Faculty Bibliography

OBJECTIVES: Great ape teeth must remain functional over long lifespans. The molars of the most folivorous apes, the mountain gorillas, must maintain shearing function for 40+ years while the animals consume large quantities of mechanically challenging foods. While other folivorous primates experience dental senescence, which compromises their occlusal surfaces and affects their reproductive success as they age, it is unknown whether dental senescence also occurs in mountain gorillas. In this article, we quantified and evaluated how mountain gorilla molars change throughout their long lifespans. MATERIALS AND METHODS: We collected high-resolution replicas of M1 s (n = 15), M2 s (n = 13), and M3 s (n = 11) from a cross-sectional sample of wild mountain gorilla skeletons from the Virunga Volcanoes, ranging in age from 4 to 43 years. We employed dental topographic analyses to track how aspects of occlusal slope, angularity, relief index, and orientation patch count rotated change with age. In addition, we measured the relative length of shearing crests in two- and three-dimensions. RESULTS: Occlusal topography was found to decrease, while 2D relative shearing crest length increased, and 3D relative crest lengths were maintained with age. DISCUSSION: Our findings indicate that shearing function is maintained throughout the long lifetimes of mountain gorillas. Unlike the dental senescence experienced by other folivorous primates, mountain gorillas do not appear to possess senesced molars despite their long lifetimes, mechanically challenging diets, and decreases in occlusal topography with age. Am J Phys Anthropol, 2016. (c) 2016 Wiley Periodicals, Inc.

Our objective in this study is to assess variation in Havers-Halberg oscillation (HHO) periodicities among domestic dogs (Canis familiaris). The HHO is hypothesized to be a biological rhythm controlled by the hypothalamus, acting as a central coordinator of multiple life history variables including body size, metabolic rate, and reproductive output. The periodicity of this clock varies among and within species, but not within individuals. It has been studied in detail among primates, though very little among other mammals. In monkeys and apes, the periodicity is strongly correlated with body mass, but lemurs show a restricted range of variation in HHO rhythm despite having a comparable range of body sizes. This raises the question of how HHO rhythms and body size evolution can be decoupled. Domestic dogs represent a potential means to shed light on this area, due to their wide range of body sizes accompanied by low variation in life history variables such as lifespan. Based on this, we hypothesize that dogs will resemble lemurs in HHO variation. To test this, we sectioned teeth of 11 previously deceased Canis familiaris from a university collection, representing a variety of breeds. Teeth preserve a histological marker of the HHO rhythm in the form of growth increments known as striae of Retzius, and the HHO rhythm can be quantified by counting the number of 24-hour growth lines between them. Teeth were cleaned, embedded in acrylic resin, thin sectioned, and mounted to microscope slides following standard dental histology protocols. They were then imaged using circularly polarized light microscopy so that their growth increments could be measured to assess HHO periodicity. Next, HHO periodicity was regressed against body mass estimate data acquired via estimation from mandibular length measurements. As predicted, domestic dogs have a low range of HHO periodicity variation for their body size range, falling between 4 and 6 days (with a modal value of 5). This suggests that dog body size variation is attributed to mechanisms beyond the HHO; conversely, the narrow range of variation in HHO can potentially explain the lack of variation in life history factors such as lifespan among dogs. Since body mass variation among domestic dogs is postulated to result from a mutation in IGF-1, this provides a possible explanation for the high body mass / low HHO variation seen in lemurs as well

A central challenge in human origins research is to understand how evolution has shaped modern human life history. As fossilized remains of our ancestors provide the only direct evidence for life history evolution, efforts to reconstruct life history in paleontological contexts have focused on hard tissues, particularly on dental development. However, among investigators of other vertebrate groups, there is a long tradition of examining primary bone microstructure to decipher growth rates and maturational timing, based on an empirical relationship between the microanatomy of primary bone and the rate at which it is deposited. We examined ontogenetic variation in primary bone microstructure at the midshaft femur of Chlorocebus aethiops, Hylobates lar, and Pan troglodytes to test whether tissue type proportions vary in accordance with predictions based on body mass growth patterns described previously. In all taxa, younger age classes were characterized by significantly higher percent areas of fibro-lamellar and/or parallel-fibered tissues, while older age classes showed significantly higher proportions of lamellar bone. In prior experimental studies, fibro-lamellar and parallel-fibered tissue types have been associated with faster depositional rates than lamellar bone. Principal components analysis revealed differences among taxa in the timing of this transition, and in the particular tissue types observed among individuals of similar dental emergence status. Among M1 and M2 age classes, higher proportions of parallel-fibered and fibro-lamellar tissues were observed in those taxa characterized by reportedly faster body mass growth rates. Further, persistence of fibro-lamellar tissue throughout DECID, M1 and M2 age classes in chimpanzees contrasts with the pattern reported previously for modern humans. Despite the necessary limitations of our cross-sectional study design and the secondary remodeling of bone in primates, large areas of primary bone remain intact and represent a valuable and independent source of information about the evolution of growth and development in the fossil record.

Large-scale patterns evident from satellite images of aeolian landforms on Earth and other planets; those of intermediate scale in marine and terrestrial sand ripples and sediment profiles; and small-scale patterns such as lamellae in the bones of vertebrates and annuli in fish scales are each represented by layers of different thicknesses and lengths. Layered patterns are important because they form a record of the state of internal and external factors that regulate pattern formation in these geological and biological systems. It is therefore potentially possible to recognize trends, periodicities, and events in the history of the formation of these systems among the incremental sequences. Though the structures and sizes of these 2-D patterns are typically scale-free, they are also characteristically anisotropic; that is, the number of layers and their absolute thicknesses vary significantly during formation. The aim of the present work is to quantify the structure of layered patterns and to reveal similarities and differences in the processing and interpretation of layered landforms and biological systems. To reach this goal we used N-partite graph and Boolean functions to quantify the structure of layers and plot charts for "layer thickness vs. layer number" and "layer area vs. layer number". These charts serve as a source of information about events in the history of formation of layered systems. The concept of synchronization of layer formation across a 2-D plane is introduced to develop the procedure for plotting "layer thickness vs. layer number" and "layer area vs. layer number", which takes into account the structural anisotropy of layered patterns and increase signal-to-noise ratio in charts. Examples include landforms on Mars and Earth and incremental layers in human and iguana bones.

OBJECTIVES: Ecological factors have a dramatic effect on tooth wear in primates, although it remains unclear how individual age contributes to functional crown morphology. The aim of this study is to determine how age and individual diet are related to tooth wear in wild mountain gorillas (Gorilla beringei beringei) from Volcanoes National Park, Rwanda. MATERIAL AND METHODS: We calculated the percent of dentine exposure (PDE) for all permanent molars (M1-M3) of known-age mountain gorillas (N = 23), to test whether PDE varied with age using regression analysis. For each molar position, we also performed stepwise multiple linear regression to test the effects of age and percentage of time spent feeding on different food categories on PDE, for individuals subject to long-term observational studies by the Dian Fossey Gorilla Fund International's Karisoke Research Center. RESULTS: PDE increased significantly with age for both sexes in all molars. Moreover, a significant effect of gritty plant root consumption on PDE was found among individuals. Our results support prior reports indicating reduced tooth wear in mountain gorillas compared to western gorillas, and compared to other known-aged samples of primate taxa from forest and savanna habitats. DISCUSSION: Our findings corroborate that mountain gorillas present very low molar wear, and support the hypothesis that age and the consumption of particular food types, namely roots, are significant determinants of tooth wear variation in mountain gorillas. Future research should characterize the mineral composition of the soil in the Virunga habitat, to test the hypothesis that the physical and abrasive properties of gritty foods such as roots influence intra- and interspecific patterns of tooth wear. Am J Phys Anthropol, 2015. (c) 2015 Wiley Periodicals, Inc.

We show that statistical modeling of analytical results is useful in providing insights into metabolism and disease in bioarcheology. Our results also imply that during the Renaissance in Europe widespread pollution of the biosphere with heavy metals such as mercury and lead affected the Italian nobility at that time.The activity of biologic clocks which control metabolism and autonomic nervous system (ANS) function can be gleaned from the analysis of hair. This provides a means of assessing the health of individuals who lived some six centuries before the present and allows the reconstruction of disease from archived tissues such as hair.

The aim of our research is to document osteocyte lacuna density (OCD) and its biological significance among humans of known life history. Twelve human midshaft femurs obtained from sub-Saharan Africans (Malawi) of Bantu origin and known life history were prepared for backscattered electron microscopy in the scanning electron microscope (BSE-SEM). Lacunae have a characteristic size and aspect ratio in BSE-SEM images that allowed them to be identified and automatically enumerated relative to the detected bone area in all of the images processed; values for adult whole femoral midshaft cross sections averaged about 100,000 osteocyte lacunae. Statistical tests reveal significant relationships between both OCD and osteocyte lacuna area with body height. It appears that the same increase in energetic efficiency observed in interspecific comparisons of the mass specific metabolic rate of bone at larger body sizes also characterizes body size categories among humans. Long period biological rhythms that regulate rates of cell proliferation explain some aspects of human body size variability. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.