Effect of Aggregations on Age-Sex Structure of Xenylla obscura (Collembola, Hypogastruridae) in the Vitim plateau (Transbaikalia)

We have investigated the seasonal dynamics and age-sex structure of the numerous species of springtails Xenylla obscura Imms, 1912 in the biotopes of the southern Vitim Plateau (Eravninskaya and Kondinskaya Basins). The study is based on material collected during the 2008–2009 field seasons. The sex ratio of X. obscura is predominantly female, accounting for 60–70 % of the population, which is typical for springtails in general. High proportions of males (75–76 %), however, were recorded in mixed-herb and dwarf birch larch forests, which are likely associated with the formation of breeding aggregations. Based on an analysis of the presence of reproductive males we have concluded that the main reproductive peak occurs in the first half of summer. By late summer, we observed mass hatching of juveniles, which had completed their growth by October and likely hibernate in a pre-reproductive state. The discovery of breeding males in August suggests the possibility of an extended reproductive period.