Archive for August, 2009

A little mite for a similar amount of time

August 26, 2009
A tiny, but complex mite: Nanorchestes sp.

A tiny, but complex mite: Nanorchestes sp.

I’m still swamped at work with too many mites and not enough time to appreciate them. So here’s a tiny example of what mites have to offer when one can take the time to look closely. Although scarcely more than a tenth of a millimetre in length when full grown, this mite comes complete with a highly ornamented cuticle, numerous highly branched (dendritic) setae, 2 pairs of simple eyes, 2 pairs of ciliated trichobothria (one of which forms a latch-trigger setacomplex), mysterious mouthparts, and an astounding ability to jump several times its body length.  Nanorchestes species also have an astounding ecology – a mysterious ability to thrive in cold deserts, including some of the coldest places in the World.

Most mites in this genus are poorly studied, but Nanorchestes antarcticus Strandtmann is well known.  Herds of hundreds of thousands of these mites roam parts of the Antarctic continent, presumably grazing on algae (lacking solid gut contents, the feeding behaviour of these mites is a bit murky).  As tiny as they are, Bill Block has been able to measure individual oxygen consumption rates (Oikos 27: 320-323), which at 5C in an adult female is around 368 micro-litres of O2 per gram per hour.  That may sound like a lot of CO2 entering the Antarctic atmosphere, but on a good day, a full grown mite weighs only about 3.6 micrograms, so no need to dob them in to  Al Gore.  It’s not 5C in Antarctica all that often.

D. E. Rounsevell and Penny Greenslade have a hypothesis  (Hydrobiologia 165: 209-212) that the ornate cuticle in Nanorchestes enables the mites to hold a layer of air around their bodies that increases their respiratory efficiency in seasonally waterlogged soils and perhaps keeps the ice away from their cuticle when they refreeze. Most of the two dozen or so described species in the genus are known from extremely cold areas of the World – but I think this is an artifact of funding. If you want to study animals living in Antarctica, then your are pretty much limited to mites, springtails, nematodes, and rotifers.  Well, I exaggerate, there are a couple of chironomids and I guess a few vertebrates must show up now and then, but who has the time for every little taxon. All those Nanorchestes living outside the Antarctic are pretty much ignored too. You can find Nanorchestes anywhere you can find a dry bit of soil, from the beach to a treehole in a rainforest. I can even find them in my city yard, but then this is Alberta, winter is on the way, and I know they are more cold-adapted than I am. I’d much rather be looking for Nanorchestes on a Queensland beach.