Cannibal Caterpillars

 Cody Wolf

Plants, like many other life forms, have to adapt in order to combat the many predators that threaten their existence. Several varieties of plants have developed various techniques to prevent becoming insect feces. A brief communication published in Nature Ecology & Evolution highlights a….. unique way plants evolve to fight their little enemies.

Although most people are fascinated by plants, many are unaware of just how amazing they really are. Many plants are able to halt insects and other potential predators by developing weapons to prevent or delay consumption.

There are several types of mechanisms plants have developed, but here are a two quick examples:

Mechanical defenses– Plants utilize this mechanism by producing thorns, needles, or perhaps other other specialized structures such as waxy resins to make feeding difficult. I am sure most of you are thinking of plants like a cactus, or perhaps a thorny rose bush. Mechanical defenses are the most common type of herbivore defenses among plants

Chemical Defenses– Another technique for defense is chemical warfare. Literally. Many plants have developed complicated chemicals with complicated names (such as terpenoids, phenolics, and nitrogen compounds like alkaloids, benzoxazinoids, and many others) that specialize in destroying/inhibiting potential threats.

These molecules work to either deter the insect from eating (like inhibiting enzymes important for digestion, making consumption extremely difficult) or can possibly destroy DNA repair mechanisms in these little buggers and render them completely helpless (aka death from weird insect cancer).

Obviously, some of these chemicals are dangerous to ingest, but there are quite a few that have inserted themselves into our everyday culture, and are relatively harmless. Caffeine, morphine, cocaine (okay, cocaine isn’t exactly harmless), and nicotine all fall into this category.

Biologists call these defense mechanisms Host-Plant-Resistance or HRP for short.

Note: There are other mechanisms of defense considered in the HRP category that we will not be discussing today.

So..let’s get back to the current article. Recently scientists at the University of Wisconsin in Madison have discovered a completely novel HRP in Solanum lycopersicum or better known as the tomato plant.

In short, when the plant was exposed to a chemical secreted normally by plants in distress (yes, they can indeed “warn each other” so to speak), and then exposed to an arch nemesis, the small mottled willow moth, they found that plants who were exposed to the warning chemical had overall more biomass compared to the control plants or those who were not “cued” as well.

Plant biomass is a fancy way biologists explain how badly plants were eaten. The research team measured biomass by clipping the visible part of the plant (aka without the roots) and weighed the shrubs to compare biomass. Plants who received the highest dose of the “warning” chemical had as much as 5x the biomass compared to the non treated plants.

Interesting……

This data suggests that those plants who get warned properly have a mechanism to ward of those evil moths. So what exactly did the plants do?`

In case you happened to miss the title, the team in Wisconsin determined that cannibalism was at play.

Further experimentation is used to highlight the relationship between plant and insect.  

Tomato plants were once again warned with the various concentrations of the chemical (or not at all), but this time they removed the leaves and fed them to the caterpillars. The team noticed that those insects fed with warned plants tended to eat dead larvae planted inside their containers sooner than the control plants.

It is important to mention at this point, that herbivores such as the lovely small mottled willow moth, will eventually eat their friends if food becomes scarce. It really is a moth-eat-moth world. But for the first time, scientists are actually seeing that plants have the possibility to trick the caterpillars into eating themselves even when they have an abundance of food.

Now, many of you may be wondering; “Why don’t all plants have a defense mechanism such as this?”

The short answer is that it’s not as easy as it seems.

Although plants may benefit from this chemical defense system, HRP mechanisms are extremely costly for vegetation. It takes a ton of energy for plants to make molecules strong enough to make fellow caterpillars look delicious. There are many plants on our planet that lack defense mechanisms. They may be potentially more exposed, but they are able to allocate energy to other important mechanisms (photosynthesis, water uptake, etc..)

As of right now specifics on the properties of these cannibal inducing molecules, and how they actually work towards influencing caterpillars to eat dead comrades is vague, at least from the news article published on Nature.com. It’s also worth mentioning that brief communications piece is not a full-fledged article. The information has not been peer reviewed and there is much left to do to piece out the details of how these species co-exist.

To wrap up: The article mentioned highlights a novel defense mechanism for plants that has previously been undiscovered by biologists. While this article is not the final word on the issue, it does create an interesting starting point for scientists to weed out specifics and potentially (a long time from now) morph this information and create potential pesticide treatments.

But let’s not get ahead of ourselves.

THANKS for reading our humble blog! Please feel free to email the crew at copernicuscalledblog@gmaill.com if you have any questions about this article, previous articles, or anything you may have heard in your own travels.

You can also follow us on Twitter(@CopernicusCalls) , and Facebook.

 

Remember to always be curious, and stay mindful!

 

Sources:

1. Castells,Laura. “Plants turn caterpillars into cannibals.” Nature News. 10, July, 2017. http://www.nature.com/news/plants-turn-caterpillars-into-cannibals-1.22281?WT.ec_id=NEWSDAILY-20170710
2. Orrock,Connelly, and Kitchen. “Induced defences in plants reduce herbivory by increasing cannibalism.”  Nature Ecology & Evolution 1, 1205–1207 (2017) .10,July, 2017.  doi:10.1038/s41559-017-0231-6.https://www.nature.com/articles/s41559-017-0231-6

3. Picture source- http://globe-views.com/dreams/caterpillar.html

 

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