The eyes of mesopelagic crustaceans

Summary In Streetsia challengeri left and right eyes have fused and become a single cylindrical photoreceptor, which occupies the basal half of a forward directed head projection. This unusual compound eye consists of approximately 2500 ommatidia, which are arranged in such a way that the animal has almost circumferential vision, but cannot look ahead or behind. It is thought that the eye operates on light-guide principles, and that the crystalline cones are the major dioptric component. Ommatidia in anterior-posterior rows show a greater overlap of visual fields than dorso-ventrally arranged ommatidia. Cone layer and retinula are separated by a 4 m thick screen-membrane, which contains tiny pigment granules of 0.15 m diameter. Cells of unknown function and origin, containing unusual multitubular organelles, are regularly found near the proximal ends of the crystalline cone threads. The twisted rhabdoms measure 18–20 m in diameter, and consist of microvilli 0.05 m in width, which belong to five retinula cells and which show no trace of disintegration. The position of interommatidial screening pigment, the density of retinula cell vesicles and inclusions, and the narrowness of the perirhabdomal space all suggest that the eyes have been light-adapted at the time of fixation for electron microscopy. The retinula cell nuclei lie on the proximal side of the heavily pigmented basement membrane. A tapetum or basal retinula cells are not developed. It is concluded that the eye optimally combines acuity with sensitivity, and that for distance estimation parallax may be important.Address until January 25th 1978: Scott Base, Ross Dependency, Antarctica (C/-Chief Post Office, Christchurch, New Zealand)     

The eyes of mesopelagic crustaceans

Summary The compound eyes of the mesopelagic euphausiid Thysanopoda tricuspidata were investigated by light-, scanning-, and transmission electron microscopy. The eyes are spherical and have a diameter that corresponds to 1/6 of the carapace length. The hexagonal facets have strongly curved outer surfaces. Although there are four crystalline cone cells, only two participate in the formation of the cone, which is 90–120 m long and appears to have a radial gradient of refractive index. The clear zone, separating dioptric structures and retinula, is only 90–120 m wide. In it lie the very large oval nuclei of the seven retinula cells. Directly in front of the 70 m long and 15 m thick rhabdom a lens-like structure of 12 m diameter is developed. This structure, known in only a very few arthropods, seems to be present in all species of Euphausiacea studied to date. It is believed that the rhabdom lens improves near-field vision and absolute light sensitivity. Rod-shaped pigment grains and mitochondria of the tubular type are found in the plasma of retinula cells. The position of the proximal screening pigment as well as the microvillar organization in the rhadbdom are indicative of light-adapted material. The orthogonal alignment of rhabdovilli suggests polarization sensitivity. Behind each rhabdom there is a cup-shaped homogeneous structure of unknown, but possibly optical function. Finally, the structure and the function of the euphysiid eye are reviewed and the functional implications of individual components are discussed.This study was begun during the 1975 Alpha Helix South East Asia Bioluminescence Expedition to the South Moluccan Islands     

The eyes of mesopelagic crustaceans: I. Gennadas sp. (Penaeidae)

Summary The eye of the deep-sea penaeid shrimp Gennadas consists of approximately 700 square ommatidia with a side length of 15 n. It is hemispherical in shape and is located at the end of a 1.5 mm long eye stalk. The cornea is extremely thin, but the crystalline cone is well-developed. A clear zone between dioptric structures and the rhabdom layer is absent. A few pigment granules are found within the basement membrane; otherwise they, too, are absent from the eye of Gennadas. The rhabdom is massive and occupies 50 % of the eye. It consists of orthogonally oriented microvilli (the latter measuring 0.07 m in diameter) and is 75 m long. In cross sections adjacent rhabdoms, all approximately 8 m in diameter, form an almost continuous sheet and leave little space for retinula cell cytoplasm. In spite of a one h exposure to light, rhabdom microvilli show no disintegration or disruption of membranes. Vesicles of various kinds, however, are present in all seven retinula cells near the basement membrane. Bundles of seven axons penetrate the basement membrane. On their way to the lamina they often combine and form larger aggregations.The authors wish to thank the director of the Meat Industry Research Institute in Hamilton and his staff for the use of their electron microscope facilities     

Some optical features of the eyes of stomatopods

The optics of a variety of stomatopod eyes has been investigated using goniometric eye-mapping techniques and anatomical measurements. The species examined come from 3 of the 4 existing superfamilies: the Gonodactyloidea, Lysiosquilloidea and Squilloidea. This paper examines acuity, optical axes and general features of eye shape. Stomatopod eyes are divided into 3 clearly distinct zones; the mid-band and two hemispheres. Each hemisphere consists of an edge region, a visual streak and a near mid-band region. The optical axes of many ommatidia from both hemispheres are skewed inwards towards the centrally placed mid-band and are rarely normal to the corneal surface. The large skew angle enables each hemisphere to examine an area which extensively overlaps that of the other hemisphere. As a result monocular distance judgement is possible. Most of the ommatidia in each hemisphere are part of a horizontally aligned but vertically acute visual streak area. There is one visual streak per hemisphere and both look into the same 5–10° strip. This narrow strip is also the area in space the mid-band ommatidia examine. An acute zone is present in the eyes of lysiosquilloid and gonodactyloid stomatopods and includes ommatidia, from both the hemispheres and the mid-band. Here inter-ommatidial angles, especially those in the horizontal direction, are reduced. Acute zone facets are enlarged to increase sensitivity rather than aid spatial resolution.Abbreviations and definitions AZ Acute Zone - MB Mid-band - D Corneal facet diameter, as MB facets are asymmetrical, values for width and height of each facet are given - DH dorsal hemisphere - f Focal length of each ommatidium, estimated from the centre of the corneal lens to the tip of the rhabdom - NeMB Near mid-band ommatidia - R Resolving power=1/2_average - R_h Horizontal resolving power=1/2_h - R_v Vertical resolving power=1/2_v - VH ventral hemisphere - Geometrical acceptance angle (a/f×57.3) of each ommatidium - _h Horizontal inter-ommatidial angle, between facets along a row - _v Vertical inter-ommatidial angle, between rows; Superfamily Gonodactyloidea - g.c. Gonodactylus chiragra - O.s. Odontodactylus scyllarus - H.e. Hemisquilla ensigera; Superfamily Lysiosquilloidea - L.t. Lysiosquilla tredecimdentata - C.s. Coronis scolopendra; Superfamily Squilloidea - O.o. Oratosquilla solicitans     

The spectral sensitivities of the dorsal ocelli of cockroaches and honeybees; an electrophysiological study

The spectral sensitivities of the dorsal ocelli of cockroaches (Periplaneta americana, Blaberus craniifer) and worker honeybees (Apis mellifera) have been measured by electrophysiological methods. The relative numbers of quanta necessary to produce a constant size electrical response in the ocellus were measured at various wave lengths between 302 and 623 mµ. The wave form of the electrical response (ERG) of the dark-adapted roach ocellus depends on the intensity but not the wave length of the stimulating light. The roach ocellus appears to possess a single photoreceptor type, maximally sensitive about 500 mµ. The ERG's of bee ocelli are qualitatively different in the ultraviolet and visible regions of the spectrum. The bee ocellus has two types of photoreceptor, maximally sensitive at 490 mµ and at about 335 to 340 mµ. The spectral absorption of the ocellar cornea of Blaberus craniifer was measured. There is no significant absorption between 350 and 700 mµ.     

Human cone-pigment spectral sensitivities and the reflectances of natural surfaces

The evolution of visual pigment spectral sensitivities is probably influenced by the reflectance spectra of surfaces in the animal's environment. These reflectances, we conjecture, fall into three main classes: i. Most inorganic and many organic surfaces, including tree bark, dead leaves and animal melanin pigmentation, whose reflectance increases gradually as a function of wavelength, ii. Living leaves, which contain chlorophyll, have a sharp reflectance peak at about 555 nm. iii. Flowers, fruit and other signaling colours that have co-evolved with animal vision typically do not reflect strongly at the same wavelength as leaves, and present a colour contrast against a leafy background. These three spectral functions we call grey-red, leaf-green and leaf-contrast respectively. This simple categorisation allows us to interpret the spectral tuning of human cone pigments in a way that might not seem possible given the wide variety of colours present in nature. In particular L-(red) cones will capture the highest possible proportion of photons reflected by leaves, and M-(green) cones will capture about 10% fewer photons both from leaves and from grey-red surfaces. These observations have some clear implications for our understanding of the evolution of trichomacy and the trade-off between chromatic and luminance vision in Old-World Primates.     

Broad spectral sensitivities in the honeybee's photoreceptors limit colour constancy

Colour constancy allows for visual systems to be view stimuli independent of changes in spectral illumination. Chromatic adaptation is likely to be an important mechanism in colour constancy and can be explained by use of the von Kries coefficient law. Chromatic adaptation is compared for the honeybee and three hypothetical visual systems. It is shown that the spectral breadth and asymmetry of photoreceptors in the honeybee may limit colour constancy. In particular, it is demonstrated that the absorption of short-wavelength radiation by the cis-band of chromophore is responsible for a poorer correction for bee colours rich in ultraviolet reflectance. The results are discussed in relation to theoretical considerations of von Kries colour constancy and the physiology of eye design in some other species for which colour constancy has been demonstrated. Accepted: 14 August 1999     

Sterol composition of steryl chlorin esters (SCEs) formed through grazing of algae by freshwater crustaceans: relevance to the composition of sedimentary SCEs

In a laboratory experiment, we studied the composition of sterols in steryl chlorin esters (SCEs) egested in fecal pellets of freshwater crustaceans (Daphnia magna and Asellus hilgendorfi) fed on a single green algae (Chlorella, Scendesmus, or Stigeoclonium) or on phytoplankton collected from a shallow pond abundant in diatoms. Both unaltered sterols present in dietary phytoplankton and sterols formed by metabolism in crustaceans were incorporated in the SCEs. C₂₇ sterols except for cholesterol (C₂₇⁵) and C₂₈ sterols, major sterols in diatoms, were scarce in the SCEs compared with those in the dietary algae, whereas cholesterol, which could be formed by crustacean metabolism, was relatively abundant in the SCEs. Therefore, the contribution of diatoms to the total phytoplankton population would be underestimated if diatom-specific C₂₇ and C₂₈ sterols in sedimentary SCEs were used in estimations as biomarkers of diatoms.     

Evolution of distinct expression patterns for engrailed paralogues in higher crustaceans (Malacostraca)

The segment-polarity gene engrailed of Drosophila melanogaster and its homologues in other arthropods possess a highly conserved expression domain in the posterior portion of each segment. We report here that the two pan-specific antibodies, Mab4D9 and Mab4F11, reveal strikingly different accumulation patterns in both of the malacostracan crustaceans Porcellio scaber (Isopoda) and Procambarus clarkii (Decapoda), compared with insects. The signal detected with Mab4D9 resides in the posterior part of each segment, including the appendages, the ventral and lateral sides of the trunk and the CNS. However, Mab4F11 reveals a signal only in small groups of neurons in the CNS and PNS, primarily localized in the pereon. We observe similar Mab4D9 and Mab4F11 patterns in the crayfish P. clarkii, except that no Mab4F11 signal is detected in the pleon. To address the possibility of multiple engrailed paralogues, we cloned partial cDNAs of two engrailed genes, Ps-en1 and Ps-en2, from P. scaber, and studied their expression patterns using whole-mount in situ hybridization. Although the Ps-en1 and Ps-en2 patterns are comparable in early development, they become distinct in late embryogenesis. Ps-en1 is expressed in the CNS, where Mab4F11 stains, but also accumulates in the epidermis. In contrast, Ps-en2 is expressed in the lateral aspect and limbs of all segments. Phylogenetic analysis of en sequences from crustaceans and insects suggests that the two en genes from the apterygote insect Thermobia domestica (Thysanura) may be related to en1 and en2 of higher crustaceans. Received: 14 February 2000 / Accepted: 1 June 2000     

Intra- and interspecific changes in retinal morphology among mesopelagic and demersal teleosts from the slope waters of New Zealand

Synopsis Retinae from mesopelagic teleosts with adult ranges in the shallow, mid and deep mesopelagic zones, respectively, were examined by light microscopy. Retinal characteristics were described, and photoreceptor densities, outer segment dimensions, and convergence ratios measured from transverse sections. Juveniles of all species had lower photoreceptor densities, outer segment lengths and convergence ratios than adults. In species with multiple banks of photoreceptors, additional banks were added as the retina increased in size. A positive correlation was found between the degree of retinal specialisation for vision in dim light, and the depth of occurrence. The retina of each specimen was given a rank based on log unit changes in photoreceptor density and convergence ratio, the length of photoreceptor outer segments and the presence or absence of multiple banks of photoreceptors. Higher ranks (indicating greater retinal specialisation) were found among species occurring at greater depths. Among species showing a change in depth preference with growth, there was a corresponding increase in retinal rank. It is suggested that the proposed system of ranks has application in predicting the depth of occurrence of a species with a given pattern of retinal morphology.     

On some mathematical techniques for the analysis of visual spectral sensitivities.

Starting from known spectral properties of visual photopigments and photoreceptors, a mathematical construction of neural response functions to visual stimuli is obtained. Included in this is a somewhat general derivation of the univariance principle. Temporal dependence of response on stimulus is included in the formulation. Special attention is given to the case of flash stimuli and their resulting spectral sensitivities. This formulation is applied to certain physiological spectral sensitivity measurements that are at variance with known spectrophometric results. An analysis of the data in these cases suggests that they correspond to "pseudo-pigments" arising from the neural interaction of several photopigments. The method of analysis is constructive and identifies the gamma-max's of the interacting photopigments. These are found to be in good agreement with existing spectrophotometric measurements.     

Visual detection of paradoxical motion in flies

Summary From psychophysics it is known that humans easily perceive motion in Fourier-stimuli in which dots are displaced coherently into one direction. Furthermore, motion can be extracted from Drift-balanced stimuli in which the dots on average have no distinct direction of motion, or even in paradox -motion stimuli where the dots are displaced opposite to the perceived direction of motion. Whereas Fourier-motion can be explained by very basic motion detectors and nonlinear preprocessing of the input can account for the detection of Drift-balanced motion, a hierarchical model with two layers of motion detectors was proposed to explain the perception of -motion. The well described visual system of the fly allows to investigate whether these complex motion stimuli can be detected in a comparatively simple brain.The detection of such motion stimuli was analyzed for various random-dot cinematograms with extracellular recordings from the motion-sensitive Hl-neuron in the third visual ganglion of the blowfly Calliphora erythrocephala. The results were compared to computer-simulations of a hierarchical model of motion detector networks.For Fourier- and Drift-balanced motion stimuli, the Hl-neuron responds directionally selective to the moving object, whereas for -motion stimuli, the preferred direction is given by the dot displacement. Assuming nonlinear preprocessing of the detector input, such as a half-wave rectification, elementary motion detectors of the correlation type can account for these results.Abbreviations EMD elementary motion detector     

Comparative morphological analysis of compound eye miniaturization in minute hymenoptera

Due to their small size, diminutive parasitic wasps are outstanding subjects for investigating aspects of body miniaturization. Information on minute compound eyes is still scarce, and we therefore investigated eye morphology in one of the smallest known hymenopteran species Megaphragma mymaripenne (body size 0.2 mm) relative to Anaphes flavipes (body size 0.45 mm) and compared the data with available information for Trichogramma evanescens (body size 0.4 mm). The eyes of all three species are of the apposition kind, and each ommatidium possesses the typical cellular organization of ommatidia found in larger hymenopterans. Compound eye miniaturization does not therefore involve a reduction in cell numbers or elimination of cell types. Six size-related adaptations were detected in the smallest eyes investigated, namely a) a decrease in the radius of curvature of the cornea compared with larger hymenopterans; b) the lack of extensions to the basal matrix from secondary pigment cells; c) the interlocking arrangement of the retinula cell nuclei in neighboring ommatidia; d) the distal positions of retinula cell nuclei in M. mymaripenne; e) the elongated shape of retinula cell pigment granules of both studied species; and f) an increase in rhabdom diameter in M. mymaripenne compared with A. flavipes and T. evanescens. The adaptations are discussed with respect to compound eye miniaturizations as well as their functional consequences based on optical calculations.     

Muscle water control in crustaceans and fishes as a function of habitat, osmoregulatory capacity, and degree of euryhalinity

This study aimed at detecting possible patterns in the relationship between Anisosmotic Extracellular Regulation (AER) and Isosmotic Intracellular Regulation (IIR) in crustaceans and teleost fish from different habitats and evolutionary histories in fresh water (FW), thus different osmoregulatory capabilities, and degrees of euryhalinity. Crustaceans used were the hololimnetic FW Aegla schmitti, and Macrobrachium potiuna, the diadromous FW Macrobrachium acanthurus, the estuarine Palaemon pandaliformis and the marine Hepatus pudibundus; fishes used were the FW Corydoras ehrhardti, Mimagoniates microlepis, and Geophagus brasiliensis, and the marine-estuarine Diapterus auratus. The capacity for IIR was assessed in vitro following wet weight changes of isolated muscle slices incubated in anisosmotic saline (~ 50% change). M. potiuna was the crustacean with the highest capacity for IIR; the euryhaline perciforms G. brasiliensis and D. auratus displayed total capacity for IIR. It is proposed that a high capacity for IIR is required for invading a new habitat, but that it is later lost after a long time of evolution in a stable habitat, such as in the FW anomuran crab A. schmitti, and the Ostariophysian fishes C. ehrhardti and M. microlepis. More recent FW invaders such as the palaemonid shrimps (M. potiuna and M. acanthurus) and the cichlid G. brasiliensis are euryhaline and still display a high capacity for IIR.     

Bumblebees directly perceive variations in the spectral quality of illumination

Individual bumblebees were tested on a task of walking along a test tunnel to collect sucrose solution in an initial training illumination condition that simulated natural daylight, and in two spectrally different illumination conditions. Compared to the training condition the bees took a significantly longer time to complete the task in conditions that simulated either an ultraviolet negative illumination environment, or an illumination environment that represented blue skylight. In a control condition, bees did not derive this cue from spectral information reflected from the dark background material. This result shows that bees can directly perceive spectral changes in illumination conditions, even in the context of a task that does not require colour processing. This potentially enables the visual system of bees to have prior knowledge about the spectral quality of illumination conditions in which they may forage. The findings are discussed in relation to both theoretical models and empirical evidence of colour constancy, and it is concluded that bees can use multiple mechanisms to solve the dilemma posed by having to find colour targets in the spectrally different illumination conditions that exist for insects visiting flowers.