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Duration:05:44
Uploaded:2021-06-10
Last sync:2021-06-10 21:30
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Some lizards will lose a tail to avoid becoming a meal, but there's more than one reason for animals to self-amputate.

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Sources:

https://www.nytimes.com/2021/03/08/science/decapitated-sea-slugs.html
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00047-6
https://academic.oup.com/beheco/article/28/4/1047/3748244
https://theconversation.com/the-extreme-tactic-of-self-amputation-means-survival-in-the-animal-kingdom-118503
https://onlinelibrary.wiley.com/doi/full/10.1111/evo.13948
https://academic.oup.com/beheco/article/28/4/1047/3748244
https://academic.oup.com/beheco/article/17/3/353/201485
https://academic.oup.com/beheco/article/16/2/377/297882


Image Sources:
https://commons.wikimedia.org/wiki/File:Elysia_marginata_(14217590519).jpg
https://en.wikipedia.org/wiki/File:Severed_skink_tail.webm
https://commons.wikimedia.org/wiki/File:Elysia_marginata_(14217590519).jpg
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00047-6
https://www.istockphoto.com/photo/green-chloroplasts-in-plant-cells-gm116864378-6143246
https://www.istockphoto.com/photo/leaf-footed-cactus-bug-on-a-prickly-pear-cactus-gm1218469776-356053220
https://www.istockphoto.com/photo/close-up-coreid-bug-on-plant-tree-on-nature-green-background-squash-bug-gm1135040766-301807999
https://www.istockphoto.com/photo/golden-orb-spider-in-its-golden-colored-web-gm1144142561-307484993
[ intro ].

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If you’ve ever tried to pick up a lizard by its tail, you may have been left with… just the tail. The process of ditching a body part on purpose is known as autotomy, and many lizards do this to confuse predators, leaving the still-wriggling tail behind while the rest of the lizard escapes. But lizards aren’t the only creatures capable of self-amputation, and there are other motivators behind dropping a body part that go far beyond escaping predation!

The most extreme type of self-amputation is decapitation. Recent research has shown that two types of nudibranch, commonly known as sea slugs, will slowly separate their heads, in order to re-grow an entirely new body. Before observing it in the laboratory, researchers had no idea this was even possible.

The heads were able to crawl freely around their aquariums, and one animal even decapitated itself twice during the study. I mean, these animals are living with no heart, stomach, or digestive tract; nothing except their brains. The researchers found the animals have a little groove right where their head meets their body, which they believe is the breakage point, and this site healed within a few days.

The heads were observed feeding a few hours after decapitation, although where the food is going is a bit of a mystery. The body did not regrow a new head, but it was able to move around and even responded to stimulation for approximately a month before it finally decomposed. Not all sea slugs perform this extreme behavior.

But these slugs can easily decapitate themselves thanks in part to what they eat: algae. The slugs incorporate algal cells responsible for photosynthesis, known as chloroplasts, into their own cells. Scientists hypothesize that these slugs get a bit of energy from the photosynthesis, keeping them alive while they’re waiting for their body, including their stomach, to grow back.

Turns out it's not to escape predators, like lizards do. Instead, the authors of the study believe the motivation for decapitation is an infestation of parasites. They found that many of the bodies belonging to one of the slug types contained internal parasites.

But when the body grew back, it was parasite-free. Willingly discarding your own head is pretty hardcore. But choosing to remove a limb is no small beans either.

And research published in 2017 shows that leaf-footed cactus bugs may choose to discard an injured body part, if they believe that the benefits outweigh the costs of living without that limb. Specifically, if one of their legs has been severely injured, they might choose to remove it to prevent an infection from setting in. Unfortunately, as adults, these bugs don’t have the luxury of growing back that limb.

So, once it’s gone, it’s gone for good. So they have a tough decision to make. While the research behind this behaviour is still on-going, scientists believe that it’s based on a few things, such as where on the leg the injury occurred, if the insect has already lost a limb, and how much they may need that limb in the future.

For example, males need their back legs for mating, so they might choose to live with the injury. But if the injury is severe enough to cause a life-threatening infection, they avoid infection by removing that limb at a specific location, a pre-established point on their bodies for self-amputation, just like our sea slug friends have on their necks. This breakage point comes in handy for other reasons, like if their limb is stuck or they’re escaping predation.

This site is more likely to heal fast and clean, because it’s meant to suffer breakage, so blood flow is minimal. A wound elsewhere could bleed more and lead to an infection. For these bugs, losing a piece of themselves to save their life is sometimes worth the sacrifice.

Ditching a limb to prevent infection seems like a smart move, but what about willingly sacrificing multiple pieces of your body in the name of reproduction? Some spiders, such as the golden orb spider, will go to great lengths to ensure they are the only ones depositing sperm in a female. The male will break off a portion of his mating organs, known as a pedipalps, inside a female.

This is referred to by researchers as a copulatory plug, and acts as a physical barrier inside the female. The benefits of this are two-fold. Not only does it keep that male’s sperm inside her, it also prevents other males from successfully mating with her most of the time.

Evolution continues to select for self-amputation over and over again throughout the animal kingdom. Many use it to avoid predation, but it serves other purposes as well, like keeping creatures from getting sick from an internal parasite infestation or a nasty infection. So while the ability to cut off a limb, or hey, even an entire body, may seem pretty extreme, for those creatures it may just be the difference between life and death.

Something that is not as hardcore but is full of amazing science are courses from Brilliant! They have an interactive and illustrated course on Physics of the Everyday which is not about dropping body parts but is about things like household objects. You’ll get to see how fridges keep things cold without turning the house into an oven.

Or how the toilet bowl keeps the water inside without it flowing away. If you’re interested, you can check out Brilliant.org/scishow for a chance to get 20% off an annual Premium subscription. And thanks! [ outro ].