New Blog

If you have stumbled across this blog, I'm sorry to say it has been closed.  However, you can find posts from me at my new blog: www.The3rdStone.wordpress.com

4th of July Festival

Because Woods Hole, MA is home to both an Oceanographic Institute and the Marine Biological Laboratory, most of the people in this small town have some connection to the scientific community. As a result, the fourth of July festival in Woods Hole, MA is a celebration of uninhibited science-geekery.

Some of the highlights included the neurobiology course:

Microbial diversity, with their giant squid:

And my personal favorite, Mendel with his peas:

Bringing up the rear was our own Embryology course.  We have a time-honored tradition of performing gastrulation through interpretive dance, which is quite possibly the best way to show gastrulation:

If that wasn’t self explanatory, let me explain.

If you’re not familiar with gastrulating, it’s a process during development where animals generate their gut.  All animals start out as a single cell, the fertilized egg.  This cell divides over and over again until it forms a hollow sphere of cells, called a blastula.  Some cells from the blastula then move inside the hollow sphere, creating a sphere with multiple layers of cells.  The inside layer, called the endoderm, will form the gut and some organs.  The middle layer, or mesoderm, will form the musculature and bones.  The outer layer, or ectoderm, forms skin and the nervous system.

This image shows endoderm (in red) moving into the blastula.  The ectoderm is in orange, the mesoderm is not shown.  Image taken from Wikipedia. 

The three different colors of our shirts represent the three germ layers: blue for ectoderm, red for mesoderm, yellow for endoderm.  In this particular display, we are performing gastrulation as it occurs in the sea urchin (that was obvious, right?) We started out as a blastula (a hollow ball of cells), and then invaginated to create the three layers of tissue. Finally, some of the mesoderm cells start to form spicules, which create the skeleton of the urchin.

Sea urchins were only the beginning. We also performed gastrulation as it occurs in frogs, nematode worms, fruit flies, as well as chaotic cleavage (like you find in some sea anemones and jellyfish) and chicken neurulation for good measure.  The parade lasted less than an hour, and only traveled a few blocks, but we got as many gastrulations as we could in there. 

If you’re ever in the area during the fourth of July, I highly recommend you check out the Woods Hole parade.  Their were a lot of people, and a lot of energy (including an epic water gun fight).  

The Course T-shirts have been Finalized

And were designed by yours truly.  Unfortunately, the quality of the images went down during processing; I'll try to get some higher resolution images up soon. Take a look:

Here's the front...

...and the back

Greetings From Woods Hole, Massachusetts

Sorry for the long delay in posting.  I am currently taking the Embryology course at the Marine Biological Laboratory. Actually, I’ve been here since the beginning of June, but the work schedule has made it difficult to get any of these blog posts up.  Every day we begin with lectures around 9am, and we often do laboratory work well past 1 or 2 in the morning!

However, I have been asked to share my experiences with The Node, a blog run by The Company of Biologists, which runs a number of important journals, including Development and The Journal of Experimental Biology. It’s a great incentive to get these posts out, despite the lack of free time.  But we’re half way done with the course, so I’ll have a lot of catching up to do. 

On June 7^th, Nicole King from Berkeley came to teach us how to work with choanoflagellates and sponges.  I have gotten to spend time with Nicole previously because we work on the same NASA astrobiology grant (which you can find more about here or here) , but this was my first chance to get some hands-on work with her model systems. 

Nicole focuses on sponges and choanoflagellates to learn more about the early evolution of animals.  Choanoflagellates are not actually animals, but DNA evidence suggests that they are the animals’ closest living relatives (e.g. King et al 2008).  An individual choanoflegellate is made up of a single cell. It has a long flagellum, which it uses to swim through the water and to trap bacteria (which it eats) in a collar made up of microvilli.  Below is a diagram of a choanoflagellate, courtesy of ChoanoWiki:

The reason that choanoflagellates have received a lot of attention recently is that they don’t always stay as single cells.  Sometimes, as a choaflagellate divides, the cells stay connected to each other.  The creatures will form a variety of shapes, including long chains and rosettes:

 Image taken from ChoanoWiki.

The fact that these creatures are (1) closely related to the animals, (2) can live as single cells or in mutlicellular groups, and (3) look suspiciously similar to the cells which line the inside of sponges, means that they might provide real insight into the origins of animals.  To find out more about what choanoflagellates can teach us regarding animal evolution, I recommend you look at the papers cited in ChoanoWiki. But for now, I’ll leave you with a very cool picture made by fellow classmate Valerie Virta using antibody staining techniques Nicole taught us.  This is a colony  of choanoflagellates, the blue is staining the bodies of the choanoflagellate bodies, the red is staining the microvillar collar, and the green is staining flagellum (for you technical folks, that’s DAPI, actin, and tubulin):

You can also see a cool (if not particularly informative) I took of a sponge below.  Most of the color is generated from natural florescence coming from the skeleton of the sponge (called spicules).  But you can see the little blue dots, which are the nuclei of cells stained with DAPI. 

Evolution of Constraint - What Causes and Breaks Dollo's Law?

When something is lost in evolution, it is rarely gained again.  The trend of was first noted in 1893 by the paleontologist Luis Dollo.  One famous example of this trend, often called Dollo’s law, is the number of digits on the hands and feet of vertebrates.  Some of the earliest fossil amphibians have eight or more toes, but that number was quickly reduced to five:

For the last 300 million years, all animals, from humans to whales, dinosaurs to birds, have had five digits or less on their hands and feet. But a good rule of thumb is that any law in biology is going to have exceptions.  Anyone who knows enough about domestic dogs and cats knows that some breeds are found with multiple toes. Here is the paw of a Norwegian Lundehund, six toes and all:

What explains this violation of Dollo’s law? What explains Dollo’s law in the first place?  For the next few posts, I’m going to look at the science behind evolutionary constraint, what causes it, and what happens when it’s broken.

Works Cited

Boisvert CA, Mark-Kurik E, & Ahlberg PE (2008). The pectoral fin of Panderichthys and the origin of digits. Nature, 456 (7222), 636-8 PMID: 18806778


Dollo, L (1893). Les lois de l'évolution. Bull. Soc. Belge Geol. Pal. Hydr, VII:164-166.

Current Debates in Animal Evolution: Lecture 1 - Why Evolution (Part 2)

Current Debates in Animal Evolution: Lecture 1 - Why Evolution (Part 1)

I'm currently teaching a seminar at UCLA for the Spring quarter.  My idea was to create a course that focuses on current scientific research in animal evolution.  The first part of my first lecture is 
on youtube; you can check it out below: