Using RGB displays to portray color realistic imagery to animal eyes

RGB displays effectively simulate millions of colors in the eyes of humans by modulating the relative amount of light emitted by 3 differently colored juxtaposed lights (red, green, and blue). The relationship between the ratio of red, green, and blue light and the perceptual experience of that light has been well defined by psychophysical experiments in humans, but is unknown in animals. The perceptual experience of an animal looking at an RGB display of imagery designed for humans is likely to poorly represent an animal’s experience of the same stimulus in the real world. This is due, in part, to the fact that many animals have different numbers of photoreceptor classes than humans do and that their photoreceptor classes have peak sensitivities centered over different parts of the ultraviolet and visible spectrum. However, it is sometimes possible to generate videos that accurately mimic natural stimuli in the eyes of another animal, even if that animal’s sensitivity extends into the ultraviolet portion of the spectrum. How independently each RGB phosphor stimulates each of an animal’s photoreceptor classes determines the range of colors that can be simulated for that animal. What is required to determine optimal color rendering for another animal is a device capable of measuring absolute or relative quanta of light across the portion of the spectrum visible to the animal (i.e., a spectrometer), and data on the spectral sensitivities of the animal’s photoreceptor classes. In this article, we outline how to use such equipment and information to generate video stimuli that mimic, as closely as possible, an animal’s color perceptual experience of real-world objects

The effect of aggregation on visibility in open water

Aggregation is a common life-history trait in open-water taxa. Qualitative understanding of how aggregation by prey influences their encounter rates with predators is critical for understanding pelagic predator-prey interactions and trophic webs.We extend a recently developed theory on underwater visibility to predict the consequences of grouping in open-water species in terms of increased visual detection of groups by predators. Our model suggests that enhanced visibility will be relatively modest, with maximum detection distance typically only doubling for a 100-fold increase in the number of prey in a group. This result suggests that although larger groups are more easily detected, this cost to aggregation will in many cases be dominated by benefits, especially through risk dilution in situations where predators cannot consume all members of a discovered group. This, in turn, helps to explain the ubiquity of grouping across a great variety of open-water taxa.PostprintPeer reviewe

Animal navigation: A noisy magnetic compass?

Diverse organisms use Earth’s magnetic field as a cue inorientation and navigation. Nevertheless, eliciting magneticorientation responses reliably, either in laboratory or naturalsettings, is often difficult. Many species appear to preferentiallyexploit non-magnetic cues if they are available, suggesting that themagnetic sense often serves as a redundant or ‘backup’ source ofinformation. This raises an interesting paradox: Earth’s magnetic fieldappears to be more pervasive and reliable than almost any othernavigational cue. Why then do animals not rely almost exclusively onthe geomagnetic field, while ignoring or downplaying other cues?Here, we explore a possible explanation: that the magnetic sense ofanimals is ‘noisy’, in that the magnetic signal is small relative tothermal and receptor noise. Magnetic receptors are thus unable toinstantaneously acquire magnetic information that is highly precise oraccurate. We speculate that extensive time-averaging and/or otherhigher-order neural processing of magnetic information is required,rendering the magnetic sense inefficient relative to alternative cuesthat can be detected faster and with less effort. This interpretation isconsistent with experimental results suggesting a long time course formagnetic compass and map responses in some animals. Despitepossible limitations, magnetoreception may be maintained by naturalselection because the geomagnetic field is sometimes the onlysource of directional and/or positional information available

A Chiton Uses Aragonite Lenses to Form Images

SummaryHundreds of ocelli are embedded in the dorsal shell plates of certain chitons [1]. These ocelli each contain a pigment layer, retina, and lens [2], but it is unknown whether they provide chitons with spatial vision [3]. It is also unclear whether chiton lenses are made from proteins, like nearly all biological lenses, or from some other material [4]. Electron probe X-ray microanalysis and X-ray diffraction revealed that the chiton Acanthopleura granulata has the first aragonite lenses ever discovered. We found that these lenses allow A. granulata's ocelli to function as small camera eyes with an angular resolution of about 9°–12°. Animals responded to the sudden appearance of black, overhead circles with an angular size of 9°, but not to equivalent, uniform decreases in the downwelling irradiance. Our behavioral estimates of angular resolution were consistent with estimates derived from focal length and receptor spacing within the A. granulata eye. Behavioral trials further indicated that A. granulata's eyes provide the same angular resolution in both air and water. We propose that one of the two refractive indices of the birefringent chiton lens places a focused image on the retina in air, whereas the other does so in water

Light and Vision in the Deep-Sea Benthos: II. Vision in Deep-Sea Crustaceans

Using new collecting techniques with the Johnson-Sea-Link submersible, eight species of deep-sea benthic crustaceans were collected with intact visual systems. Their spectral sensitivities and temporal resolutions were determined shipboard using electroretinography. Useable spectral sensitivity data were obtained from seven species, and in the dark-adapted eyes, the spectral sensitivity peaks were in the blue region of the visible spectrum, ranging from 470 to 497 nm. Under blue chromatic adaptation, a secondary sensitivity peak in the UV portion of the spectrum appeared for two species of anomuran crabs:Eumunida picta (λmax 363 nm) and Gastroptychus spinifer (λmax 383 nm). Wavelength-specific differences in response waveforms under blue chromatic adaptation in these two species suggest that two populations of photoreceptor cells are present. Temporal resolution was determined in all eight species using the maximum critical flicker frequency (CFFmax). The CFFmax for the isopodBooralana tricarinata of 4 Hz proved to be the lowest ever measured using this technique, and suggests that this species is not able to track even slow-moving prey. Both the putative dual visual pigment system in the crabs and the extremely slow eye of the isopod may be adaptations for seeing bioluminescence in the benthic environment

Light and Vision in the Deep-Sea Benthos: I. Bioluminescence at 500-1000 m Depth in the Bahamian Islands

Bioluminescence is common and well studied in mesopelagic species. However, the extent of bioluminescence in benthic sites of similar depths is far less studied, although the relatively large eyes of benthic fish, crustaceans and cephalopods at bathyal depths suggest the presence of significant biogenic light. Using the Johnson-Sea-Link submersible, we collected numerous species of cnidarians, echinoderms, crustaceans, cephalopods and sponges, as well as one annelid from three sites in the northern Bahamas (500–1000 m depth). Using mechanical and chemical stimulation, we tested the collected species for light emission, and photographed and measured the spectra of the emitted light. In addition, in situ intensified video and still photos were taken of different benthic habitats. Surprisingly, bioluminescence in benthic animals at these sites was far less common than in mesopelagic animals from similar depths, with less than 20% of the collected species emitting light. Bioluminescent taxa comprised two species of anemone (Actinaria), a new genus and species of flabellate Parazoanthidae (formerly Gerardia sp.) (Zoanthidea), three sea pens (Pennatulacea), three bamboo corals (Alcyonacea), the chrysogorgiid coral Chrysogorgia desbonni (Alcyonacea), the caridean shrimp Parapandalus sp. and Heterocarpus ensifer (Decapoda), two holothuroids (Elasipodida and Aspidochirota) and the ophiuroid Ophiochiton ternispinus (Ophiurida). Except for the ophiuroid and the two shrimp, which emitted blue light (peak wavelengths 470 and 455 nm), all the species produced greener light than that measured in most mesopelagic taxa, with the emissions of the pennatulaceans being strongly shifted towards longer wavelengths. In situ observations suggested that bioluminescence associated with these sites was due primarily to light emitted by bioluminescent planktonic species as they struck filter feeders that extended into the water column

Candidate genes mediating magnetoreception in rainbow trout ( Oncorhynchus mykiss )

Diverse animals use Earth's magnetic field in orientation and navigation, but little is known about the molecular mechanisms that underlie magnetoreception. Recent studies have focused on two possibilities: (i) magnetite-based receptors; and (ii) biochemical reactions involving radical pairs. We used RNA sequencing to examine gene expression in the brain of rainbow trout ( Oncorhynchus mykiss ) after exposure to a magnetic pulse known to disrupt magnetic orientation behaviour. We identified 181 differentially expressed genes, including increased expression of six copies of the frim gene, which encodes a subunit of the universal iron-binding and trafficking protein ferritin. Functions linked to the oxidative effects of free iron (e.g. oxidoreductase activity, transition metal ion binding, mitochondrial oxidative phosphorylation) were also affected. These results are consistent with the hypothesis that a magnetic pulse alters or damages magnetite-based receptors and/or other iron-containing structures, which are subsequently repaired or replaced through processes involving ferritin. Additionally, some genes that function in the development and repair of photoreceptive structures (e.g. crggm3 , purp , prl , gcip , crabp1 and pax6 ) were also differentially expressed, raising the possibility that a magnetic pulse might affect structures and processes unrelated to magnetite-based magnetoreceptors

Simple fixation and storage protocol for preserving the internal structure of intact human donor lenses and extracted human nuclear cataract specimens

Purpose: Increased use of phacoemulsification procedures for cataract surgeries has resulted in a dramatic decrease in the availability of cataractous nuclear specimens for basic research into the mechanism of human cataract formation. To overcome such difficulties, a fixation protocol was developed to provide good initial fixation of human donor lenses and extracted nuclei, when available, and is suitable for storing or shipping cataracts to laboratories where structural studies could be completed. Methods: Cataractous lens nuclei (n=19, ages 12 to 74 years) were obtained from operating suites after extracapsular extraction. Transparent human donor lenses (n=27, ages 22 to 92 years) were obtained from the Ramayamma International Eye Bank. After the dimensions were measured with a digital caliper, samples were preserved in 10% formalin (neutral buffered) for 24 h and followed by fixation in 4% paraformaldehyde (pH 7.2) for 48 h. Samples were stored cold (4 °C) in buffer until shipped. Samples were photographed and measured before further processing for transmission electron microscopy. Results: The dimensions of the samples varied slightly after short fixation followed by 1 to 5 months’ storage before transmission electron microscopy processing. The mean change in the axial thickness of the donor lenses was 0.15±0.21 mm or 3.0±5.4%, while that of the extracted nuclei was 0.05±0.24 mm or 1.8±7.6%. Because the initial concern was whether the nuclear core was preserved, thin sections were examined from the embryonic and fetal nuclear regions. All cellular structures were preserved, including the cytoplasm, complex edge processes, membranes, and junctions. The preservation quality was excellent and nearly equivalent to preservation of fresh lenses even for the lens cortex. Cell damage characteristic of specific nuclear cataract types was easily recognized. Conclusions: The novel fixation protocol appears effective in preserving whole donor lenses and cataractous nuclei over a wide age range. Dimensions varied only 2%–3%, and fiber cell damage correlated well with standard fixation. These methods enable researchers and clinicians in remote settings to preserve donor lenses and rare examples of extracapsular extractions for detailed examination at later times

Ultrastructural analysis of the human lens fiber cell remodeling zone and the initiation of cellular compaction

The purpose is to determine the nature of the cellular rearrangements occurring through the remodeling zone (RZ) in human donor lenses, identified previously by confocal microscopy to be about 100 µm from the capsule. Human donor lenses were fixed with 10% formalin followed by 4% paraformaldehyde prior to processing for transmission electron microscopy. Of 27 fixed lenses, ages 22, 55 and 92 years were examined in detail. Overview electron micrographs confirmed the loss of cellular organization present in the outer cortex (80 µm thick) as the cells transitioned into the RZ. The transition occurred within a few cell layers and fiber cells in the RZ completely lost their classical hexagonal cross-sectional appearance. Cell interfaces became unusually interdigitated and irregular even though the radial cell columns were retained. Gap junctions appeared to be unaffected. After the RZ (40 µm thick), the cells were still irregular but more recognizable as fiber cells with typical interdigitations and the appearance of undulating membranes. Cell thickness was irregular after the RZ with some cells compacted, while others were not, up to the zone of full compaction in the adult nucleus. Similar dramatic cellular changes were observed within the RZ for each lens regardless of age. Because the cytoskeleton controls cell shape, dramatic cellular rearrangements that occur in the RZ most likely are due to alterations in the associations of crystallins to the lens-specific cytoskeletal beaded intermediate filaments. It is also likely that cytoskeletal attachments to membranes are altered to allow undulating membranes to develop

Multilamellar spherical particles as potential sources of excessive light scattering in human age-related nuclear cataracts

The goal of this project was to determine the relative refractive index (RI) of the interior of multilamellar bodies (MLBs) compared to the adjacent cytoplasm within human nuclear fiber cells. MLBs have been characterized previously as 1-4 μm diameter spherical particles covered by multiple lipid bilayers surrounding a cytoplasmic core of variable density. Age-related nuclear cataracts have more MLBs than transparent donor lenses and were predicted to have high forward scattering according to Mie scattering theory, assuming different RIs for the MLB and cytoplasm. In this study quantitative values of relative RI were determined from specific MLBs in electron micrographs of thin sections and used to calculate new Mie scattering plots. Fresh lenses were Vibratome sectioned, immersion fixed and en bloc stained with osmium tetroxide and uranyl acetate, or uranyl acetate alone, prior to dehydration and embedding in epoxy or acrylic resins. Thin sections 70 nm thick were cut on a diamond knife and imaged without grid stains at 60 kV using a CCD camera on a transmission electron microscope (TEM). Integrated intensities in digital electron micrographs were related directly to protein density, which is linearly related to RI for a given substance. The RI of the MLB interior was calculated assuming an RI value of 1.42 for the cytoplasm from the literature. Calculated RI values for MLBs ranged from 1.35 to 1.53. Thus, some MLBs appeared to have interior protein densities similar to or less than the adjacent cytoplasm whereas others had significantly higher densities. The higher density MLBs occurred preferentially in older and more advanced cataracts suggesting a maturation process. The bilayer coats were more often observed in MLBs from transparent donors and early stage cataracts indicating that bilayer loss was part of the MLB maturation, producing large low-density spaces around dense MLB cores. These spaces were frequently observed in advanced cataracts from India as large low-density crescents and annular rings. Predicted scattering from Mie plots using particles with dense cores and low-density rims was higher than reported previously, although the most important factor was the relative RI , not the MLB coat or lack thereof. In conclusion, the measurements confirm the high protein density and RI of some MLB interiors compared to adjacent cytoplasm. This high RI ratio used in the Mie calculations suggests that for 2 000 MLBs/mm3, about half that reported for early stage nuclear cataracts from the US, the forward scattering could be more than 30% of the incident light. Therefore, the extent of forward scattering and its influence on macular visual acuity could be important components of ophthalmological evaluations of cataract patients