The first steps in subterranean evolution of spiders (Araneae) in Central Europe

Abstract

Abstract Three types of subterranean spaces are described according to their depth and degree of isolation: (1) subsurface spaces in upper soil layers, in which daily temperature fluctuations penetrate; (2) shallow spaces in stony accumulations and in the void systems in rocks, in which daily temperature fluctuations do not reach; (3) deep subterranean spaces more isolated from the surface, developed in rock massifs, i.e. void systems, caves included, in which annual temperature fluctuations do not penetrate. The shallow spaces offer a microclimatic gradient between the soil surface, with great daily and annual temperature and moisture fluctuations, and stable environments in deep subterranean spaces. Shallow spaces represent the transition zone, in which gradual adaptation to the stable environment of deep subterranean spaces take place. All troglomorphic spiders in Central Europe occur in shallow subterranean spaces. It is evidenced, that subterranean forms can develop from species inhabiting: (1) forest litter; (2) various stony habitats (rocks, surface of scree fields); (3) the surroundings of mountain snow fields and (4) peatbogs. Keywords: Subterranean Evolution Troglomorphisms Spiders Stony Debris Shallow Subterranean Spaces