Why don't mammals & birds use poison?

[Plekhanov]

The thread title pretty much says it all really most species of forms most other forms of life poison for defence and attack, warm blooded animals, apart from the platypus, don’t. Why is this?

Poison offers a significant deterrent effect for those that don’t want to get eaten and seems to come in handy for hunters too. What are the costs to animals producing and using poisons that have led to birds and mammals evolving away from using them?

[Darth Wong]

Mammals tend to use speed to evade a predator, whereas a slow-moving lizard doesn't really have that option.

[Lord of the Abyss]

Shrews have a poisonous bite. Link

The short-tailed shrew is the only poisonous mammal in North America. The poison is both a neurotoxin and a hemotoxin. The poison is produced by the submaxillary salivary gland, and is present in the saliva. It acts as a slow poison, and immobilizes insects and other prey. Immobilized insects remain alive for three to five days, and provide a source of fresh non-decomposing food. These shrews have a particularly strong musky odor. For this reason, some predators, such as foxes and bobcats, may kill these shrews but not eat them. It is one of the most widely distributed mammals in the park.

Several bird species are poisonous. Link to one

One day Dumbacher was freeing yet another hooded pitohui from his nets when its sharp beak and claws scratched his hand. Dumbacher put his hand in his mouth and got a strange numbing sensation that he recognized as the effect of some toxin. At first he thought nothing of it, because he occasionally brushed against poisonous plants in the forest. It never occurred to him to suspect the bird. But then a few weeks later another member of the team mentioned the same odd sensation when he put his injured finger in his mouth. Again the culprit was a hooded pitohui. Dumbacher’s interest was piqued, so the next year he returned to New Guinea determined to examine some of these rubbish birds more closely.

“The next time we caught a hooded pitohui,” he remembers, “I just plucked one of the feathers and tasted it: Whammo! Whatever it was, it was definitely in the feathers.”

As far as why it's rarer, here's my speculation. Critters like frogs and insects have more primitive immune systems than mammals; they rely more on chemical defenses against infections and parasites ( which is how frogs sit in swamp water all day without their skin rotting off ). Therefore, they start out with the basic genetic machinery for making poison; the only modifications necessary are for the poison to affect larger creatures. Mammals rely more on the immune system, so it takes more evolutionary steps for them to evolve poison.

[Ariphaos]

Many toxins produced by critters are found in humans and other mammals, if only in lesser quantities, as they tend to form from waste products. Mammals in particular also have vast numbers of bacteria which may infect and poison a predator.

[CaptainChewbacca]

Can I just say that I love the New Zealand guy taste-tested a feather to see if it had neurotoxin on it? That's Darwin-worthy right there.

[wautd]

The thread title pretty much says it all really most species of forms most other forms of life poison for defence and attack, warm blooded animals, apart from the platypus, don’t. Why is this?

Because they are not designed that way

[Solauren]

[Stupid Reason mode] Cause mammals and birds actually have good taste buds. Do you want to know the taste our your own poisonious shit?[/Mode]

[petesampras]

Well Mammals kick arse without it...

http://www.videotiger.com/tigercrocvideo.shtml

Don't Mammals have a more highly tuned metabolism? Could be that makes them more vunerable to the effects of poisons and thus less likely to be manufacturing them inside their bodies.

[nickolay1]

The platypus is another example of a mammal which actually produces toxin (unlike the birds previously mentioned).

[Fire Fly]

It depends on the nature of the animal and its environment in which it evolved. Animals which can move will use speed, camouflage, and hiding as their defense mechanism. Animals which cannot move as fast or are sedentary tend to develop chemical defense mechanisms. While not always true, that tends to be the trend. Why evolve an extra feature when the one presently works just fine?

[GrandMasterTerwynn]

The thread title pretty much says it all really most species of forms most other forms of life poison for defence and attack, warm blooded animals, apart from the platypus, don’t. Why is this?

Poison offers a significant deterrent effect for those that don’t want to get eaten and seems to come in handy for hunters too. What are the costs to animals producing and using poisons that have led to birds and mammals evolving away from using them?

Our early, proto-mammalian reptile ancestors were, on the balance, slow sorts, but lived among other fairly slow sorts of animals. When they were forced to go small and fast by the evolution of small and fast dinosaurs, evolutionary pressures tended to favor small, fast mammals which were quick enough to hide from the larger dinosaurs and compete with the smaller ones, so there really wasn't a niche for venomous mammals until after the dinosaurs went extinct. As a result, the majority of mammal species have no venom production capabilities.

Birds evolved from fast-moving, predatory dinosaurs, which had a long history favoring fast, brainy, animals which relied on speed and surprise. As a result, their immediate ancestors weren't apt to rely on venom either. Not until later on, when the birds diversified, did it become advantageous for a species or two to evolve venom. However, most birds aren't very venomous either.

In arthropod species, venom makes a fair bit of sense, as bugs with it can be more successful than bugs without it. And for something like a snake, which has no limbs with which to attach claws, venom can be very useful, if the snake in question didn't evolve the musculature, or didn't evolve in an environment where prey was easy enough to capture to waste energy crushing it to death.

[Broomstick]

Consider another aspect of venom (that is, a form of poison typically injected into another animal prior to eating): most are believed to have been based on digestive enzymes.

In fact, many venoms help dissolve tissue, assisting in digestion of the prey. That's one reason venoms such as those found in the brown recluse spider and diamondback rattlesnake (to give two diverse examples) cause so much damage - they destroy and digest/dissolve muscle tissue.

Now consider the animals that typically use venom - snakes swallow their prey whole, and devote a considerable amount of time/resources/energy to digesting that solid lump before it goes nasty in their stomachs. Insects and arthropods that use venom frequently allow the venom to partially, mostly, or entirely liquefy the innards of their prey, then suck up the juices. What do these critters have in common? They don't chew their food.

Obviously, if you don't chew your food you're under considerable evolutionary pressure to somehow process it in a different manner, which could lead to strong pressure to evolve much more efficient digestive enzymes. While you're at it, evolving some death-juice to paralyse a squirming and potentially-dangerous-to-you prey animal might be a good thing, too, as most critters will attempt to fight back when someone is sucking the life out of them.

Compare this with mammals and birds, who chop up their food while eating it. They process food in a different manner, thus will be under pressure to refine their consuming techniques (sharper teeth, better crop, etc.) rather than develop flesh-dissolving new ones.

Consider reptiles at large - most do not use venom, they use teeth and strong jaws. But snake jaws aren't particularly strong - being flexible enough get them around whole prey cuts down on their leverage. So snakes were forced to develop a new strategy, and even there, not all snakes are venomous. There are a few lizards that have toxic bites, but in the case of the Komodo dragon this is based on a sort of symbiotic relationship with mouth bacteria of a particularly noxious nature, not toxins directly produced by the lizard.

Consider fish - most, again, use teeth. A few have developed toxin-carrying spines, but they are a distinct minority. Likewise the platypus - a rarity among mammals with it's poison heel-spurs, demonstrating that poison/toxin production can evolve independently, but obviously most other mammals do fine without it. Among amphibians there are toxin-secreters (usually through skin glands) but some, such as the brightly-colored "poison arrow" frogs of the Amazon lose their toxicity when kept in captivity for even a short time - a fact well known to the natives who know how long each frog species is useful for harvesting poisons. This suggests that the frogs are not directly producing poison but rather harvesting it somehow from their environment, quite possibly by eating it. This is how monarch butterflies become toxic - by accumulating poisons from the milkweed plants they ate as caterpillars.

So I would suggest that toxicity - that is, being bad to eat - can evolve more easily than venom, which is produced by the animal in question. Bad Stuff can be either absorbed from the environment or produced, and can be deployed through skin glands, feathers, or even deposited in various body organs such as is done by various puffer fish. There are multiple routes to get to this state, and toxicity appears in unrelated species and in herbivores (monarch butterflies), omnivores (puffer fish), and predators (frogs, etc.)

Venom, I would suggest, is most likely to evolve in animals that either eat their prey whole or don't/can't chew/bite off/grind their prey. It's seen in predators, not herbivores - some herbivores such a ruminants require extensive processing of their food beyond chewing, but they don't have to chase down and disable their food, nor are they in danger of being attacked by hay. Predators need to disable/kill their prey relatively quickly. Venomous species tend to cluster - not just one or two unrelated snakes, for example, but a group of snake species with some relationship to each other, or a group of frog species, or a group of athropods, such as spiders.

So there's probably some "penalty" in resource and energy involved in producing venom, so unless it provides a large advantage you won't see it. But once it evolves in a species, that species tends to give rise to related species using the same techniques, so once the trick of it is learned there is apparently some incentive to keep on with it.

[Akhlut]

Awesome answer, Broomstick.

As Broomstick has so marvelously showed us, venom is really only present in animals that do not have adequate mouth parts to break up food into small, easily digested chunks. This is why tiger beetles, who have enormous (relatively speaking) mouth parts capable of rending apart their prey, and lobsters, who have both good chewing mouth parts and big ass claws to tear it apart, do not have venom, whereas spiders, who absolutely lack any sort of chewing mouth parts whatsoever have venom. This is also excellently illustrated by scorpions. Now, one of the most intimidating scorpions people can imagine is the emperor scorpion, a giant, black-carapaced beast with enormous claws. However, it is among the least venomous of scorpions, precisely because it's claws are so large that most prey can be easily shorn apart with them and it makes the prey easier to digest. However, scorpions with tiny claws have the most potent venom, which helps to digest the prey because they can't rip their prey to easily digestable pieces.

As far as why it's rarer, here's my speculation. Critters like frogs and insects have more primitive immune systems than mammals; they rely more on chemical defenses against infections and parasites ( which is how frogs sit in swamp water all day without their skin rotting off ). Therefore, they start out with the basic genetic machinery for making poison; the only modifications necessary are for the poison to affect larger creatures. Mammals rely more on the immune system, so it takes more evolutionary steps for them to evolve poison.

Actually, as far as I know, most amphibians have rather well-developed immune systems, like all chordates. Insects don't have particularly well-developed immune systems because most of them aren't long-lived and therefore don't have to worry about acute diseases.

And the parasite arguement is rather weak; frogs are well-known to be absolutely chock-full of parasites. Hell, I recall reading that at least one parasitologist in the tropics calls them "parasite bags" instead of frogs, so, whatever those toxins are doing, they ain't stopping parasites.

[weemadando]

Monotremes are also poisonous.

The male platypus has poisoned spurs which are pretty unpleasant (though VERY rarely fatal).

[Akhlut]

The other three extant monotremes aren't, though. That'd be like saying marsupials are predators despite only 2 extant species (if I'm not mistaken) are predators out of some 260ish.

[Akhlut]

My bad, that should be something like 8 species of predatory marsupials out of 260ish.