A review of snow-living Collembola

Snow-living Collembola live either on the snow surface or below the snow layer,although they can sometimes also be found in the snow layer. They are capable of migrating and feeding in cold environments,showing physiological adaptations that give them a strong tolerance to low temperatures and dehydration. Research on snow-living collembolans has made a large contribution to our understanding of their behavior in the field,their physiology,and their strategies for surviving in such a harsh climate. Studies of snow-living collembolans can be generally divided to three categories: taxonomy,physiology,and phenology. Three main geographical areas are concerned: firstly,the Arctic,mainly referring to Asia,northern Europe and North America,including Russia,Norway,Sweden,France,Germany,China,Japan,Canada and the United States of America; secondly,the high mountain regions,such as the European Alps,Himalayan glacier regions,including Nepal and other countries; thirdly,Antarctica. In total,more than 70 species in 24 genera of collembolans have been found to be active in harsh winter conditions around the world( not including those from Antarctica). Some of them should have a wide distribution,such as Hypogastrura socialis,which is found in Norway, Finland and the United States of America. Compared with other Collembola,snow-living species sometimes exhibit distinctive morphological features,such as larger teeth on the dens in the winter form. Some snow-living collembolans mayalso hibernate in summer. The physiological mechanisms of cold tolerance and drought resistance have been elucidated. As a group of arthropods with freeze-avoidance strategy,they increase glycerol levels,decrease fucose and glucose levels,and produce antifreeze proteins( AFP),as well as showing other mechanisms to protect cells from low temperature injury. However,the molecular mechanisms underlying these processes are not yet fully understood. Collembolans active on the snow surface can use sunlight to make a continuous directional migration,thereby crossing large geographical barriers to reach more suitable habitats and ensure gene flow. The activities of Collembola are greatly influenced by environmental factors. Collembolan densities on the snow surface change according to wind,temperature and pressure,and are strongly influenced by the seasons. They can be found in large numbers on the snow surface when the temperature is approximately 0℃,but withdraw to the snow layer when the temperature decreases at night. Collembolan activity increases mostly in late winter when the climate is mild. In this paper we summarize the historical studies of the snow-living collembolans from all the world,including the researchers and their study areas; provide a list of species that have been found world widely and outline their distributions; describe the methods used to trap collembolans in winter; discuss their activities in snow conditions,such as vertical migration within the snow layer and directional horizontal migration on the snow surface,their jumping ability and dispersal rates on the snow surface; their feeding behaviors and the relevant food chain in winter; their resistance to cold and drought,and other physiological characteristics; and how their activities are influenced by climate and seasonal changes. The aim is to thereby increase our understanding of the biology and ecology characteristics of snowliving collembolans.