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What do fish and ears have in common?

20 October, 2010 Leave a comment

I’ve got this great undergraduate student in my lab who is (at least for now) exhibiting all the traits of the ideal student any professor would love to have around: he volunteers ~10+ hours per week here, if no one is around, he finds things to do to teach himself new skills, he reads journal articles on his own accord that are aligned with interests of the lab, AND he’s creative! Lately, he has been trying to tackle a rather substantial challenge I presented to the lab: designing a force plate that can measure forces under granular media.

What?

OK. Here’s the context: I used force plates to measure how hard and in which directions an animal is pushing when it steps on the ground. By combining this with measured movements of the animal that I quantify by analyzing synchronized high-speed video, I can calculate how much power the muscles must produce around each joint in order for the animal to move the way it does. This technology has been commonly used since the mid-1980s or earlier, for locomotion on flat, homogeneously hard surfaces. While we know a lot about how animals move across these types of “lab environment” surfaces, we know far less about movement over natural surfaces that may shift or change squishiness, orientation, etc. with each step.

Granular media, such as sand, therefore, is a particularly interesting material to me, as it actually makes state changes as an animal moves. For example, when sand is sitting undisturbed, it resembles a solid. Yet, when an animal strikes the surface and strokes through it with its foot, the sand actually becomes a fluid for a short while. Any sand that is kicked up during the step is actually acting like a gas! With all this in mind, measuring forces on sand can be a rather challenging conundrum.

In a meeting with my undergraduate student last week, he presented a design to me that involved peppering a surface with a grid of lumps that each could sense fluid movement. Little did he know, what he was showing me was something holding remarkable resemblance to hair cells, sensory receptors that are found in our ears AND in the lateral line system of fishes!

 

A haddock with the lateral line highlighted (black line running the length of the fish).

 

Ever wonder how a school of hundreds of fish manages to… school with such regularity and neat, synchronized prowess? The next time you catch that rainbow trout, sunfish, sailfish, or whatever strikes your fancy, take a close look at the side of their body and  you’ll see a series of dashes and dots that run from the rear side of the gill margin all the down to the base of the tail. These little holes mark the external opening to the lateral line, the pressure-sensing secret for fishes.

 

Detail of a lateral lines (the dots/pores on the scales). Photo by P. Spaans.

 

Within these pores are receptors called neuromasts. Neuromasts look a little like a thimble placed open side down on a table top. Each neuromast is made up of a group of cells called hair cells, named because they (grossly) resemble a Leprocaun troll doll, with different length hair bundles mounted on top.

 

Note the uncanny resemblance between the Leprochaun troll doll's hair and neuromasts!

 

The entire neuromast is covered in a gelatinous glob, forming a cupula. Deflection of these hair bundles due to changes in fluid flow causes the production of a receptor potential. Deflection direction also stimulates the production of different types and magnitudes of potentials, enabling the fish to determine the direction of the flow. Changes in fluid flow direction or pressure can be due to an underwater obstacle, a neighboring fish, or even a predator, enabling a fish to respond seemingly magically while the approaching object is still far away.

 

Anatomy of the fish lateral line, with a neuromast pictured on the right.

 

 

It turns out that my student (I guess not so surprisingly) was not the first person to think of using the neuromast as a biomimetic sensor: a group of scientists at the University of Illinois, Northwestern University, and Institut fur Zoologie have developed nano hair cells they call ALL (for artificial lateral line) that can localize the position of a crayfish placed in a tank. Take a look at their paper, published recently in Bioinspiration and Biomimetics. Call it bias or whatever you want, I am still excited to see where (if anywhere) my student will take this biomimetic idea of his. Let me know if you have any input on how he can potentially use this to invent a new type of force plate technology, and I’ll put you in touch with my student to try to make this a reality!

Is this provocative, informative, or offensive?

8 October, 2010 1 comment

 

Different species of <i>Paramecium</i>

Several species of Paramecium. Image courtesy of the Protist Information Server.

 

Competitive exclusion is an ecological principle initially developed by Russian ecologist Georgii Frantsevich Gause in the early 1930s. In a series of experiments, Gause demonstrated that if two species of Paramecium that utilize the same resources are placed in direct competition with each other for limited resources, one will flourish, while the other will not. In my quest to clarify on the state of the field early this week, I came across a rather… interesting… paper entitled, “Competitive Exclusion: A biological model applied to the Israeli-Palestinian conflict“. Whoa.

Despite this being a rather textbook example of how biology can be used to inspire a field far outside itself (i.e., politics), it has been very interesting for me to watch the expressions as I unveil the title to fellow biologists. I have received a number of raised eyebrows and even explicit sounds of distaste. It appears that most everyone (including myself) thinks that this paper is talking about the extinction of one of the ethnic groups, a classic interpretation of competitive exclusion.

Interestingly, the author of this paper, Dr. Kristen Urban, is actually a well-traveled scholar and expert of Middle East affairs. Here is her brief biography, lifted straight from the pages of BioOne and Politics and the Life Sciences (which, by the way, is an explicit mix of biology and… politics!!):

“J. Kristen Urban, an associate professor of Political Science at Mount St. Mary’s University in Emmitsburg, Maryland, holds an MS in Biology and PhD in Political Science, and was a 2004 Fulbright Scholar to Bahrain. She is also the recipient of a 2006 Malone Fellowship from the National Council for US-Arab Relations. Her recent academic publications have appeared in the Journal of Religion,Conflictand Peace and Literature and Nation in the Middle East, edited by Yasir Suleiman and Ibrahim Muhawi (Edinburgh University Press, 2006).”

It turns out that Dr. Urban’s use of the Principle of Competitive Exclusion is a more conservative and modern interpretation, recognizing that direct competition leads to conflict and limitation of population growth, but not necessarily elimination of one species (speaking organismally), or in this case, intergroup conflict. With this paper, she strives to explore the characteristics of the long-standing Israeli-Palestinian conflict while using the biological principle to explore potential outcomes and solutions for remediation of the conflict:

“The Law of Competitive Exclusion suggests that a stable equilibrium between species/populations sharing a niche can only be achieved when the density dependent mechanisms of each population come into play before either outcompetes the other. In particular, the findings suggest that the key variable is not land, which can be utilized differentially, but relates to the competition coefficients involved in the competition, chief of which is nationhood. The competitive exclusion approach privileges process over outcomes,and would suggest that Palestinian sovereignty be recognized first as a legitimate construct, and only then the geographic boundaries of a Palestinian state be delineated through inter-party negotiations.”

For those of you intrigued by the conflict and how a biological principle has been applied towards trying to achieve resolution of a situation that has faced countless gridlocks and set-backs, I highly encourage you to read this paper, and develop your own opinion to the question: is this particular application of bioinspiration provocative, informative, or offensive?

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