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Nutrients 2017, 9(7), 743; doi:10.3390/nu9070743

Sugar Metabolism in Hummingbirds and Nectar Bats

1
Department of Zoology, University of British Columbia, #4200-6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
2
Department of Biological Sciences, University of Toronto, 1265 Military Trail, Scarborough, ON M1C 1A4, Canada
*
Author to whom correspondence should be addressed.
Received: 22 April 2017 / Revised: 3 July 2017 / Accepted: 4 July 2017 / Published: 12 July 2017
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Abstract

Hummingbirds and nectar bats coevolved with the plants they visit to feed on floral nectars rich in sugars. The extremely high metabolic costs imposed by small size and hovering flight in combination with reliance upon sugars as their main source of dietary calories resulted in convergent evolution of a suite of structural and functional traits. These allow high rates of aerobic energy metabolism in the flight muscles, fueled almost entirely by the oxidation of dietary sugars, during flight. High intestinal sucrase activities enable high rates of sucrose hydrolysis. Intestinal absorption of glucose and fructose occurs mainly through a paracellular pathway. In the fasted state, energy metabolism during flight relies on the oxidation of fat synthesized from previously-ingested sugar. During repeated bouts of hover-feeding, the enhanced digestive capacities, in combination with high capacities for sugar transport and oxidation in the flight muscles, allow the operation of the “sugar oxidation cascade”, the pathway by which dietary sugars are directly oxidized by flight muscles during exercise. It is suggested that the potentially harmful effects of nectar diets are prevented by locomotory exercise, just as in human hunter-gatherers who consume large quantities of honey. View Full-Text
Keywords: sugar; glucose transport; hexokinase; metabolism; muscle; energetics; evolution; foraging behavior sugar; glucose transport; hexokinase; metabolism; muscle; energetics; evolution; foraging behavior
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Suarez, R.K.; Welch, K.C. Sugar Metabolism in Hummingbirds and Nectar Bats. Nutrients 2017, 9, 743.

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