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Our 2006 Antarctic field season at Palmer Station was a great success! In one short month, our research team collected data for several projects. Some of these studies were a continuation from last year’s research (Science Digest 2005), whereas other projects were brand new.
In 2005, the research team deployed several HOBO temperature loggers on various islands where we collect larval and adult Belgica antarctica.
We were interested in what temperatures these insects are experiencing throughout the year in their microhabitats (a small area where an animal lives). Microhabitats of Belgica can include spots under rocks, in the top layers of soil, or in clumps of moss.
This year, we successfully recovered all of the loggers and downloaded the data to a computer for analysis. We discovered two interesting things:
- Although air temperatures at Palmer Station may drop to -20°C in the winter, microhabitat temperatures remained between 0 and -2°C for much of the winter. It was rare for the temperature in Belgica's overwintering sites (microhabitats where they spend the winter) to drop below -5°C. The temperature difference between the air and soil was due to a 1 meter-thick, insulating blanket of snow and ice over the microhabitats.
- During the Austral summer (summer in the Southern Hemisphere), microhabitats may reach temperatures of over 25°C. Additionally, it is not uncommon for microhabitat temperatures to vary by more than 20°C over the course of a single day!
The tolerance of Belgica to desiccation (drying out) was again a major focus of our research this year. Larvae commonly may be exposed to desiccating conditions as soils dry; therefore, the larvae need to be extremely tolerant to desiccation. Larvae may lose up to 65% of their body weight in water and still survive! Larvae not only lose a lot of water, but they lose it quickly: compared to other terrestrial insects, Belgica larvae have an unusually high rate of water loss.
We also collected RNA samples to investigate gene expression during desiccation and rehydration (gaining water). We are interested in determining what genes are involved in allowing Belgica to tolerate such extreme desiccation. These data will eventually allow us to determine whether Belgica uses survival strategies similar to more temperate species, or whether it has evolved unique strategies allowing it to survive in the harsh Antarctic environment.
Let's review what we have learned so far. We now know that Belgica:
- Spends much of the winter at relatively moderate subzero temperatures.
- Possess an extreme tolerance to desiccation.
- Has a high rate of water loss.
These findings made us interested in investigating the ability of larvae to use cryoprotective dehydration to survive subzero temperatures. In this strategy, a supercooled (the body fluids remain unfrozen at subzero temperatures) insect will lose water and dehydrate when exposed to an icy environment. By losing water, the insect balances its body fluid melting point with that of the surrounding temperature, thereby preventing the risk of freezing. Belgica appears to possess just such an ability to undergo cryoprotective dehydration! However, the use of cryoprotective dehydration may be constrained by larvae's ability to resist inoculative freezing (the freezing of body fluids as result of contact with ice in the environment). We collected RNA samples to examine gene expression during cryoprotective dehydration.
At times, larvae of Belgica can submerged in fresh water from rain or melting snow, or salt water from sea spray.
We examined the tolerance and physiological response of larvae to submergence in various salinities of water. We found that larvae could survive submergence in pure seawater for more than 7 days! Submergence in pure seawater can result in desiccation, as body water is osmotically drawn out to the surrounding seawater (water moves from high concentration to low concentration) — think about what happens when you put salt on a slug!
Belgica produces solutes, such as trehalose and glycerol, that limit or slow such water loss and protect membranes and proteins during desiccation.
During the Austral summer, larval Belgica may be exposed to near anoxic (complete lack of oxygen) conditions as result of immersion in muddy soils rich in oxygen-consuming bacteria.
From previous work, we know that the larvae are extremely tolerant of anoxia; therefore, we collected RNA samples to investigate what genes are involved in the tolerance and recovery from anoxia exposure. This preliminary data will allow us to focus on this topic in future trips the Antarctic!
- Mike Elnitsky and Juanita Constible