Wednesday, March 25, 2015

This Nose Knows

Biology concepts – evolution, asymmetry, bilateral symmetry, phonic lips, whales, echolocation, encephalization quotient, density



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.
Captain Ahab had an obsession for the white whale in Moby Dick. It was a killer, but not a killer whale. It swamped boats, rammed ships, and generally made a nuisance of itself. But it seemed to be intelligent as well, the way it planned attacks and how it looked at him sometimes. Is that weird for a whale?

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.”


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.
Nope, it takes more than a big brain to have big thoughts. A more telling statistic for mammals is brain size relative to the predicted brain mass based on body size, something called the encephalization quotient (EQ). Brain size does usually increase with body size, but the increase isn’t linear, so scientists include a cephalization factor (C).

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.


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.
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.


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.
At the back of the spermaceti organ is a knobbed plate in the frontal air sac. This reflects, focuses, and amplifies the vibrations. They bounces back toward the front of the whale head, through the junk (melon). This organ is also filled with waxes and oils, but the sailors didn’t think it was worth any money, so they called it the junk. This organ is made of many vertical compartments of spermaceti. When it leaves the front of the whale, it is one powerful click.

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.


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.
The position of the blowhole is way up front. All other whales have their blowholes behind the jaw, as the nasal passages go almost straight up. The blowhole being set way off to the left helps make spermaceti whales easy to identify when they surface.

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!


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.
Lest all of this hasn’t been impressive enough, the spermaceti organ may have another amazing function. P. macrocephalus dives deeper than any other animal, 3000 m or more. To swim down that far is hard, and if you sink easily, then staying on the surface would be hard. Scientists think P. macrocephalus conserves muscular energy by changing the density of the spermaceti fluid.

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.



Ridgway, S., & Hanson, A. (2014). Sperm Whales and Killer Whales with the Largest Brains of All Toothed Whales Show Extreme Differences in Cerebellum Brain, Behavior and Evolution, 83 (4), 266-274 DOI: 10.1159/000360519

Oliveira, C., Wahlberg, M., Johnson, M., Miller, P., & Madsen, P. (2013). The function of male sperm whale slow clicks in a high latitude habitat: Communication, echolocation, or prey debilitation? The Journal of the Acoustical Society of America, 133 (5) DOI: 10.1121/1.4795798

BODDY, A., McGOWEN, M., SHERWOOD, C., GROSSMAN, L., GOODMAN, M., & WILDMAN, D. (2012). Comparative analysis of encephalization in mammals reveals relaxed constraints on anthropoid primate and cetacean brain scaling Journal of Evolutionary Biology, 25 (5), 981-994 DOI: 10.1111/j.1420-9101.2012.02491.x

Montgomery, S., Geisler, J., McGowen, M., Fox, C., Marino, L., & Gatesy, J. (2013). THE EVOLUTIONARY HISTORY OF CETACEAN BRAIN AND BODY SIZE Evolution, 67 (11), 3339-3353 DOI: 10.1111/evo.12197

For more information or classroom activities, see:

Spermaceti whales –


Encephalization quotient –


Echolocation in whales –