ALBERT

Notes: Bottlenose dolphins (Tursiops truncatus) are aquatic mammals that must come to the surface to breathe. As a result, it might be expected that their eyes are adapted for both aerial and underwater vision. Earlier studies suggest that dolphins are emmetropic (i. e., focused at infinity) in water, and in some cases, emmetropic in air, although the mechanisms that permit these animals to see well in both media are not well understood. Nor is it known whether they can accommodate to focus sharply on objects at different distances. We employed video photoretinoscopy to investigate the possibility of an active accommodative mechanism in the eyes of the bottlenose dolphin in water. Measurements of the refractive state in water indicated near emmetropia for two individuals and slight myopia (nearsightedness) for the third individual. No clear cases of accommodation were observed underwater in any of the subjects examined. Vision underwater may be used to supplement echolocation. If so, such a role might not require an accommodative mechanism.

Notes: [Auszug] Systems of colour vision are normally identical in all members of a species, but a single design may not be adequate for species living in a diverse range of light environments. Here we show that in the mantis shrimp Haptosquilla trispinosa, which occupies a range of depths in the ocean, ...

Notes: [Auszug] Hydrothermal vents along the mid-ocean ridges host ephemeral ecosystems of diverse endemic fauna including several crustacean species, some of which undergo planktonic development as larvae up to 1,000 m above and 100 km away from the vents. Little is known about the role of ...

Notes: Abstract. This study examines the diverse maximum wavelength absorption (λmax) found in crayfishes (Decapoda: Cambaridae and Parastacidae) and the associated genetic variation in their opsin locus. We measured the wavelength absorption in the photoreceptors of six species that inhabit environments of different light intensities (i.e., burrows, streams, standing waters, and subterranean waters). Our results indicate that there is relatively little variation in λmax (522–530 nm) among species from different genera and families. The existing variation did not correlate with the habitat differences of the crayfishes studied. We simultaneously sequenced the rhodopsin gene to identify the amino acid replacements that affect shifts in maximum wavelength absorption. We then related these to changes that correlated with shifts in λmax by reconstructing ancestral character states using a maximum-likelihood approach. Using amino acid sequences obtained from five species (all were 301 amino acids in length), we identified a number of candidates for producing shifts of 4 to 8 nm in λmax. These amino acid replacements occurred in similar regions to those involved in spectral shifts in vertebrates.

Notes: [Auszug] The retina of P. ciliata has 11 classes of photoreceptors, or rhabdoms, below the level of the distal eighth retinular cell: the single rhabdoms of the peripheral retina and rows 5 and 6 of the central band, plus the two tiers of the main rhabdoms of rows 1 to 4 of the central band (Fig. 1). Rows 2 ...

Notes: Summary 1. ERG S(λ) were determined in darkadapted intact preparations of 6 North American firefly species (Photinus collustrans, marginellus, pyralis, macdermotti, scintillans and Bicellonycha wickershamorum) which restrict their flashing activity to twilight hours. The curves possess narrow (1/2 bandwidth=50–60 nm) peaks in the yellow (560–580 nm) and a shoulder in the violet (370–420 nm), with amarked attenuation (1.4–2.2 log units) of sensitivity in the green (480–530 nm) region of the spectrum (Fig. 1). Two additional species (Photuris potomaca and frontalis) which initiate flashing at twilight and continue on late into the night (twi-night) possess broad sensitivity maxima around 560 nm (Fig. 3). 2. Selective adaptation experiments isolated near-UV and yellow inP. scintillans (Fig. 2). In the dorsal frontal region of the compound eyes inP. frontalis, high sensitivity existed only in the short wavelength region (near-UV and blue) with a maximum in the blue (λ max 435 nm) (Fig. 4). 3. The in situ MSP absorption spectrum of the screening pigments was determined in preparations of firefly retina. a) Two kinds of dark brown granules were found in the clear zone region. These granules absorb all across the spectrum with a gradual increase in optical density in the shorter wavelength region inP. pyralis (Fig. 5). b) Besides dark granules, pink-to-red colored screening pigments were present in the vicinity of the rhabdoms. The absorption spectra of these pigments determined in five species were narrow (1/2 bandwidth=50–80 nm) with species-specific differences in their peak absorption in the green at 525 nm, 510 nm, 512 nm and 517 nm inP. scintillans, macdermotti, collustrans and pyralis, respectively (Fig. 6). A similar pigment was found inP. marginellus with aλ max at 512 nm (Fig. 7). In all cases, transmission increased both at long and short wavelengths, but more sharply in the long wavelength region (Figs. 6 and 7). Hence each twilight-restricted species has its own unique colored screening pigment. A yellow pigment whose absorption spectrum differed from those found in genusPhotinus was found in twi-night activePhoturis potomaca (λ max 461 nm) and night-activeP. versicolor (λ max 456 nm). The transmission of thePhoturis pigment increased sharply only in the long wavelength region (Fig. 8). 4. In the twilight-restricted species, pink-to-red screening pigments modify dramatically the long green wavelength part of S(λ) functions. The calculated effect of the absorption of these screening pigments (O.D.=1.6 to 2.2; ¯X=1.8, n=4) on a theoretical S(λ) curve represented by a green (P550) rhodopsin, match the shape of the experimentally obtained dark-adapted ERG S(λ) in all cases (Figs. 9, 10). These screening pigments (Figs. 6, 7, 8) then would cause attenuation of sensitivity selectively in the green in twilight-restricted fireflies (Fig. 1) with a concomitant shifting of the peak of the sensitivity in the yellow as well as a narrowing of the visual spectral sensitivity. The pink-to-red colored screening pigments presumably would enhance color and/or brightness contrast in the mesopic range of ambient illumination. 5. The presence of the colored screens attenuates absolute sensitivity from 5–25% among different twilight-active species as compared to a night-activePhoturis lucicrescens (Fig. 11).

Notes: Summary 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.

Notes: Summary Stomatopod crustaceans are visually active animals which have large, mobile compound eyes of unique design. Aspects of their ecology and behavior suggest they may be able to discriminate hues. Isolated rhabdoms of the squillid stomatopod,Squilla empusa, were investigated using microspectrophotometry and fluorometry. A single rhodopsin, ofλ max507 nm, exists in the main rhabdom. Its stable metarhodopsin, withλ max503 nm, possesses typical arthropod fluorescence characteristics. No evidence was found for a visual pigment with peak absorption in the ultraviolet. Vision in this animal might therefore be monochromatic.

Notes: Summary 1. We investigated optokinetic eye movements in 3 species of stomatopod crustaceans (Odontodactylus scyllarus, Pseudosquilla ciliata, and Gonodactylus oer stedii), all of which are members of the superfamily Gonodactyloidea, by making video recordings of their behavior when placed at the center of a rotating striped drum. Results from these species were sufficiently similar to permit a general description of optokinesis in gono dactyloid stomatopods. 2. Within the range of drum speeds tested (0.40 to 33.6° s-1), the eyes frequently moved smoothly in the direction of the drum's rotation. The movements of the 2 eyes were only weakly coordinated, and optokinesis occurred with an irregular and intermittent time course. 3. Closed-loop gains varied with the drum's speed of rotation, ranging from 0.4 to near 1.0. The gain did not depend on the orientation of the eye in space, remaining relatively constant as the eye swung on its point of at tachment to the anterior end of the animal or rotated on the eyestalk axis. 4. In O. scyllarus (the only species tested), optokinetic eye movements in the animal's vertical, dorsoventral plane occurred with characteristics similar to those in the horizontal plane.