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Abstract
ABSTRACTCell size plays a role in body size evolution and environmental adaptations. Addressing these roles, we studied body mass and cell size in Galliformes birds and Rodentia mammals, and collected published data on their genome sizes. In birds, we measured erythrocyte nuclei and basal metabolic rates (BMRs). In birds and mammals, larger species consistently evolved larger cells for five cell types (erythrocytes, enterocytes, chondrocytes, skin epithelial cells, and kidney proximal tubule cells) and evolved smaller hepatocytes. We found no evidence that cell size differences originated through genome size changes. We conclude that the organism-wide coordination of cell size changes might be an evolutionarily conservative characteristic, and the convergent evolutionary body size and cell size changes in Galliformes and Rodentia suggest the adaptive significance of cell size. Recent theory predicts that species evolving larger cells waste less energy on tissue maintenance but have reduced capacities to deliver oxygen to mitochondria and metabolize resources. Indeed, birds with larger size of the abovementioned cell types and smaller hepatocytes have evolved lower mass-specific BMRs. We propose that the inconsistent pattern in hepatocytes derives from the efficient delivery system to hepatocytes, combined with their intense involvement in supracellular function and anabolic activity.
Highlights
Whether they are bacteria, protists, fungi, plants or animals, living things have evolved a plethora of different body plans and life strategies, resulting in dramatic differences in body mass among species
In Galliformes birds and Rodentia mammals, species with a larger body mass are consistently characterized by larger cells for five cell types and by smaller hepatocytes
The first phenomenon we found demonstrates that species have evolved cells with different sizes, and this evolutionary change shows an organism-wide distribution, indicating that the cellular architecture of tissues has evolved in a coordinated manner throughout the entire body rather than occurring only in individual organs
Summary
Protists, fungi, plants or animals, living things have evolved a plethora of different body plans and life strategies, resulting in dramatic differences in body mass among species. A change in cell number may affect physiological performance if the number of cells. Received 6 September 2017; Accepted 7 March 2018 in an organ affects organ function or if tissue maintenance depends on cell number and cell size. A larger body that consists of more and larger cells has a smaller amount of cell membranes per unit of tissue mass, which should lower its metabolic costs per unit of body mass. Organs with large cells are expected to metabolize at a slower rate than are organs with small cells because of the smaller surface area of cells available for the exchange of substrates and products, the longer distances involved in intracellular diffusion, and the fewer nuclei for transcription in organs with large cells (Czarnoleski et al, 2015b)
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