LSM1303 Animal Behaviour Student Blog : evolutionary arms race

Inhuman Doctors: Zoopharmacognosy and Self Medicating Animals

Vigneshwaran Shunmugam — Fri, 21 Mar 2008 15:15:00 GMT

Many major cultures around the globe have developed some form of medical science. The Indians have Ayurveda, the Chinese have TCM and of course there is Western medicine. What these fields have in common is that they are derived from the process of observing the effects of certain herbs or foods on the health of the imbiber and thus correlating cause and effect. While medical science and its practitioners have long been held to be at the forefront of human intellectual pursuits, we now realise that this was no great achievement at all. In fact, even monkeys do it.

Observe this Orang Utan for example.

Right. This is just a monkey opening a packet of powder. Nothing fancy. However, monkeys DO develop their own medical techniques to deal with their own health issues. This is known as Zoopharmacognosy which is basically the animal form of Medical Science. Many species of animals use various techniques to deal with their maladies.

If you have seen your dog or cat eating grass you may have been puzzled at their sudden vegetarianism. They do have good reason for doing so. Eating grass "stimulates either retching or the rapid expulsion of worms in diarrhea" (Hart and Hart 1985). Compare this with the Tamil proverb which claims that a Tiger would not eat grass, no matter how hungry.

Medicine is not a purely mammalian pursuit either.Snakes too have herbological knowledge! "According to Chinese folklore, many centuries ago a farmer in the Yunnan district found a snake near his hut. Fearful for his life, he beat it senseless with a hoe and left it for dead. A few days later, the same snake returned. Again he tried to kill it, but again it returned. After he had beaten it a third time, the farmer followed the severely wounded snake as it crawled into a clump of weeds, started feeding on them, and thereby rapidly cured the worst of its injuries. The plant in the story was Panex notoginseng, which now forms the main ingredient in the herbal formulation 'Yunnan bai yao', a white powder that cauterizes cuts and stems external bleeding immediately. It was standard issue in the Vietnam War, for use when soldiers were wounded far from conventional medical treatment. "(Reid 1987).

Our closest cousins, the Great Apes have various methods by which they keep themselves in the pink of health.

Above we see a chimpanzee(Pan troglodytes) chewing on the bitter pith of the Vernonia Amygdalina plant. Chewing on the pith allows the chimp to extract the bitter juice that is within. THe chimpanzees use this method to kill parasites in their intestinal tracts. Interestingly, chimps do not usually eat this leaf due to it being slightly toxic to them. Thus, they only eat this leaf for medicinal purposes! This paper has extensive information on this phenomenon, complete with graphs. The author Michael Huffman is an eminent figure in the field of Zoopharmacognosy.

Chimps sometimes consume the leaves of the Aspilia plant, which they got to great lengths to obtain. The leaves are covered in stiff hairs and are swallowed whole, despite the difficulty of doing so. "Huffman doesn't doubt that there is a medicative function behind leaf swallowing behavior. His theory about how it gets rid of worms revolves around the hairiness of the leaves. Huffman found live worms in chimp *** stuck "like Velcro" to leaf hairs and trapped within the folds. He speculates that worms may become attached to the leaves or somehow enticed into the folds during digestion, taking a "magic carpet ride" through the gastrointestinal tract, eventually to be excreted from the body. Chemicals in the plant may also decrease the ability of the parasites to adhere to the intestine, making it easier for them to be swept out by the leaves."

Perhaps the animal use of medicines to treat themselves is not such a surprising phenomenon. In fact post-Darwinists should have predicted it regardless of evidence. Using medical methods enables an animal to prevent its death,prolong its life, to heal faster and have a survival advantage. This is an advantage that would allow those animals who use it to be more successful than those who dont. In the abscence of a consequent negative selection pressure, animals who self-medicate would definitely outsurvive those who do not. Thus, Zoopharmacognosy is not surprisingly prevalent in the animal kingdom.

Not only do animals consume herbs and plants as medicines, but they also consume certain types of soil(geophagy) and insects for the same purpose.

Even more interesting than the fact that animals employ medical science is the fact that many of the herbs and techniques employed by animals are similarly employed by humans. This highlights the cross pollination of medical knowledge from the animal kingdom to ours.

To learn more on the exciting field of Zoopharmacognosy, this book might help.

"Really Wild Remedies—Medicinal Plant Use by Animals" by Jennifer A. Biser. Zoogoer, January/February 1998

Huffman, M.A. 2001. Self-Medicative Behavior in the African Great Apes: An Evolutionary Perspective into the Origins of Human Traditional Medicine. Bioscience, 51(8):651-661.

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Evolutionary arms race between snakes and newts

SOH KWAN HUA — Fri, 21 Mar 2008 14:05:00 GMT

Rough-skinned newts (newts of the genus Taricha granulosa) are one of the most poisonous animals in the world. In certain populations, the poison in a single newt can kill up to 20 humans. However, the newt’s predator, the common garter snake (Thamnophis sirtalis), has developed resistance to the newt’s toxin over time as well. Why is the rough-skinned newt so poisonous and who will triumph in this competition between predator and prey?

The rough-skinned newt, which is found along the west coast of Northern America, is the amphibious equivalent of the deadly puffer fish that is eaten by the Japanese as a delicacy. This is because it secretes from its skin tetrodotoxin (TTX), the same poison that causes the tingling sensation on the lips and tongue when eating a fugu meal and which could lead to possible death if ingested in larger quantities.

"Ounce for ounce, some of these populations are the most toxic amphibians on the planet,"

so says Charles Hanifin, a postdoctoral scholar at Stanford's Hopkins Marine Station who recently conducted a study on the rough-skinned newt and the common garter snake. However, rough-skinned newts are mostly harmless to human beings unless eaten as the poison cannot be absorbed through the skin.

Evolution Toxic Newts

Video with 2 of the co-authors in the study

Scientists have theorized that the reason for this level of toxicity found in the rough-skinned newt is that it is in response to evolutionary pressure in the form of its predator, the common garter snake. The common garter snake, similarly, has developed resistance to TTX in response to the TTX found in its prey, the rough-skinned newt. Newts develop greater toxicity over time as snakes become more resistant to TTX and snakes become more resistant to TTX over time as newts become more toxic.

The study by Charles Hanifin uncovers a few interesting findings:

Prey toxicity and predator resistance to toxicity closely correlate with each other; in regions where newts have high levels of toxicity, the garter snakes have correspondingly high levels of resistance. In regions where there are no newts or where the newts are non-toxic, the garter snakes have no resistance to tetrodotoxin.
In 30% of the regions studied, the populations of garter snakes have developed such great resistance to TTX that snakes with the least resistance are able to eat newts with the greatest toxicity.

The first finding is further evidence of coevolution, where two species exert selective pressures on each other such that certain traits develop over time. In the case of garter snakes and newts, this results in an evolutionary arms race as the two species compete to develop traits that result in greater fitness for itself at the expense of the opposing species.

The second finding shows that the garter snakes appear to have won the evolutionary arms race with the newts. The newts have been unable to keep up in increasing its toxicity in response to the increasing resistance to TTX found in their predators.

There are two reasons why the newts have lost. Only a single mutation in the garter snakes’ genes is responsible for its resistance to tetrodotoxin, making it faster and easier for successive generations of snakes to evolve greater resistance to tetrodotoxin. A number of genes are involved in increasing the toxicity in newts however, and the increases in toxicity are more gradual than the increase in resistance to TTX in the snakes. The newt also faces limits in increasing its toxicity as the poison is only produced in the skin. Some snakes have already developed such a great resistance to tetrodotoxin that it would be biologically impossible for the newt to produce in its skin the amount of TTX needed to have an effect on the snakes.

"It is pretty much biologically impossible for the newts to ever catch up,"

Hanifin says. However, there is hope yet for the newts. There appears to be a cost to the super-resistance found in certain populations of garter snakes. These snakes crawl slower than other snakes with lower levels of resistance as can be seen in the experiment in the video above. It is thus harder for the snakes to catch the newts and the snakes are more suceptible to its own predators like birds as well because of its slower speed. Hence, the population of super-resistant garter snakes is controlled and rough-skinned newts are still found in areas with super-resistant snakes.

References:

Hanifin CT, Brodie ED Jr & Brodie ED III, 2008. Phenotypic mismatches reveal escape from arms-race coevolution. PLoS Biol 6(3): e60. doi:10.1371/journal.pbio. 0060060

“Snakes vault past toxic newts in evolutionary arms race,” by Shelby Martin. Stanford News Service, 11 March 2008

Masters of Hide and Seek

LAI SHUZHEN — Thu, 20 Mar 2008 18:15:00 GMT

I remembered watching this Discovery Channel program on cable a few years back and it was seriously one of the most brilliant and incredible documentary I’ve ever seen. It was of a dark, alien world filled with strange looking creatures, with some being absolutely hideous.

This was one part of an eight-part Blue Planet TV series produced by BBC – The Deep. It was a documentary on life one to three thousand metres beneath the ocean surface, and as quoted from the video, “more people have traveled into space than ventured this deep”, hence was extremely intriguing.

Out of all the animals introduced, many caught on tape for the very first time; the marine hatchetfish piqued my interest the most as I was very interested about the evolution for avoidance of predators and it was, as you will soon discover, truly a Master of Hide and Seek.

Side view of a marine hatchetfish

The picture above shows the marine hatchetfish, which is from the Sternoptychidae family and is the protagonist here. It inhabits the deep ocean at depths of about 200 to 1,000m and can be found in tropical and subtropical waters of the Atlantic, Pacific and Indian Oceans. There are 45 known species but most, like the marine hatchetfish here do not exceed 10cm in length.
[A point to note: There is another type of species named the freshwater hatchetfish but it is from a different family and should not be confused with the marine hatchetfish.]

At 1,000m beneath the ocean surface, the twilight zone is reached, where sunlight barely shines through. It is dark and in here, most animals are highly, if not, completely transparent (like the amphipod as seen below). This is accruing to the fact that they have to avoid being seen by their predators, hence by being transparent, serves as the best camouflage for them and increases their chances of survival.

An amphipod

The hatchetfish however, is not transparent.

This fish is no longer than 10cm and has a very flat body that is so thin that head-on, they are barely visible in the dark waters.

Three barely visible hatchetfishes. Look hard!

But what about from the side? Can its predators see it since it is not transparent?

Even though it is not transparent like the other animals in the twilight zone, it has highly silvered sides that work to the same effect. They reflect remnants of any existing light such that the hatchetfish becomes invisible from the side-view as well.

Still visible

Invisible! When mirrored sides reflect any existing light

Then again, its mirrored sides may still not be adequate to hide from its predators. This is because many of its predators have tubular eyes pointing upwards, which, even in such a dark environment, are able to search for it against any light from above, as they will be able to detect its silhouette.

Visible silhouette when seen bottom-up

However, through millions of years, the hatchetfish has evolved to ‘better itself’ in terms of avoidance from its predators.
It developed a way to deceive the eyes of any predators looking up in search of their presence with the help of photophores (bioluminescent organs). These photophores are located on the bottom of the hatchetfish’s belly and they are light-producing cells that can precisely match the changing colors of the light from the surface far above. The intensity of the light produced is controlled by the hatchetfish itself and the appropriate brightness is selected according to the amount of light that reaches it from above. This is called counter-illumination and with such a counter-shading, the silhouette is ‘broken up’, thus allowing the hatchetfish to be almost invisible from below as well!

Photophores highlighted in purple

Close-up view of photophores

Close-up view of photophores after adjusting to the light from surface

And there it goes! Hatchetfish becomes invisible again! Even from bottom-up

On the other hand, in a continuous evolutionary arms race (please click here for more information on this theory), despite the hatchetfish’s sophisticated counter-illumination to hide from its predators, some of them (predators) can, as in one example shown in this same video, react to this and also evolve accordingly in an attempt to ‘outsmart’ the hatchetfish.

Hatchetfish's yellow-eyed predator

As seen from above, this predator has enormous yellow tubular eyes and they are actually able to distinguish between light produced by photophores and sunlight. Therefore, this predator can counter the counter-illumination employed by the hatchetfish to beat it in this game of hide and seek.
[A point to note: This particular predator was not identified in the video, and even though I tried to search for it and tried to use the Internet resources to match it with the video image, I chose to not name it here so as to avoid providing inaccurate information as I could not be sure of its identity.]

In the evolution for avoidance of predators, the hatchetfish has acquired sheer abilities as evidenced from above to hide from its predators in the twilight zone. That said the predator could also evolve itself to counter this.

Such an evolutionary arms race is not unique in the case of the hatchetfish and its predator, but has been waging on for millions of years amongst other species as well in this eternal game of hide and seek between the hunter and the hunted in the animal kingdom.

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Disclaimer: All pictures on this blog are screenshots captured from the youtube video on the hatchetfishes. They are not obtained from any other websites/webpages, hence there are no photo credits.

References:

1. “About the series – The Blue Planet”, Science & Nature: Animals, BBC. Retrieved from: http://www.bbc.co.uk/nature/programmes/tv/blueplanet/

2. “Animal fact files – Hatchet fish”, Science & Nature: Animals, BBC. Retrieved from: http://www.bbc.co.uk/nature/blueplanet/factfiles/fish/hatchetfish_bg.shtml

3. "Evolutionary Arms Race", Wikipedia. Retrieved from: http://en.wikipedia.org/wiki/Evolutionary_arms_race

4. “Marine hatchetfish”, Wikipedia. Retrieved from: http://en.wikipedia.org/wiki/Marine_hatchetfish

5. Youtube video on hatchetfish: http://www.youtube.com/watch?v=W9Er4dpUfrM&feature=related

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This blog entry is based on this youtube video of "The Deep". The snippet on the hatchetfish will only start from 5'28'' onwards (ends at 8'06'') so please allow the video to load, then skip there directly to watch this evolution for avoidance from predators unfold.

Masters of Hide and Seek