Cephalopod Eyes and Light Sensing Skin

[DWhatley]

Vision and Bioluminescence in Cephalopods
Thomas, Kate Nicole 2018 (dissertation Duke University)

In the deep pelagic ocean, there are no structures to serve as hiding spots, and visual interactions among animals are potentially continuous. The light environment in the midwater habitat is highly structured due to light scattering and absorption. Downwelling sunlight becomes exponentially dimmer, bluer, and more diffuse with depth. This optical structure means that an animal’s depth and viewing direction greatly affect the distances at which it can see visual targets such as potential prey or approaching predators. Additionally, this light environment mediates the visibility of bioluminescent camouflage and signals. My dissertation examines how the midwater light environment affects the ecology and evolution of vision and bioluminescence through an examination of cephalopods, a highly visual group that exhibits a broad diversity of eye adaptations and multiple evolutions of bioluminescence. My research investigates (1) vision and behavior in a deep-sea squid with dimorphic eyes, (2) depth-dependent patterns in cephalopod eye size and visual range, and (3) evolutionary dynamics in bioluminescent cephalopods.

 

[DWhatley]

Polarisation signals: a new currency for communication
N. Justin Marshall, Samuel B. Powell, Thomas W. Cronin, Roy L. Caldwell, Sonke Johnsen, Viktor Gruev, T.-H. Short Chiou, Nicholas W. Roberts, Martin J. How

ABSTRACT
Most polarisation vision studies reveal elegant examples of how animals, mainly the invertebrates, use polarised light cues for navigation, course-control or habitat selection. Within the past two decades it has been recognised that polarised light, reflected, blocked or transmitted by some animal and plant tissues, may also provide signals that are received or sent between or within species. Much as animals use colour and colour signalling in behaviour and survival, other species additionally make use of polarisation signalling, or indeed may rely on polarisation-based signals instead. It is possible that the degree (or percentage) of polarisation provides a more reliable currency of information than the angle or orientation of the polarised light electric vector (e-vector). Alternatively, signals with specific e-vector angles may be important for some behaviours. Mixed messages, making use of polarisation and colour signals, also exist. While our knowledge of the physics of polarised reflections and sensory systems has increased, the observational and behavioural biology side of the story needs more (and more careful) attention. This Review aims to critically examine recent ideas and findings, and suggests ways forward to reveal the use of light that we cannot see.

 

[DWhatley]

The Extraordinary Secret of Cephalopod Vision
2016 article by Ines Dawson

 

[DWhatley]

Octopuses Can Feel Light with Their Arms Live Science

Octopuses can "see" light with their arms, even when their eyes are in the dark, researchers have found. When the arms of the octopus detect light, the eight-armed creature pulls them close to their body.

Because octopuses generally have a poor sense of where their body is in space, this complex instinctive behavior might help protect their arms from the pincers of predators nearby that they might otherwise not sense.

Scientists have long known that octopus arms react to light. Their skin is covered in pigment-filled organs called chromatophores that reflexively change color when exposed to light. These chromatophores are responsible for the octopus's color-changing camouflage superpowers. In fact, it was while studying these light-induced chromatophore responses that Tal Shomrat and Nir Nesher of the Ruppin Academic Center in Israel noticed something odd. ...

 

[Feder]

Heard that we could observe octopuses with red lights without being noticed. Is there any research basis for the statement that octopuses can‘t sense red light?

 

[pkilian]

Is there any research basis for the statement that octopuses can‘t sense red light?

From what I can tell after a very brief amount of googling, is that octopus likely only have photoreceptors. This means that they likely wouldn't be able to perceive the red-color from the light. Depending on the kind of light you have and whether the light is actually emitting wavelengths in the proper spectrum or just a white light with a red filter you may have mixed results. Octopus are incredibly light sensitive and if you have a poor quality light that "leaks" white light you may be unknowingly disturbing your animal.

Generally my stance is that if you can best mimic the animals natural environment (no lights at night) you will have the happiest animal. This isn't to say that you can never use red light to observe your animal without bothering them at night, but I wouldn't leave them in the red light overnight just in case the light is poor quality or it turns out they actually are able to perceive red light and we just don't know it.

I have done some hunting behavior experiments in full white light, red light (with actual red lights, not a red filter) and total darkness with an infrared light and camera. Typically in white light the animal hunts using a "distance pounce", the common type of prey capture method (for bimacs at least) where the animal pounces on the prey and balloons the mantle to surround and capture it. In red light or total darkness the animal never does a distance pounce, and relies on a "contact pounce" to predate. They do not capture they prey until after they have made contact with it with the arm. The predatory behavior is triggered by the chemoreceptors on the sucker cups, rather than input from the visual system.

I'm not making any claims about whether or not the animal is able to "see" in red light or not, and from my understanding we don't quite know for sure or not. Please correct me if I am mistaken. I just thought it was interesting that the predation strategy in white light relies on the visual system most likely, while the predation strategy in red light and total darkness shifted to a more contact-dependent method (likely no longer relying on the visual system, and instead relying on the chemotactile system in the arm suckers).

It could be interesting to hear if anyone else has experiences with their animals reacting to a red light being turned on or off near the tank when in total darkness (which is relatively difficult to achieve if not in a specialized space). Typically seeing how the pupil dilates or any changes in body posturing is a good metric for their ability to perceive the light. I can spend more time experimenting with my dark room setup and red lights and see if I can get them to react to a red light or not.

 

[DWhatley]

I have experimented with red lights of varying types (filter lens, red LED, filter paper over the tank top). For diurnal animals, I agree with @pkilian, don't disturb the slumber as they do detect the light but are not at bothered as with white light (there are thoughts that blue light, aka moon light, might actually be worse than white light but most reports are that they become accustomed without obvious stress).

However, with nocturnals, I have found that leaving a red light (I never detected a better or worse red but the brightness does seem to be a factor) on all night and providing good daytime caverns will allow observation of natural (or as natural as an aquarium can be) night time activity. The light is definitely still observed but seems to be accepted (perhaps as moon light?) as night time. I have noted that if you turn off the light at some point in the evening, nocturnal/crepuscular animals will learn wait until the light goes out (my reason for saying they definitely see the light) before coming out to hunt. Note that red light all night does not seem to change the natural hunting time. O. mercatoris seems to come out at about 9:00 if the room is dark but true nocturnals will still hunt at 3:00 AM.

As for not seeing you, that is more dependent on the ambient light behind you than the light in the aquarium.