Cephalopod Eyes and Light Sensing Skin

DWhatley

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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

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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

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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. ...
 

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