Christopher J. Vinyard’s research while affiliated with Ohio University and other places

Tusks are ever‐growing teeth present in mammals of the clade Paenungulata. Unlike the perpetually growing incisors of rodents, tusks are not used in mastication, and in at least some paenungulatans, the tusk is composed of dentin alone in adults. Few studies have provided tissue‐level information on tusks of adult paenungulatans with embedding techniques that identify epithelial and other soft tissues. In order to examine the mineralized tissues as well as the cells that form teeth, we studied a single, subadult rock hyrax (Procavia capensis) using microCT and paraffin histology with traditional staining as well as RUNX2 immunohistochemistry, and compared its teeth to scans of adult hyraxes. Three‐dimensional reconstructions from microCT volumes revealed that the tusk of this specimen is the only fully erupted replacement tooth, the first adult premolar (P1) is starting to erupt, and the first permanent molar (M1) is fully erupted, whereas all other replacement teeth and M2 remain in crypts. The tusk has a thin layer of enamel on its dorsal side; this is confirmed by histology. All deciduous premolars still possess roots that are in the process of resorption. Amelogenesis has progressed to maturation or nearly so in P1–P3. Notable histological characteristics of replacement premolars include the lack of a stellate reticulum in all except P4, and expression of RUNX2 in ameloblasts, a marker which is expressed by ameloblasts at all stages of amelogenesis. Since the pulp chambers of replacement premolars are relatively large compared to adults, a lengthy time in crypts may be important for dentin production. The results confirm that the hyrax has thin enamel on tusks, supporting the hypothesis that enamel is of limited importance for non‐feeding behaviors.

In primates and other mammals, the capacity to generate a wide maximum jaw gape is an important performance variable related to both feeding and nonfeeding oral behaviors, such as canine gape display and clearing the canines for use as weapons during aggressive encounters. Across sexually dimorphic catarrhine primates, gape is significantly correlated with canine height and with musculoskeletal features that facilitate wide gapes. Given the importance of canine gape behaviors in males as part of intrasexual competition for females, functional relationships between gape, canine height, and musculoskeletal morphology can be predicted to differ between the sexes. We test this hypothesis by investigating sex-specific relationships among these variables in a maximum sample of 32 cercopithecoid species. Using phylogenetic least squares regression, we found that, of 18 predicted relationships, 16/18 (89%) were significant in males while only six (33%) were significant in females. Moreover, 15/18 correlations were higher—10/18 significantly higher—in males compared with females. Males, but not females, showed strong and significant positive allometry of fiber lengths, indicating that increase in male jaw length is accompanied by allometric increases in the capacity for muscle stretch. While males and females showed significant negative allometry for muscle leverage, only males showed significant negative allometry of muscle leverage relative to jaw gape and canine height. Collectively, these results provide support for the hypothesis that as selection acted to increase relative canine height in male cercopithecoids, one change was an allometric increase in relative maximum jaw gape, along with allometric increases in musculoskeletal morphologies that facilitate gape. Lastly, if gape and canine display/clearance are key targets of selection on masticatory morphology in male cercopithecoids, then cercopithecoid monkeys like macaques, baboons, and sooty mangabeys may have diminished utility as models for drawing paleobiological inferences from musculoskeletal morphology about feeding behavior and diet in fossil hominins.

Objectives This study aims to quantify the areas of most concern in medical students in relation to their residency application in the setting of the COVID-19 pandemic and to identify risk factors for all that cause concern and specific areas of concern in a population with well-established high rates of anxiety at baseline. The COVID-19 pandemic introduced sweeping changes to medical education that had wide-ranging effects on medical students and their applications for medical residencies. Methods In August 2020, we utilized a cross-sectional study to quantify student’s areas of concern related to residency application related to the COVID-19 pandemic. We asked participants to rate their levels of concern in 15 different aspects related to medical residency applications and the perceived impact that COVID-19 had on each. Results The survey was distributed to 984 osteopathic medical students, with 255 complete responses. The three areas of greatest impact were shadowing opportunities (4.15), volunteer opportunities (4.09), and conferencing opportunities (4.09). The most salient demographic variables were year in school, sex, and locale. Females reported higher levels of concern across all categories in the study compared to males, with statistical significance across all categories (all p<0.05, Range d=0.16 to 0.43), except for letters of recommendation and sub-internships. Conclusions The areas of most concern identified in our study were consistent with prior studies and may implicate the pressures that female medical students may feel compared to their male counterparts. The underlying cause(s) may be subject to future research.

Systems of the body develop in a modular manner. For example, neural development in primates is generally rapid, whereas dental development varies much more. In the present study, we examined development of the skull, teeth, and postcrania in a highly specialized leaping primate, Galago moholi . Eighteen specimens ranging from birth to adult were studied. Bones, teeth, and the cranial cavity (i.e., endocast) were reconstructed with Amira software based on microCT cross‐referenced to histology. Amira was also used to compute endocast volume (as a proxy for brain size). Reconstructions of the wrist and ankle show that ossification is complete at 1 month postnatally, consistent with the onset of leaping locomotion in this species. Endocranial volume is less than 50% of adult volume at birth, ~80% by 1 month, and has reached adult volume by 2 months postnatal age. Full deciduous dentition eruption occurs by 2 weeks, and the young are known to begin capturing and consuming arthropods on their own by 4 weeks, contemporaneous with the timing of bone and ankle ossification that accompanies successful hunting. The modular pattern of development of body systems in Galago moholi provides an interesting view of a “race” to adult morphology for some joints that are critical for specialized leaping and clinging, rapid crown mineralization to begin a transitional diet, but perhaps more prolonged reliance on nursing to support brain growth.

Skeletal muscle fibre architecture provides important insights into performance of vertebrate locomotor and feeding behaviours. Chemical digestion and in situ sectioning of muscle bellies along their lengths to expose fibres, fibre orientation and intramuscular tendon, are two classical methods for estimating architectural variables such as fibre length (Lf) and physiological cross‐sectional area (PCSA). It has recently been proposed that Lf estimates are systematically shorter and hence less accurate using in situ sectioning. Here we addressed this hypothesis by comparing Lf estimates between the two methods for the superficial masseter and temporalis muscles in a sample of strepsirrhine and platyrrhine primates. Means or single‐specimen Lf estimates using chemical digestion were greater in 17/32 comparisons (53.13%), indicating the probability of achieving longer fibres using chemical digestion is no greater than chance in these taxonomic samples. We further explored the impact of sampling on scaling of Lf and PCSA in platyrrhines applying a bootstrapping approach. We found that sampling—both numbers of individuals within species and representation of species across the clade significantly influence scaling results of Lf and PCSA in platyrrhines. We show that intraspecific and clade sampling strategies can account for differences between previously published platyrrhine scaling studies. We suggest that differences in these two methodological approaches to assessing muscle architecture are relatively less consequential when estimating Lf and PCSA for comparative studies, whereas achieving more reliable estimates within species through larger samples and representation of the full clade space are important considerations in comparative studies of fibre architecture and scaling.

As bones age in most mammals, they typically become more fragile. This state of bone fragility is often associated with more homogenous collagen fiber orientations (CFO). Unlike most mammals, bats maintain mechanically competent bone throughout their lifespans, but little is known of positional and age‐related changes in CFO within wing bones. This study tests the hypothesis that age‐related changes in CFO in big brown bats ( Eptesicus fuscus ) differ from those of the standard mammalian model for skeletal aging, the C57BL/6 laboratory mouse. We used data from quantitative polarized light microscopy (qPLM) to compare CFO across the lifespan of long‐lived big brown bats and age matched C57BL/6 mice. Eptesicus and C57BL/6 mice displayed idiosyncratic patterns of CFO. Consistent age‐related changes were only apparent in the outer cortical bone of Eptesicus , where bone tissue is more longitudinally arranged and more anisotropic in older individuals. Both taxa displayed a ring of more transversely oriented bone tissue surrounding the medullary cavity. In Eptesicus , this tissue represents a greater proportion of the overall cross‐section, and is more clearly helically aligned (arranged at 45° to the bone long axis) than similar bone tissue in mice. Bat wing bones displayed a proximodistal gradient in CFO anisotropy and longitudinal orientation in both outer and inner cortical bone compartments. This study lays a methodological foundation for the quantitative evaluation of bone tissue architecture in volant and non‐volant mammals that may be expanded in the future.

A primary function of the skeleton is to resist the loads imparted by body weight. Genetic analyses have identified genomic regions that contribute to differences in skeletal load resistance between laboratory strains of mice, but these studies are usually restricted to one or two bones and leave open the question of how load resistance evolves in natural populations. To address these challenges, we examined the genetics of bone structure using the largest wild house mice on record, which live on Gough Island (GI). We measured structural traits connected to load resistance in the femur, tibia, scapula, humerus, radius, ulna, and mandible of GI mice, a smaller-bodied reference strain from the mainland, and 760 of their F2s. GI mice have bone geometries indicative of greater load resistance abilities but show no increase in bone mineral density compared to the mainland strain. Across traits and bones, we identified a total of 153 quantitative trait loci (QTL) that span all but one of the autosomes. The breadth of QTL detection ranges from a single bone to all seven bones. Additive effects of QTL are modest. QTL for bone structure show limited overlap with QTL for bone length and width and QTL for body weight mapped in the same cross, suggesting a distinct genetic architecture for load resistance. Our findings provide a rare genetic portrait of the evolution of load resistance in a natural population with extreme body size.

Background/aim: The mandible is one of the most fractured bones in the maxillofacial region. This study analyzes trends in mandibular fracture patterns, demographics, and mechanisms since the early 2000s. Material and methods: Mandibular fractures were reviewed from the 2007, 2011, and 2017 National Trauma Data Bank including 13,142, 17,057, and 20,391 patients by year, respectively. This database contains hundreds of thousands of patients annually and represents the largest trauma registry in the United States. Variables included number of fractures, sex, age, injury mechanism, and fracture location. Mechanism of injury included assault, motor vehicle crash, fall, motorcycle, bicycle, pedestrian, and firearm. Anatomic locations based on ICD-9/10 codes included symphysis, ramus, condyle, condylar process, body, angle, and coronoid process. Frequencies were compared using Chi-square tests of homogeneity with effect sizes estimated using Cramer's V. Results: Mandibular fractures represent 2%-2.5% of all traumas reported in the database from 2001 to 2017. The proportion of patients sustaining a single reported mandibular fracture decreased from 82% in 2007 to 63% in 2017. Males consistently experienced 78%-80% of fractures. Eighteen to 54-year-olds experienced the largest percentages of fractures throughout the 21st century, while median age of fracture shifted from 28 to 32 between 2007 and 2017. The most common fracture mechanisms were assault (42% [2001-2005]-37% [2017]), motor vehicle crash (31%-22%) followed by falls (15%-20%). From 2001-2005 to 2017, a decrease was observed in assaults (-5%) and motor vehicle crash (-9%) and an increase in falls (+5%), particularly among elderly females. The mandibular body, condyle, angle, and symphysis represent approximately two-thirds of all fractures without a consistent temporal trend among them. Conclusions: The temporal trends observed can be linked to shifting age demographics nationally that may aid clinicians in diagnosis and inform public safety policies aimed at reducing these injuries, particularly among the growing elderly population.