Listen to Episode 97 on PodBean, Spotify, YouTube, or wherever you’d like!
From microbes to mushrooms, spiders to snakes, urchins to us, all life engages in chemical warfare. Toxins produced by organisms are enormously varied in their origins, functions, and evolutionary histories. In this episode, we discuss the nasty chemicals that make up Venom and Poison.
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Poison, Toxin, Venom
Vocabulary time! Generally speaking, when it comes to biology and medicine:
Poisons are substances that cause chemical harm if too much is introduced onto or into a living thing. Poisoning can be caused by plants, animals, gases, metals, medications, and even too much of common things like water.
Toxins are poisons produced by the metabolic processes of living organisms.
Venoms are typically combinations of multiple toxins that are injected by one organism into another via a bite or sting.
Practically every living thing produces some form of toxin, and their functions are incredibly diverse: toxins can cause discomfort, pain, or death; various toxins can damage cells and tissues, disrupt nerve activity or digestion, impact blood flow, or cause any number of other effects; most toxins have specific effects on specific lifeforms, from bacteria to animals.
Toxins are often used defensively, as with the toxins used by our immune systems to ward off bacteria or the poisonous secretions that protect organisms like frogs and mushrooms. Other toxins are used offensively, as with rattlesnakes whose venom kills their prey, or parasitoid wasps whose venom paralyzes the soon-to-be hosts of their eggs.
Toxins are ubiquitous across life, but venom more specifically is also very widespread, having evolved numerous times in many groups of animals.
Poisons of the Past
As you might image, direct evidence of venomous, poisonous, or otherwise toxic organisms in the fossil record is pretty rare, but it’s not unheard of!
Fossil examples of vipers, stingrays, wasps, and many more animals feature the same venom-delivery adaptations seen in their living relatives. There are also some well-known cases like the “proto-mammal” Euchambersia, whose skull features a possible venom gland-and-delivery mechanism, and the reptile Uatchitodon, whose teeth were hollow tubes like some venomous snake fangs. Among dinosaurs, Sinornithosaurus was famously suspected to be venomous, although this is disputed.
Sometimes we can infer toxicity from other evidence. A fossil plant closely related to modern-day Strychnos can be inferred to have been similarly toxic; a cockroach from the Cretaceous shows the same warning color patterns as living species with chemical defenses; and any organism with an immune system would have produced some toxins!
And sometimes we’re lucky enough to catch a chemical in the act, as in the case of a Cretaceous soldier beetle caught in amber while secreting defensive compounds to ward off offenders.
Many, many studies have addressed questions of toxin evolution. Here are some examples we discussed in the episode.
Probably the best-studied group of venomous animals are snakes, which is due in large part to how medically important they are to humans. Popular hypotheses suggest that snake venom evolved one time, far back in their evolution, and that their toxins are derived from substances all over the body that have been repurposed for venom, although this 2014 paper disagrees with both of those hypotheses, and provides a nice overview of snake venom research.
Other studies have explored venom evolution – and found differing evolutionary patterns and histories – in groups as various as wasps, flies, fish, platypuses, and more.
One 2014 study experimentally found how a relatively simple gene mutation can change an antimicrobial toxin into a potentially dangerous neurotoxin. The toxin in question belongs to a group called defensins, which are extremely widespread and extremely ancient, found in the immune systems (and more) across plants, animals, and fungi.
Toxins and Venoms (pdf), from a 2009 edition of Current Biology is a nice, not-too-technical overview of toxin diversity.
If you enjoyed this topic and want more like it, check out these related episodes:
- Episode 3 – Snakes!
- Episode 123 – Spiders
- Episode 149 – Ants
- Episode 143 – Monitor Lizards
- Episode 91 – Frogs
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Hello Will, hello David
I’m a brazilian biologist, who discovered your excellent podcast during quarantine and I’m loving it! I’m still trying to catch up with all the past episodes. Started with the cats and dogs (cat lover here), the extinction ones, and of course, South America.
I really liked the 95 episode where you spent a lot of time describing the climate and biomes of the carboniferous and would like to hear that more, when it’s possible. I know it’s hard when you’re talking about evolution in a long scale of time.
I would also like to ask that you always translate measures into meters and kilograms, so I can understand hall tall and heavy something you’re talking about is.
One last wish, please do one (or two) episode on non-humanoid primates, and rodents (my phd research was on a subterranean rodent group from South America, Ctenomyidae) xD
Ps: sorry for any english mistakes
Ps2: despite the language barrier, already recommended you for my biologist fellows
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Hello Mayara! Glad you enjoy the podcast!
We’ve been working on being better at translating lengths and weights when they come up – a few listeners have reached out about that … we promise to keep working at it!
Also, great suggestions! We’ll put them on the list and be sure to get to them. We don’t know much about rodents; we might have to look into your burrowing rodents!
I am a little bit surprised that a snake fan did a whole episode about venom and poison and did not mention toxicofera! And, I would request an episode on the topic, but, it’s mainly a genetics thing, and the podcast squamates pod already did a great episode on toxicofera: http://squamatespod.com/archives/185
Toxicofera came up briefly in the episode, but there was just so much to discuss we didn’t have time to go into detail. Fortunately, you’re right that Squamates did an excellent job of it.
oh! Sorry, I missed the mention. Thanks.