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This
picture gives you a good idea of just how big
a
spermaceti whale is. Captain Ahab wanted to take
this
guy on mano y mano. He was nuts.
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Not for Moby Dick; he was a spermaceti whale. The fact that
he was white and revengeful is nothing compared to how evolution has fashioned
the real-life spermaceti whales. They have a head that is so weird - I just can’t wrap my
head around it.
First off, the spermaceti whale is often known by its
shorter name, the one that sounds like the cells in the male reproductive
fluid. I have learned that using that word gets my posts blocked from most
schools, so lets use the scientific name, Physeter
macrocephalus, where macro =
large and cephalus = head.
P. macrocephalus
is the largest of the toothed whales. It is the fifth largest whale in the
world, behind the blue, right, fin, and bowhead whales – all baleen whales that
eat krill and plankton. P. macrocephalus averages 25,000-55,000 kg (60 US tons) and can be 70
ft (21.5 m) in length.
Fully one third of that length is head - and it gets weirder.
The spermaceti whale’s head is very much an exception in the animal world. As
it just so happens, its head is asymmetric, which brings P. macrocephalus into our growing list of asymmetric animals – the
flatworm parasites of fish gills, the scale-eating cichlid fish, the flatfish,
and the narwhals. See a pattern here?
A big head suggests a big brain, and P. macrocephalus has the biggest brain on the planet, averaging
over 18 pounds (8 kg). So maybe Ahab was right when he and the other sailors
described Moby Dick as having “intelligent malignity.”
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The
model is of an 18 lb. spermaceti whale brain. I
can’t
vouch for the color. Notice how it’s as big as
your
head! Bigger! The model of the left is named
Frank
and he is available for lingerie and catalog
shoots.
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To compare relative cognitive power between mammal species,
EQ is the ratio of C over the expected value for C of an animal of given mass
(S), EQ = CSr. Humans have the highest EQ (7.4-7.8) but dolphins are
pretty hefty as well (4.14). Whales of different types have different EQs,; P. macrocephalus’ value is very high
(~3.8). But if he wanted to have a brain like humans, it would have to weigh
several hundred pounds! The blue whale’s EQ is much lower (~1.0); in general
the toothed whales (Odontocetes) have
much higher EQs than the baleen whales. In fact, the toothed whales and
dolphins as a group are pretty much second only to the humans in EQ.
A 2012 study sort of links humans and toothed whales like P. macrocephalus when it comes to EQ.
Their paper suggests that the greatest variance in EQ occurs in primates and
toothed whales, and suggests that the evolutionary constraints have been
relaxed in these two groups of animals.
A 2013 study suggests that during evolution, the toothed
whales underwent a body mass decrease, while baleen whales underwent a mass
increase – each without changing the brain size much. This led to toothed
whales having higher EQs, closer to humans than even some primates (lemurs are
often below a 1.0).
But EQ doesn’t mean everything. A new study comparing killer
whale brains and P. macrocephalus
brains suggests that the much smaller killer whale has a brain about the same
size as P. macrocephalus. While it
gives them a bigger EQ in general, the main difference in the brains of these
two cetaceans (whales and dolphins) is in their cerebellums.
In this case, the killer whale is the exception – in all
other mammals, the cerebellum size scales directly with overall brain size. The
results suggest to the authors that the differences relate to what they eat and
how they dive – the killer whales have to be much more agile, and this is one
thing in which the cerebellum functions.
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A
great illustration of the P.
macrocephalus head. The skull
is in tan, the spermaceti and junk in yellow, brain fits in
the little triangle made by the jaw bone, the frontal sac, and where the nasal passages go down to the lungs. You
can
see the two nasal passages and their different paths in
the transverse cut. See how the blowhole is so far
front?
I put an arrow where it exits in the transverse cut.
The right nasal passage goes to the phonic lips.
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All this talk of big brains in the spermaceti
whale may give you the wrong idea. Look at the picture above and you get a
better appreciation for the size of this animal. And again, the head is just so
weird. The vast majority of P.
macrocephalus’ head is outside his/her skull (the tan portion)!
The biggest part of the whale’s head is devoted to the spermaceti organ and the junk organ (or melon). The brain is in
the little case toward the back and behind the jaw. The real question is what
all those compartments and tissues above the skull are for.
P. macrocephalus is
one of the whales that uses clicks and rolls as well as echolocation. Lots of
research has been done on the vocalizations of whales so let me explain….. no,
is too long, let me sum up.
Echolocation uses high frequency short clicks, and they’re loud -
over 230 decibels. We’ve talked about these before. The lower frequency coda
(long rolls) are for gabbing, and slow clicks can be heard for 60 km so they
are for males keeping track of other females during breeding season, according
to a 2013 paper. These clicks and codas can be highly directional and are very
powerful. This is what all that equipment is for.
Here’s how it happens. A vibration
is produced just south of the blowhole (more on this below). That vibration is
projected backward, through the spermaceti organ. This organ is filled with
a whitish, waxy, fatty material. Sailors thought it was the whale’s male
reproductive fluid (it isn’t) – and that’s how the organ and the whale got
their common name. It is about 1900 L (502 gal) of very useful spermaceti oil
for lamps. This is why they were hunted almost to extinction.
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The
left image is the surface of the frontal air sac
where
the clicks and codas are reflected back through
the
melon. The right image is the phonic lips of a
spermaceti
whale. Made form a nostril, they act much
like
our vocal chords, but I know people who can make
a
heck of a noise with their nostril and a Kleenex.
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When the echolocation returns from
the target, it vibrates the lower jaw and a fat pad at the back of the jaw.
This connects directly to the auditory part of the brain, so the return click
is processed to give a distance and direction to the prey. The slow clicks and
social communication are made about the same way, but some are so powerful that
they can stun or even kill nearby prey so they can be eaten easily.
Now you know another way that P. macrocephalus is an exception, few
other animals can echolocate, although dolphins do have a much smaller melon
for the purpose. We still need to talk about how that vibration is created.
The upper respiratory portion of
the spermaceti whale is a thing to behold. There are two nasal passages as you
would expect, but they take very different paths. The left nasal passage
travels to the left of the spermaceti organ, while the right flattens out and
travels between the spermaceti organ and the junk.
Add to this that while the left
nasal passage ends in the left nostril – the blowhole, the right nostril doesn’t communicate with the outside
world! It ends at the phonic lips,
the source of the vibration. As a result, the spermaceti whales have one
nostril while all other whales have two, and the one they have is set way off to the left
side of the head. This arrangement makes the whale asymmetric.
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This
is not P. macrocephalus; it’s a blue
whale. You can
see
the difference easily. The blowhole is way back on
the
head, and there are two holes in the blowhole, one
for
each nostril.
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To explain the phonic lips, think
of the honk and rumble when some people blow their nose. That’s from vibration
of their nostrils. Well, P. macrocephalus
does the same thing, although the nostril is inside its head, only located on
the right side, and has been modified to look more like our vocal folds.
On first examination, the phonic
lips looked like the lips of a monkey, so the French name is museau de singe (see picture above).
This makes the P. macrocephalus the
only whale with one set of phonic lips, all others have two - and this
exception leads to another. Since the two nasal passages are quite separate, a 2005 study found that the spermaceti whale is the only whale that can breath
and click at the same time!
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In late 2014, seven sperm whales beached themselves
in
Australia. This presents a problem because they have
to
be cleaned up. As they decay, gas builds up inside.
Somebody
(least seniority) has to release that gas.
World’s
– worst – job.
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When diving, the whale can suck
water in through the blowhole. This cools the waxy fluid in the spermaceti
organ. The density goes up and helps the whale dive. When it wants to surface,
it can increase the blood flow around the organ. This brings more heat and melts
the spermaceti. Its lower density makes the whale more buoyant and helps it to
surface! Evolution is amazing.
Next week, let’s leave the water
and check out some asymmetric flying animals.
For
more information or classroom activities, see:
Spermaceti
whales –
Encephalization
quotient –
Echolocation
in whales –
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