Two for one Fridays: Seeing in UV/ Polarized light (Animal vision: A brief discussion of neuroethology)


Since today I am feeling adventerous, I have decided to post 2 lessions.  The first was a very breif discussion on the history of the San Francisco Bay Bridge and future designs to prevent it from being damaged during an earthquake.  This post will be more true to the nature of the blog however.  We will be discussing a topic in Neuroethology that has been studied intensivly.  That is the ability for animals to see the plane of polarized light and UV light and use it for navigation and identification of food/ communication.

First off we have to discuss what exactly constitutes polarized light.   Light waves are as some of you may know actual particles.  Think of them as molecular size pieces of dust that travel through space in a sinusodal wave like fashion.  They have both an electrical aspect to them as well as a magnetic component to them.  These two aspects are at times perpendicular to one another traveling forward.  When they hit an object they reflect off molecules and then travel at a direction 90 degrees to the original orientation.  They become horizontal rather than vertical for example when they travel through our atmosphere. 

polarizedlightfigure1

regluar light becoming polarized

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polarized light waves

Humans detect polarized light as glare.  Polarized sunglasses have microscopic grooves cut into them to block the light particles that are traveling parallell to the cuts and allow the ones that are traveling opposite to pass through.  This is why when you wear sunglasses that are polarized things seem darker than normal sunglasses.  There are animals however that can view the plane of polarized light with MUCH higher resolution than we can.  This is due to significantly different neruological structures and evolutionary designs in their eyes. 

For the purpose of this post I will use insect eyes as the standard.  Please keep in mind there are very few absoultes in biology.  There most likely are exceptions and alternatives to this.

Insect eyes are multifaceted.  That is that they are made up of hundreds of lenses rather than one single lense as typically found in the human eye.  These lenses have deep pockets each with a single neuron attached at the bottom that absorbe wavelenghts of light and report a single image towards the brain.  Think of these as pixles on a screen.  The more lenses the higher the resolution of the image. 

insect_and_spider_eyes_1

Insect eye (The dark spot is looking INTO the omatidiums)

 These lenses have cells inside them that are designed to trap the particles of light and best process them into neruonal signals.     The structure collectivly is known as an omatidium.  Think of these omatidium as cylinders stacked very closely together to form the entire eye.  the corneas of each omatidium are what make up the many facets of the insects eye.

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cross section of an insect eye showing its many omatidums

A particular protein known as opsin helps to translate the light absorption into a particular neruonal signal and color.  In order to see polarized light, there are small structures that protrude off the Rhabdomere known as microvilli that contain the rhodopsin / opsin proteins.  These structures are aligned at 90 degree angles to eachother in order to best capture those polarized light waves.  Remember the ones that suddnely were horizontal rather than verticle?  Think the same thing.  This is very different than the design of vertebrate rods and cones in which discs containing opsin / rhodopsin proteins in a scattered arrangement are stacked one on top of the other.  I will discuss this at a later post.

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The opsin protein

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Omatidia with key

These omatidiums with their specalized rhabdomere cells which absorb those particles have also become specalized to see UV wavelenght type light.  Some insects see these wavelengths as various color differences.  They use these to detect patternings on flowers or even to communicate across species.  The stomatopod, a marine crustacean, has an amazing ocular specality.  It can see the entire color spetrum, UV, polarized light and each eye can see 360 degree’s around!! Its completely difficult to even consider what that would appear like to you and I.  Some stomatopods even have the ablity to flash colored fins on either sides of their head to communicate with eachother.  These flaps have a particular coloration on them and the reflection of these means different thigns to the animal in terms of communcation.    Maybe someday scientist will devolp a way for human beings to view  the plane of polarized light, UV light fields in our own eyes.  Maybe we’ll even adapt and use this for higher communication…you never know.

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The stomatopod and its colored fins. Notice the crazy eyes?

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Posted on November 13, 2009, in Uncategorized and tagged , , , , , , , , , , , , , , , , . Bookmark the permalink. Leave a comment.

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