Browsing by Author "Marshall, N. Justin"
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Item Dynamic polarization vision in mantis shrimps(Springer Nature Publishing AG, 2016-07-12) Daly, Ilse M.; How, Martin J.; Partridge, Julian C.; Temple, Shelby E.; Marshall, N. Justin; Cronin, Thomas W.; Roberts, Nicholas W.Gaze stabilization is an almost ubiquitous animal behaviour, one that is required to see the world clearly and without blur. Stomatopods, however, only fix their eyes on scenes or objects of interest occasionally. Almost uniquely among animals they explore their visual environment with a series pitch, yaw and torsional (roll) rotations of their eyes, where each eye may also move largely independently of the other. In this work, we demonstrate that the torsional rotations are used to actively enhance their ability to see the polarization of light. Both Gonodactylus smithii and Odontodactylus scyllarus rotate their eyes to align particular photoreceptors relative to the angle of polarization of a linearly polarized visual stimulus, thereby maximizing the polarization contrast between an object of interest and its background. This is the first documented example of any animal displaying dynamic polarization vision, in which the polarization information is actively maximized through rotational eye movements.Item The Eyes Have It: Regulatory and Structural Changes Both Underlie Cichlid Visual Pigment Diversity(PLOS, 2009-12-22) Hofmann, Christopher M.; O’Quin, Kelly E.; Marshall, N. Justin; Cronin, Thomas W.; Seehausen, Ole; Carleton, Karen L.A major goal of evolutionary biology is to unravel the molecular genetic mechanisms that underlie functional diversification and adaptation. We investigated how changes in gene regulation and coding sequence contribute to sensory diversification in two replicate radiations of cichlid fishes. In the clear waters of Lake Malawi, differential opsin expression generates diverse visual systems, with sensitivities extending from the ultraviolet to the red regions of the spectrum. These sensitivities fall into three distinct clusters and are correlated with foraging habits. In the turbid waters of Lake Victoria, visual sensitivity is constrained to longer wavelengths, and opsin expression is correlated with ambient light. In addition to regulatory changes, we found that the opsins coding for the shortest- and longest-wavelength visual pigments have elevated numbers of potentially functional substitutions. Thus, we present a model of sensory evolution in which both molecular genetic mechanisms work in concert. Changes in gene expression generate large shifts in visual pigment sensitivity across the collective opsin spectral range, but changes in coding sequence appear to fine-tune visual pigment sensitivity at the shortand long-wavelength ends of this range, where differential opsin expression can no longer extend visual pigment sensitivity.Item The fish eye view: are cichlids conspicuous(The Company of Biologists Ltd, 2010-06-11) Dalton, Brian E.; Cronin, Thomas W.; Marshall, N. Justin; Carleton, Karen L.The extent of animal colouration is determined by an interplay between natural and sexual selection. Both forces probably shape colouration in the speciose, rock-dwelling cichlids of Lake Malawi. Sexual selection is thought to drive male colouration, overcoming natural selection to create conspicuous colour patterns via female mate choice and male–male competition. However, natural selection should make female cichlids cryptic because they mouthbrood their young. We hypothesize that as a result of both sexual and natural selection, males will have colours that are more conspicuous than female colours. Cichlid spectral sensitivity, especially in the ultraviolet, probably influences how colours appear to them. Here we use simple models of the trichromatic colour space of cichlid visual systems to compare the conspicuousness of male and female nuptial colours of nine species. Conspicuousness of colours was evaluated as their Euclidian distance in colour space from environmental backgrounds and from other colours on the same fish. We find in six of the nine species that breeding males have colours that are statistically more conspicuous than female colours. These colours contrast strongly with each other or with the backgrounds, and they fall within a range of spectra best transmitted in the habitat. Female colour distances were sometimes smaller, suggesting that females of some species are more cryptic than males. Therefore, selection can differentially act to generate male colours that are more conspicuous than those in females. However, in two species, females had colours that were more conspicuous than male colours, suggesting that other selective forces and possibly sexual conflicts are acting in this system.Item High levels of reflectivity and pointillist structural color in fish, cephalopods, and beetles(National Academy of Sciences, 2012-12-11) Roberts, Nicholas W.; Marshall, N. Justin; Cronin, Thomas W.Item A novel function for a carotenoid: astaxanthin used as a polarizer for visual signalling in a mantis shrimp(The Company of Biologists Ltd, 2011-11-17) Chiou, Tsyr-Huei; Place, Allen R.; Caldwell, Roy L.; Marshall, N. Justin; Cronin, Thomas W.Biological signals based on color patterns are well known, but some animals communicate by producing patterns of polarized light. Known biological polarizers are all based on physical interactions with light such as birefringence, differential reflection or scattering. We describe a novel biological polarizer in a marine crustacean based on linear dichroism of a carotenoid molecule. The red-colored, dichroic ketocarotenoid pigment astaxanthin is deposited in the antennal scale of a stomatopod crustacean, Odontodactylus scyllarus. Positive correlation between partial polarization and the presence of astaxanthin indicates that the antennal scale polarizes light with astaxanthin. Both the optical properties and the fine structure of the polarizationally active cuticle suggest that the dipole axes of the astaxanthin molecules are oriented nearly normal to the surface of the antennal scale. While dichroic retinoids are used as visual pigment chromophores to absorb and detect polarized light, this is the first demonstration of the use of a carotenoid to produce a polarizing signal. By using the intrinsic dichroism of the carotenoid molecule and orienting the molecule in tissue, nature has engineered a previously undescribed form of biological polarizer.Item Out of the blue: the evolution of horizontally polarized signals in Haptosquilla (Crustacea, Stomatopoda, Protosquillidae)(The Company of Biologists Ltd, 2014-07-09) How, Martin J.; Porter, Megan L.; Radford, Andrew N.; Feller, Kathryn D.; Temple, Shelby E.; Caldwell, Roy L.; Marshall, N. Justin; Cronin, Thomas W.; Roberts, Nicholas W.The polarization of light provides information that is used by many animals for a number of different visually guided behaviours. Several marine species, such as stomatopod crustaceans and cephalopod molluscs, communicate using visual signals that contain polarized information, content that is often part of a more complex multidimensional visual signal. In this work, we investigate the evolution of polarized signals in species of Haptosquilla, a widespread genus of stomatopod, as well as related protosquillids. We present evidence for a pre-existing bias towards horizontally polarized signal content and demonstrate that the properties of the polarization vision system in these animals increase the signal-to-noise ratio of the signal. Combining these results with the increase in efficacy that polarization provides over intensity and hue in a shallow marine environment, we propose a joint framework for the evolution of the polarized form of these complex signals based on both efficacy-driven (proximate) and content-driven (ultimate) selection pressures.Item Polarisation signals: a new currency for communication(The Company of Biologists Ltd, 2019) Marshall, N. Justin; Powell, Samuel B.; Cronin, Thomas W.; Caldwell, Roy L.; Johnsen, Sonke; Gruev, Viktor; Chiou, T.-H. Short; Roberts, Nicholas W.; How, Martin J.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.Item Spectral tuning and the visual ecology of mantis shrimps(The Royal Society, 2000-09-29) Cronin, Thomas W.; Marshall, N. Justin; Caldwell, Roy L.The compound eyes of mantis shrimps (stomatopod crustaceans) include an unparalleled diversity of visual pigments and spectral receptor classes in retinas of each species. We compared the visual pigment and spectral receptor classes of 12 species of gonodactyloid stomatopods from a variety of photic environments, from intertidal to deep water (> 50 m), to learn how spectral tuning in the different photoreceptor types is modified within different photic environments. Results show that receptors of the peripheral photoreceptors, those outside the midband which are responsible for standard visual tasks such as spatial vision and motion detection, reveal the well-known pattern of decreasing lambdamax with increasing depth. Receptors of midband rows 5 and 6, which are specialized for polarization vision, are similar in all species, having visual lambdamax-values near 500nm, independent of depth. Finally, the spectral receptors of midband rows 1 to 4 are tuned for maximum coverage of the spectrum of irradiance available in the habitat of each species. The quality of the visual worlds experienced by each species we studied must vary considerably, but all appear to exploit the full capabilities offered by their complex visual systems.Item Stomatopod photoreceptor spectral tuning as an adaptation for colour constancy in water(Elsevier B.V., 1997-12) Osorio, D.; Marshall, N. Justin; Cronin, Thomas W.Where colour is used in communication absolute judgement of signalling spectra is important, and failures of colour constancy may limit performance. Stomatopod crustaceans have unusual eyes in which the midband contains ten or more classes of photoreceptor. For constancy based on receptor adaptation to a fixed background, elementary theory predicts and we confirm by modelling, that stomatopods' narrow-band receptors outperform more broadly tuned receptors. Similar considerations could account for the small spectral separation of receptors in each midband row. Thus, stomatopods seem to trade-off sensitivity and signal-to-noise ratio for increased colour constancy.