Grants and Contracts Details
The allocation of caloric resources throughout an organism depends on body composition (fat and muscle) and on variation in the metabolic rate of particular tissues due to changes in vasculature, mitochondrial density, and gene activity. Differences in relative brain size can have profound implications for an organism's overall metabolic strategy. The Expensive Tissue Hypothesis (ETH) predicts that large-brained animals can maintain a balanced energy budget by offsetting the increased metabolic cost associated with a large brain with reductions in the size of other costly tissues (e.g., gastrointestinal tract). Currently, there is little support for the supposition that there is a trade off between the brain and the gastrointestinal tract. However, recent genetic and anatomical research suggests that brain size may constrain muscle mass. This study will investigate whether brain size constrains skeletal muscle mass, using an amalgam of novel and traditional techniques with primates as a model system. We hypothesize that skeletal muscle is in direct competition with the brain for glucose and oxygen. We have three primary predictions. First, skeletal muscle mass will negatively correlates with relative brain size. Second, skeletal muscle fiber composition will correlate with brain size, and type I muscle fibers (a muscle cell that uses glucose in a similar fashion to the brain) will correlate negatively with brain size. Third, we predict that skeletal muscle growth will peak soon after brain growth is complete. In primates, brain growth completion is correlated with the eruption of lower molar one. Accordingly, we expect the relative muscle mass will statistically lower in individuals which still have deciduous dentition compared with those with lower molar one completely erupted. Although the ETH and other hypotheses have explored the relationship between brain size and various tissues, this project is the first to explore how muscle mass and brain size covary in primates. Our findings will contribute to a better understanding of the interaction between brain size and the evolution of metabolic strategies. Intellectual merits: The expensive tissue hypothesis was first presented to the anthropological community by Aiello and Wheeler in 1995 and remains a prominent hypothesis in human evolutionary theory. Researchers have focused on visceral tissues, but little attention has been paid to skeletal muscles. Primates have relatively less muscle mass and relatively larger brains than most other non-primate mammals. So far, it has been unclear why this is. We hypothesize that the decrease of skeletal muscle mass may offset the costs of an expensive brain in primate and human evolution. This study will provide new data about skeletal muscle mass and its correlation to brain size in taxa from all major extant primate groups, and will allow us to better understand the evolution of brain enlargement during the evolutionary history of primates. Broader impact: Health Sciences: This research will shed light onto aspects of our evolutionary and developmental histories, and in doing so, will provide new perspectives on human health. A number of studies have shown that type II muscle mass is increased in patients suffering from type 2 diabetes. Our research will explore how primate evolutionary developmental history contributes to a phenotype associated with diabetes, a highly prevalent disease with serious public health consequences. Pedagogy: The results of this study will have an impact in undergraduate education. Students struggle with physiological concepts in every organ system. Inquiry-based kinesthetic learning modules can help reinforce key concepts. One of the PIs (MNM) is a former NSF GK-12 fellow and recently was awarded an eLearning Hybrid Teaching grant to develop and implement educational modeuls on anatomy and physiology. Specifically, our findings will be used to create a skeletal muscle physiology lab for a large (500+ student) anatomy and physiology course at the University of Kentucky. The module will be posted and shared on the internet and presented at conferences (e.g., American Association of Anatomists). This project will also support both undergraduate and graduate students by training them in gross anatomical dissection and histological analyses. All PIs have a deep commitment to undergraduate education and serving underrepresented students at their respective universities.
|Effective start/end date||9/15/14 → 8/7/16|
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