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Friedrich G Barth

Publications and source records attributed to Friedrich G Barth.

12 recordsLinked to original sources
PubMed2006

Finite element modeling of arachnid slit sensilla-I. The mechanical significance of different slit arrays.

Arachnid strain sensitive slit sensilla are elongated openings in the cuticle with aspect ratios (slit length l/slit width b) of up to 100. Planar Finite Element (FE) models are used to calculate the relative slit face displacements, Dc, at the centers of single slits and of arrangements of mechanically interacting slits under uni-axial compressive far-field loads. Our main objective is to quantitatively study the role of the following geometrical parameters in stimulus transformation: aspect ratio, slit shape, geometry of the slits' centerlines, load direction, lateral distance S, longitudinal shift lambda, and difference in slit length Deltal between neighboring slits. Slit face displacements are primarily sensitive to slit length and load direction but little affected by aspect ratios between 20 and 100. In stacks of five parallel slits at lateral distances typical of lyriform organs (S=0.03 l) the longitudinal shift lambda substantially influences slit compression. A change of lambda from 0 to 0.85 l causes changes of up to 420% in Dc. Even minor morphological variations in the arrangements can substantially influence the stimulus transformation. The site of transduction in real slit sensilla does not always coincide with the position of maximum slit compression predicted by simplified models.

Animals↗
PubMed2006

Arthropod mechanoreceptive hairs: modeling the directionality of the joint.

Stimulus transformation in arthropod mechanoreceptive hairs is dominated by the mechanical properties of both the hair shaft and the hair's articulation. Here a mathematical model of the hair's articulation is developed based on simple relationships relevant for every anisotropic articulation. The mechanical behavior regarding deflection under load of a variety of hairs can be described quantitatively by using only two (in the case of double symmetric characteristics) or four parameters (in the case of only one symmetry): (1) joint stiffness S p in the preferred direction of deflection, (2) joint stiffness St in a plane transversal to the preferred direction, and (3, 4) the values of stiffness S for opposite directions of deflection. The applicability of the model was tested by measuring these stiffnesses S of spider tactile hair joints by deflecting the hairs statically in different directions. For comparison, data in the literature on insect and spider hairs sensitive to air flow were analyzed. The equation presented describes the directional characteristics of a wide range of structurally different cuticular hairs. It can also be used as a mathematical description of the joint mechanics when modeling the mechanics of hairs, for instance, by applying methods such as Finite Element Analysis.

Animals↗
PubMed2006

Hexyl decanoate, the first trail pheromone compound identified in a stingless bee, Trigona recursa.

Foragers of many species of stingless bees guide their nestmates to food sources by means of scent trails deposited on solid substrates between the food and the nest. The corresponding trail pheromones are generally believed to be produced in the mandibular glands, although definitive experimental proof has never been provided. We tested the trail following behavior of recruits of Trigona recursa in field experiments with artificial scent trails branching off from natural scent trails of this stingless bee. First-time recruits (newcomers) did not follow these trails when they were laid with pure solvent or mandibular gland extract. However, they did follow trails made with labial gland extract. Chemical analyses of labial gland secretions revealed that hexyl decanoate was the dominant component (72.4 +/- 1.9% of all volatiles). Newcomers were significantly attracted to artificial trails made with synthetic hexyl decanoate, demonstrating its key function in eliciting scent-following behavior. According to our experiments with T. recursa, the trail pheromone is produced in the labial glands and not in the mandibular glands. Hexyl decanoate is the first component of a trail pheromone identified and proved to be behaviorally active in stingless bees.

Animal Communication↗
PubMed2006

Vibrating the food receivers: a direct way of signal transmission in stingless bees (Melipona seminigra).

An element common to the recruitment communication of eusocial bees (honey bees, stingless bees and bumble bees) are pulsed thorax vibrations generated by successful foragers within the nest. In stingless bees, foragers vibrate during the unloading of the collected food. In the present study on Melipona seminigra we demonstrate that during trophallactic contacts, the food receivers are directly vibrated by the foragers. As a consequence, both the temporal structure and the main frequency component of the forager's vibrations are directly passed on to the receiver. The vibrations are attenuated by about 17 dB on their way from the forager's thorax (velocity amplitude of the vibrations: approximately 70 mm/s) to the receiver's thorax (approximately 10 mm/s), the main amount of attenuation (about 12 dB) occurring during transmission from the head of the forager to that of the receiver. Vibrations conducted through the substrate between the forager and food receiver are comparatively small with velocity amplitudes of 0.3 mm/s. Possible ways of perception and the advantages of vibration transmission by direct contact within the recruitment context are discussed.

Animal Communication↗
PubMed2006

Intracellular recording from a spider vibration receptor.

The present study introduces a new preparation of a spider vibration receptor that allows intracellular recording of responses to natural mechanical or electrical stimulation of the associated mechanoreceptor cells. The spider vibration receptor is a lyriform slit sense organ made up of 21 cuticular slits located on the distal end of the metatarsus of each walking leg. The organ is stimulated when the tarsus receives substrate vibrations, which it transmits to the organ's cuticular structures, reducing the displacement to about one tenth due to geometrical reasons. Current clamp recording was used to record action potentials generated by electrical or mechanical stimuli. Square pulse stimulation identified two groups of sensory cells, the first being single-spike cells which generated only one or two action potentials and the second being multi-spike cells which produced bursts of action potentials. When the more natural mechanical sinusoidal stimulation was applied, differences in adaptation rate between the two cell types remained. In agreement with prior extracellular recordings, both cell types showed a decrease in the threshold tarsus deflection with increasing stimulus frequency. Off-responses to mechanical stimuli have also been seen in the metatarsal organ for the first time.

Action Potentials↗
PubMed2005

Viscosity-mediated motion coupling between pairs of trichobothria on the leg of the spider Cupiennius salei.

Arachnids and insects use long, thin hairs as motion sensors to detect signals contained in the movement of the surrounding air. These hairs often form groups with a small spacing of tens to hundreds of micrometers between them. For air oscillation frequencies of biological interest, the potential exists for viscosity-mediated coupling among hairs in a group affecting their response characteristics. Even a small diameter hair can, in principle, affect the flow field around it and the dynamics of the hairs in its neighborhood. The viscosity-mediated coupling between a pair of hairs is investigated here both experimentally and theoretically. The conditions for the existence of the coupling effect, and its magnitude as a function of relevant parameters, are determined. In the range of biologically relevant frequencies (30-300 Hz), viscous coupling between pairs of hairs is only very small in the case of the spider Cupiennius salei. Theoretical analysis points to the relatively large spacing between hairs (20 to 50 hair diameters) and the tuning of the hairs to the above-mentioned frequencies to explain the practical absence of coupling.

Air Movements↗
PubMed2005

Morphology and structure of the tarsal glands of the stingless bee Melipona seminigra.

Footprint secretions deposited at the nest entrance or on food sources are used for chemical communication by honey bees, bumble bees, and stingless bees. The question of the glandular origin of the substances involved, however, has not been unequivocally answered yet. We investigated the morphology and structure of tarsal glands within the fifth tarsomeres of the legs of workers of Melipona seminigra in order to clarify their possible role in the secretion of footprints. The tarsal gland is a sac-like fold forming a reservoir. Its glandular tissue is composed of a unicellular layer of specialized epidermal cells, which cover the thin cuticular intima forming the reservoir. We found that the tarsal glands lack any openings to the outside and therefore conclude that they are not involved in the secretion of footprint substances. The secretion produced accumulates within the gland's reservoir and reaches as far as into the arolium. Thus it is likely that it serves to fill and unfold the arolium during walking to increase adhesion on smooth surfaces, as is known for honey bees and weaver ants.

Animals↗
PubMed2004

Spider mechanoreceptors.

Spiders have highly developed mechanosensory systems, some of which provide access to forms of stimulation alien to our own sensations. Studies of hair-shaped air movement detectors (trichobothria) and tactile sensors have uncovered an outstanding refinement of the processes of stimulus uptake and stimulus transformation, which reflect details of both stimulus physics and behavioral significance. They also emphasize the potential contained in the seemingly simple Bauplan of arthropod cuticular hairs. Embedded into the spider exoskeleton are several thousands of strain detectors (slit sensilla) measuring compressive exoskeletal strains induced by various forms of loads and forces. A compound slit sensillum (lyriform organ) on the leg has become an important model system for studies of mechanoreceptor primary processes at the cellular and membrane level.

Animals↗
PubMed2004

A stingless bee (Melipona seminigra) marks food sources with a pheromone from its claw retractor tendons.

By depositing scent marks on flowers, bees reduce both the search time and the time spent with the handling of nonrewarding flowers. They thereby improve the efficiency of foraging. Whereas in honey bees the source of these scent marks is unknown, it is assumed to be the tarsal glands in bumble bees. According to histological studies, however, the tarsal glands lack any openings to the outside. Foragers of the stingless bee Melipona seminigra have previously been shown to deposit an attractant pheromone at sugar solution feeders, which is secreted at the tips of their tarsi. Here we show that the claw retractor tendons have specialized glandular epithelia within the femur and tibia of all legs that produce this pheromone. The secretion accumulates within the hollow tendon, which also serves as the duct to the outside, and is released from an opening at the base of the unguitractor plate. In choice experiments, M. seminigra was attracted by feeders baited with pentane extracts of the claw retractor tendons in the same way as it was attracted by feeders previously scent marked by foragers. Our results resolve the seeming contradiction between the importance of foot print secretions and the lack of openings of the tarsal glands.

Animals↗
PubMed2002

Spider senses - technical perfection and biology.

This essay deals with sensory biology in a broad sense. It takes mechanosensory systems of spiders to illustrate a few basic issues. Particular attention is given to two aspects. 1. There is a remarkable "ingenuity" in the uptake and transformation of the adequate stimuli way out in the sensory periphery, which is reflected by an intimate relationship between the physical properties of the stimuli and the characteristics of the structures receiving and transforming them. We need to understand the details of this relationship in order to understand the relationship of an organism to its environment. 2. Sensory systems represent interfaces between the environment and behavior. As highly selective filters they have not evolved to provide abstract knowledge but to guide a particular behavior. The signals sent to the central nervous system are meaningful only in regard to their behavioral significance. - Some details of stimulus transformation in biological strain gauges (slit sensilla), airflow detectors (trichobothria) and touch receptors (tactile hairs) are described. Some of the refinement in the periphery is then meshed with the behavior of the whole organism. In this way the value shall be underlined of trying to understand reductionist details as building blocks of the complexity which enables an organism to behave in its own particular way in its species specific environment.

Journal Article↗