Seasonal changes of thermogenic capacity in Melano-bellied oriental voles ( Eothenomysmelanogaster)

Abstract

Seasonal changes of thermogenic capacity in Melano-bellied oriental voles ( Eothenomys melanogaster) were studied by measurements of body mass, basal metabolic rate (BMR), non-shivering thermogenesis (NST), thermogenic properties of brown adipose tissue (BAT), relative weight of liver mass, mitochondrial protein (MP) content, and activities of mitochondrial cytochrome C oxidase (COX) in autumn (October), winter (December), spring (April) and summer (July), respectively. Results showed that: (1) Body mass of E. melanogaster was the highest in autumn, and the lowest in summer. The seasonal change in body mass was subject not only by environment temperature but also to other factors such as reproduction, feeding habit and climate in the habitat. Reproductive periods of E. melanogaster were in early spring (February–March) and late autumn (September–October), and therefore, the body mass was higher in spring and autumn. In addition, E. melanogaster feeds on leaves and stems of plants in spring and summer, whereas mainly on fruits in autumn and winter as they contain more energy. The difference in the feeding habit could result in higher body mass in the late half of the year, but lower body mass in winter. The lower body mass in winter provides E. melanogaster with an advantage in motility. (2) The BMR and NST of E. melanogaster was higher in winter than in other seasons, which suggests that the regulating thermogenic capacity is an important adaptive strategy for E. melanogaster. However, there was no difference in relative oxygen consumption (NST–BMR/BMR), suggesting that the regulative capacity of BMR is approximately equal to NST in E. melanogaster. This is different from some small mammal species in north China, which have higher regulative capacity in NST than E. melanogaster. Melano-bellied oriental voles live in mountainous area with subtropical zone monsoon climate and abundant food resource, and therefore have lower regulative capacity in NST, which can reduce an absolute request for energy. The low regulative capacity in NST can also help E. melanogaster to maintain energy balance and stable body temperature. (3) The relative mass of BAT in winter was significantly higher than that in summer. Different seasons significantly affected the MP content of BAT. The MP content of BAT was in the following order: winter > fall > spring > summer. The trend as following was observed for the mitochondrial COX activity of BAT: winter > spring > fall > summer. In experimental conditions, the thermogenic rate of many small mammal species increased under cold acclimation. Short photoperiod alone could also induce E. melanogaster to increase NST and mitochondrial COX activity of BAT. Therefore, ambient temperature and photoperiod are important environmental cues to induce seasonal changes in thermogenic capacity in E. melanogaster. (4) The relative mass of liver in summer was higher than that in other seasons, but no seasonal changes were found among other seasons. The MP contents of liver showed highest level in winter and lowest in spring and summer. Significant seasonal changes were also observed in the mitochondrial COX activity of liver. It increased significantly in winter, but not in other seasons. This indicates that liver participate in adjustment of thermogenesis. These data indicate that both increasing whole-animal thermogenesis rate and thermogenic capacity at the cells of BAT and liver play an important role in the adaption of E. melanogaster to seasonal changes, and they are also closely correlated with the habitat condition and their life habit.