Natures wonders :insect vision in the dark (Introduction)

by David Turell @, Tuesday, May 02, 2017, 14:57 (871 days ago) @ Balance_Maintained

A review of how some insects can see in the dark; the physiology of using a few photons to find nectar at night:

https://cosmosmagazine.com/biology/how-do-animals-see-in-the-dark?utm_source=Today+in+C...

"Despite their diminutive visual systems, it turns out that nocturnal insects see amazingly well in dim light. In recent years we have discovered that nocturnal insects can avoid and fixate on obstacles during flight, distinguish colours, detect faint movements, learn visual landmarks and use them for homing. They can even orient themselves using the faint celestial polarisation pattern produced by the moon, and navigate using the constellations of stars in the sky.

"In many cases, this visual performance seems almost to defy what’s physically possible. For example, the nocturnal Central American sweat bee, Megalopta genalis, absorbs just five photons (light particles) into its tiny eyes when light levels are at their lowest – a vanishingly small visual signal. And yet, in the dead of night, it can navigate the dense and tangled rainforest on a foraging trip and make it safely back to its nest – an inconspicuous hollowed-out stick suspended within the forest understorey.

***

"The nocturnal European Elephant hawkmoth, Deilephila elpenor, is a gorgeous creature cloaked in feathery pink and green scales and does all its nectar gathering in the dead of night. A number of years ago we discovered that this moth can distinguish colours at night, the first nocturnal animal known to do so.

"But this moth recently revealed another of its secrets: the neural tricks it uses to see well in extremely dim light. These tricks are certainly used by other nocturnal insects like Megalopta. By studying the physiology of neural circuits in the visual centres of the brain, we discovered that Deilephila can see reliably in dim light by effectively adding together the photons it has collected from different points in space and time.

"For time, this is a little like increasing the shutter time on a camera in dim light. By allowing the shutter to stay open longer, more light reaches the image sensor and a brighter image is produced. The downside is that anything moving rapidly – like a passing car – will not be resolved and so the insect won’t be able to see it.

"To add together photons in space, the individual pixels of the image sensor can be pooled together to create fewer but larger (and so more light-sensitive) “super pixels”. Again, the downside of this strategy is that even though the image becomes brighter, it also becomes blurrier and finer spatial details disappear. But for a nocturnal animal straining to see in the dark, the ability to see a brighter world that is coarser and slower is likely to be better than seeing nothing at all (which would be the only alternative).

"Our physiological work has revealed that this neural summation of photons in time and space is immensely beneficial to nocturnal Deilephila. At all nocturnal light intensities, from dusk to starlight levels, summation substantially boosts Deilephila’s ability to see well in dim light. In fact, thanks to these neural mechanisms, Deilephila can see at light intensities around 100 times dimmer than it could otherwise. The benefits of summation are so great that other nocturnal insects, like Megalopta, very likely rely on it to see well in dim light as well.

"The world seen by nocturnal insects may not be as sharp or as well resolved in time as that experienced by their day-active relatives. But summation ensures that it is bright enough to detect and intercept potential mates, to pursue and capture prey, to navigate to and from a nest and to negotiate obstacles during flight. Without this ability it would be as blind as the rest of us."

Comment: this is not an ability to be developed from a situation of not seeing in the dark. This insect and others like it feed on flowers. They HAD to be able to do this from the beginning of their lifestyle, which means to me, this type of vision was designed this way.


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