In the wonderland of Nature – 4
-Vagish K Jha
Parrots love chilies. Don’t they feel hot while eating chilies? How could one like such a fiery substance?
I know some people who love devouring chilies. What you call pungency is the real taste of the chilly, they swear. “Non-hot chilies, like bell peppers, is the slur in the name, even parrots don’t like”, Chandrasekhar, another chili lover, said with disdain[1]. I can understand about humans having such strange likings. “Some of them are real masochists, they love inflicting pain on themselves!” fretted Roshan. But, Madhav, a young colleague of ours, can eat half a kilo of raw pods of Imali (tamarind) in half an hour relishing every bit of it, without battling an eye lid. And, you show me the Imali pod for more than three seconds and my teeth would get numb. Maybe liking a particular taste is a personal choice. But, why do parrots like chilies? Don’t they feel the ‘heat’? Do they have taste receptors? If they do not have the taste sensation then the idea that they ‘like’ chili makes no sense. What is the taste of chili, by the way?
Chili is pungent, some may say. It is hot, others may add. Is ‘pungent’ or ‘hot’ a taste? There are only four types of taste, we were told – salt, sweet, sour, bitter. Later, a new taste seems to have been added – called ‘umami’[2], more popularly known by the food substance MSG[3] (the food additive monosodium glutamate). Chili does not figure anywhere as having any specific taste in this framework. The Indian Ayurveda, however, goes in greater detail of exploring the concept of shad ras, or six tastes– Madhur (sweet), Amla (sour), Lavana (salty), Katu (pungent), Tikta (bitter) and Kashaya (astringent). Here, rasa has a specific meaning in i.e. ‘Taste with tongue’.[4] So, chili should fall in Katu i.e. pungent category.
Eating chili does creates a sensation but it is not a ‘taste’ just as touching a hot pot creates a sensation, explained Mo, an avid chili eater himself. Like hot and cold are sensations, not a taste, similarly the pungency of chili is a sensation not a taste. This means taste is a particular type of sensation. So, what is taste?
“Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds” says Wikipedia.[5] This question has drawn some scientist’s attention, too. George Angehr, an ornithologist working for the Smithsonian Tropical Research Institute in Panama, has the following to say:
“Capsaicin itself is tasteless and odorless. What we describe as the “taste” of chili might better be described as the “pain” of chili (and we perceive this in parts of the body that clearly have no taste buds, to wit, the sphincter). One possible explanation for the appeal of chilies is that the body manufactures painkilling endorphins, akin to morphine, to counteract the pain, and endorphins themselves are pleasurable. In other words, we eat chilies because it feels so good when we stop.” [6]
That still does not explain why parrots like chili. For example, no mammal eats chili. The chili farmers are never worried that cows or buffalos would eat it; they just ensure that these animals not trample through the chili fields. The fact is the capsaicin sensitivity is actually the most well-known difference between bird and mammalian receptors. Bird receptors are largely insensitive to capsaicin, the cause of the fiery sensation. But, then do parrots really ‘love’ chili?
George Angehr again comes up with a curious explanation. He says, “When small birds consume the fruits of wild peppers the seeds pass through the gut undigested and, due to the birds’ flight range, are deposited in distant places where they can grow with less competition.”[7]
This, however, points out the seed dispersal by bird action. Similar process can be traced with animal causing seeds travel from one region to the other. H N Ridley, in his seminal book called Dispersal of Plants Throughout the World, had collated considerable empirical evidence of long-distance dispersal (LDD) and proposed mechanisms responsible for the colonisation of remote archipelagos.[8] He pointed out that the mechanisms of seed dispersal to unusually large distances are varied and diverse. It includes the transportation of seeds in updrafts, dispersal by birds in nest material, movement of seeds whilst attached to the fur of mammals and through eating fruit pulp and regurgitation or defecation. An important advantage of seed ingestion by frugivores is a presumed increase in germination percentage (germinability) and rate (speed).
Another study to find the seed germination patterns of five common western Mediterranean plant species suggested that frugivorour vertebrates, that are birds, contribute to the heterogeneity in germination characteristics not only within plant populations but also within plant communities, each frugivorour species having a particular effect on the seeds of each plant consumed[9]. Seed ingestion by birds commonly benefits plants by moving seeds to locations with fewer predators and pathogens than under the parent plant. So, birds and animals get their food from the fruits and grains and in return help them spread wide and far. Such symbiotic relationships between plants and animal / birds are mutually beneficial.[10]
It is not just that germination is more successful after seeds pass through the digestive tract of birds as some studies indicate. There is more to it.
In a scientific study published recently[11] it has been found that the when the seeds of the wild chili plant Capsicum chacoense passed through the gut of the Small-billed Elaenia it changed the seeds in ways that improved the seeds’ chances of growing into new pepper plants, which is another name for chili plants.
The plant Capsicum chacoense is a native to Bolivia, Argentina and Paraguay in South America. It is a wild chili, rarely cultivated by humans, but like other Capsicums, is edible. The plant in the study, Capsicum chacoense, grows to 5 feet (1.5 meters) tall and produces half-inch (centimeter) peppers. It produces spicy, red when ripe peppers or chilies which are hotter-tasting than jalapenos. The Small-billed Elaenia commonly eats these peppers. They inadvertently disperse seeds around the environment through their droppings. This helps peppers to not only travel to new areas but also flourish by enhancing chances of its survival and germination. Simple. Not really!
Oh, so, it is not just parrots but other birds also who like chilies! Let us explore it further.
According to Evan Fricke, the lead author of the above cited study, found that after passing through the bird guts seed survival rate increased by as much as 370 percent. What accounts for the better survival rate of the plants? Some experiments were conducted earlier in which seeds from a single plant were planted near the plant and others at some distance and seeds planted further away from the mother plant survived better. Bird gut was not involved. So it was inferred that distance from the mother plant is the crucial factor. But what does distance do to the propensity to germinate better? It protects these seeds from a large variety of predators and pathogens found around parent plants and thus better survival.
Convincing though it may sound, this distance theory failed the test with seeds of other plants including the chili-pepper plant. In their experiments, however, the scientists found that distance had no effect in reducing the seeds’ ‘removal rate’, that is the probability of the seeds being eaten (removed) by ants or other predators. In fact, the result was to the contrary. The farther away the seeds from the parent plant, the higher chance they had of getting eaten by the predators. Scientists attributed this to what they called “predator satiation”, where predators like ant had too many seeds available near the parent plant to cater to their needs and make them full. And, thus, seeds have greater ‘safety-in-number’ advantage. Does it mean that bird’s gut had no role to play in germination rate of seeds?
The second aspect of the study was the role of chemicals emitted from the fallen seeds and their role in its destruction. The research showed that in the first two days of falling on the ground the Ants picked up double the amount of unprocessed seeds as compared to the bird-processed seeds. After two days the ‘removal rate’ had no such difference. This was because, researchers reasoned out, the raw unprocessed seeds gave out strong volatile chemicals which attracted predators more. On the other hand, the seeds coming out of the bird gut got ‘conditioned’ and their changed characteristics made it less attractive to ants. This is only half as many times as unprocessed seeds in the first two days, after which the removal rates were almost identical. The researchers believe that unprocessed seeds emit volatile chemicals that make them more attractive to local ants, while the bird’s gut “conditions” the other set of seeds, changing their characteristics and making them less attractive.
The third aspect of the study was to examine the role of fungi in the process of the survival of seeds. Scientists found that insects cause certain kind of fungal action on seeds killing them while they are still attached to the plants. But further investigation revealed that the survival rate of seeds passed through the bird gut increased twice in comparison to those taken directly from the plant. This was because the laboratory examination of two types of seeds showed that the ‘fungal load’ of gut-passed seeds had reduced by more than 30 percent on its outer covering giving it much greater chances of surviving and germinating than the unprocessed seeds in natural field conditions.
All the cloud of doubt was put to rest as I had evidences provided by the scientific research. But just before I was browsing my tablet lying on my bed I got a rude shock. How do I know if scientists were not cherry-picking evidence? The article by the famous science writer Ben Goldacre created deep doubts again.[12] What I had were conclusions coming out of the experiments done by a set of scientists. How do I know if they designed their experiments in a way that it was objective and not biased such that excludes individual factors and references? So, it is not the conclusions but the examination of the ‘experimental design’ that yielded these results needs to be examined. A deluge of questions washed away my sleep.
How do we know what we know? To begin with what is ‘experimental design’? How should one design experiment to rule out what is also known as ‘confirmation bias’?
Don’t we teach students in our schools to do experiments in school labs? But, isn’t that a kind of mechanical process where we follow certain process to achieve a predetermined goals? Are the experiments conducted in the school labs experiments at all? What do we expect our students to learn by doing lab experiments? Are we not trying to make students ‘believe’ rather than understand and develop a set of abilities to do science?
And, when questions start pouring in, they barely stop. I never anticipated this pepper eating bird could create such a problem for me eventually! By the way, why is the chili plant also called pepper or chili-pepper, when the actual pepper is another species of a plant altogether?
I am still twisting and turning on my bed, twitching my thumbs and twiddling my toes…
Help…..!!
References:
[1] “Not really, my parrot Mitthu used to eat the seed part of peppers with lot of liking”, said Deepti, who lost her ‘Mitthu’ at the age of 49 recently. So, the claim of parrots not eating peppers was metaphorical rather than factual.
[2] Original word from Japanese which is translated as “pleasant savory taste” – http://en.wikipedia.org/wiki/Umami
[3] Not the ‘the Messenger of God’, a recent meaning attributed to it by a controversial Indian film of the same name, please!
[4] The rasa, according to Ayurveda, is gustatory appeal caused by the substance after coming in contact with the tongue. Ayurveda goes further in defining it finer. Rasa is recognized or perceived first after the contact of the substance with the tongue is the Pradhana Rasa (main taste) and that, which is subsequently perceived, is called Anurasa or Uparasa (secondary taste). For greater detail see: http://www.ayurvedaacademy.com/academy/media/documents/AWC/AWC-course-manuals/KAA106-Course-Manual.pdf page 11, another website takes up each one of the six taste and explains in simple language – http://vedichealing.com/tag/shad-rasa/
[5] http://en.wikipedia.org/wiki/Taste
[6] http://www.straightdope.com/columns/read/1857/are-birds-immune-to-hot-pepper-enabling-them-to-eat-vast-amounts-and-spread-the-seeds
[7] ibid
[8] Ridley H N. 1930. The dispersal of plants throughout the world. Ashford, UK: Reeve & Co.
[9] http://www.imedea.uib.es/bc/ecol_terr/all%20pdfs/2001_Traveset_et_al_FuncEcol.pdf
[10] The exciting inter-specie interactions which are mutually beneficial is known as ‘mutualism’ in biology (http://en.wikipedia.org/wiki/Mutualism_%28biology%29). The extinction of Dodo led to the sharp decline of Calvaria major tree has been established. (http://www.sciencemag.org/content/197/4306/885.short)
[11] When condition trumps location: seed consumption by fruit-eating birds removes pathogens and predator attractants” by Evan C. Fricke,*, Melissa J. Simon, Karen M. Reagan, Douglas J. Levey, Jeffrey A. Riffell, Tomás A. Carlo and Joshua J. Tewksbury. Ecology Letters, Volume 16, Issue 8, pages 1031–1036, August 2013
[12] http://www.theguardian.com/commentisfree/2011/sep/23/bad-science-ben-goldacre
VagishK 