Proc. R. Soc. B doi: 10.1098/rspb.2008.1489 (2008)

Credit: B. MILLER

Antarctic sea spiders (pictured above), some up to 90 centimetres long, are giants compared with their 1–10-millimetre-long tropical cousins. Researchers have had a simple hypothesis for this 'polar gigantism', but results from a research team co-led by Arthur Woods of the University of Montana, Missoula, have complicated the picture.

Polar water has a higher level of dissolved oxygen, and cold-water arthropods have lower metabolic rates than their warm-water counterparts. The big spiders were thus expected to perform worse in low-oxygen environments.

Woods's team repeatedly flipped over spiders from 12 species that encompassed the small, medium and large varieties for an hour each, to see how long they took to right themselves. Overall, the giants were no more sluggish than the tiny ones. This result suggests that scientists must search for other possible evolutionary or ecological mechanisms for polar gigantism.