The cost of digestion in the fish-eating myotis (Myotis vivesi)

Abstract

Flying vertebrates, such as bats, face special challenges with regards to the throughput and digestion of food. On the one hand, as potentially energy-limited organisms, bats must ingest and assimilate energy efficiently in order to satisfy high resting and active metabolic demands. On the other hand, the assimilation of nutrients must be accomplished using a digestive tract that is, compared with that of similarly sized non-flying vertebrates, significantly shorter. Despite these competing demands, and the relative breadth of dietary diversity among bats, little work has been done describing the cost of digestion, termed 'specific dynamic action' (SDA). Here, we provide the first systematic assessment of the SDA response in a bat, the fisheating myotis (Myotis vivesi). Given the shorter digestive tract and the relatively higher resting and active metabolic rates of bats in general, and based on anecdotal published evidence, we hypothesized that the SDA response in fish-eating myotis would be dependent on meal size and both significantly more brief and intense than in small, nonflying mammals. In agreement with our hypothesis, we found that the peak metabolic rate during digestion, relative to rest, was significantly higher in these bats compared with any other mammals or vertebrates, except for some infrequently eating reptiles and amphibians. Additionally, we found that the magnitude and duration of the SDA response were related to meal size. However, we found that the duration of the SDA response, while generally similar to reported gut transit times in other small bats, was not substantially shorter than in similarly sized non-flying mammals.

Metabolic Cost of the Activation of Immune Response in the Fish-Eating Myotis (Myotis vivesi): The Effects of Inflammation and the Acute Phase Response

“…Oxygen concentration was converted to ml of gas by application of standard equations [42] assuming a RER of 0.77, which was the mean RER observed in fasted fish-eating Myotis examined in a previous study [43]. V O2 at each hour after PHA or LPS injection was calculated as the lowest five-min mean value of instantaneous oxygen consumption.…”

“…Control-corrected V O2 values were converted to their oxy-joules equivalents ( MR kj in kJ hr -1 ) according to the following equation from [40] and assuming the respiratory exchange ratio (; where V CO2 is carbon dioxide production rate) was equal to 0.77, which was the average RER value observed in fasted fish-eating Myotis examined in a separate study [43]: MR kj = V O2 x [16 + 5.164 (RER)]…”

Ecology and evolutionary biology of fishing bats

“…If such analyses were coupled with microbiota transplants and digestive efficiency tests (Welch et al. ), the role of gut microorganisms in the adaptation to dietary changes could be assessed (Alberdi et al. ).…”

“…This reduction in intestinal size and volume is believed to be an adaptation to flight, the most energetically expensive form of locomotion. Moreover, bats have shorter retention times for digesta (Welch et al 2015). In spite of these apparent limitations, insectivorous bats have very high (70-90%) digestive efficiency, in part because they compensate for the loss of absorptive area by intestinal villous amplification and higher glucose absorption (Price et al 2015).…”

“…Molecular analysis of gut microbial communities would enable researchers to unveil whether taxonomic and functional differences exist between the gut microbiotas of fishing and non-fishing bats. If such analyses were coupled with microbiota transplants and digestive efficiency tests (Welch et al 2015), the role of gut microorganisms in the adaptation to dietary changes could be assessed .…”