Adhesion of Individual Attachment Setae of the Spider Cupiennius salei to Substrates With Different Roughness and Surface Energy

Dynamic adhesion is a key ability for animals to climb smooth surfaces. Spiders evolved, convergent to geckos, a dry adhesive system made of setae branching into smaller microtrichia ending as spatulae. Several previous studies concentrated either on the whole adhesive claw tuft on the spider´s foot that consists of attachment setae or on the single adhesive contact elements, the microtrichia with spatula-shaped tips. Here, the adhesion of single setae of the spider Cupiennius salei was examined and the morphology of the pretarsus and the fine structure of the setae were studied in further detail. Using individual setae fixed to force sensing cantilevers, their adhesion at different contact angles with a glass substrate was measured as well as their adhesive performance on substrates with different roughness and on smooth surfaces with different surface energies. The results show an individual variability of the adhesive forces corresponding to the seta morphology and especially to the seta tip shape. The tip shapes of the setae vary largely even in neighboring setae of the pretarsal claw tuft that comprises approximately 2,400 setae. Regarding surface energy of the substrate, the adhesion force on hydrophobic polytetrafluoroethylene was 30% of that on a hydrophilic glass substrate, which points to the importance of both van der Waals interactions and hydrogen bonds in spider adhesion.

Mechanotransduction channel Piezo is widely expressed in the spider, Cupiennius salei, mechanosensory neurons and central nervous system

Mechanosensory neurons use mechanotransduction (MET) ion channels to detect mechanical forces and displacements. Proteins that function as MET channels have appeared multiple times during evolution and occur in at least four different families: the DEG/ENaC and TRP channels, as well as the TMC and Piezo proteins. We found twelve putative members of MET channel families in two spider transcriptomes, but detected only one, the Piezo protein, by in situ hybridization in their mechanosensory neurons. In contrast, probes for orthologs of TRP, ENaC or TMC genes that code MET channels in other species did not produce any signals in these cells. An antibody against C. salei Piezo detected the protein in all parts of their mechanosensory cells and in many neurons of the CNS. Unspecific blockers of MET channels, Ruthenium Red and GsMTx4, had no effect on the mechanically activated currents of the mechanosensory VS-3 neurons, but the latter toxin reduced action potential firing when these cells were stimulated electrically. The Piezo protein is expressed throughout the spider nervous system including the mechanosensory neurons. It is possible that it contributes to mechanosensory transduction in spider mechanosensilla, but it must have other functions in peripheral and central neurons.

Complex precursor structures of cytolytic cupiennins identified in spider venom gland transcriptomes

Analysis of spider venom gland transcriptomes focuses on the identification of possible neurotoxins, proteins and enzymes. Here, the first comprehensive transcriptome analysis of cupiennins, small linear cationic peptides, also known as cytolytic or antimicrobial peptides, is reported from the venom gland transcriptome of Cupiennius salei by 454- and Illumina 3000 sequencing. Four transcript families with complex precursor structures are responsible for the expression of 179 linear peptides. Within the transcript families, after an anionic propeptide, cationic linear peptides are separated by anionic linkers, which are transcript family specific. The C-terminus of the transcript families is characterized by a linear peptide or truncated linkers with unknown function. A new identified posttranslational processing mechanism explains the presence of the two-chain CsTx-16 family in the venom. The high diversity of linear peptides in the venom of a spider and this unique synthesis process is at least genus specific as verified with Cupiennius getazi.

Mechanotransduction Channel Piezo is Widely Expressed in the Spider, Cupiennius Salei, Mechanosensory Neurons and Central Nervous Systems

Mechanosensory neurons use mechanotransduction (MET) ion channels to detect mechanical forces and displacements. Proteins that function as MET channels have appeared multiple times during evolution and occur in at least four different families; the DEG/ENaC and TRP channels, and the TMC and Piezo proteins. We found twelve putative members of MET channel families in two spider transcriptomes, but detected only one, the Piezo protein, by in situ hybridization in their mechanosensory neurons. In contrast, probes for orthologs of TRP, ENaC or TMC genes that code MET channels in other species did not produce any signals in these cells. An antibody against C. salei Piezo detected the protein in all parts of their mechanosensory cells and in many neurons of the CNS. Unspecific blockers of MET channels, Ruthenium Red and GsMTx4, had no effect on the mechanically activated currents of the mechanosensory VS‑3 neurons, but the latter toxin reduced action potential firing when these cells were stimulated electrically. It is possible that the Piezo protein contributes to mechanosensory transduction in spider mechanosensilla, but it must have other functions in peripheral and central neurons.

A spider in motion: facets of sensory guidance

Spiders show a broad range of motions in addition to walking and running with their eight coordinated legs taking them towards their resources and away from danger. The usefulness of all these motions depends on the ability to control and adjust them to changing environmental conditions. A remarkable wealth of sensory receptors guarantees the necessary guidance. Many facets of such guidance have emerged from neuroethological research on the wandering spider Cupiennius salei and its allies, although sensori-motor control was not the main focus of this work. The present review may serve as a springboard for future studies aiming towards a more complete understanding of the spider’s control of its different types of motion. Among the topics shortly addressed are the involvement of lyriform slit sensilla in path integration, muscle reflexes in the walking legs, the monitoring of joint movement, the neuromuscular control of body raising, the generation of vibratory courtship signals, the sensory guidance of the jump to flying prey and the triggering of spiderling dispersal behavior. Finally, the interaction of sensors on different legs in oriented turning behavior and that of the sensory systems for substrate vibration and medium flow are addressed.

Mechanical Properties and Weibull Scaling Laws of Unknown Spider Silks

Spider silks present extraordinary mechanical properties, which have attracted the attention of material scientists in recent decades. In particular, the strength and the toughness of these protein-based materials outperform the ones of many man-made fibers. Unfortunately, despite the huge interest, there is an absence of statistical investigation on the mechanical properties of spider silks and their related size effects due to the length of the fibers. Moreover, several spider silks have never been mechanically tested. Accordingly, in this work, we measured the mechanical properties and computed the Weibull parameters for different spider silks, some of them unknown in the literature. We also measured the mechanical properties at different strain rates for the dragline of the species Cupiennius salei. For the same species, we measured the strength and Weibull parameters at different fiber lengths. In this way, we obtained the spider silk scaling laws directly and according to Weibull’s prediction. Both length and strain rates affect the mechanical properties of spider silk, as rationalized by Weibull’s statistics.

Neurotoxin Merging: A Strategy Deployed by the Venom of the Spider Cupiennius salei to Potentiate Toxicity on Insects

The venom of Cupiennius salei is composed of dozens of neurotoxins, with most of them supposed to act on ion channels. Some insecticidal monomeric neurotoxins contain an α-helical part besides their inhibitor cystine knot (ICK) motif (type 1). Other neurotoxins have, besides the ICK motif, an α-helical part of an open loop, resulting in a heterodimeric structure (type 2). Due to their low toxicity, it is difficult to understand the existence of type 2 peptides. Here, we show with the voltage clamp technique in oocytes of Xenopus laevis that a combined application of structural type 1 and type 2 neurotoxins has a much more pronounced cytolytic effect than each of the toxins alone. In biotests with Drosophila melanogaster, the combined effect of both neurotoxins was enhanced by 2 to 3 log units when compared to the components alone. Electrophysiological measurements of a type 2 peptide at 18 ion channel types, expressed in Xenopus laevis oocytes, showed no effect. Microscale thermophoresis data indicate a monomeric/heterodimeric peptide complex formation, thus a direct interaction between type 1 and type 2 peptides, leading to cell death. In conclusion, peptide mergers between both neurotoxins are the main cause for the high cytolytic activity of Cupiennius salei venom.

Visual pathways in the brain of the jumping spider Marpissa muscosa

Some animals have evolved task differentiation among their eyes. A particular example is spiders, where most species have eight eyes, of which two (the principal eyes) are used for object discrimination, whereas the other three pairs (secondary eyes) detect movement. In the spider species Cupiennius salei these two eye types correspond to two visual pathways in the brain. Each eye is associated with its own first and second order visual neuropil. The second order neuropils of the principal eyes are connected to the arcuate body, whereas the second order neuropils of the secondary eyes are linked to the mushroom body. However, eye size and visual fields are considerably different in jumping spiders. We explored the principal- and secondary eye visual pathways of the jumping spider Marpissa muscosa. We found that the connectivity of the principal eye pathway is the same as in C. salei, while there are differences in the secondary eye pathways. In M. muscosa, all secondary eyes are connected to their own first order visual neuropils. The first order visual neuropils of the anterior lateral and posterior lateral eyes are further connected with two second order visual neuropils, whereas the posterior median eyes lack second order visual neuropils and their axons project only to the arcuate body. This suggests that the posterior median eyes probably do not serve movement detection in M. muscosa. Furthermore, the second order visual neuropil (L2) in Marpissa muscosa potentially integrates information from the secondary eyes and might thus enable faster movement decisions.