[ birds chirping ]
Warning:
To support the topic of biological regeneration
this video contains images
of flesh injuries
that may disturb some viewers.
So if you’re squeamish
then you might want to scoot on off!
[ ♪ Chill KN Theme Music by Ace Labs ♪ ]
Once upon a time...
Okay--it was just last year.
I was riding a bicycle
and one of these little skinks
ran right in front of my bike.
The young skink survived
the bike accident
and ran off safely into the woods
but the skink left behind
on the asphalt
this wonderfully spasmodic dancing tail,
a true awesomeness of evolution.
In biology we call this caudal autotomy.
That’s when a part of the tail
is purposefully discarded,
or in this case—
pretty much all of the tail.
This autotomy includes pulsing muscles,
a brainless display of flailing beauty,
and it’s considered a defense mechanism
used to distract a predator
such as this red-shouldered hawk
for just long enough
for the skink to run away
with its life.
[ hawk screeches--loudly! ]
Shhh! I’m storytelling here.
And yeah
the skink’s tail is an important body part
used for things like balance
and future mating rituals
and I suppose the self-satisfaction
of having a lovely tail.
But even though the tail
is a useful body part
it’s willingly discarded
in situations
that can save the skink’s life.
It’s better to have no tail and life
rather than never see another moon.
The skink, in time, will most likely
regenerate an entirely new tail.
And now you must be thinking...
Why we are talking about a skink
that is a reptile
when I plugged salamanders
that are amphibians
in this video title.
Well just bear with me.
The skink’s tail had me reminiscing back
to when one of my nieces
incorrectly picked up a salamander by the tail.
And again
the autotomy defense mechanism ensued.
And the squirming tail gave the salamander
a chance to get away
from the voracious predator
aka my niece.
Like the skink’s lost tail
the salamander’s tail will regenerate in time.
And salamanders,
among all of us tetrapods,
have the most amazing
regenerative abilities.
Not only can salamanders regrow tails
but they can regrow entire limbs.
And their regenerative powers
go beyond even that!
But we’ll touch on this awesomeness
in a bit.
So the salamanders'
capacities of regeneration
then had me pondering
as to my own human regenerative abilities.
Cute little things aren’t they?
You see—last year I messed up my spine
really badly on a fishing trip.
Yup, that’s me, Koaw,
lying in the mud along a river
trying to get comfortable
as a couple of discs
painfully jabbed into the nerves of spine.
I knew I’d have to get a surgery
and I knew they’d need to slice me open.
I would need some regeneration
after the impending surgery.
And this is where you turn away
if you’re squeamish.
I remembered a few other injuries
I’ve had that required some healing.
Like when my hand had
some severe burning from a fire.
But the skin regenerated
practically as good as new!
There isn’t even a scar nowadays!
Or when a fellow hockey player
managed to slice my leg open
with his skate blade.
Not quite perfect regeneration
but scar tissue filled the wounds.
Or all the other superficial wounds
I’ve endured that managed to heal up.
And if you’ve ever broken a bone
your body probably healed that bone
back into a nice functional piece.
So…we humans do have some
regenerative powers.
Then I thought:
“Well what if I lost an arm?”
Yeah—kind of a gruesome thought.
A new arm just wouldn’t regrow.
And I would likely die
unless I stopped that excessive bleeding.
Let’s plug that up.
But we humans just don’t have
the remarkable ability to regenerate
entire limbs like that of the salamanders.
And it doesn’t even stop at the limbs
and tails of salamanders.
They can regenerate so many other parts
of their bodies.
Recently a research team
peeled back the skulls of living newts
and removed up to a quarter of their brains
and sure enough in about 6 weeks
the brains started regenerating!
And newts are salamanders by the way.
The researchers also removed up to half
of the lone ventricle
in the newts’ hearts
and sure enough
even after they stopped beating
they regenerated in time.
The newts could survive
such devastating traumas
and regenerate their body parts!
And keep in mind that although
each species of salamander today
is capable of regeneration
it varies between species
and their developmental stage.
Scientists are still yet
to chop off the limbs
or cut out the brains
of every species out there
to see the extent
of each species’ regenerative powers.
I’ve said it before and I’ll say it again:
We scientists can be a-holes.
Now you might be thinking—
Well…we humans can regenerate
some of our liver and lungs.
That’s kind of impressive, right?
And it’s good news for this guy
if he can sober up.
And yeah…that limited
organ regeneration ability is cool.
But if you chopped out a part of our brain
or our heart
there wouldn’t be any complete regeneration
like the newts displayed—
even if we were lucky enough
to survive such a procedure.
And salamanders have been shown
to regenerate other complex structures
including ocular tissues of the eyes
and parts of their central nervous system
like their spinal cord.
It’s just impressive.
So then I was thinking—
Why?
Why do salamanders have
such awesome superhero capabilities
of regeneration and we humans don’t?
And fortunately for us curious nature nerds
for a long time
many scientists in the world
have been pondering the same thing
and working to figure it out.
And that power of regeneration
may be closely tied to another curiosity
that sets salamanders apart
from most other tetrapods:
Their gigantic genomes.
Ranging from about 9-120 gigabase pairs
salamanders are packed with DNA.
The record genome size for salamanders
goes to the Neuse River Waterdog
and it’s the largest out of all animals
except for the marbled lungfish
that has about 130 gigabase pairs.
Our human genome is significantly smaller
sitting around 3 gigabase pairs.
[ ♪ mellow guitar music ♪ ]
And they crazy thing is—
these salamanders with their gigantic genomes
are packed with DNA that sort of
isn’t really their own DNA.
Their genome is full of these things
called transposable elements
sometimes referred to as 'junk DNA'
which are basically
parasitic DNA sequences
that are capable of replicating
and inserting themselves throughout a genome.
In salamanders
usually around 25% to 50% of the DNA
is recognizable as transposable elements
or this parasitic DNA.
And even more of the salamander genome
is made of up these TEs
they are just ones that can’t quite be
detected with our testing methods.
So for a long time
scientists believed
that this junk DNA didn’t do anything
it just sat there
taking up space in the genome
and most of it does
but we now know
that these transposable elements
can have effects
on how our DNA encodes proteins
and offers the instructions
of cellular development.
And these TEs seem to be the reason why
salamander genomes became so large.
It’s still up for debate
when and where
the first transposable elements
entered the genome.
Maybe in the cenancestor
aka the ancestor of all life.
But as far as salamanders go
one theory suggests
that about 200 million years ago
an ancestor to today’s living salamanders
started having its genome become enlarged
as more transposable elements
began inserting and replicating
within the genome.
That ancestor and its successors
probably lived mundane lives
that could tolerate the replicating parasitic DNA
that was beginning to bloat the genome
all the while
having negative effects
on the creatures’ physiological functionalities.
But these ancestors
could endure whatever negative effects
resulted from the bloating genome
because, well...
the ancestors
like today's salamanders
didn’t need amazing brain power
or need to run fast
or need a vast amount
of super physiological functions.
Most salamanders
kind of excel at doing not much at all.
Like this guy—
He just sits on a rock at night acting all proud.
Over time
it’s theorized that
even more of these transposable elements
kept getting inserted into the genome
of salamander evolution.
A sort of positive feedback loop had occurred
because when there are already existing
transposable elements in the genome
then there are more 'hiding spots'
so to speak
for new transposable elements to fit.
And now many salamanders
just have gigantic genomes
full of a lot of transposable elements.
Now some of you nature nerds
that are up on your DNA knowledge
might be saying,
"Well about 45% of our human DNA
is composed of transposable elements."
And you’d be right.
So why don’t we have gigantic genomes?
Typically in us humans and most other animals
transposable elements are kept in check
and minimized.
They are limited by random mutations
over the course of evolution.
Also it’s hard for an individual
to survive and pass on genetic code
including that parasitic code
if there is too much parasitic DNA
messing with the functioning
of the original DNA.
For example
there seems to be a correlation
between the giant genomes of salamanders
and the size of their cells.
the cells become larger
with a larger genome because, well,
they have to hold more DNA.
And big cells seem to create fragile tissues
in important organs such as the heart.
We humans just couldn’t handle
the flimsy, rather pathetic heart
that most salamanders have.
Our metabolic demand is too high.
Our brains and our eyes
are very expensive to run metabolically.
So yeah,
salamanders have been able to endure
throughout the ages.
But they shouldn’t be too cocky
about their large genomes.
These gigantic genomes have had
tremendous negative effects
on their development and functionalities.
Their hearts are poorly developed
as well as their brains, eyes,
and other body parts.
Of the 765ish species of extant salamanders
around 40 can’t even metamorphose into adults
and at least another 39 species
only sometimes metamorphose into adults.
So—basically
some salamanders
remain in their juvenile stages their entire lives!
I guess that gives a literal meaning
to the expression:
'Parents are just kids having kids.'
But amazingly,
even with their sluggish lifestyles,
salamanders have persisted throughout the ages.
It’s almost a contradiction
when we think of survival of the fittest.
But salamanders truly have found a way
to dominate the lazy niche
in our natural world.
Most salamanders just sit and wait
for food to walk by—then they grab it.
That doesn’t require the agility of a fox,
or the amazing eyesight on an owl,
or the intelligence of a human.
So their poorly developed bones, eyes,
and brains aren’t exactly needed to survive.
But the superpower of regeneration
seems to be a welcome tradeoff
for all the negative effects.
Behind me in all of this detritus,
these rotting logs,
are a bunch of eastern red-backed salamanders.
This species can’t even respire through lungs
because—well—they don’t have any!
Yes. Their genome has made it so
they don’t develop lungs.
But they developed a nifty trick
over the course of evolution to where
they can respire through their skin.
It’s called cutaneous respiration.
And another curiosity of salamanders
is that there seems to be a negative correlation
between the size of their genome
and their ability to regenerate.
The larger a salamander’s genome
the more difficult the process of regeneration
seems to be. It’s slower.
Yet we know that
the large genomes of salamanders,
all those repetitive sequences of DNA
and not just the transposable elements,
are a reason why salamanders
are so good at regeneration in the first place.
So scientists would love to know the exactness
behind this contradiction-
-this negative correlation-
just so they can further reveal
the mystery that is salamander regeneration.
But the key probably resides
in the fact that these salamanders
are not fully maturing;
many salamanders sort of stay
in a young stage throughout life,
principally at the cellular level.
And in the young stages of life—
there are a lot of stem cells
and other immature cells capable of
differentiating into various new parts.
It’s like if you were building a Lego-kit
and you had magical pieces
that could just turn into whatever piece
you needed at the time.
So when a salamander’s limb is chopped off.
a blastema forms,
or a bunch of cells capable of differentiating
into various other cells.
So this means the vascular system can be replaced
and the muscle
and the cartilage and bone
and the nerves
and the remaining other tissues
The cells of the blastema
are very similar to the embryonic cells
you were full of when you were in your mother’s uterus.
So it’s quite handy
to have cells available
all over the body
that can turn into pretty much anything needed
for the regeneration of body parts.
However
the original cells for regenerating limbs
don’t appear to be the same
for what cells go into restoring other body parts
like the organs.
It just adds to the current mystery
of salamander regenerative powers.
Scientists nowadays would love to know
how exactly all of this works
because, well,
they want humans to have the capability
to regenerate brains
and hearts
and lost limbs.
And perhaps in the future we’ll see this happen.
There really is so much more to explore
on this amazing topic.
There are more questions than answers right now.
But we should walk away from this video
knowing that many salamanders
have gigantic genomes
and amazing regenerative abilities
And for me...
-turn around if your squeamish again-
...after getting sliced up by my back surgery
I’m still impressed with modern medicine
and my own body’s ability to heal
but I’m still quite envious of the salamanders.
Because even though I’ll heal up
it pales in comparison
to what salamanders are capable of.
Spread some knowledge. Be Nature-heroic.
[ CC by Koaw 2022 - I think it's 2022...maybe? =) ]