Anterior Median Eyes Research Articles

The Distances at Which a Primitive Jumping Spider,Portia Fimbriata, Makes Visual Discriminations

ABSTRACTThe anterior median (AM) or principal eyes of the primitive jumping spider, Portia fimbriata (Doleschall), are miniature telephoto systems (Williams & McIntyre, 1980). Another study on the AM eyes of Plexippus suggests that most salticid principal eyes may be of similar design (Blest, Hardie, McIntyre and Williams, 1982). Both studies assumed, from anecdotal evidence (e.g. Forster, 1979), that jumping spiders can make visual discriminations between prey and mates at distances of ca. 20 cm. This estimate is necessary to the functional analyses that were essayed; because it is impossible to make sufficiently accurate direct measurements of some of the parameters of these small eyes, their optics can only be modelled with confidence when something is known about what they are designed to see. Land (1969 a, b), in an elegant optical study, followed Drees (1952) in stating that jumping spiders respond to significant objects some 5-10 body-lengths in front of them. In the case of Portia, this would be a distance of no more than 10 cm at most. Recognition of objects is mediated through the AM eyes (Drees, 1952).

Importance of Calcium And Magnesium Ions for Postexcitatory Hypersensitivity in the Jumping Spider (Menemerus) Eye

ABSTRACT Hypersensitivity of the anterior median eye of the jumping spider Menemerus confusus, following illumination, was unaffected by the concentration of Na+ or K+, was depressed by increase of Ca2+ concentration, and was dependent upon the presence of Mg2+. Sensitivity of the dark-adapted eye was also inversely related to Ca2+ concentration, but to a lesser extent.

The spectral sensitivities of identified receptors and the function of retinal tiering in the principal eyes of a jumping spider

1. The functional organisation of the central retina of the anterior median (AM) eyes of a jumping spider,Plexippus (Salticidae) is examined by anatomical, electrophysiological and optical methods. A model of the eye is derived from the data. 2. The anatomy of the AM eye is similar to that of salticid eyes described by Land (1969a) and Williams and McIntyre (1980). There are four tiers of receptors of which only the most proximal (Layer I) is a regular mosaic with rhabdoms designed to have light-guide properties. The receptor population of Layer I is homogeneous, whereas in Layers II–IV more than one receptor type can be considered to contribute to each layer. 3. Intracellular recordings from AM photoreceptors reveal only two spectral classes: green cells with peak responses at ca. 520 nm, and ultraviolet (UV) cells with peak responses at ca. 360 nm. ERGs from intact retinae exhibit similar peaks. Spectral sensitivities from pooled intracellular recordings from green cells and ERGs correspond reasonably closely. The comparison does not, therefore, support the possibility that the retina contains receptors with peak responses at longer wavelengths, although it does not exclude it. 4. Spectrally characterised cells were marked by the injection of Lucifer Yellow. From the results of 13 successful injections, (a) peripheral Layer I and peripheral and central Layer II cells are green receptors; (b) Layer IV cells are UV receptors. Central Layer I and Layer III receptors were not marked. 5. The chromatic aberration, focal length and other optical parameters of the corneal lens of the AM eye were measured directly. The lens functions essentially as a single-surface lens of refractive index 1.40, and, together with the curved interface between the anterior chamber of the eye and the receptor matrix, forms a telephoto system. 6. The spacing between receptor Layers I and IV is matched to the chromatic aberration of the eye; if green light from an object in front of the spider is focused on Layer I, UV light will be focused on Layer IV (and Layer III). 7. The distal ends of Layer I receptors form a staircase, those lying laterally being closer to Layer II than those lying medially. This staircase enables the spider to receive in-focus images from objects at distances between ca. 3 cm — ∞ in front of it. It is suggested that the scanning movements of the retinae described by Land (1969b) serve to sweep an image across the staircase so that it will be in focus on some part of Layer I, provided that the object is within that range of distances. 8. Retinal tiering (including the staircase of Layer I) compensates both for the chromatic aberration of the dioptrics of the eye and for its inability to accommodate.

The principal eyes of a jumping spider have a telephoto component

Jumping spiders are a cosmopolitan family (Salticidae) of predators that can make visual discrimination between prey and mates1,2. This task is mediated through the anterior median eyes, described by Land3 as consisting of a corneal lens and a motile retina that comprises four layers of receptors embedded in a matrix. The retinal matrix contains a pit distal to the receptors and symmetrically centred on-axis. We have now found that in Portia fimbriata (Doleschall) and some other species, this pit has a refracting interface that increases the focal length of the eye beyond its axial length, thereby magnifying the retinal image and increasing visual resolving power above that possible with only a corneal lens. The most effective part of the conical pit is its rounded apex, which augments the corneal lens to provide a telephoto system that increases the overall focal length by about 1½ times. This mechanism is of particular value to small spiders like P. fimbriata, for the possible axial length of their eyes is constrained by the small size of their prosomae (Fig.1).

Visual orientation in the Salticidae (Araneae)

In both predation and escape behaviour, the jumping spiders Trite auricorma (Urquhart) and Trite planiceps Simon demonstrate open and closed loop visual orientation systems. Open loop visual orientation is mediated by the lateral eyes by visual stimuli occurring outside the fields ofview of the anterior median (AM) eyes. Closed loop control with visual feedback through the anteriorly directed median eyes enables object location and recognition of stimuli falling within the field of view of these eyes. Turning movements initiated by the lateral eyes result in object location by the AM eyes which control the animal's subsequent behaviour. Movement detection by the lateral eyes results in turning, by which action the object is brought within the range of the AM eyes. Visual stimuli located behind the body produce escape reactions without recognition and location by the AM eyes. Orientations involving turning movements include partial turns and tracking movements. There is some evidence to suggest that the sp...

Visual mechanisms of hunting behaviour inTrite planiceps,a jumping spider (Araneae: Salticidae)

Abstract Jumping spiders rely on visual stimuli when catching their prey. Each of the hunting actions employed is mediated by one or more of the three pairs of eyes responsible for this behaviour. No function has yet been demonstrated for the tiny fourth pair of eyes. Two distinct post-detection hunting strategies are used; one enables spiders to catch their prey on the run, and the other controls the capture of stationary prey. Exclusive components of each of these strategies are (i) chasing, which is a function of the anterior-lateral eyes, and (ii) stalking, which is a function of the anterior-median eyes; collaborative visual mechanisms result in a smooth transition from one mode of behaviour to another. In addition, both strategies employ common behavioural elements that exploit specialised properties of the four anterior eyes; successful prey capture is a measure of their physiological and behavioural synchronisation. ‘Short jumps’ towards targets moving at an angular velocity of more than 15°/s are...

Spectral Sensitivities of the Anterior Median Eyes of the Orb Web Spiders, Argiope Bruennichii and A. Amoena

ABSTRACT Spectral sensitivities of the anterior median eyes of the orb web spiders, Argiope bruennichii and A. amoena have been studied by recording extracellular ERGs and intracellular receptor potentials. The anterior median eyes have three types of visual cells, with maximum sensitivities at about 360 nm (u.v. cell), 480–500 nm (blue cell) and 540 nm (green cell). The blue cells are the most sensitive and have a circadian oscillation of sensitivity. The green cells show a hypersensitivity, i.e. the sensitivity is greater for about 90 s after the cessation of illumination than during dark adaptation. Respiration is necessary for the maintenance of hypersensitivity.

Hypersensitivity in the Anterior Median Eye of A Jumping Spider

ABSTRACT Changes in sensitivity of the photoreceptor cells of the anterior median eye of the jumping spider Menemerus confusus Boes, et Str. have been studied by recording electroretinograms (ERGs) and receptor potentials. The amplitudes of the responses (ERGs and receptor potentials) increase during repetitive stimulation, with a maximum increase at 3−5 s intervals. The sensitivity of the photoreceptor cell is greater for about 60 s following illumination (maximum magnitude at 3−5 s) than it is during complete dark adaptation. This phenomenon, which we call ‘hypersensitivity’, is lost within one day following surgery in physiological saline. Upon loss of hypersensitivity, the sensitivity decrease during light adaptation is greater than for the normal eye and the small increase of sensitivity following the onset of illumination observed for the normal eye is lost.

Spectral sensitivities of jumping spider eyes

Spectral sensitivities of the anterior lateral, posterior lateral and anterior median eyes of the jumping spider,Menemerus confusus Boes. et Str. have been studied by recording electroretinograms (ERGs) and receptor potentials. The anterior and posterior lateral eyes have a single type of visual cell with a maximum spectral sensitivity at about 535–540 nm. The anterior median eye has four types of visual cells with maximum sensitivities at about 360, 480–500, 520–540 and 580 nm, respectively. The ERGs recorded from the optic nerve side (posterior part of the retina) were affected greatly by long wave chromatic light and those on the corneal side (anterior part of the retina) by short wave chromatic light, suggesting that each receptor layer contains a different photopigment.

Dual sensitivities of cells in wolf spider eyes at ultraviolet and visible wavelengths of light.

Intracellular recordings have been made from visual cells in principal and secondary eyes of in vitro wolf spider preparations. The responses of all cells to all wavelengths of light were graded depolarizations; no hyperpolarizations or nerve discharges were seen. Cells in a secondary eye, the anterior lateral eye, had a maximum sensitivity in the visible at 510 nm and a secondary maximum, or shoulder, of sensitivity in the near ultraviolet at 380 nm. Cells in principal eyes, the anterior median eyes, all responded maximally both in the visible at 510 nm and in the ultraviolet at 360-370 nm or less. However, there was no typical ratio of ultraviolet to visible sensitivities; the differences in log sensitivities (log UV/VIS) varied from 3.3 to -0.5. Each principal eye had a population of cells with different ratios. These populations varied with the time of the year, possibly due to changes in light upon the animals. Chromatic adaptations of cells in anterior median (but not anterior lateral) eyes resulted in small, selective changes in spectral sensitivities, and there was some facilitation of responses from cells repeatedly stimulated. It is concluded that cells of secondary eyes contain only a visual pigment absorbing maximally in the visible, while cells of principal eyes probably contain variable amounts of both this pigment and one absorbing in the ultraviolet as well.

Innervation of the retinal muscles in wolf spiders (Araneae-Lycosidae)

The retinas of the anterior median eyes of wolf spiders are moved by two small muscles. There is a dorsal and a ventral muscle innervated, respectively, by the superior and inferior branches of a single retinomotor nerve. The superior branch of this nerve consists of only one axon and its glial sheath. The inferior branch, on the contrary, contains three axons. Neuromuscular synapses occurring in the dorsal muscle show only one axon ending contacting the muscle fiber membrane. In the ventral muscle the neuromuscular synapses are characterized by the presence of three independent axon endings converging on the same synaptic area. However, both types of neuromuscular junctions exhibit a similar structural organization. The axon endings contain numerous vesicles and mitochondria. Small dense synaptic rods have been consistently found within the nerve terminals. Pre- and postsynaptic membranes are separated by a synaptic cleft 200 A wide. This synaptic cleft is crossed by numerous osmiophilic bridges.

Revision of Japanese Spiders of Family Argiopidae (1)

This paper deals with the revision of Japaneses Meta based upon the writer's collection and the other arachnologists'. In Japan, 10 species of Meta have heretofore been recorded. Of them Meta blanda L. KOCH has already been transferred to Leucauge by E. Strand, M. doenitzi BOESENBERG et STRAND clearly comes under Neoscona according to the writer's re-examination, M. vena DOENITZ et STRAND is nothing but a fleckless type of M. kompirensis BOES. et STR., M. decimpunctata KISHIDA is a synonym of Mangora herbeoides (BOES. et STR.), and M. melanostethi KISHIDA is a species yet undescribed. Accordingly the existence of 5 species and one new (the description of which is given below) is recognized in Japan. 1. Meta segmentata (CLERCK) 1757 2. M. menardi (LATREILLE) 1804 3. M. metanicruciata SAITO 1939 4. M. kompirensis BOESENSERG et STRAND 1906 5. M. yunohamensis BOESENBERG et STRAND 1906 Among the above mentioned species, the latter two have many differences from the other Metas. Owing to their particular characteristics, it may be better that a new subgenus (or genus) is established for them. However, the writer wishes to treat them as one of the groups in Meta in the meantime. Japanese Meta should be divided into two groups. Group I. (Protometa type) 1. Paracymbium not modified. 2. Cymbium projected at the base part. 3. Embolus erect. 4. Epigastric plate with distinct transverse furrows. Meta kompirensis, yunohamensis and melanicruciata (probably) belong to this group. Group II. (Neometa type) 1. Paracymbium much modified, divided into two branches, one bearing hairs, and one well developed and strongly chitinized. 2. Cymbium without any projection. 3. Embolus coiled. 4. Epigastric plate without transverse furrows. Meta segmentata, menardi and reticutoides n. sp. belong to this group. Meta reticutoides sp. nov. Holotype (_??_) 6/XI, 1955, Osaka Pref. (Coll. T. Yaginuma) Cephalothorax longer than wide. Anterior eye row recurved, posterior almost straight. Anterior median eyes separated by their diameter, posterior median eyes separated by less than their diameter. Median eyes of each row closer to each other than to the adjacent laterals. MOA almost square, slightly longer than wide. Lateral eyes contiguous. Cervical, radial and median furrows distinct. Chelicerae well developed and geniculated at the base. Lateral condyle weak. Promargin and retromargin with 3 teeth on each. Sternum triangle in shape, anterior margin slightly procurved. Legs 1. 2. 4. 3. Anterior coxae larger than posteriors. Each leg with spines. Abdomen oval. Epigynum without scape. Total length 7.5 mm. (Deposited in Osaka Municipal Museum of Nat. Hist, ) Allotype (_??_) 24/VIII, 1957, Kumamoto Pref. (Coll. M. Yoshikura) In general appearance, the male resembles female, but it differs in following points. Chelicerae much longer than in female, as long as about 3/4 length of cephalothorax. Labium separated from chelicerae as seen in Arhcaeidae. Distal joint of palp very large and well modified, divided into two branches, one hairly and one hairless and strongly chitinized. Cymbium notched apically along the coiled embolus. Promargin of fang furrow with a tooth, retromargin with 4. Total length 4.6 mm. (Preserved in A. F. Archer's collection) Colour : Both sexes very similar. Cephalothorax yellow with a pair of black flecks along the cervical groove, and with black side margins. Chelicerae, endites, labium and sternum deep brown. Anterior legs with many black spots, but posterior legs annulated by black flecks. Abdomen grey with blackish brown spots scattered on the entire dorsum. Venter black with white lines at both sides

New Nebraska Spiders.*

Recent collections of spiders in the state of Nebraska have revealed the following new species. Brachybothrium lincolnianum n. sp. Male. In life, black or fuscous in color, the venter lighter than the dorsum and the carapace somewhat lighter than the abdomen. In alcohol, this color changes to a yellow or brown, the cephalothorax then being yellowish and the abdomen darker, a soft brown or tan. Eye area twice as wide as long; anterior median eyes separated from each other by an interval equal to more than twice the diameter of one of them and from the anterior lateral eyes by a space only slightly greater; the latter have a diameter two and one-half times that of the former. The posterior median eyes are as far apart as are the anterior lateral eyes, while the posterior lateral eye, the posterior median eye, and the anterior median eye of each side are in a row and form almost a straight line. The posterior lateral eyes have a diameter two-thirds as great as that of the posterior median eyes, while the posterior median eyes have a diameter about three-fourths that of the anterior lateral eyes, which are by far the largest eyes; posterior row slightly longer than the anterior.