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Old 14-11-2017, 09:14 AM
gary
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Cool Pushing the limits of photoreception in twilight conditions - new eye cell discovered

In a 9 Nov 2017 press release from the University of Queensland,
scientists there have discovered a new type of cell in the eye of a deep
sea fish known as the pearlside which forms part of a visual system
adapted for twilight conditions.

Quote:
Originally Posted by University of Queensland
A new type of cell has been found in the eye of a deep-sea fish, and scientists say the discovery opens a new world of understanding about vision in a variety of light conditions.

University of Queensland scientists found the new cell type in the deep-sea pearlside fish (Maurolicus spp.), which have an unusual visual system adapted for twilight conditions.

The Queensland Brain Institute's Dr Fanny de Busserolles said the retina of most vertebrate animals – including humans – contained two photoreceptor types: rods for vision in dim light, and cones for daytime vision. Each had different light-sensitive proteins.

“Deep-sea fish, which live at ocean depths below 200m, are generally only active in the dark, so most species have lost all their cones in favour of light-sensitive rods,” Dr de Busserolles said.

Pearlsides differed in that they were mostly active at dusk and dawn, close to the water’s surface where light levels are intermediate.

“Previously it was thought that pearlsides had retinas composed entirely of rods, but our new study has found this isn’t the case,” Dr de Busserolles said.

“Humans use their cones during the day our rods at night, but during twilight, although not ideal, we use a combination of both.

“Pearlsides, being active mainly during twilight, have developed a completely different solution.

“Instead of using a combination of rods and cones, they combine aspects of both cells into a single and more efficient photoreceptor type.”

The researchers found that the cells – which they have termed “rod-like cones” for their shapes under the microscope – were tuned perfectly to the pearlsides’ specific light conditions.

Research leader Professor Justin Marshall said the study was significant.

“It improves understanding of how different animals see the world and how vision might have helped them to conquer even the most extreme environments, including the deep sea,” Professor Marshall said.

“Humans love to classify everything into being either black or white.

“However our study shows the truth might be very different from previous theories.

“More comprehensive studies, and caution, are needed when categorising photoreceptor cells into cones and rods.”

Quote:
Originally Posted by Fanny de Busserolles, Science Advances

Pushing the limits of photoreception in twilight conditions: The rod-like cone retina of the deep-sea pearlsides

Abstract

Most vertebrates have a duplex retina comprising two photoreceptor types, rods for dim-light (scotopic) vision and cones for bright-light (photopic) and color vision.

However, deep-sea fishes are only active in dim-light conditions; hence, most species have lost their cones in favor of a simplex retina composed exclusively of rods.

Although the pearlsides, Maurolicus spp., have such a pure rod retina, their behavior is at odds with this simplex visual system.

Contrary to other deep-sea fishes, pearlsides are mostly active during dusk and dawn close to the surface, where light levels are intermediate (twilight or mesopic) and require the use of both rod and cone photoreceptors.

This study elucidates this paradox by demonstrating that the pearlside retina does not have rod photoreceptors only; instead, it is composed almost exclusively of transmuted cone photoreceptors.

These transmuted cells combine the morphological characteristics of a rod photoreceptor with a cone opsin and a cone phototransduction cascade to form a unique photoreceptor type, a rod-like cone, specifically tuned to the light conditions of the pearlsides’ habitat (blue-shifted light at mesopic intensities).

Combining properties of both rods and cones into a single cell type, instead of using two photoreceptor types that do not function at their full potential under mesopic conditions, is likely to be the most efficient and economical solution to optimize visual performance.

These results challenge the standing paradigm of the function and evolution of the vertebrate duplex retina and emphasize the need for a more comprehensive evaluation of visual systems in general.
The work was done at the University of Queensland Brain Institute.
Established in 2003, the institute is home to more than 450 scientists
and 42 laboratory leaders. Researchers there have made important
advances in fundamental neuroscience and in diseases such as ageing
dementia, schizophrenia and motor neurone disease.

Press release here :-
https://www.uq.edu.au/news/article/2...t-vision-trick

Paper titled "Pushing the limits of photoreception in twilight conditions: The rod-like cone retina of the deep-sea pearlsides" by Fanny de Busserolles
available here :-
http://advances.sciencemag.org/conte.../eaao4709.full
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