Mammals that possess elaborate antipredator defences such as body armour, spines and quills are usually well protected, intermediate in size, primarily insectivorous and live in simple open environments. The benefits of such defences seem clear and may relax selection on maintaining cognitive abilities that aid in vigilance and predator recognition, and their bearers may accrue extensive production and maintenance costs. Here, in this comparative phylogenetic analysis of measurements of encephalization quotient and morphological defence scores of 647 mammal species representing nearly every order, we found that as lineages evolve stronger defences, they suffer a correlated reduction in encephalization. The only exceptions were those that live in trees-a complex three-dimensional world probably requiring greater cognitive abilities. At the proximate level, because brain tissue is extremely energetically expensive to build, mammals may be trading off spending more on elaborate defences and saving by building less powerful brains. At the ultimate level, having greater defences may also reduce the need for advanced cognitive abilities for constant assessment of environmental predation risk, especially in simple open environments.

Polychlorinated biphenyls (PCBs) are a large class of persistent organic pollutants that are potentially harmful to human and wildlife health. Although a small number of dioxin-like (DL) PCBs are well characterized, the majority of PCBs have non-dioxin-like (NDL) modes of action and biological effects that are less understood. We conducted a dose-response study of the skeletal and dental effects of in utero/lactational exposure to 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB 180), a NDL PCB congener that is abundantly present in the environment and foods, including mother’s milk. In a sample of 35- and 84-day-old male and female offspring from pregnant rats exposed to different doses of PCB 180 (0, 10, 30, 100, 300, and 1000 mg/kg bw), we measured the three-dimensional (3D) coordinates of 27 landmarks on the craniofacial skeleton with a Microscribe G2X system, the buccolingual width of all molars with digital sliding calipers, and a variety of tibial parameters with peripheral quantitative computed tomography (pQCT) and a biomechanical testing apparatus. The landmark coordinates were analyzed for variation in size, shape, and fluctuating asymmetry (FA) using MorphoJ software, showing no effects on cranial size, on FA in females only (i.e., decreased asymmetry), and on shape in both sexes (i.e., decreased facial length and shift in the palatal suture). In the maxillary teeth, females in the highest dose group showed a significant decrease of 0.1 mm (p = 0.033) of the second molar only, whereas males in most dose groups showed average increases of 0.1 mm (p = 0.006–0.044) in all three molars. In the mandibular teeth, the only significant response to PCB 180 exposure was the average increase of 0.1 mm (p = 0.001–0.025) in the third molars of males only. Males also shower greater sensitivity in postcranial effects of increased tibial length and decreased cortical bone mass density, although only females showed significant effects on tibial bone area and thickness. These results demonstrate marked sex differences in effects of PCB 180, which can be attributed to differences in their underlying biological mechanisms of toxicity. Furthermore, although tooth and bone development are targets of both DL and NDL compounds, this study shows that there are marked differences in their mechanisms and effects.

Objectives: Craniofacial fluctuating asymmetry (FA) refers to the random deviations from symmetry exhibited across the craniofacial complex and can be used as a measure of developmental instability for organisms with bilateral symmetry. This article addresses the lack of data on craniofacial FA in nonhuman primates by analyzing FA magnitude and variation in chimpanzees, gorillas, and macaques. We offer a preliminary investigation into how FA, as a proxy for developmental instability, varies within and among nonhuman primates. Materials and Methods:We generated 3D surface models of 121 crania from Pan troglodytes troglodytes, Gorilla gorilla gorilla, and Macaca fascicularis fascicularis. Using geometric morphometric techniques, the magnitude of observed FA was calculated and compared for each individual, sex, and taxon, along with the variation of FA across cranial regions and for each bilateral landmark.Results: Gorillas and macaques exhibited higher and more similar magnitudes of FA to each other than either taxon did to chimpanzees; variation in magnitude of FA followed this same trend. No significant differences were detected between sexes using pooled data across species, but sex did influence FA magnitude within taxa in gorillas. Further, variation in FA variance across cranial regions and by landmark was not distributed in any particular pattern. Conclusion:Possible environmentally induced causes for these patterns of FA magnitude include differences in growth rate and physiological stress experienced during life. Developmental stability may be greatest in chimpanzees in this sample. Additionally, these results point to appropriate landmarks for future FA analyses and may help suggest more urgent candidate taxa for conservation efforts.

With increased tablet ownership in the United States comes increased levels of neck flexion compared to desktop or laptop computer use, and these neck postures have been linked to increases in neck pain. Importantly, tablet viewing postures can be achieved in multiple ways and could be determined by the morphology of the individual and/or other extraneous factors. In this study, we aim to preliminarily evaluate how neck postures vary during tablet use among individuals and link this variation to other factors such as sex, height, weight, presence/absence of temporomandibular joint disorder (TMD), and morphology of the head and neck. We analyzed two-dimensional landmarks placed on lateralview radiographs of 22 participants (10 female and 12 male) seated in neutral, upright, fully flexed, semi-reclined, and reclined postures. We utilize geometric morphometric techniques, which are advantageous for evaluating shape variation and have not been extensively applied to biomechanical analyses. We found skeletal morphology to be significantly related to sex and height in all but the neutral posture (P < 0.05), and weight was marginally significantly related to shape in the semi-reclined posture (P = 0.047). Morphologically, male participants exhibited more flexion at the articulatio atlantooccipitalis than females, and females showed greater mandibular protrusion than males, although this result is likely related to height. No relationship was found between posture and TMD. This research establishes a framework for future work that uses geometric morphometric analyses to evaluate how neck postures vary in relation to TMD.

Tablet ownership in the United States has increased rapidly in the past decade. With this increase in tablet use comes increased levels of neck flexion compared to using a desktop or laptop computer use. These neck postures have been linked to increases in neck pain. Importantly, tablet viewing postures can be achieved in multiple ways and could be determined by either the morphology of the individual or other extraneous factors. In this study, we aim to preliminarily evaluate how neck postures vary among individuals with the goal of further examining how neck morphology and postures may be related to other factors such sex and height of the subject. We utilize geometric morphometric methods to evaluate the biomechanics of the cervical spine and skull in various neck postures; this technique is excellent for evaluating shape variation and has not been extensively applied in the biomechanical literature. Lateral‐view radiographs of 22 college‐aged subjects (10 female, 12 male) were taken seated in 5 neck postures: neutral, maximum neck flexion, upright seated tablet viewing, semi‐reclined tablet viewing, and reclined tablet viewing. In addition to the radiographs, a participant survey was completed to indicate the presence or absence of discomfort and/or abnormalities of the neck and mandible (e.g., pain, clicking/popping at the TMD, stiffness). Eighty‐seven two‐dimensional landmarks were placed on the cervical spine and skull on each radiograph signifying osteological features of the face, positions of the posterior‐most occlusal molars, the mandible, and the morphology of the cervical vertebrae. Variation among positions and subjects was visualized using principal components analysis and thin‐plate spline analysis. A series of ANOVAs and regression models were performed to examine relationships between morphology and other factors such as sex, weight, height, and the presence of symptoms related to temporomandibular joint disorder (TMD). Separate one‐way ANOVAs for each neck posture indicate that every posture but neutral is achieved differently by sex, with males tending to flex more at the atlanto‐occipital joint than females, and females showing greater protrusion in the neck than males. We further observed a significant relationship between neck flexion and height, suggesting that neck length may influence how subjects adopt specific postures. Though we did not observe a significant relationship between neck morphology or postures and the presence of TMD, these findings may provide some insight into why females experience higher rates of TMD, given that increased neck protrusion has been linked increased stresses on the temporomandibular joint and jaw. This study establishes a framework for future research that focuses on evaluating how neck postures vary in relation to TMD.Support or Funding Information Arkansas Student Undergraduate Research Fellowship University of Arkansas Provost's Collaborative Research Grant This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.