The overall theme of this thesis was a comparative analysis comarping different features of the visual ecology of some coleoid cephalopod species (cuttlefish, octopus and squid). These animals inhabit a wide diversity of marine environments and possess both a remarkable and complex visual system and body pattern repertoire. Their sensitivity to, and utilization of, polarized light greatly enhances their predatory and communicative capabilities, whilst their ability to use coloured patterns and textures (generated in the skin) has resulted in a stunning array of communicative and camouflage behaviours. Coleoids are masters of disguise thanks to structurally-pigmented and reflective elements in their skin, all under neural control, and can change pattern and texture within milliseconds.
Perhaps the most unusual fact about these animals is that they are almost all functionally colour-blind – possessing just one visual pigment peaking in sensitivity at around 470-500nm (except for a set of deep-sea species which possesses three pigments). Here we investigate how different visual features, such as pupil shape, retinal topography and photoreceptor specialisation, polarization sensitivity, corneal structure and habitat features may be adaptive. We found that seven previously untested species possess an area of specialisation on their retina, correlating directly with their pupil shape and habitat characteristics. We investigated the potential for polarization sensitivity using microscopic anatomical analyses, supported by behavioural demonstrations using modified, classic visual response techniques: optomotor and optokinetic responses. We observed positive visual responses to polarized light in seven species of previously untested coleoid cephalopod, following anatomical descriptions of their retinae. These analyses revealed that they possessed the cellular structure and arrangement necessary for sensitivity to polarized light, and that this is maintained throughout the specialised regions of the retina. These structures are the orthogonally-arranged microvilli in the photoreceptors in the retina – an arrangement that is set to align vertically and horizontally with the outside world in several species.
Primary body patterns (uniform, mottled and disruptive) were manipulated in four previously untested species. This was achieved using a variety of non-polarized and polarized substrate stimuli, both in the lab and in the field. Furthermore, we found that the outer surface of the cornea (in species which possess a cornea) are covered in a nipple-like array of microprojections which may, as in many arthropods and teleosts, aid in tasks related to increasing transmission of light waves onto the retina, and assist in maintaining a mucus layer across the surface of the eye. These features were compared between species which are distantly related, yet inhabit similar environments, and between closely related species which inhabit different environments. From this, we speculate that environmental pressures are primarily driving evolutionary changes in many of these features (polarization sensitivity, body pattern repertoire and retinal topography), as we see distantly related species inhabiting the same environments as one another. That is, phylogenetically-derived characteristics have been modified between the coleoid groups to allow adaptation to life in different photic environments.