Apposition Compound Eyes Research Articles

Application of intracellular optical techniques to the study of stomatopod crustacean vision

1. The noninvasive techniques of intracellular optical physiology were used to measure reflectance changes in the deep pseudopupils of various regions of the apposition compound eyes of 3 species of stomatopod crustaceans. 2. Upon exposure to light, prominent changes in reflectance were observed in all eye regions of all species studied. Generally, the response was an increasing reflectance following stimulus onset; however, in the lateral rows of the central ommatidial band of gonodactyloid stomatopods, the response was a rapid decrease in reflectance. Halftimes for the normal, increasing response were about 5 s in the gonodactyloid species and an order of magnitude longer in the squilloid species. 3. The reflectance changes were probably produced by pupillary mechanisms similar to those previously described for insects. Evidence for this included the form and speed of the response, the observation that fluorescence from the visual pigment diminished with a similar time course to the increase in reflectance, and the tendency of the response to sensitize to repeated stimulation. 4. Two spectral classes of photoreceptor were distinguishable in both the peripheral and central band regions of the eye. These classes were most sensitive to ultraviolet (360 nm) or long-wavelength (500 nm) light. The classes were distinguishable by the form and speed of the reflectance changes they produced when stimulated. Results of univariance experiments suggested that only these 2 classes existed in each eye region examined. 5. In all species and ocular regions examined, the reflectance-change response operated over an intensity range of 3–4 orders of magnitude.

The optics of animal eyes

Eyes with well-developed optical systems evolved many times at the end of the Cambrian period. 500 million years ago. There are now about ten optically distinct mechanisms. These include pinholes, lenses of both multi-element and inhomogeneous construction, aspheric surfaces, concave mirrors, apposition compound eyes that employ a variety of lens types, and three kinds of superposition eye that utilize lenses, mirrors, or both. Because the number of physical solutions to the problem of forming an image is finite, convergent evolution has been very common. The best example is the inhomogeneous Matthiessen lens, which has evolved independently in the vertebrates, several times in the molluscs and annelids, and once in the crustaceans. Similar cases of convergence can also be found among compound eyes.

A unique colour and polarization vision system in mantis shrimps.

The apposition compound eyes of mantis shrimps (stomatopods) are divided into three sections, the dorsal and ventral hemispheres and the midband. Many ommatidia of both hemispheres, and all those in the midband, sample the same narrow band in space. The function of the morphologically distinct midband region is not clear, but new evidence suggests that it may be adapted in a unique manner for colour and polarization vision. A series of carotenoid colour filters screen the photopigment and potentially provide a tetrachromatic input for contrast-enhanced vision or true colour vision. The filters are blocks of coloured droplets (red, orange, yellow, purple, pink or blue) within the rhabdoms of two rows of midband ommatidia. The arrangement of tiered microvilli in two other midband rows suggests that they provide a unique form of polarization vision.

A new type of imaging optics in compound eyes

Many arthropods have compound eyes, made up of numerous separate visual units or ommatidia. In apposition eyes, the ommatidia are optically isolated from each other and provide a poor photon catch because the lenses are so minute1. Much more efficient use of the eye's surface is obtained in superposition eyes, where many ommatidia cooperate to form a superimposed image on the retina1. I report here that, contrary to previous belief2, the eyes of many crabs and hermit-crabs work as superposition eyes by employing imaging optics of a conceptionally new kind. Imaging is accomplished by a remarkable combination of ordinary lenses, cylindrical lenses, parabolic mirrors and light-guides. Despite the impressive complexity of the new mechanism, it is easy to see how this parabolic superposition eye must have evolved from an ordinary apposition compound eye.

Afocal apposition optics in butterfly eyes

In most apposition compound eyes there are two components to the optical system of the ommatidium1,2, the cornea and the crystalline cone. The focusing power of the cornea is well documented3,4 whereas the crystalline cone is usually regarded as a mere optical spacer5,6; consequently, the ommatidial optics will consist of a simple focusing lens. To the contrary, we now demonstrate the existence of a complete afocal telescope in each ommatidium of butterfly apposition eyes. The optical system is an extreme variant of that found in refracting superposition eyes, thereby providing a connection between butterflies and moths.

Eye camouflage in the isopod crustacean Astacillalongicornis (Sowerby)

The stick-like Astacilla longicomis (Sowerby) (Isopoda, Crustacea) is found mainly on the anthozoan Funiculina. The unusual development of its eyes is interpreted as a part of a refined overall camouflage. The apposition compound eyes have two functional features related to camouflaging. 1. (1) The major part of each protruding eye-bulb is transparent owing to the lack of screening pigment around the crystalline cones. Optical isolation of the ommatidia is maintained by a proximal refractive index gradient in the crystalline cones. 2. (2) The proximal cone tips are surrounded by a layer of reflecting pigment cells resulting in a golden hue in the depth of the eye. Probably, neither of these properties has any impact on vision. Thus concealment is the only functional explanation. Both adaptations together prevent the eyes from appearing as large dark spots on the otherwise relatively well camouflaged animal.

A crustacean compound eye adapted for low light intensities (Isopoda)

The optical performance of the apposition compound eye of the marine isopodCirolana borealis Lilljeborg (Crustacea) was investigated. The ommatidia comprise large lenses (diam. ca. 150 μm), spherical crystalline cones and hypertrophied rhabdoms. The 7 rhabdomeres are fused distally and open proximally. We have designated this rhabdom type as semifused. Distal pigment cells screen neighbouring ommatidia, and a well developed reflecting pigment layer surrounds the rhabdom. The focal length was determined in situ and refractive index measurements, raytracings, and eye mappings were made. The focus was found to lie well below the distal rhabdom tip. A theoretical acceptance function was constructed and a 50% acceptance angle of 45 ° was estimated. The eye parameter (p, according to Snyder 1977) of different ommatidia was between 44 and 14. This together with the anatomy demonstrate an optimation to extremely low light intensities. TheCirolana eye provides an example where acuity is sacrificed for the eye to be able to see at the low light intensities of the inhabitat.

A new mechanism for light-dark adaptation in theArtemia compound eye (Anostraca, Crustacea)

The apposition compound eye ofArtemia sp. (a brine shrimp) has a glycogen lens inside the crystalline cone. Owing to the absence of a corneal lens, the glycogen lens is solely responsible for the focusing on the rhabdom tip. Examination of the light-dark adaptation mechanism revealed the following: 1. No pigment migration and only small changes in the palisade. 2. A slight increase in diameter of the distal part of the rhabdom during dark adaptation. 3. A pronounced shortening of the cone during dark adaptation, resulting in a reduced distance between the glycogen lens and the rhabdom. 4. Simultaneous with (3), the glycogen lens elongates as the radii of curvature of the refracting surfaces decrease.

The separation of visual axes in apposition compound eyes.

The separation of visual axes in apposition compound eyes.

Changes in retinal fine structure induced in the crab Libinia by light and dark adaptation.

The cytological influence of light and dark adaptation (LA and DA) on the retinular cells of the spider crab Libinia emarginata has been studied by light and electron microscopy in four adaptive states: 17 hours darkness, 5 hours darkness, 5 hours diffuse light and 17 hours diffuse light. The rhabdom's fine structure is typical of decapods but its dual overall form and position mingle certain features of both apposition and superposition compound eye types. Distal and proximal retinal pigments both showed adaptive migration, but the distal pigment cells moved over a restricted range, and DA separated the retinular cell pigment granules into two groups, perinuclear and basilar. In the rhabdom no changes in its position, dimensions or microvillus fine structure were observed with LA or DA. But at the base of the rhabdom microvilli the rate of pinocytosis was strongly affected by the eye's adaptive state, being lowest after 17 hours DA and greatest after 17 hours LA; the wall of the 0.1 μ microvesicles so formed, looked like the membrane of the rhabdom microvillus and they were the same size as the vesicles in multivesicular bodies and in vesicular lamellar bodies. Three categories of complex cytoplasmic particles about 1 μ in diameter (multivesicular bodies, vesicular lamellar bodies and purely lamellar bodies) were all increased in number by decreased DA and by increased LA; similar quantitative effects occurred in the endoplasmic reticulum and in the ribosomes. The pinocytotic vesicles and the complex cytoplasmic bodies may represent part of an intracellular system to dispose of rhabdom metabolites whose production was initiated or increased by light absorption. Cytoplasmic and perirhabdomal vacuoles mainly distal in location, were also affected by light, but inversely; their maximal extent occurred after 17 hours DA; less DA or any LA significantly decreased their presence and aggregation. The data reported are of interest not only because they correlate retinal fine structure with the metabolism of vision but also because they provide a new and specific tool for distinguishing active from inactive neurosensory cells in the optic pathway.