The humble squid’s extraordinary service to neuroscience
Michael Viney: Everything we know about how nerves work gleaned from squid nerves
Giant squid: The squid, like the octopus, edits thousands of genes, using RNA, to serve an exceptional and complex nervous system. Illustration: Michael Viney
I first saw them by night, or rather by flashlight aimed beside the dinghy as we fished a mile beyond Brighton’s pier. A whole shoal of them appeared beneath the boat, waving their arms, their button eyes glistening.
We were not fishing for squid – too foreign a taste for England in those days. But this early glimpse left me fascinated with their kind, not least their giant, still greatly mysterious relative with eyes the size of hubcaps.
The Brighton squids were the regular, long-fin Doryteuthis of inshore waters, not the huge, deep-water Architeuthis dux, snared this summer as trawler by-catch on the Porcupine Bank. The Cú na Mara (a nice echo) landed two separate specimens at Dingle a few weeks apart.
Expiring on they way up, each was around 6m long, counting in the tentacles. They brought to seven the number landed in 350 years, including a remarkable three in 1995 alone.
Abandoning external shells to work on jet propulsion, they have developed genes and nerves of special interest to science.
Two of those were trawled from the Porcupine Bank by a Marine Institute survey vessel. Dr Kevin Flannery, the Dingle marine biologist, would now like the institute to send its remote cameras for a proper look around. Meanwhile, the second squid, as dead as the first but in better shape, will soon be on display in the Dingle Oceanworld aquarium.
What could seem strangest is that giant squid are soft-bodied molluscs, like limpets or winkles. Abandoning external shells to work on jet propulsion, they have developed genes and nerves of special interest to science.
“Practically every darn thing we know about how nerves work,” wrote Martin Wells (HG’s grandson), “has been worked out from squid nerves.”
I remembered the late Dr Wells, a zoologist at Cambridge University, when watching a grisly YouTube video of New Zealand scientists dissecting an Architeuthis with their students. Wells did his own share of slicing into cephalopods – squid, octopus and cuttlefish – and as a pioneer researcher found the whole group fascinating and wonderfully alien: I’m sure he loved ET. (Find his 1998 book Civilisation and the Limpet.)
Out of water, a giant squid makes a flaccid and slithery corpse, much smaller than when living, reeking of ammonia, and far from the sinister Kraken of Nordic myths. Those tipped ashore in Ireland tend to be young and rather small, well short of the 18m now seen as maximum total length of the bigger females.
Giant squid hunt by sight, snatching at fish (and smaller squid) with velcro-tipped tentacles and pulling them in with suckered arms to a sharp, hard, parrot’s beak. These durable remnants were found in the stomachs of sperm whales, the squid’s chief predator, at the Belmullet, Co Mayo, whaling station of the early 1900s.
The Porcupine Bank may, indeed, prove a special local haunt of Architeuthis, where blue whiting and horse mackerel have been found in their food. But giant squids live worldwide, short of the polar seas, and were first filmed alive off Japan in 2004 .
There has been speculation about their variety, with strong claims for eight species or more. But a recent project, led by the University of Copenhagen, studied the genomes of giant squid from 43 tissue samples across their world range. Among the team was Dr Louise Allcock, a leading researcher on cephalopods, at the Martin Ryan Institute at NUI Galway.
Heavy fishing of tuna may have changed the hunting pressure on squid
It found so little variation in the squid DNA as to plump for Architeuthis dux as a single global species (see the study at http://iti.ms/2vL1T91). But this posed questions for evolution and biogeography: how had the squid spread so widely without mutation and adaptive change?
Global numbers must be large to withstand the steady, substantial appetite of sperm and other toothed whales and the hunting of squid juveniles by dolphins, fish and even sea birds.
Heavy fishing of tuna may have changed the hunting pressure on squid: the increase in tuna catches, referred to in this study, are said to result in an extra 20 million tonnes of squid of all kinds in the world oceans.
A sudden inflation in an original, small population of giant squid could explain the sameness of their global DNA. But the team guessed at the possible migration of adults, unusually tolerant of changing regional conditions, and drifting of the squids’ young in the great oceanic conveyor belt that carries deep north Atlantic water to surface again in the Pacific.
The squid’s fellow mollusc, the octopus, is renowned for extraordinary intelligence and colour-change camouflage. A recent sequencing of its genome found it has about 10,000 more genes than humans, with hundreds that don’t have counterparts in other animals (nature.com/articles/nature14668).
The squid, like the octopus, edits thousands of genes, using RNA, to serve an exceptional and complex nervous system. This is the largest among invertebrates and for decades has made the ordinary, inshore, fishmonger’s squid the main model organism of neuroscience.
Michael Viney’s Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks; email@example.com