Abstract:

Testacea (or testate amoebae, thecamoebians) are free-living amoeboid protozoa inhabiting a shell or test and they play an important role in material cycle and energy flow in terrestrial and aquatic ecosystems. The fauna of Testacea was analyzed from three polar regions of the Earth (Arctic, Antarctic and Tibet). In total, 315 species from 62 genera were recorded in the polar regions, i.e. 232 species (51 genera) in the Arctic, 131 species (30 genera) in the Antarctic, and 173 species (42 genera) in Tibet. In each polar region, the most diverse genera were Arcella, Centropyxis, Difflugia, Euglypha, Nebela; they accounted for 51.3%, 63.4% and 60.1% of the total species number in the Arctic, Antarctic and Tibet, respectively. Seventy-three species (23.2% of all species) and twenty-four genera (38.7% of all genera) were common to the three polar regions. One hundred and sixty-seven species (53.0% of species) were found only in one of the polar regions. Both Assulina muscorum and Centropyxis aerophila were widely distributed with the highest frequency (90%) in 40 subregions from the Arctic, Antarctic and Tibet. Cluster analysis revealed that the highest species-level similarity of Testacea was between the Arctic and Tibet (56.3%). Further, species similarity was the highest between the Arctic and Tibet based on Arcellinida species data, but the lowest based on filose Testacea species. Distinct differences in Testacea fauna indicate that some species are not ubiquitously distributed in spite of better passive long-distance dispersal than macro-organisms. Geographic distributional patterns of Testacea diversity are closely related to body size, habitat type and historical events, and our perception of these patterns are strongly influenced by taxonomic resolution (morphological criteria), sampling effort and spatial scales. We propose that study of genetic diversity among and within common Testacea morphospecies in relation to ecological and historical factors will elucidate geographic distributional patterns within this interesting group.