By Dani Cooper in Australia:
Cephalopods share common toxic armoury
Wednesday, 15 April 2009
In a paper published in the latest Journal of Molecular Evolution, the researchers also show that the different species of cephalopod all share a common, ancient venomous ancestor.
Venom researcher and lead author Dr Bryan Fry, of the University of Melbourne‘s Bio21 Institute, says one of the limits in adapting animal toxins for medical use has been the narrow range of animals studied.
“New insights into the evolution of venom systems and the medical importance of the toxins cannot be advanced without recognition of the true … diversity of venoms and associated venom systems,” he says.
Fry says although the blue-ringed octopus (Hapalochlaena sp.) remains the only cephalopod species dangerous to humans, it does not make the deadly toxin.
Instead it is produced by endosymbiotic bacteria, which live in a symbiotic relationship within the tissues of the invertebrate.
For the study, Fry and his colleagues obtained tissue samples from octopuses, squid and cuttlefish ranging from the Antarctic, Hong Kong, Coral Sea and Great Barrier Reef.
They found cephalopods use venom for predation as part of a joint attack with their beaks.
For example, cuttlefish drill into clam shells with their beaks and inject a toxin that makes the clam open its shell.
Fry says interestingly the size of the species’ beak is inversely related to the size of venom glands.
Through DNA analysis they also discovered different species have similar venom glands, and use similar venom proteins as other toxic animals such as snakes.
Because “there are no coincidences in nature”, Fry says the universal presence of these proteins suggests they have structural or chemical properties that make them predisposed to be useful as toxins.
“Not only will this allow us to understand how these animals have assembled their arsenals, but it will also allow us to better exploit them in the development of new drugs from venoms,” he says. …
Analysis of the genes for venom production also revealed the cephalopods as a prime example of convergent evolution, where species independently develop similar traits.
They found one common set of venom proteins were produced by an ancient ancestor.
But as the octopus and cuttlefish lineages diverged and moved into new ecologies, new proteins were added over time to their chemical arsenals, says Fry.
The collection of specimens for the study from the Antarctic, which was conducted as part the Census of Marine Life, may have also uncovered two or three new species of octopus, he says.
The squid family Ommastrephidae includes my favorite Humboldt squid, along with a lot of other big-time commercial fishery species: here.
Speaking of cephalopods which have surprised by not being too heavy to fly after all, I was reminded of one little cuttlefish who is actually too heavy to swim: Metasepia pfefferi, or Pfeffer’s Flamboyant Cuttlefish: here.