In the constant struggle for survival,
animals have developed
novel defences. Some fight back,
some look scary, and others are almost
impossible to see. But one of the strangest
defences in the natural world comes from the animals that
detach parts of their own body. [man] It's the work of science.
[Laughing] [videographer]
He pinched his own leg off.
Said, "Nah, screw that." There, now we have a specimen.
This is autotomy. [videographer] Yo!
Let 'em go, dawg. [♪♪♪]
Hi, I'm Danielle, and
you're watching Animalogic: Second Nature.
[videographer] A female iguana, probably less than a year old.
Scared the crap out of me. Ran across my legs.
I didn't even step on the tail and it broke.
Deliberately dropping body parts is called autotomy,
and it's extremely rare among vertebrates.
However, it's an adaptation that's evolved several times
since the early Permian.
An ancient reptile group called captorhinids
had built-in fracture plains in the vertebrae
to drop their tails. When this group died out,
tail autotomy didn't re-evolve To be considered true autotomy,
it needs to meet three conditions.
One, it's done for self-defence
as a response to a dangerous situation.
Two, there are weak spots to facilitate the breakage.
And three, the animal has control over when to do it.
Most lizard families have members that meet
all three criteria. Among vertebrates, they're the undisputed queens of autotomy.
Most lizards who can autotomize
have fracture plains on each of their tail vertebra.
These are weak spots that make it easier
to severe the tail if necessary. [videographer] Let's see
how these fracture plains work.
That's pretty strong actually. [Danielle] If they're
caught by the tail, they contract the
muscles surrounding the highest free vertebra
and break it in half. After this, the muscles separate
and the skin is torn. The tail falls off.
Though not all lizards can lose their tails.
Generally speaking, species that use their tails
in their daily lives are less likely to be able to autotomize.
Chameleons that use their tails to climb,
monitors that use their tails as a weapon,
and Jesus lizards that need it for balance
when running on water are all unable to lose
their tails on command. Losing your tail is
a cheap price to pay to avoid losing your life.
But there are a lot of costs to losing parts of your body.
[male announcer] And every order was especially tailored
to meet individual needs. Many try-ons are necessary,
and trained personnel see that each patient
has a perfect fit. [Danielle]
Lizards without tails lose social status,
as they seem smaller than their tailed relatives.
And as a result, get less tail.
They also require a lot of energy
to regenerate their tails, so they need
a lot of food. This means more time
out in the wild and a higher risk of
encountering predators. And females who've lost
their tails are less reproductively fit,
as they produce fewer and smaller eggs.
Losing a tail also means losing an important fat reservoir.
If a predator doesn't eat the whole tail,
the lizard might come back
and eat it to recoup some of its energy.
To improve their likelihood of survival,
many species can regrow their lost tails.
Some, like the common agama, grow clubbed tails,
which might give them an
advantage when fighting agamas with their original thin,
weak tails. The new tails have cartilage
instead of bone, but they lack weak spots
in the vertebrae. If they ever needed
to lose their tail, they'll eject from
a higher vertebra than in the previous occasion.
Lizards, as well as some species of spiny mice, salamanders,and tuatara are
the only vertebrates that exhibit this behaviour,
but among invertebrates it's much more common.
Ah! [Danielle]
Hundreds of invertebrate species
are known to autotomize, and there could be
thousands more. In North America,
the most well-known tail droppers
are the creatively named, mm, tail-dropper slugs.
These cute little slugs are mostly found
along the West Coast and autotomize part of
their tails when threatened, usually by bigger slugs
or children with sticks. It's hard to imagine b
eing too lazy to chase a slug,
but sometimes you just wanna snack on a little slug nub.
Some of these slugs' aquatic cousins
also have the ability to drop part of their body.
The beautiful phyllodesmium nudobranks
can drop some of their noodly appendages.
Unfortunately, they're used for camouflage,
so dropping them makes them more visible to future predators.
Some crustaceans such as stone crabs
can autotomize their claws and grow a new
full-sized set in about a year. [videographer]
Oh, you want some crab leg? He pinches his leg,
his own leg off. Said, "Nah, screw that."
That's crazy. [Cra
b] So you have wounded me. I must grow a new claw.
Well, then good, for I can do it in a day.
But will you grow new legs when I have taken yours from you?
This adaptation has been exploited by fisherman
who declaw crabs and toss them back into the water.
They claim that this is
a sustainable way of getting those juicy,
delicious, nutritious crab claws.
Unfortunately, losing their only means of protection
has a very high cost for crabs. Under experimental conditions,
about half of crabs who had both claws removed
died within an hour. In the wild,
even fewer might survive. Ah! Ah! Ah! Ah! Ah!
A crab! Look, a crab!
Ah! Ah! [Laughing]
Ah! Ah! Ah! [Danielle] A
mong arachnids orb weaver spiders
are the most common autotomizer. They can shed their legs
if bitten by venomous prey like wasps or bees.
This prevents the venom from travelling into their abdomen and killing them.
A study on damselfly larvae showed that in addition
to reduced foraging and mating success,
damselflies that autotomize parts of their body
had less resources to maintain strong immune systems,
so they were also more vulnerable to diseases
and parasites. As a whole,
autotomy is a fascinating evolutionary adaptation
that gives animals a change to live another day
but severely limits their survival and reproductive rates.
I said it before and I'll say it again.
Limbs are friends, not food.
Thanks for watching, and see ya! [♪♪♪]
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