Orientation and Shape Discrimination in Juveniles and Adults of the Mangrove Crab Aratus pisonii (H. Milne Edwards, 1837): Effect of Predator and Chemical Cues

Behavioral responses of juveniles and adults of the mangrove crab Aratus pisonii (H. Milne Edwards, 1837) to black geometric shapes of equal surface area was measured. Crabs were tested either in presence or absence of chemicals generated from two common predator species, the portunid crab Callinectes ornatus Ordway, and the soapfish Haemulon aurolineatum Cuvier, 1830. The present study tested the hypothesis that A. pisonii (1) has the capacity to orient to visual cues; (2) it discriminates between different visual objects based on a combination of chemical and visual information and (3) this behavior changes with age. When presented with single black targets in background water, juveniles oriented toward all shapes. This behavioral response was interpreted as visual orientation toward potential shelter. Among shapes, juveniles showed preference for the vertical rectangle, probably due to the recognition of natural visual elements like mangrove roots. In predator conditioned water, juveniles exhibited a stronger response than in background water. Thus, juveniles were able to detect by odor the potential presence of predators. Change in responsiveness between adults and juveniles was also demonstrated.     

Photoreceptor-specific efficiencies of β-carotene,zeaxanthin and lutein for photopigment formation deduced from receptor mutant Drosophila melanogaster

Summary Drosophila rearing media had only -carotene, zeaxanthin or lutein as precursors for photopigment chromophores. Zeaxanthin and lutein are potentially optimum sources of the 3-hydroxylated retinoids of visual and accessory photopigments. Mutants made the electroretinogram in white (w) eyes selective for compound eye photoreceptors R1–6, R7 and R8: R1–6 domiantes w's electroretinogram; R7/8 generates w;ora's (ora = outer rhabdomeres absent); R8 generates w sev;- ora's (sev = sevenless). Microspectrophotometry revealed R1-6's visual pigment. In w, all 3 carotenoids yielded monotonic dose-responses for sensitivity (Fig. 4) or visual pigment (Fig. 7). An ultraviolet sensitivity peak from R1-6's sensitizing pigment was present at high but not low doses (Fig. 1). In w;ora, all 3 carotenoids gave similar spectra dominated by R7's high ultraviolet sensitivity (Fig. 2). For w sev;ora, all spectra were the shape expected for R8, peaking around 510 nm (Fig. 3). The sensitivity dose-response was at its ceiling except for low doses in w;ora (Fig. 5) and zero supplementation in w sev;ora (Fig. 6). Hence, without R1-6, most of our dose range mediated maximal visual pigment formation. In Drosophila, -carotene, zeaxanthin and lutein mediate the formation of all major photopigments in R1-6, R7 and R8.Abbreviations ERG electroretinogram - MSP microspectrophotometry - HPLC high pressure liquid chromatography - n.a. numerical aperture - w, sev, ora Drosophila mutants - y, p, r marg types of R7 and R8     

Structure of retinular cells in a Drosophila melanogaster visual mutant,rdgA, at early stages of degeneration

Summary A Drosophila visual mutant rdgA has photoreceptive cells which degenerate gradually after eclosion. Fine structure of the retinular cells of rdgA ^KS60 and rdgA ^K014 was studied during early stages of degeneration to determine the initial morphological defects. The retinular cells of these two alleles showed the following structural abnormality within 1 day after eclosion: (1) rhabdomeres were small and irregular in shape; (2) cisternae of the rough endoplasmic reticulum were more numerous than those in normal retinular cells; (3) submicrovillar cisternae were absent; and (4) lysosomes were fewer than normal. Three-dimensional reconstruction of serial sections of the ommatidia showed that the degeneration of mutant rhabdomeres proceeds more rapidly in regions remote from the nuclei. These results suggest that the process of turnover of rhabdomeric microvilli is abnormal in rdgA. We also confirmed an increase of lysosomes and destruction of cellular organelles, as reported by previous investigators at more advanced stages of degeneration.     

The role of visual cues in the facilitation of growth in a schooling fish

Synopsis This study tested the hypothesis that visual contact between fish may result in enhanced rates of growth in a schooling fish. Juvenile chum salmon, Oncorhynchus keta, were held singly and reared in isolation or in visual contact with conspecifics. Fish were fed at either a low (6% body weight d^–1) or high (20% body weight d^–1) ration for 42d. Specific rates of weight gain were 18% greater at low ration and 38% greater at high ration for fish in visual contract with conspecifics than for those held in isolation. The results demonstrate a selective advantage of visual cues associated with schooling behavior and suggest that the efficacy of growth models for schooling fishes may be enhanced by the consideration of social interactions which may facilitate growth.     

Retino-fugal projections in congenitally monophthalmic fish and anurans

Summary Intra-ocular deposition of horseradish peroxidase was used to visualize optic tract projections in normal and congenitally monophthalmic catfish and Xenopus. In neither species was evidence for an increased ipsilateral visual component found in congenitally one-eyed specimens. This indicates that competition between axons from both eyes is not an important mechanism for fiber distribution in the chiasm during ontogeny. Furthermore, it suggests that enhanced ipsilateral components, previously noted in unilaterally enucleated fish and anurans, are caused by debris of degenerated axons.     

Waterstriders (Gerris paludum F.) compensate for drift with a discontinuously working visual position servo

Waterstriders on ponds and creeks compensate for displacement caused by wind or water current with periodical jumps against the direction of drift. This behavior is mediated by visual stimuli.

On the coordination of motor output during visual flight control of flies

Summary In tethered flying houseflies (Musca domestica), the yaw torque produced by the wings is accompanied by postural changes of the abdomen and hindlegs. In free flight, these body movements would jointly lead to turning manoeuvres of the animal. By recording the yaw torque together with the lateral deflections of either the abdomen or the hindlegs, it is shown that these motor output systems act in a highly synergistic way during two types of visual orientation behavior, compensatory optomotor turning reactions and orientation turns elicited by moving objects. This high degree of coordination is particularly conspicuous for the pathway activated by moving objects. Here, orientation responses either may be induced or may fail to be generated always simultaneously in all three motor output systems. This suggests that the pathway mediating orientation turns towards objects is gated before it segregates into the respective motor control systems of the wings, the abdomen and the hindlegs.     

A Bioluminescence Method for the Measurement of l-Glutamate: Applications to the Study of Changes in the Release of l-Glutamate from Lateral Geniculate Nucleus and Superior Colliculus After Visual Cortex Ablation in Rats

We have developed a rapid, simple, specific, and very sensitive bioluminescence method for the measurement of L-glutamate (L-Glu). Oxidation of L-Glu by glutamate dehydrogenase has been coupled with bacterial FMN reductase and luciferase. Light production (i.e., peak height or integral) was linear from less than 0.5 to 500 pmol of L-Glu. Potential interfering substances that may be encountered in brain tissue have been identified. The most potent inhibitors were ascorbate and the biogenic amines. Procedures that conferred long-term stability of the reagent mixture (greater than 8 h) were established. Bioluminescence analysis of L-Glu content in brain tissue extracts, fractions from release experiments, and human CSF corroborated respective results obtained by HPLC analysis. In this study, we have applied the method to monitor changes in the KCl-evoked release of endogenous L-Glu from milligram amounts of brain tissue, i.e., from lateral geniculate nucleus and superior colliculus after visual cortex ablation.     

Electron microscopy of the fate of exogenous ferritin in the feline visual cortex

Summary The ultrastructural changes occurring in the feline visual cortex 3 hours after the injection of 0.02 mls of ferritin in 1% trypan blue in artificial cerebrospinal fluid have been studied.Near the site of injection, disrupted cells contained free and membrane-bound ferritin. In less damaged areas, some signs of oedema were present in the cells, especially in astrocytes. Membrane-bound ferritin occurred occasionally in neurones and more frequently in astrocytes and oligodendrocytes. Considerable amounts of ferritin were also accumulated in phagocytic cells of unknown origin. In blood vessels, ferritin collected in the basement membrane and around collagen and, in membrane-bound form, in pale cells at the periphery of the vessels. Ferritin occurred in all parts of the intercellular space except in interglial junctions and tight junctions between vascular endothelial cells.This work was supported by a research grant from the National Health and Medical Research Council of Australia to Professor M. J. Blunt, of the School of Anatomy, University of New South Wales. The author wishes to thank Professor Blunt for his constant encouragement and support. The assistance of Mrs. Ruth Mather is gratefully acknowledged.     

Phylogeny and physiology of Drosophila opsins

Phylogenetic and physiological methods were used to study the evolution of the opsin gene family in Drosophila. A phylogeny based on DNA sequences from 13 opsin genes including representatives from the two major subgenera of Drosophila shows six major, well-supported clades: The blue opsin clade includes all of the Rhl and Rh2 genes and is separated into two distinct subclades of Rhl sequences and Rh2 sequences; the ultraviolet opsin clade includes all Rh3 and Rh4 genes and bifurcates into separate Rh3 and Rh4 clades. The duplications that generated this gene family most likely took place before the evolution of the subgenera Drosophila and Sophophora and their component species groups. Numerous changes have occurred in these genes since the duplications, including the loss and/or gain of introns in the different genes and even within the Rhl and Rh4 clades. Despite these changes, the spectral sensitivity of each of the opsins has remained remarkably fixed in a sample of four species representing two species groups in each of the two subgenera. All of the strains that were investigated had R1-6 (Rhl) spectral sensitivity curves that peaked at or near 480 nm, R7 (Rh3 and Rh4) peaks in the ultraviolet range, and ocellar (Rh2) peaks near 420 nm. Each of the four gene clades on the phylogeny exhibits very conservative patterns of amino acid replacement in domains of the protein thought to influence spectral sen sitivity, reflecting strong constraints on the spectrum of light visible to Drosophila.