This thesis investigated the behaviour and physiology of the visual system of Sepia officinalis by studying systematically its visual sensitivity and its spatial resolution. The cephalopod retina is composed of only photoreceptors and supporting cells, thereby providing a unique opportunity to study the interactions between photoreceptors, without the influence of other neurons, such as those typically found in the vertebrate retina. The minimum separable angle (MSA), a measure of spatial resolution, of S. officinalis was determined from behavioural experiments to be 42' for animals of 8 cm mantle length at 15 µW/cm² light intensity. As the animals grew in size and as the ambient light intensity was increased, S. officinalis showed improved visual acuity. Through these experiments, it was revealed that each tested size of animal adapted to light with similar efficiencies, and that factors other than retinal growth were involved in the improvement of behavioural MSA with increasing size. The minimum light intensity to which the retina of S. officinalis responded was 0.1 µW /cm2 , which was slightly higher than that to which individual photoreceptor cells responded. Retinal sensitivity decreased with increasing animal size. This was unexpected, as previous theoretical and behavioural studies in other species have shown sensitivity to increase with increasing animal size. Possible reasons for the decrease in sensitivity were a reciprocal decrease in cell resistance or an increase in dark noise. The visual sensitivity of S. officinalis was also affected by the stimulus flash wavelength and duration. Its retina adapted to background light in a way similar to vertebrate photoreceptors and the extracellular calcium concentration of the solution perfusing the retina affected this process. Finally, two series of experiments provided some evidence that functioning gap junctions exist in the retina of S. officinalis. By completing a study of the visual sensitivity of S. officinalis at the three levels of single cell, retina and whole animal, the visual processing that occurs between these physiological levels was investigated. From the work presented in this thesis, it is concluded that, although S. officinalis did not prove comparable in every aspect to other species on an intracellular level, it would be a useful model of behavioural and extracellular visual processes for both invertebrate and vertebrate species.

The statistical structure of natural images has sparked interest in regards to both visual processing of such images and the aesthetic responses they elicit. We bring together these two lines of research under the simple proposition that early visual processing, more specifically visual sensitivity, may mediate visual preferences. In our first set of experiments, we measured both visual preference and visual sensitivity in the same observers, using patterns varying in the slope of their amplitude spectrum. Our results found similar functions for both variables, supporting our hypothesis. In a second set of experiments, we investigated the same question with regards to simple spatial frequency variations, and found even more convincing results. We conclude that early visual processing is implicated in visual preference, supporting the recently emerging sensory-based approaches to understanding visual preference.

Signal reception and production form the basis of animal communication, and are largely constrained by environmental biophysical factors such as environmental light. However, the role of environmental light in producing variation in either signal reception or production has not been fully investigated. Using two distinct environmental light treatments, as well as a third treatment for a sampling of adults, I recorded corneal electroretinograms, lens transmission, and spectral reflectance of the body pattern of juvenile and adult Nile tilapia to chart the effect of environmental light on visual sensitivity and body colouration throughout ontogeny. Environmental light had an age-dependent effect on spectral sensitivity and an age-independent effect on spectral reflectance. Spectral sensitivity in juveniles reared under a broad-spectrum light treatment and a red-shifted light treatment differed mostly at short wavelengths, where the irradiance of the two environmental light treatments differed the most. In contrast, adults reared under the two environmental light treatments did not differ in spectral sensitivity. Lens transmission did not differ significantly between environmental light treatments, indicating that differences in spectral sensitivity of juveniles originated in the retina. Both juveniles and adults reared under the two environmental light treatments differed in spectral reflectance, and adults transferred to the third environmental light treatment differed in spectral reflectance from their counterparts reared under the two original treatments. These results demonstrate that environmental light plays a large role in shaping signal reception in juveniles and signal production throughout ontogeny, suggesting that environmental light has the capacity to drive ecological speciation. / Thesis (Master, Biology) -- Queen's University, 2012-12-03 11:32:59.441

abstract: Although mimetic animal coloration has been studied since Darwin's time, many questions on the efficacy, evolution, and function of mimicry remain unanswered. Müller (1879) hypothesized that unpalatable individuals converge on the same conspicuous coloration to reduce predation. However, there are many cases where closely related, unpalatable species have diverged from a shared conspicuous pattern. What selection pressures have led to divergence in warning colors? Environmental factors such as ambient light have been hypothesized to affect signal transmission and efficacy in animals. Using two mimetic pairs of Heliconius butterflies, Postman and Blue-white, I tested the hypothesis that animals with divergent mimetic colors segregate by light environment to maximize conspicuousness of the aposematic warning signal under their particular environmental conditions. Each mimetic pair was found in a light environment that differed in brightness and spectral composition, which affected visual conspicuousness differently depending on mimetic color patch. I then used plasticine models in the field to test the hypothesis that mimics had higher survival in the habitat where they occurred. Although predation rates differed between the two habitats, there was no interactive effect of species by habitat type. Through choice experiments, I demonstrated that mimetic individuals preferred to spend time in the light environment where they were most often found and that their absolute visual sensitivity corresponds to the ambient lighting of their respective environment. Eye morphology was then studied to determine if differences in total corneal surface area and/or facet diameters explained the differences in visual sensitivities, but the differences found in Heliconius eye morphology did not match predictions based upon visual sensitivity. To further understand how eye morphology varies with light environments, I studied many tropical butterflies from open and closed habitats to reveal that forest understory butterflies have larger facets compared to butterflies occupying open habitats. Lastly, I tested avian perception of mimicry in a putative Heliconius mimetic assemblage and show that the perceived mimetic resemblance depends upon visual system. This dissertation reveals the importance of light environments on mimicry, coloration, behavior and visual systems of tropical butterflies. / Dissertation/Thesis / Doctoral Dissertation Biology 2016

The overall objective of this thesis was to understand better the mechanisms that shape the diversity in colour vision of fish, and to explore the adaptive significance of this divergence. Among the vertebrates, teleost fish show the greatest diversity in colour vision systems. The cichlid model system illustrates that the visual system of fish may differ among species, sexes, individuals, and life stages of individuals. The large number of available cone opsin genes, which have resulted from multiple opsin gene duplications, facilitates this high degree of variation in the mechanisms of colour vision. In general, cichlids possessed complements of four to five cone pigments, and these complements varied across species, sexes, and individuals. Additionally, lens transmission, cone pigment expression, post-receptoral sensitivity, and retinal circuitry differed across life stages of individuals. My results suggest that the diversification of colour vision across species and across life stages of individuals contributes to sensory adaptations that enhance both the contrast of zooplanktonic prey, and the detection of optical signals from conspecifics. Therefore, both natural and sexual selection may have worked in concert to shape colour vision in fish. Since light is more complex under water than on land, fish required four to six cone classes to reconstruct the colour signals reflected from aquatic objects. This suggests that the large number of cone pigments in fish have likely evolved to enhance the reconstruction of the complex colour-signals in aquatic environments. Taken together, these findings improve our understanding of the variable nature of fish colour vision, and, more generally, help unravel the evolution of photoreceptors and colour vision. / Thesis (Ph.D, Biology) -- Queen's University, 2012-05-14 13:16:50.276

High visual sensitivity is a common but important characteristic of animal eyes. It is especially critical for night vision. In animal eyes, photoreceptors are the first to receive the incoming rays of light and they convert the light signals to electrical signals before passing the information to interneurons in the eye and finally to the brain. To function in dim light conditions, photoreceptors have developed high sensitivities to light. It is reported that both mammalian rod photoreceptors and Drosophilaphotoreceptors can detect single photons. The high sensitivities of photoreceptors largely depend on a high content of rhodopsin, a light-stimulated G protein-coupled receptor (GPCR), in light sensory organelles, outer segments in mammals and rhabdomeres in Drosophila. Two shared characteristics, the tightly packed photoreceptive membrane and the high concentration of rhodopsin in the membrane, work together to enable the photoreceptors to achieve the high content of rhodopsin in photosensory organelles in both mammals and Drosophila. In this thesis, I have used the Drosophilaeye as a model system to study the molecular mechanisms required for the maintenance of these two characteristics. In the second chapter, I present a new molecular mechanism of preventing Gq-mediated rhabdomeral degeneration. A new gene named tadr (for torn and diminished rhabdomeres), when mutated, leads to visual sensitivity reduction and photoreceptor degeneration. Degeneration in the tadr mutant is characterized by shrunken and disrupted rhabdomeres. The TADR protein interacts in vitro with the major light receptor Rh1 rhodopsin, and genetic reduction of the Rh1 level suppresses the tadr-induced degeneration, suggesting the degeneration is Rh1-dependent. Nonetheless, removal of phospholipase C (PLC), a key enzyme in phototransduction, and that of Arr2 fail to inhibit rhabdomeral degeneration in the tadr mutant background. Biochemical analyses reveal that, in the tadr mutant, the Gq protein of Rh1 is defective in dissociation from the membrane during light stimulation. Importantly, reduction of Gq level by introducing a hypomorphic allele of Gαq gene greatly inhibits the tadr degeneration phenotype. These results may suggest that loss of a potential TADR-Rh1 interaction leads to an abnormality in the Gqsignaling, which in turn triggers rhabdomeral degeneration independent of the PLC phototransduction cascade. We propose that TADR-like proteins may also protect photoreceptors from degeneration in mammals including humans. In the third chapter, I present a Drosophila CUB- and LDLa-domain transmembrane protein CULD that counteracts the visual arrestin Arr1-mediated endocytosis to retain rhodopsin in rhabdomeral membrane. CULD is mostly localized in rhabdomeres, but is also detected in scarce rhodopsin endocytic vesicles that contain Arr1. An intracellular region of CULD interacts with Arr1 in vitro. In both culdmutant and knockdown flies, a large amount of rhodopsin is mislocalized in the cell body of photoreceptors through lightdependent, Arr1-mediated endocytosis, leading to reduction of photoreceptor sensitivity. Expressing a wild-type CULD protein in photoreceptors, but not a mutant variant lacking the Arr1-interacting site, rescues both the rhodopsin mislocalization and the low sensitivity phenotypes. Once rhodopsin has been internalized in adult mutant flies, it is reversed only by expression of CULD but not by blocking endocytosis, suggesting that CULD promotes recycling of endocytosed rhodopsin to the rhabdomere. Our results demonstrate an important role of CULD in the maintenance of membrane rhodopsin density and photoreceptor sensitivity. We propose that a common cellular function of CUB- and LDLa-domain proteins, in both mammals and invertebrates, is to concentrate receptors including GPCRs in particular regions of cell membrane. In summary, the work addressed in this thesis has identified new molecular mechavii nisms underlying the maintenance of visual sensitivity in Drosophila, either through preventing Gq-mediated rhabdomeral degeneration or through antagonizing arrestin-mediated rhodopsin endocytosis. This work has advanced our understanding of visual biology and the general regulatory mechanisms of GPCR signaling, and may provide valuable clues to pathologic studies of human retinal degeneration disorders.