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Giant Squid: Mighty to Resist Speciation

If you never saw the first-ever footage of a live giant squid, released in January, look here and get a case of the chills. Then contemplate this evolutionary curiosity. Darwin's Gal´┐Żpagos finches come in 15 (very similar) species, dispersed across a small archipelago of islands. Giant squid, dispersed across the oceans of the world, now turn out to come in just one species: Architeuthis dux, initially described in 1857. Reporting in Proceedings of the Royal Society B, researchers used genetic analysis on 43 samples to arrive at their result ("Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species").

That's surprising -- once, it was thought there could be 21 species or more -- so there will need to be some kind of evolutionary rationalization. Coming up.

Although specimens of Architeuthis are becoming more readily available owing to the advancement of deep-sea fishing techniques, considerable controversy exists with regard to topics as varied as their taxonomy, biology and even behaviour. In this study, we have characterized the mitochondrial genome (mitogenome) diversity of 43 Architeuthis samples collected from across the range of the species, in order to use genetic information to provide new and otherwise difficult to obtain insights into the life of this animal. The results show no detectable phylogenetic structure at the mitochondrial level and, furthermore, that the level of nucleotide diversity is exceptionally low. These observations are consistent with the hypotheses that there is only one global species of giant squid, Architeuthis dux (Steenstrup, 1857), and that it is highly vagile, possibly dispersing through both a drifting paralarval stage and migration of larger individuals. Demographic history analyses of the genetic data suggest that there has been a recent population expansion or selective sweep, which may explain the low level of genetic diversity.
So the helpless paralarvae float here, there, and everywhere as plankton while the more mature squid purposefully migrate and somehow, notwithstanding our own inability to find them, find each other with ease. There seem to be a lot of them around the globe, since they must provide meals and mighty battle partners for the world's sperm whales. A mysterious creature now seems a little more mysterious.

If you've never seen the diorama of a giant squid fighting a sperm whale at the American Museum of Natural History, fake-looking yet haunting all the same because it's in darkness that makes you feel like your deep underwater, that's a must on your next New York City visit.