Comparison of Spermophilus dauricus gastrointestinal phenotypic flexibility between hibernating and non-hibernating seasons

Abstract

Traits of the gastrointestinal (GI) tract are phenotypically flexible and seem to reflect the ecological features of animals. The Daurian ground squirrel (Spermophilus dauricus) is a typical fat-storing, hibernating animal. However, information on seasonal GI plasticity in this species is limited. The aim of the present study was to characterize the morphology, histology, and genetic regulation involved in GI motility in the ground squirrel during non-hibernating and hibernating seasons. The morphological and histological results showed that the body weight, total fresh weight, and total net fresh weight of the GI tract in summer and autumn were higher than those in spring and the winter hibernation season, although the total length of the gut did not change seasonally. The fresh weight and net fresh weight of the small intestine, cecum, and large intestine were significantly greater in autumn and summer than in winter, but the lengths of these segments showed no significant seasonal differences. The mucosal and muscular layer thicknesses of the stomach, illum, cecum, and colon were greater in autumn or summer than in winter, and the small intestine diameter and villus height were decreased in winter compared to those in the spring or summer. Moreover, the expression of nNOS and NPY genes in the small intestine in autumn and winter was higher than that in spring or summer. VIP expression in winter was the highest across seasons; in contrast, CHRM2 expression in autumn was the highest across seasons. These results indicate that morphological and histological traits of the gut, as well motility adjustments, exhibit seasonal plasticity in the ground squirrel, and these are especially affected by the hibernating cycle. This work will expand our knowledge of GI phenotypic plasticity in hibernating rodent species.