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On Parasitism

On Parasitism

October 2010: It’s been over 150 years since Charles Darwin’s seminal work, On the Origin of Species. Yet, the molecular foundation for natural selection, a key driver of evolution, continues to elude us.


Credit:Yuwaraj Gurjar


When you read that line did you sort of go “hmm” just before your mind began to wander? That happens to me all the time! But occasionally an apparently esoteric line worms its way into my brain and refuses to go away. Like when Shardul Bajikar wrote and said: “parasites probably keep the populations of their hosts in balance more effectively than predators!” With his mail he sent this incredible image shot by Yuwaraj Gurjar in Mumbai’s Sanjay Gandhi National Park. It is a grass demon butterfly caterpillar Udaspes folus, infested with a horsehair (Gordiacea) worm parasite (the white string-like creature) clearly visible through its camouflage-assisting transparent body.


Shardul got me thinking about the word ‘parasite’. Humans have imbued the word with negative values, but the likes of Darwin, J.B.S. Haldane and W.D. Hamilton were fascinated by parasites and studied them to unravel evolutionary knots. Parasites, after all, select diverse host traits and parasitism could well turn out to be one of the most dynamic fields in evolution and ecology. Studying the co-evolution of parasites and hosts is particularly critical to human health given our faulty use of antibiotics, leading to drug-resistant bacteria, but let’s go back to this lowly worm and its unfortunate caterpillar host. The worm belongs to a group of creatures called Nematomorpha (nematode-like) whose lifecycle could provide Homo sapiens with a strategy to survive climate change,  provided we live up to our name – sapiens (wise).


Here’s the deal. Nematode-like worms go through four stages or moults before metamorphosing into adults capable of reproduction. But, when resources are scarce, or circumstances less than ideal (life-threatening temperature instability, food shortages, over-population), the worms tend to skip the third stage of their development, using special enzymes, and opt instead for a hardier dauer-larval stage (dauer in German means duration). Put simply, they change their development strategy for extended periods until they sense that they have a better chance to mature and reproduce.


That’s it! That’s the climate survival strategy the worm is trying to teach us. If it could talk, the parasitism home truth the worm would deliver might sound like this: “Look. My kind of parasite has been around for much longer than your kind. Your host (the entire planet!) is pretty unstable right now. Instead of hurtling towards pre-determined growth targets (the reason why Jairam Ramesh is being threatened with daily eviction) why not pause, let the planet’s climate and population stabilise, and then refine economic growth targets? After all, if your host dies… you die!”


Bittu Sahgal, Editor, Sanctuary Asia Vol XXX No. 5, October 2010


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