The Ecology of Vision Laboratory within the School of Biological Sciences at the University of Bristol uses a range of techniques and a multidisciplinary approach is emphasised. These techniques include:
These models analyse visual tasks in terms of the statistics of photon capture by photoreceptors, considering the Poisson process of photon capture as the principle irreducible noise source in the visual systems. The models have successfully predicted visual pigment pairs of dichromatic species living in temperate woodland and in coastal marine waters and are now being extended to trichromats and other polychromats by combination of the models with multispectral images. Current work focusses on visual pigment optimisation in the deep-sea and modelling animal camouflage.
A major deficiency in all current investigations of the ecology of visual systems is an understanding of the visual environment. There are almost no comparative data about what information may be extracted, in different spectral regions, from different visual environments. We have 46-channel multispectral video camera which can be used to obtain images of natural environments or animals and images obtained using this camera will be used to test models that predict the optimal visual pigment palettes of polychromatic animals.
Knowledge of the light environment is essential for the understanding of both visual behaviour and the evolution of vision. We have two portable UV-VIS spectrometers and a laboratory based diode array spectrometer which is used for measurements of spectral reflexions. Spectral reflexion measurements are combined with statistical processing of the data. We have also constructed a UV-Vis spectral radiance meter which allows direct measurement of the raw (radiance) signal available in animal communications and visual tasks.
MSP involves measuring absorption spectra of individual retinal rods or cones by passing a fine light beam through the receptor which is positioned on the stage of a microscope. No suitable MSP is available commercially and the only machines in the UK are in Bristol and at the Institute of Ophthalmology, London. A new wavelength-scanning, computer-controlled instrument is under continual development in Bristol and is taking MSP to the limits imposed by the physical nature of light and the photolability of visual pigments. MSP is the only method which can determine the precise visual pigments present in single photoreceptors and the method has been used extensively for work on deep-sea fishes, but also eels, guppies and, more recently, crustaceans and birds.
The ultimate expression of the photon catch by an animal's retina is visually mediated behaviour. The group has experience with various behavioural methods, including the Dorsal Light Reaction to measure the spectral sensitivity of fishes, mate-choice apparatus, and operant experiments. Funding from NERC and BBSRC extended these studies to investigate the role of UV wavelengths in mate choice and foraging in birds. This work was linked to MSP data of photoreceptor spectral sensitivities of several species linking retinal physiology to visual behaviour. A recent BBSRC grant investigated the spatio-chromatic visual abilities of birds using behavioural methods.
MSP measurements of deep-sea fish visual pigments have shown that these pigments are more blue sensitive than those of shallow-living fishes, and have a discontinuous interspecific distribution of peak sensitivity which cannot be due to environmental factors. In collaboration with Professor David Hunt (Institute of Ophthalmology, London) the molecular basis for these observations was investigated by molecular biological techniques including visual pigment protein (opsin) gene sequencing (see Research Funding). Opsin sequences have also been obtained for the European eel, which is unusual in switching opsin production in its retinal rods to shift from a pigment typical of coastal fishes to that typical of a deep-sea fish, and probes based on these sequences have been used to investigate the cellular mechanism underlying this shift. This work continued with a grant from the BBSRC which allowed the control of opsin expression in eel and guppy retinal models to be investigated. A further collaborative BBSRC research grant with Professor Hunt and Professor Martin Warren, University of Kent, enabled this work to be extended to the specific investigation of pressure adaptations, at the molecular level, in a variety of proteins extracted from deep sea fishes. This work continues with specially constructed chambers for visual pigment spectroscopy at elevated pressures.