The spinning apparatus of Uloboridae in relation to the structure and construction of capture threads (Arachnida,Araneida)

Summary Besides the two axial fibers and the mass of cribellum fibrils, a third component is present in the capture threads of uloborids. This is a substructure originating from the paracribellum. It probably helps to fasten the axial fibers in their position. The axial fibers are secreted from the two glandulae pseudoflagelliformes whose spigots are situated on the posterior spinnerets. It is hypothesized that the cribellum fibrils become jammed and thus fixed between the axial fibers by periodical abduction and adduction of these spinnerets.     

中国长妩蛛属3新种记述(蜘蛛目:妩蛛科)

记述中国妩蛛科长妩蛛属3新种:匙长妩蛛,新种Miagrammopes spatulatus sp.nov.,双叉长妩蛛,新种Miagrammopes bifurcatus sp.nov.和蹄形长妩蛛,新种Miagrammopes unguliformis sp.nov..     

On the spinning apparatus and the structure of the capture threads ofDeinopis subrufus (Araneae,Deinopidae)

Summary The spinnerets and spigots of two adult femaleDeinopis subrufus and one adult male were studied with the scanning electron microscope. The organization of the spinning apparatus corresponds very closely to that of Uloboridae. The capture threads produced by the male while subadult were studied with the light microscope and with the SEM. This study includes the questions of the glandular origin and the functions of the components of these threads. A hypothesis for howD. subrufus constructs capture threads is proposed.     

Factors governing the stickiness of cribellar prey capture threads in the spider family Uloboridae

The surface of a cribellar prey capture thread is formed of thousands of fine, looped fibrils, each issuing from one of the spigots on an oval spinning plate termed the cribellum. This plesiomorphic capture thread is retained by members of the family Uloboridae, in which its stickiness differs among genera. An examination of five cribellar thread features in nine uloborid species shows that only the number of fibrils that form a thread explains these differences in thread stickiness. Neither the physical features of these fibrils, nor the manner in which they are combined to form threads differs among species. Threads produced by orb-weaving species contain fewer fibrils than those produced by species that build reduced webs. Relative to spider weight, the number of fibrils that form a cribellar thread is greatest in simple-web species of the genus Miagrammopes, less in triangle-web species of the genus Hyptiotes, and least in orb-weaving species representing five genera. A transformational analysis shows that change in the number of cribellum spigots is directly related to change in the stickiness of cribellar thread. This direct relationship between the material invested in a cribellar thread and its stickiness may have been a limiting factor that favored the switch from the dry cribellar threads of uloborids to the adhesive capture threads produced by other orb-weaving families. © 1994 Wiley-Liss, Inc.     

Visual fields of orb web and single line web spiders of the family Uloboridae (Arachnida,Araneida)

Summary In the family Uloboridae, web reduction is associated with changes in web monitoring posture and prosomal features. A spider must extend its first pair of legs directly forward to monitor the signal line of a reduced web. This posture is facilitated by shifts in prosomal musculature that cause reduced web uloborids to have a narrower anterior prosoma, a reduced or absent anterior eye row, and prominent posterior lateral eye tubercles. The eye tubercles and larger posterior eyes of these uloborids suggest that web reduction may also be accompanied by ocular changes that compensate for reduction of the anterior eyes by expanding the visual fields of the posterior eyes. A comparison of the visual fields of the eight-eyed, orb web species Octonoba octonaria and a four-eyed, reduced web Miagrammopes species was made to determine if this is true. Physical and optical measurements determined the visual angles of each species' eyes and the pattern of each species' visual surveillance. Despite loss of the anterior four eyes, the Miagrammopes species has a visual coverage similar to that of O. octonaria. This is due to (1) an increase in the visual field of each of the four remaining Miagrammopes eyes, accruing from an extension of the retina and an increase in the lens' rear radius of curvature, and (2) a ventral shift of each visual axis, associated with the development of an eye tubercle and an asymmetrical expansion of the retina. Miagrammopes monitor their simple webs from twigs or moss where they are vulnerable to predation. Therefore, maintenance of visual cover may enable them to detect predators in time to assume or maintain their characteristic, cryptic posture. It may also allow them to observe approaching prey and permit them to adjust web tension or prepare to jerk their webs when prey strikes.     

The spinning apparatus of Polenecia producta (Araneae,Uloboridae): Structure and histochemistry

Summary The spinning apparatus of the uloborid spider Polenecia producta was studied to complete previous studies on the same family of spiders. The structure of spinnerets and spigots, under scanning electron microscopy, and the main anatomical and histochemical characteristics of the spinning glands of adult females and males are described. In addition some observations on the spinning apparatus at three successive stages of development are made. There are nine kinds of silk glands in Polenecia, i.e. one more (aciniform — B glands) than found in other uloborids. The spinning apparatus of Polenecia is, therefore, the most complex so far known. It is also more complex than that presently known of Araneoidea. The characteristics of the spinning glands of Polenecia are compared with those of other uloborids. Present knowledge of the spinning apparatus of uloborids leads to a renewed discussion of the origin of the orb web in this family and in araneids. It is concluded that these two types of orb webs emerged from independent evolutionary processes.     

The influence of web monitoring tactics on the tracheal systems of spiders in the family Uloboridae (Arachnida,Araneida)

Summary Uloborids that spin reduced webs more actively monitor them than those that construct orb webs. Hyptiotes use both their first and fourth legs to tense their triangle-webs, whereas Miagrammopes rely principally on their first legs to monitor and jerk the threads of their irregular webs. The respiratory systems of these spiders include tracheae that extend into the prosoma, bifurcate, and enter the legs. To determine if the legs responsible for active web-monitoring tactics have more extensive tracheal supplies, the total cross sectional area has been computed of the tracheae entering the legs of mature female orb web and reduced web uloborids. Each leg's value has been divided by the cross sectional area of the tracheal trunks that enter the prosoma. These indexes reveal no significant differences between the relative tracheal supplies of the orb weavers investigated (Waitkera waitkerensis, Tangaroa beattyi, Uloborus glomosus). But the first, third, and fourth legs of H. cavatus and the first legs of M. animotus and M. pinopus have greater relative tracheal supplies than those of the three orb weaving species. Relative to leg volume, the first and fourth legs of H. cavatus have the greatest and the first legs of Miagrammopes species the next greatest tracheal supplies. When tracheal lengths are considered, these differences in potential oxygen supplies remain, showing that area differences do not simply compensate for differences in the distances over which oxygen must diffuse. These differences are leg-specific and not species-specific, and uloborids with the most extensive tracheal supplies are found in moist habitats. Thus the observed differences are best explained as adaptations to meet the greater oxygen demands of legs responsible for active web-monitoring tactics and not as adaptations to reduce respiratory water loss.     

Fine structural analysis on triad spinning spigots of an orb‐web spider's capture threads

Capture threads of the golden orb‐web spider Nephila clavata are produced from the silks of a pair of triad spinning units composed of a flagelliform gland (FLG) and two aggregate glands (AGG). In N. clavata, arrangement of the triad spigots is closely related to coating an axial supporting fiber with sticky aqueous droplets on a continuous and consistent basis for capture thread production. The central spigot of FLG and peripherally located AGG spigots are aligned along a single plane, and both have bullet‐type spigots with flexible segments. In particular, the pear‐shaped spigot of the AGG with a wide‐aperture nozzle provides not only sufficient luminal space for controlling transient storage of the aqueous gluey substance but also an effective spatial system that thoroughly coats the axial fibers with a viscous aqueous solution.     

Foraging behavior of the communal spider,Philoponella republicana (Araneae: Uloboridae)

The communal orb-weaving spider, Philoponella republicana,was observed in the subtropical moist forest of Southeast Peru. These spiders live in colonies of conspecifics whose individual orbs are connected by silk. The wrapping of a prey prior to feeding is a large component of the prey capture process because P. republicanahas no venom with which to kill an insect. Wrapping time was the only aspect of prey capture that was strongly correlated with the size of the insect captured. Occasionally we observed several individuals working together to wrap a prey item. These joint efforts were more frequent on prey larger than the capturing spider. Although group captures accounted for only 5.5% of captures, they represented 14.7% of the biomass obtained. A comparison of the relationship between wrapping time and prey size for solitary and group efforts suggested that, by working together, the spiders reduced their total handling time. In most cases only one spider fed on the captured prey.     

Polenecia producta and its web: structure and evolution (Araneae,Uloboridae)

Summary The web of Polenecia producta is interpreted as being a modified orb web. The position of the hub directly upon a twig amongst irregularly placed branches decides the web's structure. Since the radii have to be fixed in the vicinity corresponding to the local possibilities, and since these possibilities vary very much from case to case, a great variety of web scaffoldings results. All of them are characterized by a lack of symmetry. These asymmetries, for their part, prevent the production of capture threads by circling around and fixing them obliquely to the radii as do orb weavers. P. producta adapts itself to this situation by attaching the adhesive material along the radii. Under these circumstances temporary spirals, like those of orb weavers, would be without function. The short pieces of such spirals present in the webs of P. producta are interpreted as vestiges of once functional structures. The silk deposits P. producta lays down upon the hub can, in certain respects, be compared with stabilimenta of other Uloboridae. The relatively late onset of web building in P. producta (instar II spiderlings) is related to the ontogeny of the spinning apparatus.     

Wiederaufstellung der Gattung Sericopelma Ausserer, 1875 (Araneida,Theraphosidae, Theraphosinae)

After the examination of the types of Mygalarachne brevipes Ausserer, 1871, and Sericopelma rubronitens Ausserer, 1875, we declare M. brevipes, a juvenile female, as a species “incertae sedis” since the specimen doesn't present sufficient characteristics which allow a secure identification of the genera and species.     

Proprioceptors and sensory nerves in the legs of a spider,Cupiennius salei (Arachnida,Araneida)

Summary Retrograde CoS-impregnation was used to trace and map the course of sensory nerves and the distribution and innervation of the various proprioceptor types in all leg segments of Cupiennius salei, a Ctenid spider.1. Sensory nerve branches. In both the tibia and femur, axons of all proprioceptor types ascend in just two lateral nerves which do not merge with the main leg nerve until they reach the next proximal joint region. In the short segments — coxa, trochanter, patella, and tarsus — axons of the internal joint receptors often run separately from those of the other sensilla. Axons of the large lyriform slit sense organ at the dorsal metatarsus and of the trichobothria join with only a few hair axons and form their own nerve branches (Figs. 1, 2, 3).2. Proprioceptors. Each of the seven leg joints is supplied with at least one set of the well-known internal joint receptors, slit sensilla (single slits and lyriform organs), and long cuticular hairs. In addition, we found previously unnoticed hair plates on both sides of the coxa, near the prosoma/coxa joint; they are deflected by the articular membrane during joint movements (Fig. 4).3. Sensory cells and innervation. CoS-impregnation shows that each slit of the slit sense organs — be it a single slit or several slits in a lyriform organ — is innervated by two bipolar sensory cells (Fig. 6). We also confirm previous reports of multiple innervation in the internal joint receptors and in the long joint hairs and cuticular spines.Most of the ascending nerve branches run just beneath the cuticle for at least a short distance (Fig. 5); hence they are convenient sites for electrophysiological recordings of sensory activity even in freely walking spiders.     

Neuroanatomy of the central nervous system of the wandering spider,Cupiennius salei (Arachnida,Araneida)

Summary In Cupiennius salei (Ctenidae), as in other spiders, the central nervous system is divided into the supraoesophageal ganglion or brain and the suboesophageal ganglia (Fig. 1). The two masses are interconnected by oesophageal connectives. The brain gives off four pairs of optic and one pair of cheliceral nerves. From the suboesophageal ganglia arise a pair of pedipalpal, four pairs of leg, and several pairs of opisthosomal nerves (Fig. 2). 1. Cell types. In the brain a total of 50900 cells were counted, in the suboesophageal ganglia 49000. They are all monopolar cells, found in the ganglion periphery and may be classified into four types: (a) Small globuli cells (nuclear diameter 6–7 m) forming a pair of compact masses in the protocerebrum (Fig. 10b); (b) Small and numerous cells (cell diameter 12–20 m) with processes forming the bulk of the neuropil in the brain and suboesophageal ganglia; (c) Neurosecretory cells (cell diameter ca. 45 m) in the brain and suboesophageal ganglia; (d) Large motor and interneurons (cell daimeter 40–112 m), mostly in the suboesophageal ganglia (Figs. 10a and c). 2. Suboesophageal mass. The cell bodies form a sheet of one to several cell layers on the ventral side of each ganglion and are arranged in groups. Three such groups were identified as motor neurons, four as interneurons. At the dorsal, dorso-lateral, and mid-central parts of the ganglion there are no cell somata. The fibre bundles arising from them form identifiable transverse commissural pathways (Fig. 9b). They form the fibrous mass in the central part of the suboesophageal mass.Neuropil is well-formed in association with the sensory terminations of all major nerves (Fig. 9a). As these proceed centrally they break up into five major sensory tracts forming five layers one above the other. There are six pairs of additional major longitudinal tracts arranged at different levels dorsoventrally (Fig. 8). They ascend into the brain through the oesophageal connectives and terminate mostly in the mushroom bodies and partly in the central body. 3. Protocerebrum. Fine processes of the globuli cells form the most important neuropil mass in the fibrous core, called the mushroom bodies. These consist of well developed glomeruli, hafts, and bridge which are interconnected with the optic masses of the lateral eyes and most fibre tracts from the brain and suboesophageal mass (Fig. 7). The median eye nerves form a small optic lamella and optic ganglia, connected to the central body through an optic tract. Each posterior median and posterior lateral eye nerve ends in large optic lamellae (Fig. 13a). These are connected through chiasmata to a large optic mass where fibres from globuli cells form conspicuous glomeruli. There are 10–12 large fibres (diameter 9 m) of unknown origin on each side, terminating in the optic lambella of the posterior lateral eye.The central body, another neuropil mass (Fig. 13b) in the protocerebrum, is well developed in Cupiennius and located transversely in its postero-dorsal region (Fig. 10d). It consists of two layers and is interconnected with optic masses of the median and lateral eyes through optic tracts. Fibre tracts from the brain and suboesophageal mass join the central body.     

Secondary retinae of a primitive jumping spider,Yaginumanis (Arachnida,Araneida, Salticidae)

Summary Retinae of the secondary eyes of a primitive salticid spider, Yaginumanis sexdentatus (Yaginuma 1967) are described at the ultrastructural level. The structures of the anterior lateral, posterior lateral and posterior median eyes are identical. Receptor somata lie in the retinal cups. Each receptor bearing twin rhabdomeres is ensheated by (i) much-divided processes of non-pigmented glial cells whose somata lie distally in the retinal cups; and (ii) four processes of pigmented glial cells whose somata lie basally, below the receptive segments. Pigment granules in the latter are concentrated in the basal retina, and are not present at the level of the rhabdoms. The present findings support the placement of Yaginumanis in a newly erected Subfamily Spartaeinae by Wanless (1984), because of the likelihood of homology in the fine structural organisation of the secondary retinae of this genus and of the genus Portia.     

Functional associations between the metabolome and manganese tolerance in Vigna unguiculata

Genotypic- and silicon (Si)-mediated differences in manganese (Mn) tolerance of cowpea (Vigna unguiculata) arise from a combination of symplastic and apoplastic traits. A detailed metabolomic inspection could help to identify functional associations between genotype- and Si-mediated Mn tolerance and metabolism. Two cowpea genotypes differing in Mn tolerance (TVu 91, Mn sensitive; TVu 1987, Mn tolerant) were subjected to differential Mn and Si treatments. Gas chromatography-mass spectrometry (GC-MS)-based metabolite profiling of leaf material was performed. Detailed evaluation of the response of metabolites was combined with gene expression and physiological analyses. After 2 d of 50 μM Mn supply TVu 91 expressed toxicity symptoms first in the form of brown spots on the second oldest trifoliate leaves. Silicon treatment suppressed symptom development in TVu 91. Despite higher concentrations of Mn in leaves of TVu 1987 compared with TVu 91, the tolerant genotype did not show symptoms. From sample cluster formation as identified by independent component analysis (ICA) of metabolite profiles it is concluded that genotypic differences accounted for the highest impact on variation in metabolite pools, followed by Mn and Si treatments in one of two experiments. Analysis of individual metabolites corroborated a comparable minor role for Mn and Si treatments in the modulation of individual metabolites. Mapping individual metabolites differing significantly between genotypes onto biosynthetic pathways and gene expression studies on the corresponding pathways suggest that genotypic Mn tolerance is a consequence of differences (i) in the apoplastic binding capacity; (ii) in the capability to maintain a high antioxidative state; and (iii) in the activity of shikimate and phenylpropanoid metabolism.     

An organic coating keeps orb‐weaving spiders (Araneae,Araneoidea, Araneidae) from sticking to their own capture threads

More than 95% of orb‐weaving spider species ensure prey capture success by producing viscous threads equipped with gluey droplets. However, this trap may bear serious risks for the web‐inhabiting spider as well. The obvious question, how a spider avoids getting stuck in its own capture spiral, has gained little scientific attention up till now. In 1905, the French naturalist Jean‐Henry Fabre concluded from anecdotal observation that orb‐weaving spiders protect themselves by a fatty surface coating. Here, we test this hypothesis by indirectly measuring the force necessary to detach an autotomized spider’s leg from the capture spiral of its own web (here called ‘index of adhesion’, IOA). Three groups of legs, each of the species Araneus diadematus Clerck, 1757 and Larinioides sclopetarius (Clerck, 1757), were tested. One was left untreated, one was washed with distilled water (H₂O), and one was washed with the organic solvent carbon disulphide (CS₂). In both species, we found a weak IOA between the spider leg and the gluey capture spiral in untreated and water‐washed legs without significant differences between the two. The IOA approximately doubled, when spider legs had been washed with carbon disulphide prior to measurement, that is, the CS₂‐washed legs stuck significantly more strongly than the untreated and water‐washed legs. These results provide indirect evidence for a protective anti‐adhesive organic coating on the spider’s body surface and so support Fabre’s hypothesis.     

The ultrastructure of chemoreceptor sensilla in Ciniflo (Araneida,Arachnida)

The morphology and ultrastructure of chemoreceptive hairs on the legs or the cribellate spider Ciniflo are described. About 20 bipolar sensory cells innervate each hair. The dendrites of two of these terminate at the hair base and are probably mechanoreceptive in function. The others continue into the hair shaft, where they terminate without branching. The associated sheath and enveloping cells are fully described and their physiological roles discussed. This sensillum is compared with the chemoreceptors of other arthropods.     

The material cost and stickiness of capture threads and the evolution of orb-weaving spiders

Prey capture threads are essential to the operation of spider orb-webs because they prevent insects that have been intercepted from escaping before a spider can subdue them. The volume of material invested in a web's capture threads is related to spider weight and is the same for primitive orb-weavers that produce cribellar capture thread and modern orb-weavers that produce adhesive capture thread. However, as adhesive capture thread achieves greater stickiness relative to its volume, adhesive orb-webs have a greater total stickiness and, consequently, a greater prey capture potential than cribellate orb-webs. These differences appear to have favoured the transition from cribellate to adhesive capture threads and the success of adhesive orb-weavers, which include 95% of all orb-weaving species. Differences in the thread economy and the total stickiness of webs constructed by spiders of different weights also suggest that adhesive orb-weavers should grow more rapidly and be capable of attaining a larger size than cribellate orb-weavers.