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The problem with diversity (Part 2)

In the last blog, I described how differences in geographic distributions and varying food sources can impact the toxic arsenal of snakes and other venomous creatures. There is, however, another key factor can play a significant role in the makeup of these toxin cocktails: Predators. Toxins are not only used to subdue prey, but also to defend yourself against evil foes that see you as a yummy afternoon snack. As it turns out, some species can rapidly adapt their venoms to new predators. I know this first-hand, since I participated in a study in Australia that aimed to investigate whether, how, and over what time span scorpion venom would change, when the scorpions faced predators compared to when they were left in peace. The predators that were chosen were rats, which often hunt these scorpions in the wild.

To kick off the study, we stalked into the night to collect a bunch of nocturnal Australian rainforest scorpions (Liocheles waigiensis). We then placed them in individual enclosures at the university, where we separated them into two groups:

  • Group 1 would be stimulated/harassed (depending on which you find less disturbing) with a stuffed rat
  • Group 2 would be spared and only use its venom to prey on insects
Illustration: Mark Crocker (left) & Robert Whyte (right)

Liocheles waigiensis: The Australian rainforest scorpion.

To monitor whether any changes occurred in the scorpion venom, we had to analyse what the scorpion venom composition was like at the outset of the experiment. How did we do this? We started by milking the 80 or so scorpions we had caught. This involved placing each scorpion on a foam block and pinning it down with a rubber band. We then held its tail and stimulated it with a tiny bit of electrical current to activate the venom glands and make the scorpion eject venom from its stinger, which allowed us to collect the venom in a vial and, thereafter, move on to the next scorpion.

Illustration: Jurgen Freund

Scorpion hunt: Collecting these scorpions at night was definitely an experience.

For the particularly awesome readers amongst you, you might now be reminded of something I mentioned in my first blog: ‘I have also had my fair share of venom by being bitten by no less than a snake and a spider, and even being stung by a bunch of scorpions during my time in Australia’. You are not mistaken – the time has come. ‘Take one’ of me being envenomated…

First off, I should say that these scorpions aren’t super venomous, though their typical insect prey might disagree with this statement. I would say something along the lines of a particularly nasty hornet. However, the problem was not the quality of the venom or the pain of an individual sting, but rather the quantity of stings I received. It turns out that milking scorpions is not as easy as you might think; in fact, they are surprisingly uncooperative and tend to show their hurt feelings from being man-handled by providing the venom voluntarily. Unfortunately, this voluntary donation rarely made its way into one of the designated vials, but rather (just like nature intended) into my (the evil predator’s) hand – thoroughly and repeatedly…

Illustration: Timothy Jenkins

Milking Scorpions: Not as easy as it sounds (that's if you are crazy enough to think that it sounds easy - like I did).

The first time I got stung really sucked. Pain shot up my arm and my first instinct was to hurl this hellish monster out of the window. Luckily, I managed to control my instincts and instead played it cool and pretended to barely feel the sharp pain; my colleague also assured me that this happened to him all the time, so I figured I’d better toughen up to not lose face. After I had managed to milk a few scorpions without being stung (i.e., using a vial rather than my limbs to collect the venom), he left me to it and I continued to work my way through the remaining scorpions.

Here is the thing – I had a success rate of approximately 60-70%, which wouldn’t be too bad if I was milking 10 scorpions. Don’t get me wrong 3-4 stings aren’t great, but I would have happily taken them rather than endure what actually happened. When I had milked 60 of the 80 scorpions, I had been stung somewhere between 18 and 24 times. On the upside, I had kind of gotten used to the pain (as much as one can at least), and my arm was beginning to feel unpleasantly numb. In a less fortunate turn of events, this numbness slowly progressed into total paralysis of my arm, while my hand was swelling to a concerning size and shape.

Illustration: Alan Sirnulnikoff

Not so swell swelling: Whilst the hands in this photo aren't mine, the swelling is rather similar to what I experienced.

I decided that I would come back to milk the remaining 20 scorpions the following day and, on my way out, quickly dropped by my colleague’s office to check whether my arm having been rendered useless was also ‘normal’. Apparently, it wasn’t. After providing me with some solid Australian healthcare advice (“you’ll be alright” and “what doesn’t kill ya makes ya stronger”), my colleague suggested that I see how the paralysis progressed now that I had stopped getting stung and, fortunately, by noon the next day all was back to normal. Needless to say that I have not milked scorpions since.

Moving away from my incompetence and returning to the study and cool science, it turned out that within six weeks the scorpions were able to change their venom composition to contain more vertebrate (predator-harassed group 1) or invertebrate (insect prey hunting group 2) targeting toxins. This was exciting, since our findings provided the first evidence for an animal’s ability to adjust its venom within a very short period of time, something that is scientifically known as ‘adaptive plasticity’.

There you have it; whilst venoms and the toxins within them are already fascinating in their own right, I hope this blog entry, as well as the previous one, were able to convince you of how intriguing the stimuli that are responsible for the diversity within venoms are. And if not, at least you got to read about how I managed to get myself envenomated multiple times…

Timothy Jenkins holds a PhD in biomedicine and is an aspiring biotech entrepreneur. He recently completed his doctoral studies at the University of Cambridge, where he was awarded the ABCAM award for top PhD candidate at his department. Now, Tim is working as a postdoctoral fellow at the Technical University of Denmark with biotechnology-based antidotes to snake bites. Timothy Jenkins har en ph.d. i biomedicine og er biotek-entreprenør in spe. Han er uddannet ved University of Cambridge, hvor han modtog ABCAM-prisen for bedste ph.d.-kandidat i sin afdeling. Nu arbejder Tim som postdoc fellow på DTU med biotek-baserede modgifte mod slangebid.
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How does the scorpion know how to adapt the venom to a specific type of predator? Are they using some "knowledge" from being predators themselves or is it another mechanism in action? It seems as a very quick adaption.

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Hi Axel, thanks for reading the blog and for your comment. Your question is very interesting, but unfortunately I have no definitive answer for you.

Studies of this phenomenom (i.e. phenotypic plasticity) are seldom concerned with the mechanisms that underlie the environmental sensitivity. However, some studies suggest that the effects of the external environment (in this case being confronted with a predatory rat) may involve transmission via neural or hormonal pathways to affect gene expression or gene-product activation associated with particular physiological changes. So it is possible that there already exists a blueprint in the genetic code of these scorpions that states 'if repeatedly faced with this mammalian predator, then produce more of these (anti mammal) toxins'. This code is then activated through the 'environmental' interaction.

I hope this at least can somewhat answer your question. If you are super keen, then this goes into a lot more depth:

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