The consequences of seasonal fasting during the dormancy of tegu lizards (Salvator merianae) on their postprandial metabolic response

Abstract

Tegu lizards (Salvator merianae) aestivate for up to 5 months during Brazil's winter, when they retreat to burrows and halt most activities. Dormant tegus reduce their gastrointestinal (GI) mass, which allows a substantial energy economy. This strategy however, implies that the first post-dormancy digestion would be more costly than subsequent feeding episodes due to GI atrophy. To address this, we determined the postprandial metabolic response (SDA) of the first (M1), second (M2) and several (RM) feeding episodes after tegus' dormancy. Another group of tegus (PF) was subjected to an extra 50-days fasting period after arousal. Glucose, triglycerides, and uric acid levels were checked before and after feeding. M1 digestion lasted twice as long and cost two-fold more when compared to M2 or RM, in agreement with the idea that GI atrophy inflates digestion cost at the first post-dormancy meal. SDA response was similar in M2 and RM suggesting that the GI tract was fully reorganized after the first feeding. SDA cost was equal in PF and RM implying that the change in state per se (dormant-to-arousal) triggers the regrowth of GI, independently of feeding. Fasting M1 presented higher triglycerides and lower uric acid levels than fed tegus, indicating that fasting is mainly sustained by fat storages. Our results showed that seasonal fasting imposes an extra digestion cost to tegus following their next feeding, which is fully paid during their first digestion. This surplus cost, however, may be negligible compared to the overall energetic savings provisioned from GI tract atrophy during the dormancy period.