Fruit bats (Pteropodidae) fuel their metabolism rapidly and directly with exogenous sugars

Abstract

SUMMARYPrevious studies reported that fed bats and birds mostly use recently acquired exogenous nutrients as fuel for flight, rather than endogenous fuels, such as lipids or glycogen. However, this pattern of fuel use may be a simple size-related phenomenon because, to date, only small birds and bats have been studied with respect to the origin of metabolized fuel, and because small animals carry relatively small energy reserves, considering their high mass-specific metabolic rate. We hypothesized that ~150g Egyptian fruit bats (Rousettus aegyptiacus Pteropodidae), which are more than an order of magnitude heavier than previously studied bats, also catabolize dietary sugars directly and exclusively to fuel both rest and flight metabolism. We based our expectation on the observation that these animals rapidly transport ingested dietary sugars, which are absorbed via passive paracellular pathways in the intestine, to organs of high energy demand. We used the stable carbon isotope ratio in exhaled CO 2 ( 13 C breath ) to assess the origin of metabolized substrates in 16 Egyptian fruit bats that were maintained on a diet of C3 plants before experiments. First, we predicted that in resting bats 

Flight is the key to postprandial blood glucose balance in the fruit batsEonycteris spelaeaandCynopterus sphinx

“…In general, they select the fuel resource according to their nutritional and activity status (Amitai et al., 2010). Chiroptera, commonly called bats, are the second largest order of mammals, with relatively high species diversity and various feeding habits, and they are also the only mammals that can fly.…”

“…Thus, it is conceivable that fruit bats are well‐equipped with intestinal sucrase, a digestive enzyme that enables a rapid absorption of ingested sugar (Hernandez & del Rio, 1992). Both flying and resting fruit bats can use ingested sugars as a direct fuel, just like hummingbirds (Amitai et al., 2010; Voigt & Speakman, 2007; Welch & Suarez, 2008). Additionally, an elevated amount of sugar intake is parallel with an increased speed of paracellular nutrient absorption in fruit bats (Caviedes‐Vidal et al., 2008; Tracy et al., 2007).…”

Physiological benefits of nectar feeding by a predatory beetle

“…Nectar is molecularly simple, and most animals can use this ready source of energy with little digestive investment. As such, nectar meals are important in supporting high-energy needs like flight, foraging, or aggression (Hausmann, Wäckers & Dorn, 2005;Tschinkel, 2006;Wanner, Gu & Dorn, 2006;Grover et al, 2007;Taylor & Bradley, 2009;Amitai et al, 2010). Finally, nectar and other simple sugars are seldom nutritionally sufficient to support the reproduction of animals, but sugar meals in concert with other, higher quality foods may increase reproductive capacity over these foods on their own (Geng et al, 2006;Venzon et al, 2006;Lundgren, 2009a;Taylor & Pfannenstiel, 2009).…”

Seasonal assessment of the reproductive cycle and energy reserves of male batsSturnira lilium(Chiroptera: Phyllostomidae)

“…The increased breast muscle glycogen concentrations observed in animals captured during the rainy season might be associated with the fact that the animals are using the nutrients from their diet to invest in flight, because this substrate in breast muscle is mainly used for energy expenditure by the muscle itself, as previously described for frugivorous and nectarivorous bats (Yacoe et al 1982;Welch et al 2008;Suarez et al 2009;Amitai et al 2010).…”