Following my previous post on wildlife diseases, I've been in a fairly multicellular mood. Rather than try and turn my mind back to bacteria I decided to get it out of my system by finishing the month with a two part mini-series on creepy-crawlies that survive in some of the harshest conditions on earth; the frozen arctic.
Part I: the ice worms
Related to common earthworms, these annelids spend their entire lives in glaciers. They are the largest multicellular eukaryotes that require below-freezing temperatures to survive. First discovered in Alaska, ice worms are found across the northern United States [edit: and Canada]; in Alaska, Washington, Oregon and British Columbia. They haven't been found in any other parts of the world, even those with glaciers.
The ice-worms live inside glaciers, although it is uncertain whether they are able to tunnel through the ice by releasing some form of antifreeze or just take advantage of natural breaks in the ice. They feed on snow algae, and come to the surface of the glaciers during the morning and evening to feed, spending the rest of the day safely tucked inside their icy home. Ice worms are so well adapted to the freezing conditions that they cannot live anywhere else. Exposing them to even 5 degrees above freezing and their internal membranes start to fall apart causing the whole worm to liquefy and essentially melt.
There are some fascinating biochemical changes that allow the ice worms to survive below zero (and are responsible for their rather gruesome death if they get too hot). One example is tubulin - the protein that forms little networks inside the cell to aid with structure and transport. These networks are formed by subunits of the tubulin all joining together, and in most species tubulin breaks apart at low temperatures. The ice worms have tweaked the protein structure of their tubulin to form more stabilising contacts between subunits in a way that is distinct from other cold-adapted organisms.
Another adaptation the ice worms have made is to adjust their levels of ATP, the molecule that is used as energy currency inside the cell. In most temperate organisms ATP production decreases in the cold, leading to animals becoming lethargic and sluggish. In the ice worms ATP is kept at very high levels within the cell, and production increases as temperatures drop.
They might not sound, or look, like the most romantic creatures but to my surprise I've found they feature in the odd love poem, including this sweet little one by the English poet Robert William Service written in 1910:
"In the land of the pale blue snow
Where it's ninety-nine below,
And the polar bears are dancing on the plain,
In the shadow of the pole
Oh, my Heart, my Life, my Soul,
I will meet thee when the ice-worms nest again."
Tartaglia LJ, Shain DH. Cold-adapted tubulins in the glacier ice worm, Mesenchytraeus solifugus, Gene. 2008 Nov 1;423(2):135-41.
Napolitano MJ, Nagele RG, Shain DH. The ice worm, Mesenchytraeus solifugus, elevates adenylate levels at low physiological temperature. Comp Biochem Physiol A Mol Integr Physiol. 2004 Jan;137(1):227-35.