The development of taste and tactile hairs in the pharate fly Protophormia terraenovae (Diptera,Calliphoridae) and in the embryonal cricket Acheta domestica (Orthopteroidea,Ensifera)

Summary 1. The development of taste hairs and tactile hairs of the fly Protophormia terraenovae is described using light microscope, scanning, and transmission electron microscope methods.2. The development of taste hairs proceeds in the same way on tarsi, labella, and wings. First the dendritic outer segments of ciliary origin become visible above the hypodermal cell surface [2 days after pupariation (AP) at 19° C]; then the dendritic sheath starts growing out and finally the trichogen process follows. In a typical intermediate stage (stage C) the distal sections of the dendrites float freely in the fluid surrounding the pharate adult. The more proximal sections are enclosed by the dendritic sheath around which the trichogen process is wrapped (4 days AP). The protruding dendrites disappear when the cuticle starts being deposited on the fully grown trichogen process, and the sheath vanishes later (9–10 days AP or 1 day before eclosion). The development is discussed with respect to the known structural organization of the adult hair.3. In the tactile hairs the single dendrite which grows outwards is completely covered by the dendritic sheath and lies beside the trichogen process [stage C(m)].4. The taste and tactile hair development proceeds in the same way on legs isolated from the pupa after disc eversion in an artificial medium containing ecdysterone.5. To check that both these patterns of development are widespread the development of taste and tactile hairs of the first instar cercus of the cricket Acheta domestica was studied with the light microscope: Both hair types pass through identical early stages.     

Quantitative characterization of the filiform mechanosensory hair array on the cricket cercus

Background

Crickets and other orthopteran insects sense air currents with a pair of abdominal appendages resembling antennae, called cerci. Each cercus in the common house cricket Acheta domesticus is approximately 1 cm long, and is covered with 500 to 750 filiform mechanosensory hairs. The distribution of the hairs on the cerci, as well as the global patterns of their movement vectors, have been characterized semi-quantitatively in studies over the last 40 years, and have been shown to be very stereotypical across different animals in this species. Although the cercal sensory system has been the focus of many studies in the areas of neuroethology, development, biomechanics, sensory function and neural coding, there has not yet been a quantitative study of the functional morphology of the receptor array of this important model system.

Methodology/Principal Findings

We present a quantitative characterization of the structural characteristics and functional morphology of the cercal filiform hair array. We demonstrate that the excitatory direction along each hair''s movement plane can be identified by features of its socket that are visible at the light-microscopic level, and that the length of the hair associated with each socket can also be estimated accurately from a structural parameter of the socket. We characterize the length and directionality of all hairs on the basal half of a sample of three cerci, and present statistical analyses of the distributions.

Conclusions/Significance

The inter-animal variation of several global organizational features is low, consistent with constraints imposed by functional effectiveness and/or developmental processes. Contrary to previous reports, however, we show that the filiform hairs are not re-identifiable in the strict sense.     

Structure and kinematics of the prosternal organs and their influence on head position in the blowfly Calliphora erythrocephala Meig.

Summary The blowfly Calliphora has a mobile head and various, presumably proprioceptive, sense organs in the neck region. The prosternal organs are a pair of mechanosensory hair fields, each comprising ca. 110 sensilla. We studied their structure (Figs. 2–4), kinematics (Figs. 5, 6) and, after surgery, their influence on head posture (Figs. 7–11) in order to reveal their specific function.The hair sensilla are structurally polarized, all in roughly the same direction, and are stimulated by dorsoventral bending of the hairs (Figs. 3, 4). This occurs indirectly by flap-movements of two contact sclerites (Figs. 3, 6); they move in the same direction during pitch turns of the head, in opposite directions during roll turns, and barely at all during yaw turns of the head (Fig. 5).Bending and arresting all hairs of one field elicits a head roll bias to the non-operated side (Fig. 7) during tethered flight in visually featureless surroundings. In contrast, shaving all hairs of one field elicits a head roll to the operated side (Figs. 8–10). The surgically induced bias of head posture is not compensated within three days (Fig. 10). Our results show that the prosternal organs of Calliphora sense pitch and roll turns of the fly's head, and control at least its roll position.Abbreviations HP° TP° angular positions of the sagittal planes of the fly's head and thorax, respectively, relative to an external reference - HR° = HP — TP head roll angle of the fly's head relative to its thorax, HR>0° for clockwise head roll, looking in flight direction - N number of flies - n number of measurements - PO prosternal organ - SD standard deviation - SEM standard error of the mean     

Central projections of campaniform sensilla on the cerci of crickets and cockroaches

Summary Campaniform sensilla associated with filiform hairs comprise an important receptor type of the multimodal sensory system of the cerci of crickets and cockroaches. Their axon projections were investigated using iontophoretic cobalt injection into single sensilla.In crickets (Gryllus bimaculatus, Acheta domestica), six different types of cereal campaniform sensilla projections can be distinguished on the basis of their axonal arborizations and terminations. Typically, a proportion of cereal campaniform sensilla, associated with long filiform hairs, give rise to axons that ascend as through fibres from the terminal ganglion to reach the sixth abdominal ganglion. Cereal campaniform sensilla associated with clavate hairs have projections restricted to the terminal ganglion alone.Whereas in crickets axons of cercal campaniform sensilla invade only certain segmental neuropils in the terminal ganglion, in cockroaches (Periplaneta americana) axons from cercal campaniform sensilla branch in every segmental neuropil. A proportion of cereal campaniform sensilla in this species also gives rise to through fibres to the fifth abdominal ganglion.We discuss morphological and functional interpretations of differences between crickets and cockroaches and consider the significance of this type of receptor in the context of previous studies of the cercal system.     

Influence of phosphate and nitrate supply on root hair formation of rape,spinach and tomato plants

Summary Experiments with tomato, rape and spinach in nutrient solutions have shown that the formation of root hairs is strongly influenced by phosphate and nitrate supply. Decreasing the phosphate concentration of the nutrient solution from 100 to 2 M P resulted in an increase of root hair length from 0.1–0.2 to 0.7 mm of the three plant species. Root hair density also increased by a factor of 2–4 when the P concentration was lowered from 1000 to 2 M. The variation of these two root properties raised the root surface area by a factor of 2 or 3 compared to plants well supplied with P. Root hair length was closely related to the phosphate content of the root and shoot material. On the other hand, spinach plants grown in a split-root experiment produced root hairs in solutions of high P concentration (1000M P) if the major part of the total root system was exposed to low P concentration (2 M P). It is therefore concluded that the formation of root hairs does not depend on directly the P concentration at the root surface but on the P content of the plant.Similar experiments with nitrate also resulted in an increase in length and density of root hairs with the decrease of concentration below 1000 M. In this case marked differences between plant species occurred. At 2 M compared to 1000 M NO₃ root hair length of tomato increased by a factor of 2, of rape by a factor of 5 and of spinach by a factor of 9. Root hair length was correlated, but not very closely, to the total nitrogen content of the plants. It is concluded, that the influence of nutrient supply on the formation of root hairs is a mechanism for regulating the nutrient uptake of plants.Dedicated to Prof. Dr. E. Welte on the occasion of his 70th anniversary.     

Modeling arthropod filiform hair motion using the penalty immersed boundary method

Crickets are able to sense their surrounding environment through about 2000 filiform hairs located on a pair of abdominal cerci. The mechanism by which the cricket is able to sense a wide range of input signals using these filiform hairs of different length and orientation is of great interest. Most of the previous filiform hair models have focused on a single, rigid hair in an idealized air field. Here, we present a model of the cercus and filiform hairs that are mechanically coupled to the surrounding air, and the model equations are based on the penalty immersed boundary method. The key difference between the penalty immersed boundary method and the traditional immersed boundary method is the addition of forces to account for density differences between the immersed solid (the filiform hairs) and the surrounding fluid (air). The model is validated by comparing the model predictions to experimental results, and then the model is used to examine the interactions between multiple hairs. With multiple hairs, there is little interaction when the hairs are separated by more than 1mm, and, as they move closer, they interact through viscous coupling, which reduces the deflection of the hairs due to the air movement. We also examine the computational scalability of the algorithm and show that the computational costs grow linearly with the number of hairs being modeled.     

A Model of Filiform Hair Distribution on the Cricket Cercus

Crickets and other orthopteran insects sense air currents with a pair of abdominal appendages resembling antennae, called cerci. Each cercus in the common house cricket Acheta domesticus is covered with between 500 to 750 filiform mechanosensory hairs. The distribution of the hairs on the cerci, as well as the global patterns of their movement axes, are very stereotypical across different animals in this species, and the development of this system has been studied extensively. Although hypotheses regarding the mechanisms underlying pattern development of the hair array have been proposed in previous studies, no quantitative modeling studies have been published that test these hypotheses. We demonstrate that several aspects of the global pattern of mechanosensory hairs can be predicted with considerable accuracy using a simple model based on two independent morphogen systems. One system constrains inter-hair spacing, and the second system determines the directional movement axes of the hairs.     

Soil-binding pilosity and camouflage in ants of the tribes Basicerotini and Stegomyrmecini (Hymenoptera,Formicidae)

Summary Workers of the tropical ant tribes Basicerotini and Stegomyrmecini possess two dominant forms of setae on the dorsal surfaces of the body and outer surfaces of the legs: longer brush hairs with splintered distal ends, and shorter holding hairs that vary among species from plumose to blade-shaped or filiform. The two usually but not invariably occur together to create a double layer. The brush hairs evidently scrape or otherwise capture fine particles of soil, while the holding hairs help to keep them in place next to the surface exoskeleton. As the worker ages, the soil accumulates as a thin, mud-like layer, greatly enhancing the overall camouflage of the body. The material appears to be primarily or entirely exogenous; no special secretory cells were found (in Basiceros manni, studied for this purpose) that might contribute cryptically colored chemicals or adhesive substances to hold the soil in place.     

Zur Richtcharakteristik der Fadenhaare von Periplaneta Americana

Summary The structure of the filiform hairs on the cerci of Periplaneta americana has been studied by light microscopy (fixed in osmium, 1 sections). The aim was to correlate the structure with previous physiological results.The lower end of the hair opens out into an irregular flange. Located beneath the surface of the cercus, the flange is inserted at two opposite points into a cuticular cylinder which contains the flange. Other points along the flange rim move freely within the cylinder. The two insertion points constitute the axis of rotation. Thus the hairs can be bent easily only in a single plane perpendicular to this axis. The plane of movement of identical hairs was determined by physiological measurements and by morphological observations. The results are in good agreement.Near the lower rim of the hair the distal nerve process is surrounded with a tong-shaped sheath on three flanks, but exposed on the fourth. A generator potential develops on the distal nerve process by bending the hair in the direction in which the exposed flank faces and hyper-polarization by bending it in the opposite direction. In the case of depolarization, the lower rim of the hair approaches the exposed flank of the distal nerve process and recedes from it in the case of hyper-polarization. Probably the stimulus is transmitted only to the exposed flank of the distal nerve process.

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Herrn Doz. Dr. J. Wersäll danke ich für einen Arbeitsplatz und vielfältige Unterstützung bei der Arbeit. Für Unterstützung danke ich auch Herrn Doz. Dr. P.-G. Lundquist. — Die Untersuchungen wurden mit Unterstützung der Deutschen Forschungsgemeinschaft und mit Mitteln der National Institutes of Health, Grant No. NB 3956-04 (Doz. Wersäll), durchgeführt.     

Temperature-induced modifications in the surface features of stamens of a tomato mutant: An SEM study

Summary Stamenless-2 (sl₂/sl₂) is a temperature-sensitive mutant of tomato (Lycopersicon esculentum) which exhibits altered stamen development under different temperatures (Sawhney 1983). By using scanning electron microscopy, this study was conducted to investigate the differentiation of surface features of mutant and normal stamens grown under different temperatures, with the view to further determine the role of temperature in gene expression in stamen development. Mutant stamens grown under intermediate temperatures (23 °C day/18 °C night) differed from the normal in hair production, the shape of epidermal cells and in the pattern of cuticular thickenings. Under low temperatures (18 °C day/15 °C night), all surface features of mutant stamens closely resembled the normal, whereas under high temperatures (28 °C day/23 °C night), the patterns and types of hairs, epidermal cells, stomata, and cuticular thickenings on mutant stamens were similar to that of a gynoecium. The staminal features of normal stamens were not affected by different temperatures. This study shows that the expression of the sl₂/sl₂ allele is influenced by temperature conditions to the extent that the pattern of cellular differentiation characteristic of either the stamens or the carpels can be induced in mutant stamens.     

Structure of the afferent terminals in terminal ganglion of a cricket and persistent homology

We use topological data analysis to investigate the three dimensional spatial structure of the locus of afferent neuron terminals in crickets Acheta domesticus. Each afferent neuron innervates a filiform hair positioned on a cercus: a protruding appendage at the rear of the animal. The hairs transduce air motion to the neuron signal that is used by a cricket to respond to the environment. We stratify the hairs (and the corresponding afferent terminals) into classes depending on hair length, along with position. Our analysis uncovers significant structure in the relative position of these terminal classes and suggests the functional relevance of this structure. Our method is very robust to the presence of significant experimental and developmental noise. It can be used to analyze a wide range of other point cloud data sets.     

Elektronenmikroskopie am sensorischen Apparat der Fadenhaare auf den Cerci der Schabe Periplaneta americana

Summary The filiform hairs are sensitive for week air currents. Each receptor unit consists of an elastically inserted cuticular hair, a single sensory cell, and a surrounding fluid filled cavity lined partly by the cuticle and partly by special lining cells, exhibiting many villiform protrusions. The mentioned cavity — at least by adult cockroaches — is extracellular and the authors suggest the nomenclature receptorlymph cavity. The expression vacuole of the trichogen cell should not be used.The distal process of the sensory cell protrudes into the base of the cuticular hair and contains a tubular body consisting of more than 1000 microtubuli which, in the resting position of the hair, are slightly bent.It is suggested that the stimulus is transmitted to the tubular body, where bending of the tubuli causes depolarization and straigthening repolarization, when bending the hair in opposite directions.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

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Mit Unterstützung durch: Grant No. NB 3956-04-05 des US Public Health Service; Swedish Medical Research Council B 67-12 x-720-02; Stiftelsen Therese och Johan Andersson Minne.     

Hair morphology and the relationships of species inSolanum sect.Basarthrum

The usefulness of features of leaf hairs in distinguishing subgenera and sections is well documented in bothRhododendron andSolanum. In this analysis of the taxa ofSolanum sect.Basarthrum (23 species), and of a sample of closely related taxa from sect.Petota (22 species), it is shown that such features serve to delineate subsectional groups such as series and some species as well. SectionBasarthrum has an unexpected diversity of hair types. Although this group has been characterized by 2-celled bayonet hairs, more than one half of the taxa in the section bear multicellular finger hairs, and 3 species also possess branched hairs. Thus, major rearrangements of the species previously assigned to sect.Basarthrum are indicated or supported by pubescence features. The taxa studied from seriesEtuberosa andJuglandifolia (both of sect.Petota) show hair types that a) are relatively primitive for the section, and b) show linkage between sects.Petota andBasarthrum.     

Long,smooth hair sensilla on the spider leg coxa: Sensory physiology,central projection pattern,and proprioceptive function (Arachnida,Araneida)

Summary Rows of long, smooth hair sensilla situated on both sides of the leg coxae were examined in the spider Cupiennius salei (Ctenidae). The hair shafts point into the space between adjacent legs and are deflected when the hairs of one coxa touch the cuticle of the neighboring coxa. 1. Unlike the serrated hair shafts of the ubiquitous tactile and chemosensitive setae of spiders, these hairs are entirely smooth. At their base they are articulated in a socket with an asymmetrical groove that determines the direction of hair deflection. Hair shafts are up to 1000 m long. The exact grouping of smooth hairs in rows is typical of the coxae for each pair of legs. 2. Unlike the other, multiply innervated cuticular sensilla of spiders, smooth hairs are supplied by only a single mechanosensitive neuron. This is confirmed by electrophysiological recordings from single hairs. Threshold deflection to elicit a spike response lies near 1°. The response to maintained, step-like stimuli declines rapidly. 3. All central endings of these hair receptors in the fused segmental ganglia are confined to dorsal neuropil of the ipsilateral neuromere. The specific arborization pattern resembles an elongated, three-pronged fork with a long central prong. Topography, natural stimulus situation, and the phasic response characteristic of smooth hairs suggest that spiders use these sensilla to monitor the relative distance between leg coxae during locomotion.     

Electrophysiology of trichobothria in orb-weaving spiders (Agelenidae,Araneae)

Summary Trichobothria of the house spidersTegenaria atrica (C.L. Koch) andTegenaria derhami (Scopoli) were stimulated by linear deflection of the hair from its resting position to one side. The pulse response of the receptor cell was analyzed. At angular deflection velocities of 10^–21 deg/ms the receptor begins to discharge at an angle of 3 degrees. While the mean pulse rate remains constant during deflections of 10^–210^–1deg/ms the pulse train may be interrupted by repeated breaks. Discharge continues when the hair is bent proximally beyond the bothrium edge. When the hair is bent distally and touches the bothrium edge, however, discharge ceases. Responsible for this phenomenon seems to be an asymmetry of hair suspension. — Repeated deflection leads to logarithmically ascending latency curves and logarithmically falling curves of the pulse numbers. The function coefficients depend on velocities and repetition rates of the deflections. The adaptational effect is heightened by preceding stationary deflection in the direction of the dynamical stimulus. The mean pulse rate as a function of hair deflection velocity increases logarithmically. The mean pulse rate as a function of hair movement direction obeys a cosine law, provided that a given velocity and a definite deflection angle are used.Supported by grants of the Deutsche Forschungsgemeinschaft given to Prof. Dr. P. Görner in the field of the Schwerpunktprogramm RezeptorphysiologieThe present paper is part of a doctoral thesis. My thanks are due to Prof. Dr. P. G6rner for the theme, many valuable discussions and his constant readiness to help.     

Directional selectivities of near-field filiform hair mechanoreceptors on the crayfish tailfan (Crustacea: Decapoda)

Directional selectivities of mechanoreceptors that innervate filiform hairs on the crayfish tailfan were investigated with unidirectional, sinusoidal, water-motion stimuli. These recordings provide the first representative sample from filiform hair sensilla on the entire tailfan. The filiform hair receptors exhibit unimodal directional selectivity patterns that were well fitted by a cardioid function with a half-width of 122°. The preferred directions correspond to the major axis of hair motion, and are perpendicular to the orientation of lateral branches on the main hair shaft. Pooled plots of preferred directions demonstrate quadrimodal patterns on the telson and endopods which are associated with hair location, and a bimodal pattern on the exopods. For each appendage, the combination of the overall pattern of preferred directions with “coarse coding” of direction by individual receptors provides sensitivity to a full 0–360° range of water motion and the potential to discriminate the direction of water motion throughout this range. The results demonstrate several similarities to the wind-sensitive cercal receptor system in orthopteroid insects, and suggest that crustacean filiform hair receptors provide a sufficient sensory basis for behavioral orientation to water currents and shorelines. Accepted: 5 January 1998     

Coated vesicles and other cytoplasmic components of growing root hairs of radish

Summary Root tips of radish,Raphanus sativus, were fixed in glutaraldehyde followed by osmium tetroxide. The fine structure of young root hairs, not exceeding about 130, in length, was studied to relate their apical growth pattern to their cytoplasmic organization. The cytoplasm in the terminal 3–5 it of the root hair is characterized by an electron dense matrix in which lie numerous smooth-surfaced vesicles, large irregularly-shaped fibrous inclusions, and clusters of ribosomes. Other organelles are largely or entirely excluded from this region. Farther than about 5, from the tip, the hair cytoplasm is filled with plastids, rough endoplasmic reticulum, mitochondria, and dictyosomes. The latter produce smooth vesicles similar in size and morphology to those present in the apical dome. Vesicles of a different kind appear in the peripheral cytoplasm along the entire length of the hair. These vesicles possess an alveolate or chambered coat about 20 m thick and have a diameter of about 85 m, including coat. They originate by evagination from the large, smooth-surfaced vesicles in the vicinity of dictyosomes. It is suggested that proteins and carbohydrates are concentrated in the dictyosomes and then segregated in the smooth vesicles released from the dictyosome cisternae. The coated vesicles which bud from the smooth vesicles may serve to isolate the proteins and transport them to the hair surface for participation in wall synthesis. The smooth vesicles are believed to convey carbohydrates to the region of active wall extension at the hair apex.This work was supported in part by grant GM-10493 from the National Institutes of Health. United States Public Health Service, to Dr. H. T. Bonnett, Jr., and grant RG-628 from the National Science Foundation to Dr. E. H. Newcomb.     

Turgor-dependent efflux of assimilates from coats of developing seed of Phaseolus vulgaris L.: water relations of the cells involved in efflux

The turgor-homeostat model of assimilate efflux from coats of developing seed of Phaseolus vulgaris L. was further characterised. The turgor pressure (P), the volumetric elastic modulus () and hydraulic conductivity (L_p) of the seed coat cells responsible for assimilate efflux and cotyledon storage parenchyma cells were determined with a pressure probe. In addition, turgor of the seed coat and cotyledons was estimated by measuring the osmolalities of symplastic and apoplastic fluids extracted by centrifugation. Osmolality of symplastic and apoplastic saps collected from the seed coat declined significantly over the period of seed development from a cotyledon water content of 80% to 50%. However, the difference in osmolalities of the apoplastic and symplastic saps remained relatively constant. For cotyledons, osmolality of the apoplastic sap exhibited a significant decline during seed development, while the osmolality of symplastic sap did not change significantly. Hence cotyledon P increased as the water content dropped from 80% to 50%. For both detached and attached empty seed coats, a small decrease (ca. 40mOsmol·kg^–1) in the osmolality of the bathing solution, led to a rapid increase in P of cells involved in assimilate efflux (efflux cells) by about 0.07 MPa. Thereafter, cell P exhibited a rapid decline to the original value within some 20–30 min. When P of the efflux cells was reduced by increasing the osmolality of the bathing solution, P exhibited a comparable rate of recovery for attached empty seed coats but there was no P recovery to its original value in the case of detached seed coats. In contrast, the cotyledon storage parenchyma cells did not exhibit P regulation when the osmolality of the bathing solution was changed. The observations that the efflux cells of P. vulgaris seed coats can rapidly adjust their P homeostatically in response to small changes in apoplastic osmolality are consistent with the operation of a turgor-homeostat mechanism. The volumetric elastic modulus () of the seed coat efflux cells exhibited a mean value of 7.3±0.8 MPa at P=0.15 MPa and was found to be linearly dependent on cell P. The e of the cotyledon storage parenchyma cells was estimated to be 6.1±1.0 MPa at P=0.41 MPa. Hydraulic conductivity (L_p) of the seed coat cells and the cotyledon cells was (8.2±1.5) × 10^–8m·s^–1·MPa^–1and (12.8±1.0) × 10^–8 m·s^–1·MPa^–1, respectively. The relatively high , i.e., low elasticity, for the seed coat cell walls would ensure that small changes in water potential of the seed apoplast will be reflected in large changes in cell P. The high L_p values for both the seed coat and the cotyledon cells is consistent with the rapid changes in P in response to changes in water potential of the seed apoplast.Abbreviations LYCH Lucifer Yellow CH - volumetric elastic modulus - L_p hydraulic conductivity - P turgor pressure - osmotic pressure - t_1/2 half-time for water exchange The investigation was supported by funds from the Australian Research Council. We are grateful to Louise Hetherington for competent technical assistance and to Kevin Stokes for raising the plant material.