New paper on the evolution of visual pigments in the deep sea

Understanding the link between how proteins function in animals that live in extreme environments and selection on specific properties of amino acids has proved extremely challenging. Here we present the discovery of how the compressibility of opsin proteins in two evolutionarily distinct animal groups, teleosts and cephalopods, appears to be adapted to the high-pressure environment of the deep-sea. We report how in both groups, opsins in deeper living species are calculated to be less compressible. This is largely due to a common set of amino acid sites (bovRH# 159, 196, 213, 275) undergoing positive destabilizing selection in six of the twelve amino acid physiochemical properties that determine protein compressibility. This suggests a common evolutionary mechanism to reduce the adiabatic compressibility of opsin proteins. Intriguingly, the sites under selection are on the proteins’ outer faces at locations known to be involved in opsin-opsin dimer interactions.

The full paper can be found http://dx.doi.org/10.1016/j.ympev.2016.08.007

New paper on multifocal fish lenses!!

Cool new paper from the lab on the maths behind multifocal fish lenses: Gagnon YL, Wilby D, Temple SE (2016) Losing focus: how lens position and viewing angle affect the function of multifocal lenses in fishes. J Opt Soc Am A 33:1901-1909

Summer Students Wanted: Hermit Crab Vision

The Ecology of Vision lab is looking for two students to help over the summer with our hermit crab behavioural experiments. We have been investigating the visual behaviour of european hermit crabs (Pagurus bernhardus) particularly with reference to their selection of different shells and have a few more experiments to complete our study. Initially some field work will be required in order to collect the animals and the remainder of the summer will be spent performing and analysing behavioural experiments.

Image: (c) Alex Hyde Photography

Matt Wheelwright (MSci Zoology) & Andy Bird (BSc Biology) volunteered as summer students last year: "This project is a lot of fun and explores a really fascinating area of science, I would highly recommend applying for this project if you are interested in going into research."

This is a great opportunity to get some experience of behavioural biology and sensory ecology and is open to all students whether they study biology or not (although a science/engineering background is helpful). Ideally, we hope to find students who are available for as much of the summer (mid June-end August) as possible. The two volunteers will be working closely with one another as well as with Dr David Wilby, Ilse Daly and Dr Nick Roberts of the Ecology of Vision Lab.

Unfortunately we are unable to pay, but this should be an excellent experience and a valuable contribution to your CV. We're also happy to be pretty flexible to accommodate your summer plans. Please direct any questions to david DOT wilby AT bristol.ac.uk

3 Stories of biological manipulation of light

At the Ecology of Vision lab, one of our major fascinations is the way that animals have evolved to use light in many different and novel ways. Not only do they use their eyes to extract optical information from the environment, their bodies are designed to allow them to signal to one another using complex optical manipulations. In this news article, we explore three new studies from our lab and collaborators along this theme.

New type of optical material discovered in the secret language of the mantis shrimp

Mantis shrimp like to keep their conversations private, which is why they communicate using the polarization of light. These animals have evolved bright reflectors that control the polarization of their visual signals, a property of light not commonly used for animal communication. Most eavesdroppers can’t see this type of light information and so animals that use it are less likely to attract the attention of predators or unwelcomed competition.

Image credit: Roy Caldwell, University of California, Berkeley

In a quest to understand how these uncommon light signals are produced in mantis shrimp, researchers from the Ecology of Vision Lab discovered that they use a polarizing structure unlike anything ever seen or developed by humans.  The research is published in Scientific Reports.

Using a combination of careful anatomy, light measurements, and theoretical modelling, it was found that the mantis shrimp polarizers work by manipulating light across the structure rather than through its depth, which is how typical polarizers work. Such a photonic mechanism affords the animal with small, microscopically thin and dynamic optical structures that still produce big, bright and colourful polarized signals.

Dr Nicholas Roberts said: “When it comes to developing a new way to make polarizers, nature has come up with optical solutions we haven't yet thought of. Industries working on optical technologies will be interested in this new solution mantis shrimp have found to create a polarizer as new ways for humans to use and control light are developed.”

‘A shape-anisotropic reflective polarizer in a stomatopod crustacean’ by Thomas M. Jordan,  David Wilby, Tsyr-Huei Chiou, Kathryn D. Feller, Roy L. Caldwell, Thomas W. Cronin and Nicholas W. Roberts 2016 Scientific Reports [open access]

Under a polarized sky

If you're lucky, when you look up the sky will appear a clear blue. But for many animals, the sky is awash with useful information which they may use to help find their way around.

As light from the sun interacts with particles in the atmosphere, certain angles of polarization make their way to the Earth more easily than others. This results in a complex pattern in the sky which can help some insects to navigate and orient.

Xin Wang is a PhD student visiting the Ecology of Vision group for 2 years from the Hefei University of Technology, China. His research centres on developing technology in order to build a robot which will navigate using the skylight polarization pattern.

On course to this goal, Xin has built a new, computational model of the skylight polarization pattern. Which is published this week in the Journal of Optics.

'An analytical model for the celestial distribution of polarized light, accounting for polarization singularities, wavelength and atmospheric turbidity' by Xin Wang, Jun Gao, Zhiguo Fang and Nicholas W. Roberts 2016 Journal of Optics

Magnetic Micromirrors

Guanine is best known as one of the 4 bases of DNA or as a major constituent of bat droppings! But we know it as a highly capable optical biological material. Its high refractive index and large birefringence (different refractive properties for different polarizations) mean that it appears in reflective structures which need to control their polarization properties, such as the silvery reflections from fish skin.

In a new investigation, Masakazu Iwasaka (HIroshima University) and colleagues found that the application of magnetic fields could manipulate the position of guanine crystals. This allows the manipulation of their reflection of light along particular axes, effectively switching the reflection on and off.

The authors hope that this observation can be applied in the design of a synthetic array of organic micromirrors in future optical technology.

'Magnetic Control of the Light Reflection Anisotropy in a Biogenic Guanine Microcrystal Platelet' Masakazu Iwasaka, Yuri Mizukawa and Nicholas W. Roberts 2016 Langmuir