Biologist PZ Myers, while something of an over-the-top culture warrior -- he makes Richard Dawkins seem tactful and restrained in comparison -- does definitely light up when he's talking science and particular his specialty, cephalopods (squids, octopus, cuttlefish, etc). He recently posted an interesting set of notes on PANDA'S THUMB on the work of fellow biologist Bryan Grieg Fry, who has been exploring the evolution of animal venom. It appears that Fry's main focus has been on the evolution of lizard and snake venoms, but he has also investigated the venoms of cephalopods -- squids, cuttlefish, octopus and the like -- which is Myers' specialty. His notes followed, heavily edited for a posting on my own BBS:
BEGIN QUOTE:
When we examine what venomous reptiles inject into their prey, it's a set of proteins that display a nested "evolutionary" hierarchy of descent. Ancient reptiles had a small and nasty set of poisons, and to improve their effectiveness, more and more have been added to the cocktail. Some lizards produce venomous proteins, while the really dangerous snakes produce those same proteins, plus a large number of others. A toxin like "Cysteine RIch Secretory Protein (CRISP)" is common to all, but only the most deadly add "phosopholipase A2 (PLA2)" -- an enzyme that breaks down cell membranes -- to the mix.
IMAGE VIA FLICKR / SEE RICHARD LING'S ALBUM
Fry has also investigated toxins in cephalopods. Fry examined the products of the venom glands of octopus, squid, and cuttlefish, and found a range of proteins -- some unique, others familiar:
There are several interesting lessons in that list. First, evolution doesn't just invent something entirely new on the spot to fill a function. What we find instead is that existing proteins are recycled for the new job. This is how evolution generally operates, taking what already exists and adapting it to a new function. PLA2, for example, is a perfectly harmless and extremely useful non-venomous protein in many organisms. We humans use to control the inflammation response to infection and injury , in moderation, it's a good thing. What venomous animals can do, however, is inject an overdose of this regulator to send a victim's repair and recovery systems berserk, producing swelling that can incapacitate a tissue.
Similarly, a peptidase is a useful enzyme for breaking down proteins in the digestive system "¦ but a poisonous snake or cephalopod biting your hand can squirt it into the tissues to digest your muscles and connective tissue. Some effective venoms are simply common helpful proteins being used in an unhelpful fashion -- or at least unhelpful to the victim.
Second, cephalopods and vertebrates like snakes have independently converged in using some of the same venoms. Partly this is due to the fact that the proteins were commonly available , all animals have phospholipases, which are important regulator proteins, so they are part of the common toolbox. It's also part of an inflammation pathway that can be exploited by venomous predators, in the same way that we have shared proteins used in the operation of the nervous system that can be targeted by neurotoxins.
Different animals will independently make use of these proteins as toxins, but the range of candidate proteins for toxins is common because of shared ancestry. Some of these candidates end up being more suitable for use as toxins than others. We normally don't use anything in the kitchen drawer as a weapon, but if we have to improvise the butcher knife ends up being selected far more often than the eggbeater. The CRISP proteins -- the cysteine-rich secretory proteins -- and proteins that resemble them end up being strongly preferred as toxins. The end result is that entirely different lineages of animals end up independently producing venom drawn from the same small subset of proteins.
END QUOTE
The posting included an evolutionary tree of the "Lepidosaurs" -- the snakes, lizards, and the iguana-like tuataras. I had to puzzle over it a bit because I only recognized a handful of the groups. What was striking was that the group not only includes snakes, but also two -- not one but two -- entirely separate groups of legless lizards, the "amphisaenids" and the very obscure "dibamids". The legless configuration just gets repeatedly invented by the lizard family.
BEGIN QUOTE:
When we examine what venomous reptiles inject into their prey, it's a set of proteins that display a nested "evolutionary" hierarchy of descent. Ancient reptiles had a small and nasty set of poisons, and to improve their effectiveness, more and more have been added to the cocktail. Some lizards produce venomous proteins, while the really dangerous snakes produce those same proteins, plus a large number of others. A toxin like "Cysteine RIch Secretory Protein (CRISP)" is common to all, but only the most deadly add "phosopholipase A2 (PLA2)" -- an enzyme that breaks down cell membranes -- to the mix.
IMAGE VIA FLICKR / SEE RICHARD LING'S ALBUM
Fry has also investigated toxins in cephalopods. Fry examined the products of the venom glands of octopus, squid, and cuttlefish, and found a range of proteins -- some unique, others familiar:
- CAP (a CRISP protein)
- PLA2
- chitinase (chitin digestive enzyme)
- peptidase S1 (protein digestive enzyme)
There are several interesting lessons in that list. First, evolution doesn't just invent something entirely new on the spot to fill a function. What we find instead is that existing proteins are recycled for the new job. This is how evolution generally operates, taking what already exists and adapting it to a new function. PLA2, for example, is a perfectly harmless and extremely useful non-venomous protein in many organisms. We humans use to control the inflammation response to infection and injury , in moderation, it's a good thing. What venomous animals can do, however, is inject an overdose of this regulator to send a victim's repair and recovery systems berserk, producing swelling that can incapacitate a tissue.
Similarly, a peptidase is a useful enzyme for breaking down proteins in the digestive system "¦ but a poisonous snake or cephalopod biting your hand can squirt it into the tissues to digest your muscles and connective tissue. Some effective venoms are simply common helpful proteins being used in an unhelpful fashion -- or at least unhelpful to the victim.
Second, cephalopods and vertebrates like snakes have independently converged in using some of the same venoms. Partly this is due to the fact that the proteins were commonly available , all animals have phospholipases, which are important regulator proteins, so they are part of the common toolbox. It's also part of an inflammation pathway that can be exploited by venomous predators, in the same way that we have shared proteins used in the operation of the nervous system that can be targeted by neurotoxins.
Different animals will independently make use of these proteins as toxins, but the range of candidate proteins for toxins is common because of shared ancestry. Some of these candidates end up being more suitable for use as toxins than others. We normally don't use anything in the kitchen drawer as a weapon, but if we have to improvise the butcher knife ends up being selected far more often than the eggbeater. The CRISP proteins -- the cysteine-rich secretory proteins -- and proteins that resemble them end up being strongly preferred as toxins. The end result is that entirely different lineages of animals end up independently producing venom drawn from the same small subset of proteins.
END QUOTE
The posting included an evolutionary tree of the "Lepidosaurs" -- the snakes, lizards, and the iguana-like tuataras. I had to puzzle over it a bit because I only recognized a handful of the groups. What was striking was that the group not only includes snakes, but also two -- not one but two -- entirely separate groups of legless lizards, the "amphisaenids" and the very obscure "dibamids". The legless configuration just gets repeatedly invented by the lizard family.
