Here's a good Trivial Pursuit™ question: what is the largest entirely terrestrial animal on Antarctica? Answer: a midge, Belgica antarctica. Sizing up at 5 mm, the flightless adults crawl around like ants during their brief lives. However, the larvae remain submerged near the surface of the Antarctic soil for two years, waiting for the brief summer's return. Michael Elnitsky and Richard Lee were curious to know how the hardy larvae successfully survived not one, but two Antarctic winters. They already knew that the insects could survive freezing solid to –15°C, but they suspected that the secret of the insect's resilience may also reside in its remarkably leaky skin. Could the insects survive by desiccating in the dehydrating environment ()? Elnitsky and his colleagues headed south to find out how the larvae weather winter.
Travelling to the USA's Palmer Station on the Antarctic Peninsula,Elnitsky, Scott Hayward, Joseph Rinehart, David Denlinger and Lee spent several weeks crawling through the summer mud, flipping over rocks searching for the bright purple larvae. Elnitsky explains that the larvae can be hard to find, but fortunately they tend to cluster in groups of up to several hundred. It was simply a matter of flipping enough stones before the team had sufficient 4th-instar larvae ready for the week-long journey north.
Returning with the larvae on ice to Lee's Ohio laboratory, Elnitsky tested the insects' dehydration tolerance by simulating an idealised Antarctic environment. Placing the larvae in small plastic tubes and then placing the tubes inside larger sealed vials, each filled with a few grams of ice, the team slowly cooled the vial from –1°C to –3°C over a period of days. Measuring the larvae's water levels and body fluid melting point after 14 days at –3°C the team found that the larvae had lost 40% of their body fluids. Their body fluid melting point had also dropped to–3°C. And when Elnitsky measured the levels of antifreeze compounds in the larvae's body fluids, he found that they had increased by approximately 10 fold. The larvae had equilibrated their body fluid vapour pressure with the vapour pressure of the ice and dehydrated so they could no longer freeze. And when Elnitsky gently warmed the larvae to 4°C and supplied them with water, more than 95% of the larvae revived. The insects could survive dehydration, but how would they fare under more natural conditions?
This time Elnitsky placed the larvae in direct contact with Antarctic soil at three different moisture levels before freezing the soil and slowly cooling to –3°C. Measuring the insects' body fluid levels after a fortnight in the icy conditions, Elnitsky found that the larvae in dry soil had remained in equilibrium with the dry environment and dehydrated. However, the larvae in the moist soil couldn't dehydrate; they quickly froze solid and retained high body fluid levels.
So it appears that Antarctic midge larvae have two strategies –freeze tolerance and dehydration – to survive the harsh Antarctic winter, which could be the answer to another good Trivial Pursuit™question.
