The 90 million year long evolutionary arms race that brought you... Wasabi

Ever wondered why wasabi makes your eyes water? What possible reason a plant could have to develop such powerful chemicals as seen in mustard? The answer lies with a butterfly. Or more specifically, the butterfly's larvae.

A Pierid butterfly

This is War

In nature, conflicts between closely associated species often take the form of what's known as an ‘evolutionary arms race.’ Essentially, one organism develops a defense to stop itself being predated or parasitised by others (this may be a general defense or a specifically targeted one). A predator or parasite of that organism then evolves a mechanism to overcome that defense (i.e. being able to metabolize a harsh chemical) and the resulting predation pushes the original organism to develop further, often more complex defenses and so on.

In the case of plants in the Brassicaceae family (which includes cabbage, mustard and wasabi), this is a process which has been going on for over 90 million years.

A sting in the tale

Brassicale plants responded to their predation pressure by Lepidopteran larvae by developing a class of compounds known as glucosinolates.

A glucosinolate - variation in the 'R' group attached to the central carbon causes the different chemical properties found in different Brassicale plants.

It is these compounds, or more specifically the products of their breakdown, which are responsible for the sharp taste that makes wasabi so delicious. It is only when glucosinolates react with an enzyme called myrosinase, that these tasty secondary compounds are formed. Under normal conditions, this happens when the plant is damaged, thus resulting in an immediate chemical defense. Perfect self defense unless the thing attacking you is this:

Looks innocuous, doesn't it?

A harmless little butterfly….

For most insects, the presence of glucosinolates render a plant inedible. Caterpillars from the family Pieridae however have learnt a neat little trick to get around their host plants’ chemical defenses. Using a specially developed protein named ESP (Epithiospecifier protein), these larvae are able to hijack the enzyme-glucosinolate reaction and produce far more easily dealt with compounds as a result. The amount of time they needed to learn that little trick? Only around 10 million years after the plants first started producing their repellent compounds.

Subsequently, the butterflies specialised to colonise further members of the plants in this group and so was born an arms race that has been raging for longer than we as a species have been on the planet.

Burning man

So the next time you're sitting there, wasabi tears streaming down your face, wondering why in the hell you do this to yourself, spare a thought for the millions of years long evolutionary process that even made it possible in the first place.

Until next time,
Happy Steeming People,
The Wise Fox

Papers you can check out on this topic:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2673275/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4500235/
Additional info:
http://lpi.oregonstate.edu/mic/food-beverages/cruciferous-vegetables

Images:

1. http://www.britishbutterflyaberrations.co.uk/species/pieris-brassicae/aberrations
2. https://en.m.wikipedia.org/wiki/File:Glucosinolate-skeletal.pn
3. http://www.commanster.eu/commanster/Insects/Butterflies/butterflies2.html