Once in awhile I find something that piques my interest that is different from the usual WUWT fare. This was one of those. I like this fellows blog because 1) I like hot peppers 2) I enjoyed his writing style 3) Given all the hot talk on climate lately, this seemed like a good topic to cool everybody off with – Anthony
Hot Peppers – Why Are They Hot?
From a Blog around the clock by Coturnix
Some plants do not want to get eaten. They may grow in places difficult to approach, they may look unappetizing, or they may evolve vile smells. Some have a fuzzy, hairy or sticky surface, others evolve thorns. Animals need to eat those plants to survive and plants need not be eaten by animals to survive, so a co-evolutionary arms-race leads to ever more bizzare adaptations by plants to deter the animals and ever more ingenious adaptations by animals to get around the deterrents.One of the most efficient ways for a plant to deter a herbivore is to divert one of its existing biochemical pathways to synthetise a novel chemical – something that will give the plant bad taste, induce vomiting or even pain or may be toxic enough to kill the animal.
But there are other kinds of co-evolution between plants and herbivores. Some plants need to have a part eaten – usually the seed – so they can propagate themselves. So, they evolved fruits. The seeds are enveloped in meaty, juicy, tasty packages of pure energy. Those fruits often evolve a sweet smell that can be detected from a distance. And the fruits are often advertised with bright colors – red, orange, yellow, green or purple: “Here I am! Here I am! Please eat me!”
So, the hot peppers are a real evolutionary conundrum. On one hand, they are boldly colored and sweet-smelling fruits – obvious sign of advertising to herbivores. On the other hand, once bitten into, they are far too hot and spicy to be a pleasant experience to the animal. So, what gives?
Back in 1960s, Dan Johnson had an interesting proposal he dubbed “directed deterrence” which suggested that some plants may make choices as to exactly which herbivores to attract and which to deter. Hot peppers are prime candidates for such a phenomenon. What is hot in peppers is capsaicin, a chemical that elicits a sensation of pain when it bind the vanilloid receptors in the nerve endings (usually inside the mouth) of the trigeminal nerve. As it happens, all mammals have capsaicin receptors, but it was found, relatively recently, that birds do not.
To test that hypothesis, Josh Tewksbury used two variants of hot peppers – one very hot (Capsicum annuum) and the other with a mutation that made it not hot at all (Capsicum chacoense) – and offered both as meals to rodents (packrats and cactus mice) and to birds (curve-billed thrashers).
All species ate the sweet kind about equally. When Josh offered them identically prepared meals made out of the hot stuff, the two rodents refused to eat it while the birds happily munched on it.
The study appeared in 2001 in Nature (pdf) and I saw Josh give a talk about it at that time as he was joining our department to postdoc with Dr.Nick Haddad. While my lab-buddy Chris and I gave him a lot of grief in the Q&A session on his lenient criteria of what constitutes a “hungry animal” (he needed them to be hungry for the feeding tests), still the main conclusions of the study are OK.
More importantly, it really happens in nature. Mammals avoid hot peppers out in Arizona where Josh studied them (and made videos of their behavior), but the birds gorged on peppers. When he analyzed the droppings of rodents and birds fed peppers, he saw that seeds that passed through avian intestinal tracts were fully fertile, while seeds eaten by mammals were chewed, crushed, broken or semi-digested and not fertile at all.
Additionally, the thrashers tend to spend a lot of time on fruiting shrubs of different kinds. While there, they poop. The hot pepper seeds in the droppings germinate right there and this is an ideal shady spot for them to grow.
What a great example of (co)evolutionary adaptations. Next time on this blog, the second Big Question: Why do we like to eat hot peppers?
UPDATE: I’ve added this chart of Pepper “hotness” below, to help you gauge what to eat and what not to eat (or spray). – Anthony
Source: Calbob.com and Wikipedia’s Scoville Scale
Ironic, isn’t it, that the pepper’s “defence” against being eaten by man has turned into an advantage. We now cultivate these plants in far greater numbers than they would appear in the wild.
Why do we like to eat hot peppers?
Years ago a pack of us macho 16,17 y/o boys were sitting around a table when one announced he could swallow a spoon full of tobasco sauce….he bellowed roughly the same question.
That’s just silly! Everyone agrees that it’s the CO2 in the peppers that makes them hot.
I don’t know about Arizona rodents not eating hot chillies however,
My wife is from North Sumatera Indonesia. The western, northern parts of Sumatera plus Aceh are renown for having very hot (chillli hot) food.
My wife tried to grow some very hot chillies in our garden in Melbourne Australia. The local possums not only ate the extremely hot chilli fruit off the bush but also consumed the leaves, stems and the bush structure down to ground level.
Anthony,
How funny you should post this. I made a fish stew for dinner that required one finely diced, red hot pepper. I wasn’t sure whether the pepper would be too hot, so I made my son taste it. He barely touched it to his mouth, then ran around the kitchen yelling, followed by massive water drinking (which doesn’t wash away the capsaicin, by the way). Nonetheless, diluted in the stew, the pepper added just the right touch.
Cheers!
Les Francis (16:46:20) :
Perhaps with Australia being biologically isolated for so long, the marsupials do not have capsaicin receptors.
The pepper in the pic with this article looks just like what a friend of mine grows. He calls it a “Medusa” and it is a tasty little number. As a poster above noted, not all mammals are deterred by the capsaicin (certainly man is not, well, THIS man is not). The reasons he gives for the existence of hot peppers is, of course, pure speculation, but it makes me want to go home and eat some right now. I think I will!
I am very interested in hearing why we like to eat them, since I ask myself that question every time I eat them.
Birds and rodents be damned. Target a species that will transport you across the globe and plant your seedlings in every suitable habitat. A species that will kill your competitors and predators whilst feeding you all you can eat.
Chilli – the only evidence of intelligent design.
Have these guys never had a pet parrot?
Peppers are one of the few things that I can manage to grow without killing outright. I have never seen any evidence that the birds take a fancy to them, even though I have to pick (the paltry few) tomatoes early ’cause the birds get them as soon as they turn fully red.
We have a good crop (enough to make pizza spice for a few dozen units) of cayennes which are redder than tomatoes, before I pick ’em, and don’t get eaten. One amazing crop is Aji Amarillo Picante (yellow hot peppers) from Peru. These things grow as big as carrots and have a strong, but quite different flavor compared to local peppers. The plants take two years to produce and haven’t had even one bird strike. My wife wants to plant the whole yard in them. As mower-in-chief, I say “Go for it!”
The curious thing about hot peppers (with respect to Texas and Mexico certainly) is that the chillies get hotter the closer you approach the border.
From either directions.
(Clearly, the marsupials of Aus and Oz haven’t gotten across the Sumatran border yet ….)
So, if I can make an OT analogy to tie climate change to hot peppers.
The religion of Global Warming is like the hot Capsicum annuum. That is, it contains a high heat index (analogous to Scoville heat units [SHU] indicating a large amount capsaicin annum present) but in this case, it is hot air and greenhouse gasses.
Those who imbibe on Global Warming are similar to curve-billed thrashers such as Hansen, the IPCC, politicians and the mainstream news media…who can eat the Al Gore climate change theory with no problems, depite the resulting poisonous poop output such as taxes and carbon offset that causes great harm to the economy and lifestyle of other human creatures.
However, we, the AGW skeptics are like the packrats and cactus mice. Who may not be as showy as the curve-billed thrashers…who get all the attention with their headlines and sensational appearances…but we are wise not to eat the poison fruit.
If you grow hot peppers, do NOT pick them bare handed and then pick your nose, dig sleepies out of your eyes, or scratch your privates. If you do, you will spend a very miserable 24 hours wishing you were dead. And it’s worse for women. Don’t ask me how I know this.
The Joseph Cerniglia Woodchuck Draft Cider is a really good
liquid to cut the hot pepper sensation. Give it a try if you are
into food. The right combination of carbon dioxide, alcohol,
tannic acid and water does the trick.
A few years back I read a piece on the chemical composition
of hot stuff. One tidbit was that the hot pepper is just one
misplaced nitrogen molecule away from ginger. Probably the
same evolutionary biology at work.
Not only no capsicum receptors, carnation , lily, camellia and many other flower variety as well (Although the draw the line at azaleas.) Chives, mints and many other herbs are fair game for them also.
My wife is having none of this one or two chillies in her dishes either. A handful is a minimum. Some of our western friends eyes water just looking at the food let alone tasting it.
The Indonesian way of easing a “Chilli attack” . Tomato slices, cucumber slices, Chrysanthemum tea.
Here is a typical picture of some West Sumateran Food. Note the little side dishes of extra cut up chilli to add in.
http://farm4.static.flickr.com/3133/3084514160_7ce1a03844_o.jpg
How apropos a subject as I sit down to eat my pizza, very liberally covered with crushed red pepper. For the uninitiated, you want a slice of my pizza, bring your own roll of paper towels to sop up the tears.
REPLY: Must be a pizza called “The Red Menace” – Anthony
I can see a reason why the pepper would evolve: the fruit needs an animal to pick it, to masticate it a bit, and then spit it out so that the fruit fertilizes the ground the seeds will germinate in. Being digested would cause too much damage to the seed capsule, but the ground the plant grows in is generally either undernourished, or otherwise lacking in nutrients needed to promote speedy germination.
Robinson (16:38:28) :
“Ironic, isn’t it, that the pepper’s “defence” against being eaten by man has turned into an advantage. We now cultivate these plants in far greater numbers than they would appear in the wild.”
Any plant or creature that man loves and/or consumes will never have to worry about extinction. Can you imagine cows becoming extinct?
Of course in the new crazy world we live in, I guess cows could be taxed into extinction… and maybe man too.
Wyatts microbrewery in Albany, Oregon makes the best chilli beer. They serve it on tap. I wait till I know that the tap is getting to the bottom. For some reason, the beer is hotter when the tap is almost dry. While served cold, it will set your teeth on fire. I miss my chilli beer now that I have moved back to NE Oregon.
The “antidote” for too much pepper-capsaicin… ice cream! Not only does it offer immediate relief from the feeling of heat, the calcium in the ice cream binds to the receptor that’s stimulated by the capsaicin and helps stop the pain reaction. Some restaurants that offer super spicy food have creamsicles on hand for folks that think they can handle the supa-hot stuff, but then end up realizing the error of their macho ways.
Bruce
Queen1: as you state, capsaicin doesn’t dissolve in water.
However, it is slightly soluble in alcohol. Which is why good, hot mexican food goes so well with Tequila.
Or, at least, that’s what I tell my wife…
Pamela,
Sorry, but I cannot resist. How do you know it is worse for a woman?
Robert A Cook PE (17:18:33) :
The curious thing about hot peppers (with respect to Texas and Mexico certainly) is that the chillies get hotter the closer you approach the border.
From either directions.
This may be due to the fact that fungi also don’t like capsaicin, but they do like warm temperatures.
http://www.rsc.org/chemistryworld/News/2008/August/11080802.asp
A brief synopsis of a pepper experience:
My son, age 6 at the time.
My garden, happy healthy veggies, including some Thai chilies.
Blood curdling screams, “My eyes, my eyes”
I quickly put 2 + 2 together and realized that he was in excruciating pain, but thankfully not in any real danger. (I learned the hard way with a Habenaro Pizza)
A quick Google search came up with a suggestion of flooding the eyes with milk.
So I am in the back yard, calmly talking to my son, telling him it is OK to scream, pinning him on the ground, holding his arms down with my knees, prying his eyes open and pouring a gallon jug of milk in his eyes.
I was sure a neighbor would call the police! I don’t know if the milk helped, but time did, after a few hours he was fine, but the first 30 minutes he was in PAIN.
It is kinda funny now, 4 years later, I tease him about it sometimes. It is almost as funny as when he took a small chunk out of his tongue when he licked the metal rack in the freezer. Good story, but a bit of topic, lol.