Do prolonged fasting periods influence the postprandial metabolic responses in turtles? What can Trachemys scripta elegans teach us about this?

Abstract

The postprandial period is characterized by a modification of the gastrointestinal activity after food intake, accompanied by an increase in metabolic rate, secretion of acids, and absorption of nutrients. For ectothermic vertebrates, those changes are particularly prominent given the relatively low metabolic cost and the low frequency of food uptake. However, prolonged fasting periods decrease energy reserves and may compromise the upregulation of costly processes, such as the increase in metabolic rate after resuming the meal intake. Assuming that the main source of energy needed to support such events is provided from the animal's own body reserves, our aim with this study is to test the hypothesis that the longer the period of fasting, the smaller the metabolic rate increase during the postprandial period, since lesser energy reserves trigger these increases. For this, we measured the oxygen consumption rates (V̇O 2) of red-eared slider turtles, Trachemys scripta elegans, submitted to different periods of fasting (47 and 102 days), before and after the ingestion of meals equivalent to 5% of their body masses. Despite the longer fasting period, which led to a reduction of 10.77% in the body mass of the turtles, there were no differences between the two experimental groups regarding maximum V̇O 2 values after food intake (V̇O 2 peak), postprandial metabolic scope, mean time to V̇O 2 peak, and postprandial duration. Results indicate that 102 fasting days does not compromise aerobic metabolic increase during postprandial period and does not impair digestive process of the turtles, even with a loss of body mass.

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“…Where FR is the incurrent flow rate (300 mL/min); FiO 2 is the incurrent fractional concentration of oxygen (from baseline as a reference to 0.2095 of O 2 in the atmospheric air); FeO 2 is the excurrent fractional concentration of oxygen (from the metabolic chamber with an animal) (Lighton, 2008; Figueiredo & Carvalho, 2020).…”

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“…Concomitant with meal digestion, the upregulation of costly processes such as the secretion of gastric acid, the production of digestive enzymes, the intestinal activity of nutrient transporters, and the protein synthesis increase the aerobic metabolic rate McCue, 2006;Wang and Rindom, 2021). The scope and the time course of such metabolic increment are affected mainly by the size and type of the prey, body temperature, fasting period, and level of diet specialization (Secor et al, 1994;Andrade et al, 1997;Gavira and Andrade, 2013;Stuginski et al, 2018b;Figueiredo et al, 2020). In addition to all the physiological processes directly associated with meal digestion, the immune function and the release of immunomodulatory hormones are also upregulated after meal intake, as observed in mammals, amphibians, and in the Pantherophis guttatus corn-snake (Bubenik et al, 1996;.…”

“…Increased metabolic rates have been previously observed in virtually all animals (reviewed in . Meal digestion demands a considerable amount of energy to support the physiological and morphological processes related to nutrient uptake and incorporation Figueiredo et al, 2020;Araújo et al, 2022); in opposition to the low investment in prey constriction, inspection, and swallowing (Canjani et al, 2003). The adjustments in baseline CORT plasma levels are essential for energy reserve mobilization Yang et al, 2019) and may be necessary in the postprandial period to support the energy demand during meal digestion.…”

“…We measured the rates of oxygen consumption (V ̇O2) to assess the aerobic metabolic rate of the boas in the 'fasting' and 'fed' groups, following the procedures described in Figueiredo and Carvalho (2020). We used open respirometry with a portable oxygen analyzer (FOXBOX, Sable Systems Inc.) calibrated with dry atmospheric air, maintaining a constant flow of 200 ml/min.…”

“…at 30 ± 2 ºC during the entire postprandial period -based on the comfortable median temperature for these animals during their absorption period . We acclimated the snakes for one to two hours before beginning V ̇O2 measurements, according to Figueiredo and Carvalho (2020). Then, we ventilated each chamber with atmospheric air for 20 min.…”