Biochemical Soul Musings on Nature, Science, Evolution, Biology, and Education

6Mar/09Off

Great Darwin Beard Challenge – Week 3

Stripped of all biologically advantageous or meaningful body hair, there comes a time in every man's life when he ponders just why the eons of molding, shaping, and changing forces of natural selection have left what little remains.

The answer comes, quite naturally, to all who discover that certain magical stage of hirsute facial existence. There is but one purpose - one singular defining function of this keratinized expression of manhood: to look like a bad-ass.

Thus, we now present to you Week 3 of the Great Darwin Beard Challenge in a new order of presentation.

Great Darwin Beard Challenge Week 3

Great Darwin Beard Challenge Week 3 (click for larger version)

Though our voyage of Darwinian proportions has only just begun, in time we shall bridge our initial childish faces with the woolen wisdom of Darwin himself gracing our chins.

Unless I get an interview...

Join us over at Deep-Sea News for Week 4 in our quest to look a little more like the man himself in our Great Darwin Beard Challenge.

Great Darwin Beard Challenge History:

3Mar/09Off

Adaptation of the Week – Bird/Crocodile Symbiosis?

Earlier this week, thanks to the wonderful science & nature Twitter community, I followed a link from someone now forgotten to an article entitled "7 Symbiotic Wonders of the Aerial World."

Therein, in symbiotic relationship number one, sat a photograph that I found utterly astonishing:

WP00955. Nile Crocodile (Crocodylus niloticus) with Egyptian Plover or Crocodile Bird (Pluvianus aegyptius) - digital reconstruction of popular myth attributed to Herodotus, 5th Century BC.

"Plovers and Crocodiles"

According to the WebEcoist website which published this list of "symbiotic wonders."

"It looks like something out of a storybook - and in fact it can be traced back to accounts told thousands of years ago - a crocodile opens its mouth, invites a bird in before … what?  ::Chomp:: it swallows the sap alive? Amazingly, the crocodile remains still while the plover picks meat from its mouth. This cleans the crocodile’s teeth and prevents infection while providing a somewhat scary meal for the hungry bird."

The image stewed in my head for a couple of days, and I mentally bookmarked it as an excellent adaptation to cover in my Adaptation of the Week series. The story began to write itself as I drove to and from work.

It's quite easy to see how such a relationship, once begun, would be reinforced over successive generations, with the daring plovers becoming well-fed and the tolerant crocodiles' pearly whites gleaming like Smilin' Bob's.

Egyptian Plover (Pluvianus aegyptius)

Egyptian Plover (Pluvianus aegyptius)

But how would such a symbiotic relationship begin, I wondered?

Regardless of the incremental steps that naturally must have occurred, at some point a single dumb, brave, or incredibly hungry bird had to have been the pioneer to first brave the feast-laden crocodilian death-trap. Imagine being the first bird to firmly plant talons on that massive reptilian tongue. No doubt others had come to this place before - but none had survived unscathed.

And what of the first crocodile. Was he just so stuffed that he couldn't bear the thought of shoving one more feathered morsel down his gullet ("it's only wafer thin"). Or perhaps he was the Einstein of the ancient crocodiles, somehow sensing the advantage of letting the little plover do its thing.

In reality, I thought, the relationship probably came in many fits and starts, with the birds initially pecking around the crocs, grabbing whatever leftover bits they could. The crocs tolerated them, much as cattle do with egrets. Perhaps a fair number of plovers did end up as croc snacks. But over time, the crocs most friendly to the plovers gained a slight advantage, with the "friendly alleles" slowly increasing in frequency throughout the population. The birds, of course, now had to compete with one another, becoming bolder and more adventurous.

Nile Crocodile (Crocodylus niloticus) with Human Hand (Lucas skywalkerus)

Nile Crocodile (Crocodylus niloticus) with Human Hand (Lucas skywalkerus)

In the end, this beautiful relationship was forged and stabilized, to the benefit of both parties (though I imagined that crocodiles who break the contract probably continuously cropped up).

I had my article, plainly written right there in my brain. But of course, as with any good article dealing with science..er...well, anything, I first had to do a little bit of research. What species of bird is it? How common is the relationship?

I make my way back to the original "7 Symbiotic Wonders" article and click on the above image to get the image credits.

The photography website (Warren Photographic) immediately opens to the same image with the following caption:

"WP00955. Nile Crocodile (Crocodylus niloticus) with Egyptian Plover or Crocodile Bird (Pluvianus aegyptius) - digital reconstruction of popular myth attributed to Herodotus, 5th Century BC." [emphasis mine]

Wait...what?!

That's not a real image, but a photoshopped one?  I immediately googled the bird (Pluvianus aegyptius), which pulled up this Wikipedia article:

"It is also sometimes referred to as the Crocodile Bird because it is famous for an unconfirmed symbiotic relationship with crocodiles. According to a story dating to Herodotus, the crocodiles lie on the shore with their mouths open, and the plovers fly into the crocodiles' mouths so as to feed on bits of decaying meat that are lodged between the crocodiles' teeth. The crocodiles do not eat the plovers, as the plovers are providing the crocodiles with greatly-needed dentistry. Two prominent ornithologists have supported this story anecdotally,[who?] but the behaviour has never been authenticated (Richford and Mead 2003)." [emphasis mine]

You mean to tell me that after all of this thought, the whole thing is only an ancient myth?!

Apparently the author over at WebEcoist didn't do his research for the article (sorry Ecoist). I mean, c'mon! The original image they used as the lede explicitly states that it's only a myth.

So much for my Adaptation of the Week...

What a croc!!

In the end, I decided to do some research and find a REAL symbiotic relationship:

And in return?

And in return?

(I photoshopped this)

Update: I found a great post on SkepticWiki that discusses this exact supposed phenomenon, and it even talks about how some creationists  use the "crocodile bird" (erroneously) as an example of a behavior that could not have evolved naturally. Right...


Previous Adaptations of the Week:

  1. Timber Rattlesnake Camoflage
  2. The Aye-Aye’s Freaky Finger (I’ve Been Cursed by an Aye-Aye!)
  3. Flatfish Eyes & Recapitulation Theory
1Mar/09Off

Carnival of Evolution #9 – Moneduloides

The next edition of the Carnival of Evolution is now live over at Moneduloides!

It's clear that moneduloides put alot of work into this edition, which contains a great amount of commentary on each submission.

So waste no more time here - go check it out now!

26Feb/09Off

The Great Darwin Beard Challenge – Week 2

This week's installment of the Great Darwin Beard Challenge is live over at Southern Fried Science. We are in week two now, our sandpaper faces replaced by millimeter stubble.

It seems a long way from here to our bushy-bearded Darwinian goals. The "contest" will end on October 1st, the 150th anniversary of the inside cover date of the 1st edition of The Origin of Species - we began on Darwin's 200th birthday, February 12th.

Tiring of simple photographs of our burgeoning bearded faces, Andrew instituted a theme of "hats" this week. Apparently in the Southern Fried Science world, "enormous fake afro" is synonymous with "hat."

What will next weeks theme be?  Who knows. Give us some ideas.

We will be rotating through the blogs of Deep Sea News, Southern Fried Science, and here - so be sure to visit all three weekly :)

Great Darwin Beard Challenge History:

25Feb/09Off

Adaptation of the Week – Flatfish Eyes & Recapitulation Theory

Most biologists at one time or another in their training have learned of the 19th century theory expounded upon by Ernst Haeckel called "Recapitulation Theory".

The theory's thesis: "Ontogeny recapitulates phylogeny." Don't worry - it's not as complicated as the biological jargon might imply.

Ernst Haeckels Drawings (1892 Romane copy)

Ernst Haeckel's Drawings (1892 Romane copy). Note: Haeckel oversimplified these drawings. I use them here as a simple illustration of the concept of developmental similarity.

The idea boils down to a simple one - one that seemed to make sense in light of the fact that the science of developmental biology had only just begun from a systematic standpoint. The idea: if you watch an organism develop from an embryo to an adult, you can watch it slowly move through the evolutionary steps that had created it. That is: development repeats evolution.

So a human embryo would first look like a fish, then a reptile, then a mammal, and finally a human. Of course, we now know that in a literal sense, the theory is completely and utterly wrong. No stage of human development, or of any other organism, correlates with a discrete step in evolution.

We are never fish. (Though we do have embryonic tails).

However, that doesn't mean that there aren't kernels of truth to the idea, if applied loosely. Take the most famous and classic example: embryonic human gills. You may have heard yourself that humans have gills as embryos. Unfortunately this claim arises from misconception and incomplete understanding of developmental biology. Humans do not - ever - have gills. But as embryos we do have "pharyngeal arches." These are little bumps around what you might consider the neck area of a developing embryo (see Haeckel's drawings above). And these little mounds of tissue do in fact remarkably resemble similar mounds found in fish - mounds that in fish develop into gills (Note: Haeckel vastly oversimplified these drawings. I use them here as a simple illustration of the concept of developmental similarity. See: http://zygote.swarthmore.edu/evo5.html. Thanks Bjørn!).

One of the amazing aspects of developmental biology that much of the public does not generally understand is that evolution does not occur by adding new organs, appendages, or tissues to adult animals (whether through gradual steps or not). Evolution works by slowly sculpting the early embryonic clay of an organism.

Fish evolved these gill pouches as embryos - pouches that could then be sculpted into gills. As evolution waltzed and hopped along at its geological pace, genetic mutations began to change how these little mounds were sculpted, such that now in humans, these arches are sculpted into various parts of the face and head. A genetic program was already in place to control the shaping of the pouch. All that natural selection did was slightly tweak that program. For example, instead of a group of cells moving one direction, they moved another. Instead of becoming blood vessel cells, they became cartilage or bone cells.

Thus, while we now understand that we are not witnessing evolution in miniature during development, we are seeing pieces of our evolutionary history - little remnants that remind us of our relationships to our ancestors and also help inform us on what morphogenetic processes underlie evolution.

Which brings us to our adaptation of the week: the freaky asymmetric eyes of the flatfish.

Flatfish (www.seawater.no)

Flatfish (www.seawater.no)

Most people have probably seen a flounder - one member of the flatfishes. They have adapted to lie amongst the silty ocean bottom, hidden from predators and prey, flat on their sides. For a normal fish this might be maladaptive - they would constantly have one eye buried in the sand. Of course the negative of being one-eyed might be offset by being much more camouflaged and undetectable.

Luckily for the flounder, the eye that should be buried in the sand has moved around its forehead so that both eyes are on one side.

The flatfish eye served as one line of attack against natural selection back in the day - and Darwin himself didn't quite know how to answer the charges. Evolutionary gradualism would predict that through successive steps, the eye slowly moved upward toward the forehead and eventually to the other side of the face. But what advantage could a slightly moved eye give, if it still was on the wrong side? Alternatively, as Richard Goldschmidt postulated in the 1930s and 40s, perhaps a single monstrous freakfish was born with both eyes on one side, and this allowed it to lie flat without losing half its vision. It could have then survived and had lots of little freak fish babies of its own.

So how did the flatfish become the strange creature it is now? Let's first look at the developmental biology of the flatfish eye.


WANDERING EYES from Science News on Vimeo.


FROM FRY TO FISH from Science News on Vimeo.

Flatfish Metamorphosis

Flatfish Metamorphosis (Schreiber 2006)

It's been know for quite some time that flatfish larvae look like perfectly normal, symmetrical, and upright fish. The picture to the right is from a study by Alexander Schreiber in the Journal of Experimental Biology from 2006. As you can see, at early stages the larvae are normal, but progressively tilt and become horizontal as one eye moves across the face. He also showed in this study that eye movement and flattening behavior occur independently during development - but that's a much longer story.

Alright, so one eye gradually moves across the skull during development. What about during evolution? Do we have any clues as to the steps involved? Well, as many biologists know, the fossil record has now answered the question for us.

In a well-known study that was published last summer in Nature and received much media attention, Matt Friedman showed findings from a series of fossils delineating a clear gradual evolution from symmetrical to asymmetrical flaltfishes. (For excellent in-depth coverage looking at this study and the debate over flatfish evolution, see one of my favorite science bloggers, Ed Yong at Not Exactly Rocket Science, and also see the popular science writer Carl Zimmer at The Loom, and GrrlScientist at Living the Scientific Life).

Flatfish Evolution

Flatfish Evolution (Friedman 2008)

The evolution of the flatfish eye seems to mirror what we see during development. Thus, here we have a case of ontogeny appearing to recapitulate phylogeny quite wonderfully. There are many excellent examples of this throughout the biological world, though few that show such incredible similarity between the two processes of development and evolution. Nonetheless, this isn't really evolution we're watching during flatfish development - we're merely seeing how slight changes of the developmental programs are themselves responsible for the changes we see over time through evolution. Generally speaking, earlier developmental processes appear much more similar across varied species than later processes.

Development is in fact one of the primary constraints against evolution.

So while you were never a fish, you still showed remnants of fishy development during your own development. For it was these fishy developmental process that allowed the evolution of your own.

Scientific References:

Previous Adaptations of the Week:

  1. Timber Rattlesnake Camoflage
  2. The Aye-Aye’s Freaky Finger (I’ve Been Cursed by an Aye-Aye!)