Thorny Trees and 20 Inch Tongues: A Case of Coevolution

A few days ago, I saw a very spiky-looking tree on the Bird of Prey Route near my house.  A few weeks ago, I saw another tree, much larger than this one, along the banks of Boulder Creek that had some enormous thorns on its branches as well, some of them easily six inches long, and super sharp on the end!  I don't know for certain what kind of tree this, or the Boulder Creek tree, is, but a good candidate I think is the honey locust (Gleditsia triacanthos), or some other tree closely related to the honey locust.  Below is the picture of the tree that I took on the Bird of Prey Route.

And here is the picture that I took on my iPhone at Boulder Creek of this tree.  The thorns look pretty similar to those of the honey locust, and I think that the trunk of the tree looks pretty similar, too.

Now why do these trees have such huge thorns?  When it comes to nature, everything evolves with a purpose.  There is no reason why a living organism would evolve something without a purpose, especially something as involved as giant, six-inch long thorns.  The question is, what purpose do these thorns serve?  Well that's a darn good question, and I am very pleased you asked.  Much like the "thorns" that you can see on the tail of a Stegosaurus, they likely were to help keep the organism from being consumed.  We see similar thorns on the branches of some trees in the genus Acacia in Africa today.  There, the thorns help protect the tree from attacks from one of the largest plant predators alive today, the giraffe.  This tree....well, suffice it to say that you probably won't see many activists hugging this tree.

"Oh, maybe these thorns look deceptively big," you're thinking.  Wrong.  These thorns do not look deceptively big.  If anything, they look deceptively small.  These thorns are frickin' HUGE.

So the real question is, why the long thorns, Goldilocks?  Many paleontologists believe that, during the Pleistocene Epoch (which lasted from between around 2.5 MYA to about 12,000 years ago), many of North America's mega-herbivores, everything ranging from mammoths and mastodons, to giant ground sloths and the North American camel Camelops, could have been preying upon these trees.  Selective pressures slowly caused these trees to evolve protection against these mammalian mega-herbivores.  Mastodons especially had very robust teeth, which would almost certainly have made them excellent bark-munchers.

In Africa, the acacia tree, also known as the whistling thorn, the thorntree, or (my personal favorite) the wattle, has a very similar defense.  Unlike the honey locust of North America, however, the acacia tree still has to deal with intense predation today, and from a wide variety of herbivores, everything from gerenuk to giraffe, elephants to more giraffes.

You see, the giraffes love the acacia tree.  If giraffes had Facebook, then they all would like the "I <3 Acacia Trees" page.  I remember reading somewhere that they can eat up to 60 or 65 pounds of acacia leaves per day.  (To understand this, try imagining a large hunk of butter that weighs 60 or 65 pounds.  Now you have an idea of how many pounds that is.)  They love it so much that, if the acacia tree hadn't adapted to keep up with the continual browsing pressure, the giraffes might have loved the acacia trees to death!  In response, the acacia trees convergently evolved these sharp thorns, just like the honey locust tree in North America.  (We talk about convergent evolution quite a lot as it is one of my favorite topics, so click HERE to learn more about it!)  

The giraffes love the acacia, though.  They aren't going to give up on those lovely leaves, just like that!  So while these acacia trees evolved their thorns to protect their leaves, the giraffes evolved something spectacular: a prehensile tongue!  Don't believe me?  Well, one of my favorite things about the Cheyenne Mountain Zoo is that you can feed the giraffes there.  And guess what: their tongues are HUGE!  Below, I have a video of my good friend Masaki Kleinkopf also feeding the giraffes!  Check out my gangsta hoodie, yo.  

So, yeah.  Suffice it to say, giraffes have frickin' long tongues.  And they use these TWENTY INCH LONG TONGUES to help circumnavigate through the acacia tree's poky and spiny maze of thorns to reach the leaves!  The acacia tree wasn't going to just take this lying down, though: no giraffe is going to be feeding on my leaves, yo!  So the acacia tree adapted again.  This time, by employing the use of tannins.

Long story short, tannins are used by humans in a variety of ways, including tanning, food processing, and making cocoa and wine.  They also apparently taste terrible.  Don't ask me, I've never tried it, but then again I don't have a 20 inch prehensile tongue, so it's a whole different ballgame.*

Not only do tannins taste terrible, but they inhibit the digestion of the leaf matter in a number of nasty ways, none of which would be all that fun for the giraffe.  So when a giraffe starts munching on the leaves of the acacia tree, that tree will release tannins to make the leaves taste like....well, leather I suppose.  (Again, haven't tried either.)  This tannin releasing is a pretty cool adaptation all on its lonseome.  The giraffe begins to move off to another acacia tree nearby.  However, if it's within 50 yards or so (especially downwind) of the original, now tanniny acacia, then the giraffe is out of luck: the nearby acacias react in turn, releasing their own tannins, and rendering their leaves almost indigestible to the giraffes, as well!  I would imagine that, because of this, giraffes have in turn developed the behavior of moving upwind as they eat, and a cursory glance over the Internet indicates that this does seem to be a behavior observed in giraffes!  Coevolution at its finest!

Make sure to check back soon for our next episode in our coevolution series, all about a very fun little squirrel!  See you then!  In the meantime, you can read about what coevolution actually is, by clicking HERE.

*The second baseball metaphor that I believe has been used on this blog.  Refer to "23-Fact Tuesday: Prairie Falcon, Red-Tailed Hawk, and Great-Horned Owl at the Dino Hotel" and "Eye Black: What Works for Football Players Works for the Cheetah" to learn more about this sport.  

Works Cited:

Baby Prairie Dogs and Birdwatching on the Bird of Prey Route!

Today, with the summer weather and the lack of school, I decided to take my car over to what I like to call the "Bird of Prey Route," a little dirt road in between Superior and Boulder about ten minutes from my house here in Colorado.  You can usually see at least one or two different types of raptors there, and there are a number of other awesome animals that I have spotted there, as well!  Today, I saw a lot of really cool birds, as well as some baby prairie dogs, as you can see below!

This particular species of prairie dog is the black-tailed prairie dog (Cynomys ludovicianus).  Like the other species of prairie dog, the black-tail is a highly social little rodent.  Below you can see two pups "kissing" each other, a type of interaction that members of the same family group will employ.  I think this is just to help solidify familial bonds, but I'm not sure if anybody knows for certain.

Today, the bird of prey route did not disappoint!  Perched in the tree in the picture below is the red-tailed hawk (Buteo jamaicensis), definitely the raptor that I see most often when on the route.

I also saw a pair of American kestrels (Falco sparverius), the species of raptor that I see second most often.  I don't usually see the kestrels so close together, however, so perhaps this was a mated pair.  I did see one of them fly into a hollow in a tree, which might be where a nest is hidden away!

As I was watching the hollow in the tree where the American kestrel swooped off into, I noticed several European starlings (Sturnus vulgaris) flying into other hollows on the tree.  Then I realized that the angle of one of the hollows was just right, and that I could actually see the adult starling feed its young!  If you zoom in on the picture, you can see that the baby already looks pretty big, maybe even as big as the parent!

Black-billed magpies (Pica hudsonia) are especially abundant in the area, and I saw several of them as well.

This magpie looks like it is molting!

Now this particular tree presents a particularly provocative puzzle, as it is almost completely covered in some very sharp looking thorns.  A few weeks ago, I saw another tree, much larger than this one, along the banks of Boulder Creek that had some enormous thorns on its branches as well, some of them easily six inches long, and super sharp on the end!  I don't know for certain what kind of tree this, or the Boulder Creek tree, is, but a good candidate I think is the honey locust (Gleditsia triacanthos), or some other tree closely related to the honey locust.  Below is the picture of the tree that I took on the Bird of Prey Route.

Here is a picture of the thorns of the honey locust tree.

And here is the picture that I took on my iPhone at Boulder Creek of this tree.  The thorns look pretty similar to those of the honey locust, and I think that the trunk of the tree looks pretty similar, too.

Now why do these trees have such huge thorns?  That's a really good question.  I started answering (or at least trying to answer) the question here in this blog post, but everything rapidly started spiraling out of control and off focus as I started talking about giraffes, tiny squirrels, cheetahs, and extinct North American elephants.  For those of you who know me, it should come as no surprise that I spiraled so quickly off topic.  But regardless, what I had written ended up having enough material for at least three or more posts, so I have moved the answer to a different post, which I will hopefully be publishing soon.  Keep an eye out for that!  In the meantime, back to the future birds!  Here, we see a pair of barn swallows (Hirundo rustica) perched on a wire.

I'm not quite as sure about the identity of this particular bird.  Also a swallow, I am thinking that it might be a violet-green swallow (Tachycineta thalassina).

I believe this to be a vesper sparrow (Pooecetes gramineus).

A western kingbird (Tyrannus verticalis), another bird that I see all the time here, at least in the summer!

At last, we have one of the most exciting birds that I saw on the route today, the blue grosbeak (Passerina caerulea), a bird that I don't remember ever seeing before!

Remember to check back soon to learn all about those massively spiky trees!

Works Cited:

Robbins, C. S., Bruun, B., & Zim, H. S. (1983). Birds of North America. New York: Golden Press.

Stokes, D. W., & Stokes, L. Q. (2010). The Stokes field guide to the birds of North America. New York: Little, Brown.

The Magic of Mariposa Grove

One of the coolest places that we went while in California was the Mariposa Grove, home to the Giant Sequoias, just a short drive outside of Yosemite.  It was absolutely incredible!  These trees were just simply massive, you couldn't even begin to get over their enormous size!  Here are some pictures of it, with myself, my sister, my father, my mother, and some other random people randomly in there for a size comparison!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We also saw these really cool and weird looking red flowers all over the place!  These flowers belong to a plant called the "snow plant," and belong to the genus Sarcodes.  Related to the heaths (i.e. rhododendrons, blueberries  and cranberries), the snow plant is an interesting parasitic plant.  Instead of living off of dead plant and animal material, they infect fungi.  However, they don't kill the fungi once its been infected.  Instead, the fungi and the flower help each other out in a classic case of mutualism!

Finally, I was really excited by this burnt log that, in my opinion, greatly resembled the devil.  Other members of my family thought it resembled a bison more, but clearly they are insane.

 The photo credit for all of the photos in this post go to Julie Neher.

Mariposa on Dwellable

Milling About in Muir Woods

When our family visited Muir Woods in California, we were all completely blown away by the immensity and the wonder of the trees.  They were simply enormous!  The coastal redwood can grow to enormous proportions, and now one really knows exactly how big they can grow.  The tallest one, however, is a stunning 379.1 feet tall.  That's about the size of a 37 story building.  Holy cow.  Anyways, I definitely recommend checking out Muir Woods if you are ever in the area, it will definitely make you feel pretty humble!

 

 

 The photo credit for all of the photos in this post go to Julie Neher.

Stinson Beach on Dwellable

Digest This: Or Can You? A Koala Could

I've been reading some interesting things about the koala (Phascolarctos cinereus) that I thought you might be interested in hearing.  As we all know, koalas are one of the sleepiest animals, and can be found sleeping and resting around eighteen or nineteen hours a day.  That means that out of their thirteen year life span, they are sleeping for around ten of those years. By comparison, a human with a lifespan of seventy-five years that sleeps an average of eight hours a day would sleep around 25 years of their life.  While a lot more than twelve years for the koala, keep in mind that humans only sleep around 33% of their life, while koalas sleep around a whopping 75-80%. But why do they sleep so much? The answer lies in what they eat: Eucalyptus leaves.

The leaves of the Eucalyptus trees are incredibly hard to digest.  Not only are the leaves very fibrous, much like celery (think about how hard celery is to chew), but they are also chock-full of toxins that very few animals can digest, with especially high concentrations of volatile oils and phenolic compounds.  What does that mean in English?  Well, phenolics are a type of organic chemical that naturally occur in plants, where they can act as deterrents against predatory browsing at the hands (or rather the mouths) of herbivores.  As stated before, the concentration of phenolics in the Eucalyptus leaves are so high that most animals would simply be unable to digest the leaves.  The koala decided not to take this lying down (ironic, as that is most of what koalas do in a day), and have evolved in a few key ways to help them deal with these toxins.

A fascinating moment of a koala's life: being awake.  Quite the statistical anomaly.

The first is simple; they have teeth that are great for chewing.  The broad, high-cusped molars possessed by the koala help it to thoroughly mash the food in its mouth prior to further digestion.  In our own mouth, we also have molars, along with a wide assortment of other types of teeth. When you are chewing your dinner, you tear bite-sized chunks off with your front teeth, or incisors and canines. Then, you move the food to the back of your mouth for further processing, and you further chew the food with your molars. The cusps on our teeth make it so the food is crushed fairly thoroughly. However, the koala doesn’t eat food like lettuce that can be torn up fairly easily. Thus, the koala has higher cusps on their molars, allowing for the Eucalyptus leaves to be ground up quite nicely.

A koala skeleton on display at the American Museum of Natural History in New York, New York.  Note the molars in the back.

The second major evolutionary adaptation is that the koala has a very long cecum, a pouch of sorts that is considered to be the first part of the large intestine.  In fact, at four times its own body length, the cecum of the koala is proportionally longer than that of any other mammal on the planet! The bacteria in the cecum help to break down the tough tissues in plants, such as cellulose, an important structural component of the cell wall in plants.  This gives our fuzzy marsupial friend a whole lot more time and space for that tough plant material to be digested.  Apparently, it takes a whole lot of guts to be a koala.

Believe it or not, I don't have a picture of a koala cecum on file.  So instead, take a look at this other interesting adaptation of the koala.  Instead of having a single thumb like we humans have, it has two!  Its first two digits are both functional thumbs, and are opposable to the other three digits on their hand.  You can see part of the hand skeleton the picture above this one.

Koalas aren't born with those important cecum bacteria, though, and to my knowledge no animals really are.  After five months of suckling from mom, the koala joey starts to enjoy the "partially digested leaf material produced from the female's anus" (MacDonald, 1984), or, as I like to call it, "Mom's Butt Leaves."  This delicious meal is actually thought to come from the cecum, giving the joey those essential bacteria and microbes, not to mention a delightful, pre-digested meal of Mom's Butt Leaves.  (Check out our other post about butt bacteria and eating poop HERE.)

Get yours at your local King Soopers today!

A fourth innovation of the koala is simply the exorbitant amount of time that the marsupial spends sleeping.  When you sleep, you are burning fewer calories than you would be if you were running around or hunting, or moving through a Eucalyptus tree browsing on its leaves.  Therefore, the more time the koala spends sleeping, the more energy it saves in exchange.  (The popular myth that the koala gets "stoned" by the Eucalyptus leaves is nothing more than that: a myth.)  The koala is able to delicately walk the line that we all desire to find: the maximum amount of sleep that one can get without dying.  It's truly a marvelous achievement, one which the koala handles with much grace and aplomb.

During the Pleistocene, there existed a larger species of koala, Phascolarctos stirtoni, a slightly larger koala than the modern species, P. cinereus.  Based on dentary measurements of both species from Price et. al., I came up with an approximate size increase of 1.4.  That is, take the length of a body part of P. cinereus, the modern koala, and multiple that value by 1.4, and you should get the approximate length of the same body part for the robust koala, P. stirtoni.  Not exactly the most precise method, but one that'll work for our purposes.  Below, you can see an approximate size comparison that I made of the two koalas, our modern species in gray and the extinct species in brown.

An approximate size comparison between the modern Phascolarctos cinereus (right) and the extinct P. stirtoni, with a can of Mom's Butt Leaves for scale.

More recently, scientists have realized that there is actually no evidence that does not support the idea that the hypothetical Laser-Eyed Koala (Phascolarctos oculaser) could have maybe possibly existed.  Scientists have been quoted as saying "We have never found it but that's not to say that who's to say that we aren't all koalas."  Below is the first unrefuted photographic evidence of the Laser-Eyed Koala in action.

That incredible, hands-on natural history museum in scenic Morrison, Colorado never stood a chance against that koala.  Fortunately, repairs to the facility should be completed on time for tomorrows 10:15 AM tour, which is included with your admission fee and well worth the time.  Talk about great free advertising, am I right?

Works Cited:

Hättenschwiler, S., & Vitousek, P. (2000). The role of polyphenols in terrestrial ecosystem nutrient cycling. Trends in Ecology & Evolution, 238-243.

Logan, M., & Sanson, G. (2002). The effect of tooth wear on the feeding behaviour of free-ranging koalas (Phascolarctos cinereus, Goldfuss). Journal of Zoology, 63-69.

Macdonald, D. (1984). The Encyclopedia of mammals. New York, NY: Facts on File.

Nagy, K., & Martin, R. (1985). Field Metabolic Rate, Water Flux, Food Consumption and Time Budget of Koalas, Phascolarctos Cinereus (Marsupialia: Phascolarctidae) in Victoria. Australian Journal of Zoology Aust. J. Zool., 655-655.

Piper, K. (2005). An early Pleistocene record of a giant koala (Phascolarctidae: Marsupialia) from western Victoria. Australian Mammalogy Aust. Mammalogy, 221-221.

Price, G. (2008). Is the modern koala (Phascolarctos cinereus) a derived dwarf of a Pleistocene giant? Implications for testing megafauna extinction hypotheses. Quaternary Science Reviews, 2516-2521.

Price, G., Zhao, J., Feng, Y., & Hocknull, S. (2009). New records of Plio-Pleistocene koalas from Australia: Palaeoecological and taxonomic implications. Records of the Australian Museum Rec. Aust. Mus., 39-48.