Browsing by Subject "body size"

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    Mean mass-specific metabolic rates are strikingly similar across life’s major domains: Evidence for life’s metabolic optimum
    (National Academy of Sciences, 2008) Makarieva, Anastassia M; Gorshkova, Victor G; Li, Bai-Lian; Chown, Steven L; Reich, Peter B; Gavrilov, Valery M
    A fundamental but unanswered biological question asks how much energy, on average, Earth’s different life forms spend per unit mass per unit time to remain alive. Here, using the largest database to date, for 3,006 species that includes most of the range of biological diversity on the planet—from bacteria to elephants, and algae to sapling trees—we show that metabolism displays a striking degree of homeostasis across all of life. We demonstrate that, despite the enormous biochemical, physiological, and ecological differences between the surveyed species that vary over 1020-fold in body mass, mean metabolic rates of major taxonomic groups displayed at physiological rest converge on a narrow range from 0.3 to 9 W kg 1. This 30-fold variation among life’s disparate forms represents a remarkably small range compared with the 4,000- to 65,000-fold difference between the mean metabolic rates of the smallest and largest organisms that would be observed if life as a whole conformed to universal quarterpower or third-power allometric scaling laws. The observed broad convergence on a narrow range of basal metabolic rates suggests that organismal designs that fit in this physiological window have been favored by natural selection across all of life’s major kingdoms, and that this range might therefore be considered as optimal for living matter as a whole.
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    Regulation of Body Size by TGF-β Signaling
    (2018-09) Moss-Taylor, Lindsay
    Nearly all life history traits scale with body size, imparting incredible importance on control of growth and size during animal development. Nutrition, genetic and environmental inputs influence the growth rate during development to determine final body size. These inputs are processed by the insulin/insulin-like growth factor signaling pathway (IIS), which is the major regulator of growth, and other pathways, like TGF-β, which modulate tissue growth or IIS. Mutations in the gene coding for the Drosophila TGF-β ligand Activinβ (Actβ) cause reduced final body size and accelerated growth termination. Using the Gal4/UAS system, I show Actβ is expressed in distinct cell types in the nervous system. Using rescue experiments, I show the Actβ phenotypes can be rescued by overexpression of Actβ in some, but not all, of the cell types in which it is endogenously expressed. Additionally, the growth rate of Actβ mutants is reduced, demonstrating the size phenotype is not simply due to early growth termination from precocious timing. Muscle-specific knockdown of the TGF-β signaling transducer/transcription factor dSmad2 also reduces body size, identifying muscle is a target tissue of the Actβ signal. The change in body size is due to a reduction in the size of skeletal muscles, not a systemic reduction in size. Autophagy markers are upregulated in Actβ mutants but, surprisingly, overexpression of autophagy regulators does not rescue the Actβ size phenotype, indicating Actβ regulation of autophagy is TOR-independent. These results provide new insights into mechanisms of body size and muscle size control during animal development. This thesis details the functions of Actβ in the regulation of body size and developmental timing. Chapter 2 describes the study of how Actβ controls body size and developmental timing. Chapter 3 investigates the roles of Actβ in regulating metabolism and IIS.