A new organ discovered in baleen whales

Baleen whales have been hunted and ripped apart for hundreds of years, especially their mouths, where the baleen (extensions of the oral mucosa) was once used as stays in women’s corsets and in making buggy whips.  So it’s really surprising that only now have scientists discovered that there is a unique organ in their mouths that helps them feed.  This organ, described in a new paper in Nature by Nicholas Pyensen and five other authors (reference below), is found in rorqual whales, a subset of baleen whales that include blue whales, humpback whales, minke whales, and fin whales.

Baleen whales, which include the largest living animals on Earth, have a unique form of feeding: “lunge-feeding,” in which they suddenly ingest a  huge mouthful of water and then expel it, leaving the edible contents sticking to the sieve that is formed by the baleen. They then lick off the prey. The process is described in a nicely written editorial in the same issue of Nature, “A whale of a story“:

Rorqual whales capture much of their food by an extraordinary procedure known as lunge feeding. When a rorqual comes across a dense patch of prey, it accelerates through the water and open its mouth. As it does so, its mouth fills with water, suspended within which are the tiny animals that the whale wants. The amount of water that flows into the whale can more than double the creature’s weight, and to accommodate it, blubbery pleats under the lower jaw expand, just as an accordion grows as it fills with air. The once sleek and streamlined whale now has the shape of a bloated tadpole. And it has a lot of water in its mouth.

To squeeze the water out again, the whale closes its jaws and pushes the water out through plates of keratin filters, which trap the food. In this way, rorqual whales can gulp and graze for hours, repeatedly slowing down then lunging through the water.

I was stunned that they take in an amount of water equal to their weight: these are the most massive creatures on Earth!

Now I’ve posted on baleen whales several times before, including discussions of transitional forms and vestigial tooth buds, and I also posted the following video of the lunge-feeding of a blue whale, which I reproduce again so you can see this amazing behavior (watch the first 10 seconds only):

So what did the authors find? Examining hunted specimens of fin and minke whales (both rorquals), they discovered a strange organ in the middle of the lower jaw (actually, the lower jaw consists of two bones that aren’t connected, allowing them to open their mouths even wider. Here’s a diagram of where that organ is (it’s the bit labeled “so” in the upper part of the diagram below; click to enlarge).  There are also “vibrissae” (“vib”), or whiskerlike protrusions that probably aid in detecting prey.

Here are the keratin “bristles” on the baleen plates that filter out the prey (largely krill, or small crustaceans); the whales literally comb the prey out of the water:

The sensory organ is a unique feature in these animals. It’s a fibrous capsule, about 40 cm (16 inches) across, filled with a gel-like substance that contains connective tissue with nerves and nerve terminals, as well as “mechanoreceptors” (nerve receptors that sense changes in position or deformation) embedded in that tissue. Here’s a picture of the organ from the paper:

Mandibular symphysis in sagittal section, showing bony and soft tissue around the sensory organ (so) and papillae (pa) within it. raf, relictual alveolar foramen.

The authors suggest that, based on its position, its anatomy, and its possession of nerves that run to the brain, this organ provides sensory input to the brain when the whale is opening and twisting its jaws during bouts of lunge-feeding.  In other words, it helps coordinate the critical feeding movement and makes sure it’s done correctly. The authors suggest this scenario for how lunge-feeding works. It’s in scientific jargon but not too hard to follow:

We propose a three-step lunge-feeding model to explain the organ’s role during a lunge: (1) using vibrissae present on the external surface of the chin, rorquals register prey fields of sufficient density; (2) the jaws disengage and rotate6, thereby compressing and shearing the organ; and (3) the oropharyngeal cavity reaches full expansion, with drag forces acting on the inside of the mouth transmitted to the organ through the YSF8 (Fig. 2). According to dynamic modelling studies, rorquals must actively control the rate of mouth openingand throat-pouch expansion to effectively maximize volume captured; we propose that the sensory organ has a key role in coordinating this movement.

It’s surprising that given the history of whaling, nobody either noticed or took an interest in the organ before.  How it evolved, and what its precursor was, are mysteries that remained to be solved. It just goes to show that many of these mysteries have been right under our noses for a long time. What’s important is to notice them, get curious, and ask the right questions.

______

Peyensen, N.D., J. A. Goldbogen, A. W. Vogel, G. Szathmary, R. L. Drake and R. E. Shadwick. 2012. Discovery of a sensory organ that coordinates lunge feeding in rorqual whales. Nature 485: 498–501; doi:10.1038/nature11135

35 Comments

  1. gbjames
    Posted May 24, 2012 at 5:33 am | Permalink

    “lunge-feeding”, not “lung-feeding”!

    • Reginald Selkirk
      Posted May 24, 2012 at 5:48 am | Permalink

      Would you care to buy a vowel?

    • E.A. Blair
      Posted May 24, 2012 at 5:55 am | Permalink

      I would have spent a lot of time wondering what breathing had to do with feeding (other, of course, than keeping the whale alive so it can continue feeding) had it not been for the quoted section cluing me in on the actual term.

      It’s another symptom of self-publishing – print media had the virtue of having more than one set of eyes reviewing every piece of text before it went out. I believe they were known as “copy editors”, and even “typesetters”. Ceiling cat alone knows how many times I’ve sent out comments with embarrrasing typu tipo typograf MISTEAKS!!

  2. darrelle
    Posted May 24, 2012 at 5:38 am | Permalink

    From 1st para., a duplication error.

    “This organ, described in a new a new paper in Nature . . .”

    Spelling error in second para.

    “lung-feeding”

    Typo in the para. just after the third picture inset.

    “The atuhros suggest . . .”

    Fascinating post, thank you. Whales have always been a favorite of mine. I’ll have to show this to the kids. A good real world example of discovery, modeling, and scientific methods in general.

    So it seems that this organ acts as a stress detector.

    • whyevolutionistrue
      Posted May 24, 2012 at 6:03 am | Permalink

      Yes, I got distracted and didn’t proofread the post until now. Thanks for catching those typos, which have been fixed.

      –Mgmt.

      • gbjames
        Posted May 24, 2012 at 6:06 am | Permalink

        It appears further down in the copy, too… “…during bouts of lung-feeding.”

      • Barney
        Posted May 24, 2012 at 6:10 am | Permalink

        There are still a couple in a later paragraph (after the picture of the organ) – “bouts of lung-feeding” and “scenario for how lung feeding works”.

  3. Woody Tanaka
    Posted May 24, 2012 at 5:47 am | Permalink

    “It is surprising that given the history of whaling, nobody either noticed or took an interest in the organ before.”

    I’m not surprised. The people who kill and have killed these magnificent creatures are barbarians, vultures who are looking to do nothing more than turn living natural wonders into dirty pocket money.

    • Gregory Kusnick
      Posted May 24, 2012 at 10:35 am | Permalink

      Sorry, I’m not buying it. Barbarians they might be, but that doesn’t make them stupid. If you want to turn whales into pocket money efficiently, the smart thing is to learn as much about whale anatomy as you can while doing it, so as to maximize opportunities for making profits off the profitable bits.

      • gravelinspector
        Posted May 25, 2012 at 7:22 am | Permalink

        If you want to turn whales into pocket [?] money efficiently, the smart thing is to learn as much about whale anatomy as you can while doing it, so as to maximize opportunities for making profits off the profitable bits.

        Well, that would probably be true if you were breeding them or actively herding them. But for a basic exploitative hunt with no consideration of future stocks, you don’t need to know the life style and anatomy of your prey in any detail.
        The history of whaling started quite small, and by the time they got onto the “great whales” the market for products was fairly mature. Baleen (“whalebone”) gets stowed there in the ship ; the blubber goes into the blubber cauldrons to be rendered into oil ; for some whales, “ambergris” is a target (which suggests that someone knew to look for it ; the results of taking a beached whale apart, perhaps), then the rest of the carcass is set adrift. Chopping up a whale at sea would have been a pretty dangerous activity (I must have got bored with Melville’s style before I got to that point), not very conducive to detailed anatomical investigation.
        It does beg the question of whether anyone ever did a proper autopsy on the deck of a factory ship, and missed this. Possibly. But again, well before the design of whaling vessels reached this size, then whaling was an industry, not a research programme.
        I recall, about 15 years ago, human anatomists discovered a previously unknown muscle in the human face. Not exactly the least studied lumps of anatomy on the planet ; but no-one had noticed this muscle before.

    • Posted May 24, 2012 at 5:39 pm | Permalink

      Well, have the Japanese, who have done so much “research” on whales (that end up in Japanese restaurants, though I gather there is also a huge stockpile on ice – against the day they are stopped?) ever published any papers on this?

  4. Dominic
    Posted May 24, 2012 at 5:52 am | Permalink

    Fascinating stuff. I was reading Ed Yong’s bit on this earlier.

    Whales are great illustrators of evolution as you have shown on WEIT before. Hmmm… the great WEIT Whale!

    • gbjames
      Posted May 24, 2012 at 6:03 am | Permalink

      !!! excellent !!!

  5. Kevin Alexander
    Posted May 24, 2012 at 6:14 am | Permalink

    I’ve wondered where are the muscles that open and close those huge jaws?

    It turns out that they only need to rotate the two flat bones that then act as hydrofoils so it’s the forward motion through the water that does the work. Twist the jaw one way and the mouth opens, twist it the other way and the mouth closes. The swimming muscles in the body do the work.

    I’m an inventor and as an intelligent designer I am constantly amazed by the elegant solutions that a mindless process can find.

  6. Posted May 24, 2012 at 6:43 am | Permalink

    That is fascinating. Thanks (& thanks for the correction) & as Woody above says, not surprising it wasn’t known about before considering they were merely ‘harvest material’. I love that despite all we’ve explored and discovered, there’s always more

  7. still learning
    Posted May 24, 2012 at 7:28 am | Permalink

    /snark Maybe humans should have the same organ to prevent overeating…

    • Posted May 24, 2012 at 8:12 pm | Permalink

      My reading of it was that this organ helped in getting as much into the mouth as possible. So, if it was present in humans, it may only exacerbate the problem…

      • gravelinspector
        Posted May 25, 2012 at 7:59 am | Permalink

        this organ helped in getting as much into the mouth as possible.

        I can’t say I got that impression. The forces on a lunge-feeding rorqual’s jaw and mouth are major, and will need fine control to avoid breaking the jaw or splitting the floor of the mouth. Try an acrobatic trick of running forward, then having an assistant stop you by pushing a stick into your mouth so that it meets the floor of your mouth, then using that stick’s force to bring your body to a halt in about a body-length.
        So, controlling the opening of the jaws will need fine information about the load on the jaws, their position, the degree of distrension of the floor of the mouth … and that is what this sensor is for.
        I recall a recent article (I forget if it was discussed here, or on SlashDot) which suggested that a rorqual could achieve a Return On Investment of about 70-fold. Viz : if the whale expended a 1000 kilocalories on performing a lunge in a dive, it might harvest 70000 kilocalories of food value. That’s impressive.

  8. Litchik
    Posted May 24, 2012 at 9:53 am | Permalink

    Woody- what an odd way to describe the Inuiat.

  9. Gregory Kusnick
    Posted May 24, 2012 at 10:38 am | Permalink

    For what it’s worth, my guess on the origin of this sensory organ is that it’s an elaboration of the sensory nerves already present in the lips of mammals.

    • gravelinspector
      Posted May 25, 2012 at 8:03 am | Permalink

      The abstract that Jerry linked to indicated that the authors consider the structure and nerves derive from the first incisor tooth. Which would make it a nice example of evolutionary re-purposing of a redundant structure.

  10. Posted May 24, 2012 at 11:41 am | Permalink

    I was just looking up rorqual whales on Wikipedia and noticed that the Latin name of the group is “Balaenopteridae,” and the genera names within that group are “Balaenoptera” and “Megaptera.” Why do these names contain “-ptera”? Baleen wing and mega wing?

    • Posted May 24, 2012 at 3:33 pm | Permalink

      Is it because of the huge, wing-like flippers of some species?

      /@

      • Posted May 24, 2012 at 3:45 pm | Permalink

        I just remembered I had Lyall Watson’s Whales of the World on my bookshelf… and this is indeed the case (p. 81).

        These are proportionally largest in humpback whales, yielding the generic name, Megaptera.

        /@

  11. Tim
    Posted May 24, 2012 at 11:52 am | Permalink

    Haven’t whalers historically hunted toothed whales? That would explain why they’d miss this organ.

    • Posted May 24, 2012 at 3:32 pm | Permalink

      No, not just toothed whales (sperm whales, for ambergris, if not other things). Modern whalers hunt mainly minke whales, which are rorquals, although historically right whales (also baleen whales, but not rorquals) were regarded as the right ones to hunt, hence their name.

      If I understand this correctly, the “so” is found only in rorquals… but minkes (and others) must still have been hunted for many years…

      /@

      • Posted May 24, 2012 at 8:15 pm | Permalink

        With all the ‘scientific research’ that the Japanese are doing on minke whales, you’d have thought they might have found it by now.

  12. emmageraln
    Posted May 24, 2012 at 12:28 pm | Permalink

    Reblogged this on emmageraln.

  13. emmageraln
    Posted May 24, 2012 at 12:28 pm | Permalink

    Fascinating, thank you!

  14. eric
    Posted May 24, 2012 at 1:21 pm | Permalink

    The baleen is the bit hanging down from the upper lip, right? I thought it was bigger.

    Still trying to visualize how this works. Whale opens mouth and lunges forward. Closes mouth 90% of way, then pushes water out through remaining slit, over which the baleen sits. Is that right?

    Sort of like a human squirting water out between their teeth?

  15. Sameer
    Posted May 24, 2012 at 2:22 pm | Permalink

    Japan has been killing hundreds of Minke whales under the guise of “research” – ICRW approved no less. Minke whales are part of the Rorqual (Balaenopteridae) family.

    I think their “research” is focused only on those parts of the whale which can be made into burgers.

    Whaling has a long tradition in Japan, Norway and a lot of native American cultures. But after all we know about these majestic animals, we need to put a stop to such wanton killing. What kind a culture is it that doesn’t change in the face of new knowledge?

    • Posted May 24, 2012 at 3:34 pm | Permalink

      A religious one?

      /@

      • Mark Joseph
        Posted May 24, 2012 at 6:43 pm | Permalink

        +1. Zing!

  16. gravelinspector
    Posted May 25, 2012 at 8:11 am | Permalink

    There is also coverage of this on the Nature Podcast at http://www.nature.com/nature/podcast/index-2012-05-24.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+nature%2Fpodcast%2Fcurrent+%28Nature+Podcast%29&utm_content=My+Yahoo
    But I don’t know what it says ; it’ll take around an hour to finish downloading.

  17. Posted May 25, 2012 at 12:28 pm | Permalink

    Fascinating stuff. I was reading Ed Yong’s bit on this earlier.

    Whales are great illustrators of evolution as you have shown on WEIT before. Hmmm… the great WEIT Whale!


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