Reproduction and growth of Collembola under snow in a cold temperate region

Abstract

The population and developmental dynamics of Collembola under snow were studied throughout the winter in two different habitats; a) a deciduous forest whereby in-vitro fungal cultures were used as bait in traps, and b) a lichen site where fresh thalli of Cladonia sp. were collected. Three species of collembolans, Paronychiurus japonicas (Yosii, 1967), Desoria gracilliseta (Börner, 1909), and Folsomia octoculata Handschin, 1925, were found to be winter-active under snow. In the forest site, P. japonicus was almost exclusively collected from the bait and grew synchronously until snowmelt. This species was never recovered during summer months, and considered to be univoltine. Desoria gracilliseta and F. octoculata predominated on Cladonia sp. Small individuals of D. gracilliseta was first observed on Cladonia sp. in October, steadily grew to more than 2 mm long in May but individuals were absent during summer months. Gut contents were consistently observed in individuals of the D. gracilliseta population throughout the winter. Also, this species was often collected from fungal bait traps placed on the lichen colony under snow in March. These findings indicate that D. gracilliseta was also univoltine and winter-active. In contrast, F. octoculata was never recovered from the traps under snow. Its mean body lengths of individuals decreased from December, 2014 to March, 2015, and small individuals, which were absent in December, were frequently collected in March. The trend was not evident in the 2015/16 winter when snow cover in January was thin; the rate of large individuals (> 0.96 mm) was consistently high, ranging between 20.1 and 40.3%. All F. octoculata individuals possessed empty guts in December but gut contents were observed in many individuals during March in both winters suggesting that F. octoculata stays dormant during early winter and starts to reproduce under snow when climatic conditions are favorable in late winter. Thus, populations of these collembolan species in the snowy region are active in winter but have developed different overwintering strategies.