Photonic Crystal Light Collectors In Fish Retina Improve Vision In Turbid Water

Elephantnose retina

Fish have some of the most amazing retinas in the animal kingdom.  Like other fish species that live in environments with little to no light, the elephantnose fish (Gnathonemus petersii) use electrical fields to navigate through dark and murky waters.  However, unlike some of those species, the elephantnose fish has not lost its eyes through evolution and uses vision for some functions.

This paper published in Science back in May, 2012 by authors Moritz Kreysing, Roland Pusch, Dorothee Haverkate, Meik Landsberger, Jacob Engelmann, Janina Ruiter, Carlos Mora-Ferrer, Elke Ulbricht, Jens Grosche, Kristian Franze, Stefan Streif, Sarah Schumacher, Felix Makarov, Johannes Kacza, Jochen Guck, Hartwig Wolburg, James K. Bowmaker, Gerhard von der Emde, Stefan Schuster, Hans-Joachim Wagner, Andreas Reichenbach, and Mike Francke shows that the elephantnose fish has absolutely unique and interesting structures that optimize light capture ability and make them insensitive to spatial noise.  Also in the mesopic range they match the rod and cone opsin sensitivity curves allowing the use of both rods and cones throughout large ranges of light intensities, but importantly, arrange the cone photoreceptors in functional assemblies that act as photonic reflectors, creating lightwells in a sense that optimize photon capture.  The rod photoreceptors meanwhile are positioned *behind* the photonic lightwells or reflectors.  The result is that the photonic lightwells or reflectors become wavelength sensitive light intensifiers that functionally match the dynamic range of both rods and cones while boosting sensitivity in the red wavelengths that are the first wavelengths filtered out by water.  The thinking is that this allows the elephantnose fish to easily see large predators in murky or turbid environments.


Notable Paper: Photomechanical Responses In Drosophila Photoreceptors

This notable paper by Roger C. Hardie and Kristian Franze looks at phototransduction in the fruit fly, Drosophila melanogaster.  Drosophila melanogaster has a long history in vision research of informing our understanding of the biochemical processes involved in phototransduction going back almost 40 years to this paper.  However, the Hardie and Franze paper looks at transient receptor potential (TRP) channels, which coincidently were also first found in Drosophila in a series of papers from Montel and Rubin, Hardie and Minke and Niemeyer et. al. and have proved themselves to be fairly ubiquitous and involved in wide areas of cell function from growth cones to cellular guidance and chemotaxis.  As expected, there are also many other areas where TRP channels are involved in the retina including store operated calcium channels and functions in ganglion cell calcium modulation, spiking rate and apoptosis.

This particular paper answers a fundamental question of how light functionally opens the TRP channels.  It turns out that there is a surprising mechanical force that is created that then generates an electrical response far quicker than using standard chemical second messenger based systems seen in mammalians.  Very interesting…



Image Credit: Bbski on Wikipedia