Patterns of oxygen consumption during simultaneously occurring elevated metabolic states in the viviparous snake, Thamnophis marcianus

Abstract

Snakes exhibit large factorial increments in oxygen consumption during digestion, and physical activity, and long-lasting sub-maximal increments during reproduction. Under natural conditions, all three physiological states may occur simultaneously, but the integrated response is not well understood. Adult male and female Checkered Gartersnakes (Thamnophis maricanus) were used to examine increments in oxygen consumption (i.e., V̇O2) and carbon dioxide production (i.e., V̇CO2) associated with activity (ACT), digestion (DIG), and post-prandial activity (ACT+DIG). For females, we carried out these trials in the non-reproductive state, and also during the vitellogenic (V) and embryogenic (E) phases of a reproductive cycle. Endurance time (i.e., time to exhaustion, TTE) was recorded for all groups during ACT and ACT+DIG trials. Our results indicate that male and non-reproductive female Thamnophis marcianus exhibit significant increments in V̇O2 during digestion (∼5 fold) and activity (∼9 fold), and that ACT+DIG results in a similar increments in V̇O2 (∼9-10 fold). During reproduction, resting V̇O2 increased by 1.6–1.7 fold, and peak increments during digestion were elevated by 30 to 50% above non-reproductive values, but values associated with ACT and ACT+DIG were not significantly different. During ACT+DIG, endurance time remained similar for all of the groups in the present study. Overall, our results indicate that prioritization is the primary pattern of interaction in oxygen delivery exhibited by this species. We propose that the metabolic processes associated with digestion, and perhaps reproduction, are temporarily compromised during activity.