Sex differences in postprandial blood glucose and body surface temperature are contingent on flight in the fruit bat, Cynopterus sphinx

Abstract

The postprandial blood glucose level is very high for the body size in frugivorous bats. Like other homeotherms, bats release heat during digestion of dietary macronutrients. Despite males and females of the same species exhibiting different foraging behaviour, empirical support for sex differences in blood glucose and body surface temperature in fruit bats is poor. Moreover, while flight affects postprandial metabolism, whether such effects are different in each sex of fruit bats is unclear. Here, we studied these questions in the fruit bat, Cynopterus sphinx. We first assessed whether there are sex differences in the postprandial level of blood glucose and body surface temperature over time in rested bats. We then assessed whether flight affects outcomes of sex differences in both traits. We found that the estimated marginal means of both traits were generally higher in females than males, in rested bats. Notably, the sex difference in both traits was only significant at specific sampling time of the assay. Further, the trait means significantly differed between the sexes only in the rested, but not active, bats, meaning that signals of sex difference in metabolic traits eroded when bats were active. Taken together, our findings suggest that in C. sphinx, the sex specificity in the expression of metabolic traits is significantly dependent on physical activity.

Keywords

• high-sugar diet
• hyperglycaemia
• intralocus sexual conflict
• nutritional ecology
• physical activity
• thermal imaging
• thermogenesis