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
Sorry janama, if you feed then it only encourages them. I caught 14 living in a four gallon drum, in my garage. I took them to the bush and released them. In a matter of days another family had moved in. Give them more food and they breed like r…. possums.
Adolfo, a South American friend of my wife gave her a variety of some chillies that were so hot they were inedible. If my wife cant eat a variety of chili then it is definitely inedible.
PLANTS DON”T THINK!
Of course they do. My geraniums have plotted against me for years, and I suspect they also talked the Johnny Jumpups into populating the grass rather than the flowerbeds.
Adolfo Giurfa (18:35:59) : “As Peruvian…I can answer the question of why do we eat them: Because they usually contain an alkaloid, RUTINE, which causes addiction as coffe´s caffein or chocolate´s theobromine.”
I think you’ve got it, Adolfo. Only something akin to chocolate could explain why people eat the treacherous things. A package of dried habaneras at the market was labeled ‘wear rubber gloves when handling.’ And I’m going to send something down my innards that I shouldn’t touch bare-handed? I don’t think so!
Jorge
How does the plant “know” which chemical produces which effect?
Just curious.
Hot peppers are a curiosity all right. Seeds in general are even more curious. Some seeds aren’t even capable of germination until they’ve been crunched up by a cooperative animal!
I’m not sure what Ray is getting at about “THINKING” being required for evolution. Evolution is a matter of whether a random variation happens to enhance the reproductive survival of an organism. If it does, then that organism’s descendants will likely gain that same variation and same reproductive advantage. It’s only in a tiny minority of situations that “thought” actually comes into the process, largely in the form of idiosyncrasies of mate selection leading to such things as baboons with red butts.
As far as hot peppers go, I prefer to enhance flavor rather than replace it, so I tend toward the milder side of the scale. Unless my mother-in-law was the cook.
How does the plant “know” which chemical produces which effect?
It’s the plant that lives to tell about it.
Plant and offspring inhabits an acre.
Mammal type A comes along, eats all of it.
Except one. That one had a slight mutation (smell/colour/texture) the mammal didn’t like.
The mutant lives. Propagates. All seedlings now have the mutation. Acre is refilled.
Mammal type A comes along. Passes by. Mammal type B comes along, though, and….
Rinse. Lather. Repeat.
When you’re hot, you’re not.
When you’re not, you’re not.
Or something like that.
Love chilies, am totally addicted to hot sauces of all kinds and dried/fresh chilies. They grow quite well on my property too (santa cruz, CA), which is about a 1/2 acre clearing in the middle of majestic redwoods, Oak and Acacia. The long growing season and Indian summers keeps me in fresh chilies even into December. Had very hot Thai chilies up the wazoo the first year I tried. Last year was the year of the cayenne (also very hot). Have had success with just about every variety I’ve tried except Habanero.
Have never seen the birds go for them, but the deer around here love em. Even the hot ones. Totally serious, so not sure about the “birds only” theory. Any Chili or Tomato plant left outside of a barricade will be enthusiastically chomped by our deer neighbors.
hareynolds (21:51:15) : wrote [snip]:
“In fairness, it’s mostly what you’re used-to; almost anybody can be trained to enjoy a good helping of capiscum. The only consistent exceptions to this that I’ve seen are fair-skinned Englishmen.”
“I had a pasty English boss about 25 years ago who would break out in a torrential sweat if a drop of Tabasco touched his lips. Naturally, we bought him a gallon of the stuff as a nice parting gift on his return to the Auld Sod. [Once I was with him in Dehradun, India, and he ordered a HAMBURGER for dinner so as to avoid the spicy Indian fare. I’ve never really recovered my respect for the English since then.]”
Well, “hareynolds”, silly machismo aside, you obviously have never visited Britain and are basing your opinion on a single acquaintance. The Brits FAMOUSLY love Indian cuisine, much of which was globally pioneered in British Indian restaurants, and the average “fair-skinned Englishman” who goes out for a few pints on a Saturday, comes home with a Vindaloo (very, very HOT) takeaway. Save your prejudicial hot air next time, won’t you?
Pamela Gray (17:26:10) :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.
Hey, how do you know this?
mMrkL
Canberra
I cannot spell my own name, either…
looks suspiciously at rum bottle
Nope, can’t be that!
MarkL
Canberra
I went to to an Ethiopian restaurant once where they served extremely hot food. My friend and I ate the stuffed chilli – which they explicitly told us was really very hot, honest guv. My friend spent the rest of the evening trying to recover.
This is when I learnt that eating sugar stops the spice – the restaurant had pots of it on standby. Anyone have any idea how?
(The chilli didn’t seem to hit me as hard, but I was completely hammered.)
Ahh, hot chillies. Nothing better than when liberally sprinkled on a hot pepperoni pizza.
The mouth numbing pain. Looking for relief with a guzzle of ice cold beer. And the bubbles accentuate the pain many times over. But you’ve been told cheese will relieve it. And there’s cheese on the pizza. The cycle continues until the pizza is gone – or the beer.
As the good professor Julius would say – “Why is it so?”
If you get hot pepper from your fingers in your eye – agony! – rub the eye with hair. Your own, if you have long locks, or someone else’s. It works – can anyone explain why? I was given this tip by a Mexican friend & pepper afficionado.
I didn’t understand hot until I spent a month on Cozumel, shopping at the local food markets and discovered habaneros. While they are allegedly each the equivalent of a couple dozen jalapenos, I find them more tolerable. I like peppers for their heat and flavor, thus always removing the pulp and seeds as they have heat and no flavor. I find the habanero’s intense heat comes on quickly and just as quickly goes away, while jalapenos heat just sits in the mouth obscuring other flavors. My suspicion on why humans like them aside from the flavor and preservative qualities is the endorphins from stimulating the pain receptors, I find them intoxicating.
“”which suggested that some plants may make choices as to exactly which herbivores to attract and which to deter.””
blithering nonsense but it describes the problem of correctly describing evolution..
claiming that plants make choices is like claiming elephants choose to get large to survive better
when the correct description would be larger elephants survive longer and leave more descendants…
plants that make vile chemicals get eaten less…the herbivore gets the choice…to eat or not
Speaking of weird animal eating habits: When we’d prune our rose bushes, they had so many sharp thorns that we had to wear thick gloves. Then we’d feed the trimmings to our goats, who simply loved them. It made us wince in wonderment watching them eat those thorny trimmings.
Just a friendly warning to everybody,
Don’t cut jalepenos and then scratch your balls.
Dill Weed
“If you grow hot peppers, do NOT pick them bare handed’
That goes for culinary activity as well. Some years ago, never mind how many exactly, a young short-order cook sliced some jalpeños and then went to to the facility for purposes of urination.
Wash you hands *before* and after.
I am sure this will get squashed by somenone from the medical field, but my theory to why we like hot peppers is the following…
Upon cooking in an Indian Restuarant for a few years I witnessed many excited responses to hot food. I truly believe it is an adrenaline addiction. As your body experiences the pain of the hot pepper it responds with adrenaline and off you go. Give me more give me more….
Now…why do jalapenos and peppers in general get hotter when they are under stress?
Happy, well-watered peppers = mild peppers.
As my dad said: “Never go to the bathroom after chopping hot peppers.”. We never asked why he said that.
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
Maybe the local possums in Australia are to stupid to taste the capsaicin in the chilli peppers. I know a lot of guys that are just to dumb to know the sauce is hot. (
Steven Horrobin:
You may be right. I’ve only been going to Europe (including Britain) since 1969.
Watched the first moon-landing on a B&W Telly in a French campground. Been to Aberdeen more times than I can count. (Scotland IS Britain, right?) Had a cuppa in Peterhead (pronounced Peeterheed) once just for fun. Drove on the wrong side of the road through the Lake District and got pissed in St. Bee. 20 years ago was accused of being a “religious fanatic” in a London Pub because I said “Oh, my God, tomorrow’s Easter!”. Been to Thanksgiving service for the Yanks at St. Paul’s. Supposedly, I’m the 9th generation descendant of Sir Joshua, first president of the Royal Academy, who painted the offical portrait of George III, argot-addled king who lost the American colonies.
Been in at least 20 restaurants called “The Star of India” within the UK.
PLUS been to the subcontinent over two dozen times. Including sunny Dhaka (!), Agra, Kalcut, Dilli (the hindi spelling), and Bombay. Used to go to Hyderabad every quarter before it was fashionable. OK it’s still not fashionable, but at least there’s some money being made there now.
Once at a “cafe” in the Comilla Cantonment in Bangladesh (sandwiched between an army barracks and a British WWII cemetery on a sunny hill) I questioned the proprietor about the “stuff” floating in the water he had served: “Is this water from a tube-well?”. “it’s good enough for army officers, suh, it’s good enough for you.” I like India better, at least they call you Sahib.
I think I know what I’m talking about.
Suggest this: wait for Monsoon, pack-up your Wellies, and take a week or two in interior India. No fair eating in the tourist hotels; get out with the locals. Report back on any “delta” you might notice on the Scoville Scale between the real stuff and the anglicized version.
Oh, and don’t drink unboiled water, including ice, or eat anyhting that might have been washed in unboiled water (e.g. salads). Shigella tends to be rampant in those parts.
When you’re done with that bit, I got a taqueria in South Houston you need to try.
On the other hand, many plants/fruits are tasty for the very reason that they want to be eaten for their reproduction via the spread of their seeds (bird droppings etc).