The environmental physiology of Antarctic terrestrial nematodes: a review

Abstract

The environmental physiology of terrestrial Antarctic nematodes is reviewed with an emphasis on their cold-tolerance strategies. These nematodes are living in one of the most extreme environments on Earth and face a variety of stresses, including low temperatures and desiccation. Their diversity is low and declines with latitude. They show resistance adaptation, surviving freezing and desiccation in a dormant state but reproducing when conditions are favourable. At high freezing rates in the surrounding medium the Antarctic nematode Panagrolaimus davidi freezes by inoculative freezing but can survive intracellular freezing. At slow freezing rates this nematode does not freeze but undergoes cryoprotective dehydration. Cold tolerance may be aided by rapid freezing, the production of trehalose and by an ice-active protein that inhibits recrystallisation. P. davidi relies on slow rates of water loss from its habitat, and can survive in a state of anhydrobiosis, perhaps aided by the ability to synthesise trehalose. Teratocephalus tilbrooki and Ditylenchus parcevivens are fast-dehydration strategists. Little is known of the osmoregulatory mechanisms of Antarctic nematodes. Freezing rates are likely to vary with water content in Antarctic soils. Saturated soils may produce slow freezing rates and favour cryoprotective dehydration. As the soil dries freezing rates may become faster, favouring freezing tolerance. When the soil dries completely the nematodes survive anhydrobiotically. Terrestrial Antarctic nematodes thus have a variety of strategies that ensure their survival in a harsh and variable environment. We need to more fully understand the conditions to which they are exposed in Antarctic soils and to apply more natural rates of freezing and desiccation to our studies.

Osmoregulation in the Antarctic nematodePanagrolaimus davidi

“…Panagrolaimus davidi Timm 1971 is an Antarctic nematode associated with ornithogenic soils (Porazinska et al, 2002) in coastal areas that are ice-free during spring and summer but which receive sufficient meltwater from adjacent snowbanks to support the growth of algae and/or moss. The water content of these sites varies from saturated to completely dry (Wharton, 1998) and the nematode would thus be expected to face changes in external osmotic concentration (Wharton, 2003), as do other free-living nematodes (Wright, 1998).…”

Freeze tolerance, supercooling points and ice formation: comparative studies on the subzero temperature survival of limno-terrestrial tardigrades

“…In many freeze tolerant organisms, polyols and sugars are accumulated to protect membranes and proteins against phase transition and to control the ice fraction size and minimum cell volume resulting from freeze concentration and osmotic dehydration (Ramløv, 2000;Sinclair et al, 2003;Zachariassen, 1985). Ice active proteins are also sometimes present and may act as recrystallization inhibitors, which prevent the growth and redistribution of ice crystals once these have formed (Duman, 2001;Wharton, 2003).…”

Responses of invertebrates to temperature and water stress: A polar perspective

“…Key to this process is the 97 accumulation of ice nucleating agents (INAs), such as specialised proteins ), food 98 particles, crystalloid compounds and microorganisms (Klok and Chown 1997;99 Worland and Block 1999), which act as heterogeneous surfaces for the promotion of water molecule 100 aggregation (Bale 2002 Wharton 2003aWharton , 2003bWharton , 2011b. 112…”