Sensory Setae Research Articles

Ultrastructural identification of three types of sensory setae on copepod antennae

Crustaceans, as well as other arthropods, are covered with sensory setae and hairs, including mechanoand chemosensory sensillae with a ciliary origin. Calanoid copepods are small planktonic crustaceans forming a major link in marine food webs. In conjunction with behavioral and physiological studies of the antennae of calanoids, we undertook the ultrastructural characterization of sensory setae on the antennae of Pleuromamma xiphias.Distal mechanoreceptive setae exhibit exceptional behavioral and physiological performance characteristics: high sensitivity (<10 nm displacements), fast reaction times (<1 msec latency) and phase locking to high frequencies (1-2 kHz). Unusual structural features of the mechanoreceptors are likely to be related to their physiological sensitivity. These features include a large number (up to 3000) of microtubules in each sensory cell dendrite, arising from or anchored to electron dense rods associated with the ciliary basal body microtubule doublets. The microtubules are arranged in a regular array, with bridges between and within rows. These bundles of microtubules extend far into each mechanoreceptive seta and terminate in a staggered fashion along the dendritic membrane, contacting a large membrane surface area and providing a large potential site of mechanotransduction.

ASSOCIATION OF PHYTOPATHOGENIC FUNGI FOR THE SCOTS PINE (PINUS SYLVESTRIS L.) WITH THE EUROPEAN PINE WEEVIL HYLOBIUS ABIETIS (L.) (COL. CURCULIONIDAE)

AbstractIn 1989 and 1990, the contamination rate of the European pine weevil Hylobius abietis (L.) by several pathogenic fungi for the Scots pine was measured [Leptographium procerum (Kendrick) Wingf. — 45% of the specimens; Pachnodium canum (Upadh. and Kendr.) — 14%; or Ophiostoma piliferum (Fries) H. and P. Syd — 3% (Piou 1993)]. To understand the processes of transportation, a detailed study was conducted by scanning electron microscopy. Several types of spores vectored are found mainly in the thoracic cuticular rounded wells located near the sensorial setae. These wells are connected with an epidermal glandular apparatus whose ultrastructural description is given. We question the origin and composition of these secretions which are believed to protect the spores and contribute to the infection process.

Role of the male claw sensilla in perception of female mounting sex pheromone in Dermacentor variabilis, Dermacentor andersoni and Amblyomma americanum

The foreleg claw sensilla of male D. variabilis, D. andersoni and A. americanum ticks indlude the receptors that perceive the female contact mounting sex pheromone (MSP). In all three tick species, the foreleg claw sensilla comprise six anteriorly-directed setae arranged in three symmetrical pairs, two each on the opposite sides of the apotele of the claw and one on the ventral side. Morphological study and behavioral bioassays of these setae revealed that only the dorsal and middle (=lateral) pairs of claw sensilla are mechanogustatory. While the ventral pair are strictly mechanoreceptors. The dorsal and middle sensory setae exhibit a single pore-like structure located at or near their tip, a feature characteristic of mechanogustatory sensilla. These setae are similar to those found on the palps that are believed to function as pheromone receptors. In all three tick species, male mounting and postmounting behaviors were suppressed only when the dorsal and middle pairs of claw sensilla were ablated or covered with gelatin; normal behavior was restored when the gelatin was removed. Doscresponse bioassays were conducted with D. variabilis males to authenticate the results of the gelatin tests. The results of these bioassays demonstrated that the gelatin coat was impervious to the pheromone. The characteristics of the ixodid tick mating system that distinguish it from mating processes in other arthropods are discussed.

Proliferation of microtubules from discrete electron-dense bodies in the ciliary dendritic portion of mechanosensory setae of copepod antennae

Sensory setae on the appendages of most arthropods contain microtubules in their innervating dendrites. Both mechano- and chemoreceptors are of ciliary origin. Mechanoreceptive dendrites typically contain more microtubules than do chemoreceptive dendrites, perhaps reflecting a role for microtubules in stiffening the setae. The presence of microtubules may also increase the sensitivity of mechanotransduction.The overall arrangement of calanoid copepod mechanoreceptors has been described elsewhere. In calanoid copepods the arrangement of microtubules in the distal ciliary segment of the dendrites is dramatic: as many as 3000 microtubules per dendrite are found in parallel rows (fig. 1,3a). These bundles of microtubules extend some distance into the setae themselves. The basal bodies within these dendrites are especially electron-dense and give rise to a circlet of 9 + 0 microtubules (fig. 2,3f)- Just distal to the circlet electron-dense material begins to form adjacent to the microtubules (fig. 3e), eventually forming elongate electron-dense bodies radiating outward (fig. 3d).

GEOGRAPHICAL VARIATION, CLASSIFICATION, RECONSTRUCTED PHYLOGENY, AND GEOGRAPHICAL HISTORY OF THECICINDELA SEXGUTTATAGROUP (COLEOPTERA: CICINDELIDAE)

AbstractA systematic review was conducted for theCicindela sexguttatagroup taxa. Comparative methods of examination were applied to adult structural and ecological characters for purposes of taxa diagnoses, and to establish a basis for the derivation of the group’s history.Based on 13 adult exoskeletal characters and 25 tests on populations throughout the group’s geographical range, a discriminant analysis identifies the most significant characters as being elytral maculation, body size, pilosity of the stipes, and number of sensory setae on the antennal scape. In addition, selected characters of the male and female genitalia are shown to identify all taxa within the group. Among biological comparisons the different number of mature eggs found in adult females ofC.sexguttataFabricius andC.denikeiBrown indicates that their fecundity differs; and the larval burrow ofC.denikeiopens directly beneath rocks and stones, a habit unique inCicindela. Seasonality profiles of taxa appear to be dictated by geographical location, and by phylogeny to a smaller degree. Species–soils associations indicate thatC.sexguttatahas a strong affinity to warm, moist and loamy soils, butC.denikeiis correlated with sandy, silty till. For all species of the group, habitats occupied and limits of distribution to eastern Canada and the United States appear to be governed by soil and forest types.Three species of the group are recognized:C.sexguttataconsisting of geographical populations varying considerably in adult characteristics and the problematic formC.harrisiiLeng which may be considered a cryptic species;C.denikei; andC.patruelaDejean consisting of two subspeciesC.p.patruelaandC.p.consentaneaDejean.A reconstructed phylogeny of theC.sexguttatagroup based on methods of Hennig (1966) alliesC.sexguttataandC.denikeias sister species, andC.patruelaas an earlier lineage. Recognized as a stem group of theC.purpureacomplex, theC.sexguttatagroup is postulated to have had its origins in forested eastern North America during the Late Miocene. Speciations ofC.patruelaand lineageC.sexguttata–C.denikeiare perceived to have occurred in the Pliocene, followed by speciations ofC.sexguttataandC.denikeiin the Late Pleistocene effected by continental ice mass advances and recessions.

Comparative morphology and actuopalaeontology of mysid statoliths (Crustacea, Mysidacea)

A comprehensive and comparative study of the external statolith morphology of the family Mysidae is presented. The study covers 48 species from major systematic groups occupying a large number of habitats in different biogeographical zones of the globe. Statoliths generally show high morphological diversity. The traditional classification scheme of subtaxa and the correlation of statolith characters with segmentation patterns of body appendages suggest that the organic composition and the nearly spherical structure of the statoliths of Boreomysinae and Rhopalophthalminae are plesiomorphic compared with the more complex mineralized statoliths found in all other subfamilies. During ontogenetic development the number of sensorial setae and associated pores and pore groups on the statolith increase with body size and statolith diameter. Although patterns of caudal pores are highly specific for some genera, the high intraspecific variance of pore numbers strongly reduces the diagnostic value of this feature in most species. Statolith characters can be successfully used for identification of subfamilies, tribes, and especially genera. For future palaeontological applications a proper diagnosis of fossil mysid statoliths is essential. Therefore, we provide a key to subfamilies and tribes based exclusively on statolith characters.

BIOLOGICAL CHARACTER ANALYSIS, CLASSIFICATION, AND HISTORY OF THE NORTH AMERICAN CICINDELA SPLENDIDA HENTZ GROUP TAXA (COLEOPTERA: CICINDELIDAE)

AbstractComparisons of selected biological attributes were made to establish a phylogenetic basis for the classification of the Cicindela splendida Hentz group taxa. Recognized members of the group, C. splendida, C. limbalis Klug, and C. denverensis Casey, are spring-fall species, and northern populations emerge later during spring than southern populations. Despite differences in time of peak abundance, the three species overlap in time and space. The absence of large numbers of hybrids of these three species suggests that although closely related, their adults can distinguish from each other, and thus their rank as species should be retained.Comparison of geographical distribution of these species with that of dominant soil types revealed that they had similar soil preferences. The geographical distribution of all three species was smaller than the range of their preferred soil types, probably because of the same factors that influence their local distributions.Morphometric analyses of these species revealed a closer similarity between C. splendida and C. limbalis. In both sexes elytral pattern, percentage maculation, elytral colour, and non-sensory setae number collectively distinguish these species from each other, whereas body measurements, body ratios, sensory setae, and labral setae collectively fail to distinguish them.Based on plesiomorph/apomorph character polarization, and the C. purpurea Olivier group as outgroup, it was determined that C. denverensis represents an early lineage of the C. splendida group, whereas C. splendida and C. limbalis are more recent sister species.The ancestor of the C. splendida group probably evolved during late stages of the Tertiary Period as a North American resident and was a continental, riparian, cool-temperate form that ranged across Canada and northeastern and central United States. Extant forms speciated during the late Pleistocene as a result of spatial fragmentation of populations, isolation, and adaptation during glacial and interglacial periods.

Ultrastructural and histochemical investigations of peripatus integument

The integument of Euperipatoides leukarti (Onychophora) has been studied by SEM and TEM-histochemical techniques. The thin (2–3 μ) cuticle is essentially arthropodan in design, comprising a thin, lamellate outer epicuticle, a homogeneous inner epicuticle, and an extensive fibrous procuticle. Five tanned lipoprotein lamellae constitute the outer epicuticle, the innermost showing a cross-striated pattern and the outermost also containing carbohydrates. The inner epicuticle contains untanned lipoproteins. The chitin-protein composite procuticle reveals a fibrous ultrastructure but no trace of helicoids. Distally it may be tanned, producing a sclerotin layer (exocuticle), pronounced in the sensory setae, claws and mandibles. Penetrating the epicuticle and extending into the procuticle are numerous, minute pore canals through which mobilised procuticle is resorbed prior to ecdysis. Beneath the procuticle is a monolayered epidermis traversed by tonofibrils and containing dense pigment granules. The membrane junctions are strongly convoluted and include an apical zonula adherens, septate desmosomes and a proximal lymph space. The epidermis is underlain by a thick (5–25μ) basement membrane of helicoidally organised collagen fibres. Functional and phylogetic implications of the integumental structure are discussed. Arthropod affinities are clear and the Onychophora should be included in that phylum if it is to be retained in modern taxonomic nomenclature.

Early Insect Diversification: Evidence from a Lower Devonian Bristletail from Québec

The earliest insect for which there is significant structural data, a bristletail (Archaeognatha) from the Early Devonian (Emsian Stage) of the Gaspé Peninsula of Québec, Canada, is described. Detailed analysis of the head indicates that this insect had large, bulging, separated, compound eyes, monocondylic mandibles, and numerous sensory setae. This fossil, the oldest record of terrestrial animal life from North America, suggests that early hexapod diversification occurred contemporaneously with the emergence of the first vascular land plants during the Silurian.

Postlarval changes in the external morphology of dactyl setae in the kelp crab, Pugettia producta (randall)

AbstractMorphological changes, which include growth, encrustation, and abrasion, occur in the sensory setae and nonsensory denticles located on the dactyls of the walking legs during the postlarval development of the kelp crab, Pugettia producta (Randall). The growth of the denticles is isometric (slope ∼ 1), while the growth of the setae is negatively allometric (slope < 1), relative to the growth of the dactyls. The increase in the sizes of the setae, but not of the denticles, appears to slow before growth stops at maturation, when molting ceases. The most striking morphological changes in the setae occur after maturation. While the setae of all but recently molted juvenile crabs are heavily encrusted by epibionts, the dactyls of most mature crabs are clean, and both the setae and denticles are so abraded that only their bases remain. The consequences of these morphological changes are discussed in relation to the sensory capabilities of a long‐lived, nonmolting majid crab.

The surface microstructure of marine and terrestrial isopoda (Crustacea, Peracarida)

The microstructure of the surface of thirteen marine littoral and two terrestrial isopods was investigated by scanning electron microscopy. A great diversity of surface ornamentation is present, including non-sensory microscales, pits, tubercles, and ridges, and sensory tricorns, pit organs, pores, papillae and setae. Microscales are common features of the integument surface; their shape and size are highly variable. Tricorns were not observed on the marine littoral isopods. Several hitherto undescribed structures were observed including spade-like projections from the tergite surface of Oniscus asellus, hair-like filaments associated with the microscales of Jaera and ridged conical protuberances on Edotea triloba and E. montosa. The possible function of certain surface microstructures is discussed.

Sense Organs of Two Marine Arthrotardigrades (Heterotardigrada, Tardigrada)

The sense organs of the marine arthrotardigrades Halechiniscus greveni Renaud-Mornant & Deroux and Batillipes noerrevangi Kristensen were investigated with the aid of interference phase-contrast and transmission electron microscopy. The sense organs of the two species are quite different in outer cuticular morphology, but the inner cellular parts are constructed after the same model: the arthropod sensory setae. All investigated sensilla contained ciliary structures. Regeneration of the cirri during moult is very similar to the regeneration process in insects and spiders, but in the two arthrotardigrades the trichogen cell is not retracted from the cuticular part of the setae after moult. The clava is presumed to be olfactory; the cephalic cirri and the leg spines are contact chemoreceptors with one mechanoreceptive cilium terminating at the sensillum shaft. Cirrus E is compared with the trichobothrium of arthropods and the phylogenetic implications of the investigated structures are discussed.

ANTENNULAR SENSILLA OF THE BRINE SHRIMP,ARTEMIA SALINA

1. Scanning electron microscopy was used to characterize the external morphology of setae found on the antennules of adults and nauplii of the brine shrimp, Artemia salina (L.). The permeability of the antennular setae was studied by means of Slifer's crystal violet method. 2. Each antennule of an adult brine shrimp possessed a terminal cluster of sensory setae. Within a cluster there were two morphologically distinct kinds of sensilla, here designated type 1 and type 2. Three type 1 sensilla were observed on every antennule examined. The number of type 2 sensilla per antennule was usually four or five. 3. Type 1 sensilla of adults were 43 to 80 micrometer long and simple in external morphology. They were widest at the base, decreased in diameter gradually, and terminated as a finely tapered tip. No pores were resolved by scanning electron microscopy. 4. Type 2 sensilla of adults were shorter (shaft length, 12 to 23 micrometer) and displayed a single pore at the tip (average pore diameter, 0.4 micrometer). In thin section they were seen to possess a distinctive articular specialization of the cuticle at the base of the seta. 5. Dye penetration experiments indicated that type 2 sensilla were permeable to aqueous crystal violet, whereas type 1 sensilla were not. 6. The antennular setae of nauplii resembled type 1 sensilla in general shape, in being impermeable to crystal violet, and in lacking a terminal pore and basal articular specialization. Moreover, a total of three setae was normally present on each naupliar antennule, and the same number of type 1 sensilla was found on each adult antennule examined. If the three naupliar setae represent a developmental stage in the formation of three adult sensilla, available observations suggest that the larval setae are developmentally related to type 1, rather than to type 2 adult sensilla.

Experiments on food preference and chemical sense in Pycnogonida

Food choice experiments were carried out with three species of pycnogonids: Nymphon rubrum, N. gracile, and Endeis spinosa. Running sea-water that had circulated over different possible food-sources (hydroids, actiniarians, octocorals, synascidians) was offered to the pycnogonids at one side of a basin, pure sea-water or se-water that had flowed over a different source of food at the other. The experiments, though few in number, seemed to indicate that: (1) Pycnogonids are capable of detecting the presence or absence of various coelenterate species. (2) They are able to discriminate between different food-sources, i.e. the nature of the chemical substances produced by the food determines the degree of attraction. (3) The preferential sequence for the three pycnogonids tested is: Nymphon rubrum prefers Dynamena over Tubularia and Laomedea; these are preferred over Actinia and Metridium; there is no attraction to Alcyonium. Nymphon gracile prefers Laomedea over Dynamena. Endeis spinosa prefers Laomedea over Dynamena; these are preferred over Actinia; there is no attraction to Morchellium. (4) Experimental amputation of appendages indicates a high probability that the chemo-receptors of the pycnogonids are not located on the chelifores, palps, or ovigers. They may be located (a) all over the body, possibly in innervated epidermal bristles; and/or (b) in the distal part of the proboscis, bearing sensory setae; and/or (c) on the walking legs.

Abdominal grooming in the cockroach: Development of an adult behavior

Chemical or tactile irritants delivered to the dorsomedial region of the abdomen of the cockroach Periplaneta americana. evoke a complex grooming response. In larvae the response consitsts of extension of all six legs and arching of the abdomen which is rubbed against any solid surface presented. In adults, leg extension and arching are accompanied by side to side wagging of the abdomen and rapid scissoring of the wings. In some decapitated late instar larvae, abdominal wagging behavior can be evoked by chemical or tactile stimulation of the dorso-medial region of the abdomen. The form of the wag is somewhat different in these animals than in the adults, and it occurs at a lower frequency. Neuronal circuitry underlying the rhythmic wagging response of the adult may therefore be laid down or made functional in the mid- to late-larval stages. The wagging behavior is not normally expressed until the final ecdysis. A population of sensory setae is found on the abdomen at all stages of development, and some of these are presumed to trigger the grooming behavior when stimulated. The morphology and distribution of some of the adult receptors differs from some of the larval receptors. All larvae, including those late-instar individuals which show an adult-like response (wagging) have identical receptors on the abdomen in terms of morphology, distribution, and general responsiveness. Thus, no obvious changes in abdominal sensory receptors are correlated with the emergence of the wagging behavior. Anatomical and/or functional changes within the central nervous system are most likely responsible for the emergence of adult wagging behavior.

THE SENSORY NERVOUS SYSTEM OF THE ADULT CATTLE TICK BOOPHILUS MICROPLUS (CANESTRINI) IXODIDAE PART II. SCANNING ELECTRON MICROSCOPY

AbstractThe morphology of the sensory receptors on tarsus I and on the mouthparts of the cattle tick Boophilus microplus were examined by means of scanning electron microscopy. Features not resolved by light microscopy were revealed. The number of sensilla and their morphology are unique to B. microplus though similar to those of other tick species already described. The sensory setae found include mechanoreceptors, contact and olfactory chemoreceptors. Of special interest, on each inner cheliceral digit, is a denticle bearing a papilla at its tip and a pit at its base. The functions of these two newly described features are not known but it seems likely that they may include contact chemoreceptors capable of tasting host tissue chemicals. These observations provide the foundation for transmission electron microscopy of the receptors, which is the subject of the third paper in this series.

Surface structures and sense organs of the cypris larva of Balanus balanoides as seen by scanning and transmission electron microscopy.

Various features of the settlement stage larva (cyprid) of the barnacle, Balanus balanoides(L.), were studied using scanning and transmission electron microscopy. The cuticle of the valves is pitted and in section has a characteristic ultrastructure. Small sensory setae protrode from the surface of this cuticle and are probably mechanoreceptors able to sense water movement around the larva. Each of the pair of caudla appendages which protrude from between the larval valves posteriorly, is made up of several sensory setae. These appendages are able to sense settlement surface topography. Certain other features of the larva are alos described and their roles discussed; such features include the frontal filaments, antennules and thoracic limbs.

The fine structure and possible function of the sensory setae of the penis of Balanus balanoides (L.)

The structure and innervation of the sensory setae which are present in large numbers on the penis of Balanus balanoides (L.) have been established by scanning and transmission electron microscopy. Each seta contains a small number of sensory dendrites surrounded by an extracellular supporting tube which is presumed to be secreted by the enclosing sheath cell. The dendrites, which distally extend beyond both the sheath cell and supporting tube, terminate at the tip of the seta within a pore-like invagination of the cuticle and thus are in direct contact with the environment. Proximally bundles of dendrites pass into the penis tissue where they are surrounded by several sheath cells. The supporting tube terminates at a point within the body of the penis where a series of intracellular rods arise. The ciliary character of the dendrites is evident in this region, the microtubules being organized into the (9 × 2) +2 pattern. It is deduced that the sensilla are chemosensory; their structure is compared with that of other crustacean sensilla which are presumed to be chemosensory.

The morphology and histology of the cirripede pemis

The general morphology and detailed histology of the penis of two common boreo-arctic cirripedes, Balanus balanoides (L.) and B. balanus (L.) have been investigated. The penis is a highly extensible, annulated organ beset with four rows of sensory setae. The paired vesiculae seminales unite within the pedicel of the penis to give the single ductus. Distally, the exoskeleton is invaginated into this ductus. Circular muscles are present in the vesiculae seminales but do not continue into the penis. The histology of the ductus epithelium indicates a secretory nature as does that of a specialized group of cells, termed the ‘cushion’, towards the distal end: this group of cells is surrounded by circular muscle bands. Longitudinal muscles extend virtually the whole length of the penis; they give off fibres which are inserted at the junctions of the annulations. The muscles of the pedicel are described. Paired nerves in the pedicel give rise to four in the penis. The sensory innervation of the setae is described. The possible functional relations of the structure to the activities of the penis at copulation and during the emission of semen is discussed.

Reflex Organization in the Swimmeret System of the Lobster

ABSTRACT The intrasegmental feedback reflexes in the swimmeret system of the lobster Homarus americanas were activated while recording the responses from the swimmeret nerves and muscles. Two main sources of sensory feedback were identified; proprioceptors in the coxal region of the swimmeret, and sensory setae on the edges of the two rami of each swimmeret. The reflexes activated by these inputs are described. Reflexive feedback from the powerstroke movement to the powerstroke excitatory motor neurones is positive, further reinforcing the movement. Intrasegmental reflexes capable of independently initiating or terminating the powerstroke activity are absent, however. Therefore the powerstroke movement of each cycle can begin and end only in response to a purely central nervous motor command. It follows that the intrasegmental swimmeret reflexes are incapable of contributing to the periodicity seen in the motor output pattern which underlies swimmeret beating. In addition to strengthening the powerstroke, the intrasegmental reflexes strengthen the linkage between the powerstroke and the returnstroke within each movement cycle. The reflexes may also reinforce the reciprocity between excitor and inhibitor axon activity to the main powerstroke and returnstroke muscles. It is shown, however, that these three features of the motor output pattern are programmed into the CNS independently of the sensory feedback. The intrasegmental reflexes thus act as subservient amplifying devices for cyclic motor patterns which are produced independently by purely central nervous mechanisms.