeological sites of Peru, all part of the anthropology collection at the American Museum of Natural History. Teeth were cleaned, embedded in acrylic resin, thin-sectioned, and polished according to standard dental histology protocols. They were imaged in circularly polarized light using a Zeiss Axioskop II microscope. Photomicrographs of dental enamel were used to count the number of 24-hour growth lines (cross-striations) between striae of Retzius, indicating the number of days taken to form each successive stria (RP). An average of cross-striation breadths was also divided into an average of striae of Retzius breadths in the same region of each tooth to verify the counted value. For each individual, orbital height and foramen magnum length were used as proxy variables to assess body size. Individuals were sexed based on standard cranial characteristics. Regressions of RP against body size proxies demonstrate a statistically significant negative correlation in the total combined sample. There is no significant difference in RP variation between the sexes, nor in body size between low and high altitude populations. However, the higher altitude population has significantly longer RP values. In conclusion, our analysis suggests that as predicted, an intraspecific relationship exists for RP and body size among our sample, and that altitude elicits as yet unidentified life history/metabolic differences expressed in RP, warranting further study. The high vs. low altitude pattern appears to be independent of the relationship we find between body size and RP in studies of other human populations

Osteoclasts are large multinucleated giant cells that actively resorb bone during the physiological bone turnover (BTO), which is the continuous cycle of bone resorption (by osteoclasts) followed by new bone formation (by osteoblasts). Osteoclasts secrete chemotactic signals to recruit cells for regeneration of vasculature and bone. We hypothesize that a biomaterial that attracts osteoclasts and re-establishes BTO will induce a better healing response than currently used bone graft materials. While the majority of bone regeneration efforts have focused on maximizing bone deposition, the novelty in this approach is the focus on stimulating osteoclastic resorption as the starter for BTO and its concurrent new vascularized bone formation. A biodegradable tyrosine-derived polycarbonate, E1001(1k), was chosen as the polymer base due to its ability to support bone regeneration in vivo. The polymer was functionalized with a RGD peptide or collagen I, or blended with β-tricalcium phosphate. Osteoclast attachment and early stages of active resorption were observed on all substrates. The transparency of E1001(1k) in combination with high resolution confocal imaging enabled visualization of morphological features of osteoclast activation such as the formation of the "actin ring" and the "ruffled border", which previously required destructive forms of imaging such as transmission electron microscopy. The significance of these results is twofold: (1) E1001(1k) is suitable for osteoclast attachment and supports osteoclast maturation, making it a base polymer that can be further modified to optimize stimulation of BTO and (2) the transparency of this polymer makes it a suitable analytical tool for studying osteoclast behavior.

Quantitative analysis of multi-element concentrations in aqueous solutions, such as water, beverages and biofluids, has long been performed by sequential inductively coupled plasma-mass spectrometry. Recently, a fully simultaneous mass spectrum monitoring ICP-MS instrument that fits a compact Mattauch-Herzog geometry (MH-ICP-MS) with a permanent magnet and a large, spatially resolving semiconductor ion detector has been introduced. This technology allows coverage of the complete inorganic relevant mass range from ⁶Li to ²³⁸U in a single measurement, which helps to mitigate the restriction on the number of inorganic elements whose concentrations may be routinely measured from one sample, thus reducing operational assay times and aqueous sample volumes for evaluations across the breadth of the periodic table. We report here on a detailed method for utilizing MH-ICP-MS to detect all elements of the relevant inorganic spectrum in aqueous samples; 7 types of water, 4 types of beverage, and 4 biofluid biological samples. With this method 71 elements can be routinely detected simultaneously in seconds and in as little as 1-4 mL sample, when using a specific set of calibration and internal standards. Quantitative results reveal distinct element patterns between each sample and within types of samples, suggesting that different types of aqueous solutions can be recognized and distinguished by their elemental patterns. The method has implications for understanding elemental distribution and concentration for many fields, including nutrition, studies of the biosphere, ecological stoichiometry, and environmental health fields, among others, where broad elemental information is actually required.

Studies of variation in orientation of collagen fibers within bone have lead to the proposition that these are preferentially aligned to accommodate different kinds of load, with tension best resisted by fibers aligned longitudinally relative to the load, and compression best resisted by transversely aligned fibers. However, previous studies have often neglected to consider the effect of developmental processes, including constraints on collagen fiber orientation (CFO), particularly in primary bone. Here we use circularly polarized light microscopy to examine patterns of CFO in cross-sections from the midshaft femur, humerus, tibia, radius and ulna in a range of living primate taxa with varied body sizes, phylogenetic relationships and positional behaviors. We find that a preponderance of longitudinally oriented collagen is characteristic of both periosteal primary and intracortically remodeled bone. Where variation does occur among groups, it is not simply understood via interpretations of mechanical loads, although prioritized adaptations to tension and/or shear are considered. While there is some suggestion that CFO may correlate with body size, this relationship is neither consistent nor easily explicable through consideration of size-related changes in mechanical adaptation. The results of our study indicate that there is no clear relationship between CFO and phylogenetic status. One of the principle factors accounting for the range of variation that does exist is primary tissue type, where slower depositing bone is more likely to comprise a larger proportion of oblique to transverse collagen fibers

OBJECTIVES: While dental development is important to life history investigations, data from wild known-aged great apes are scarce. We report on the first radiographic examination of dental development in wild Virunga mountain gorillas, using known-age skeletal samples recovered in Rwanda. MATERIALS AND METHODS: In 43 individuals (0.0-14.94 years), we collected radiographs of mandibular molars, and where possible, cone beam CT scans. Molar crown and root calcification status was assessed using two established staging systems, and age prediction equations generated using polynomial regression. Results were compared to available data from known-age captive and wild chimpanzees. RESULTS: Mountain gorillas generally fell within reported captive chimpanzee distributions or exceeded them, exhibiting older ages at equivalent radiographic stages of development. Differences reflect delayed initiation and/or an extended duration of second molar crown development, and extended first and second molar root development, in mountain gorillas compared to captive chimpanzees. However, differences in the duration of molar root development were less evident compared to wild chimpanzees. DISCUSSION: Despite sample limitations, our findings extend the known range of variation in radiographic estimates of molar formation timing in great apes, and provide a new age prediction technique based on wild specimens. However, mountain gorillas do not appear accelerated in radiographic assessment of molar formation compared to chimpanzees, as they are for other life history traits. Future studies should aim to resolve the influence of species differences, wild versus captive environments, and/or sampling phenomena on patterns observed here, and more generally, how they relate to variation in tooth size, eruption timing, and developmental life history.