The major contribution to biodiversity of permafrost protozoa is made by species of ecological relevance, which can be found in modern polytypic aqueous and soil ecosystems.
All the extracted protozoa were characterized by relatively small sizes (5-60 |im) and the ability to use various nutrition strategies. Their life cycle includes a crypto-biotic stage, which comes under unfavorable conditions (food deficiency, water shortage, low oxygen content, low temperatures) and is often accompanied by formation of a cyst (Keilin 1959). Such adaptive properties are typical of organisms that utilize the advantages of a so-called "r-strategy", which enables them to survive under unstable or persistently extreme environmental conditions (Odum 1986). The r-strategy is a strategy of evolutionary development of a species, which implies intensive reproduction and short life duration, high degree of conformity to environmental changes and increased viability. This results, in particular, in a wide adaptive reaction of the organisms and in the successful colonization of polar eco-topes (MacArthur 1972; Luftenegger et al. 1985).
It is known that at high latitudes of the Arctic and Antarctic, under extremely low conditions of temperature, organisms that apply passive-tolerant adaptive strategies (r-strategies) have an advantage. Correspondingly, more progressive taxons that realize strategies of the resistant-active type (K-strategies), and provide the basis for biodiversity of the global biota, are rare in the ecosystems of polar regions (Chernov 1984; Chernov and Matveeva 2002).
The modern soil and freshwater protistofauna of the east Arctic is practically unexplored; this makes it difficult to perform a comparative faunistical analysis of the regional ecosystems. However, the results of similar investigations in other polar regions confirm the observations described above. For example, the communities of Arctic and Antarctic soil protists were reported to be dominated by colpo-dean ciliates, especially by Colpoda steinii and C. inflata (Colpodea), which are typical r-strategists (Foissner 1996; Petz 1997).
Studies on the diversity of protozoan species isolated from permafrost have shown that the fauna of ancient ciliates is represented mainly by colpodean specimens. The species of the Acanthamoebida genus, which prevail among permafrost amoebas, are also evident r-strategists, and are distributed worldwide (Page 1988).
The fauna of heterotrophic flagellates isolated from permafrost consists mainly of eurybiontic species, and is highly similar to the typical fauna of freshwater polar ecosystems. Some species (Allantion tachyploon, Bodo curvifilus, B.designis, Monosiga ovata, Apusomonasproboscidea, Cercomonas sp., Heteromita globosa, Spumella sp.) were described earlier as inhabitants of freshwater biotopes of the Arctic and Antarctic (Mylnikov and Zhgarev 1984; Tong et al. 1997; Butler 1999; Mylnikov 2002; Tikhonenkov and Mazei 2007). Other species (Allantion tachyploon, Bodo curvifilus, B.designis, Heteromita globosa, Heteromita minima, Monosiga ovata, Spumella sp., Goniomonas truncata) are euryhaline, and can be found in high-latitude sea ecosystems (Patterson et al. 1993; V0rs 1993; Tong et al. 1997; Mazei and Tikhonenkov 2006). Most species of the ancient heterotrophic flagellates were described earlier in the freshwater and soil ecosystems of temperate latitudes (Zhukov 1993; Foissner 1991b; Ekelund and Patterson 1997; Auer and Arndt 2001).
It can be supposed that the adaptive mechanisms that help certain taxons to thrive in extreme ecotopes also allow them to sustain successfully an ultra-long anabiosis under permafrost conditions.
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