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. ( full text ) – Fanny de Busserolles1,2,*, Fabio Cortesi1, Jon Vidar Helvik3, Wayne I. L. Davies4,5,6, Rachel M. Templin1, Robert K. P. Sullivan1, Craig T. Michell2,7, Jessica K. Mountford4,5,6, Shaun P. Collin4,5,6, Xabier Irigoien2,8,9, Stein Kaartvedt2,10 and Justin Marshall1, Pushing the limits of photoreception in twilight conditions: The rod-like cone retina of the deep-sea pearl sides, Science Advances 08 Nov 2017:Vol. 3, no. 11, eaao4709 DOI: 10.1126/sciadv.aao4709
“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.” Sometimes, clearing the decks is a good beginning. Once we have established an appropriate fee and fine structure for non-Darwinian thinking, just pay it and think.
Also, Michelle Starr, for clarity, at ScienceAlert
Many species use a combination of their rods and cones, called mesopic vision, in low to moderate light conditions.
Humans use this for low light, as do crepuscular species. Cats, for instance, use cone cells but have more rod cells for better night and twilight vision.
“Pearlsides, being active mainly during twilight, have developed a completely different solution,” said de Busserolles.
“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 have called these newly discovered cells “rod-like cones,” because under a microscope they appear to be a combination of both types of cells.More.
See also: Science Mag: Scallop’s eye “Fine-tuned for image formation” Thought: The way things are going, the war on reason and common sense required to protect Darwinian naturalism will run into problems with the English language, and any other language that is needed to convey meaning. Could researchers buy the right to use conventional meaningful terms now and then without Darwin’s Dobermans let loose on them? Maybe they could apologize in advance and pay a fee… with a special fine levied if the paper is cited anywhere?
Note: News posting will be light till this evening due to other deadlines.
Hat tip: Pos-Darwinista