Complex Sense Organs Research Articles

Morphology and scaling of compound eyes in the smallest beetles (Coleoptera: Ptiliidae)

The coleopteran family Ptiliidae (featherwing beetles) includes some of the smallest insects known with most of the representatives of this family measuring less than 1 mm in body length. A small body size largely determines the morphology, physiology, and biology of an organism and affects the organization of complex sense organs. Information on the organization of the compound eyes of Ptiliidae is scarce. Using scanning electron microscopy we analyzed the eyes of representatives of all subfamilies and tribes and provide a detailed description of the eye ultrastructure of four species (Nephanes titan, Porophila mystacea, Nanosella sp. and Acrotrichis grandicollis) using transmission electron microscopy. The results are compared with available data on larger species of related groups of Staphyliniformia and scale quantitative analyses are performed. The eyes of Ptiliidae consist of 15–50 ommatidia 6–13 μm in diameter and all conform to the apposition acone type of eye with fused rhabdoms of banded organization. Each ommatidium has the typical cellular arrangement present also in the eyes of larger staphyliniform beetles, but strongly curved lenses, short cones, reduced pigment cells, a high density of pigment granules and certain modifications of the rhabdom seem typical of ptiliid eyes. Allometric analyses show that as body size decreases, the number of facets drops more steeply than their average size does.

A Short History of Nearly Every Sense-The Evolutionary History of Vertebrate Sensory Cell Types.

Evolving from filter feeding chordate ancestors, vertebrates adopted a more active life style. These ecological and behavioral changes went along with an elaboration of the vertebrate head including novel complex paired sense organs such as the eyes, inner ears, and olfactory epithelia. However, the photoreceptors, mechanoreceptors, and chemoreceptors used in these sense organs have a long evolutionary history and homologous cell types can be recognized in many other bilaterians or even cnidarians. After briefly introducing some of the major sensory cell types found in vertebrates, this review summarizes the phylogenetic distribution of sensory cell types in metazoans and presents a scenario for the evolutionary history of various sensory cell types involving several cell type diversification and fusion events. It is proposed that the evolution of novel cranial sense organs in vertebrates involved the redeployment of evolutionarily ancient sensory cell types for building larger and more complex sense organs.

Molecular clocks and the early evolution of metazoan nervous systems.

The timing of early animal evolution remains poorly resolved, yet remains critical for understanding nervous system evolution. Methods for estimating divergence times from sequence data have improved considerably, providing a more refined understanding of key divergences. The best molecular estimates point to the origin of metazoans and bilaterians tens to hundreds of millions of years earlier than their first appearances in the fossil record. Both the molecular and fossil records are compatible, however, with the possibility of tiny, unskeletonized, low energy budget animals during the Proterozoic that had planktonic, benthic, or meiofaunal lifestyles. Such animals would likely have had relatively simple nervous systems equipped primarily to detect food, avoid inhospitable environments and locate mates. The appearance of the first macropredators during the Cambrian would have changed the selective landscape dramatically, likely driving the evolution of complex sense organs, sophisticated sensory processing systems, and diverse effector systems involved in capturing prey and avoiding predation.

Sensational placodes: Neurogenesis in the otic and olfactory systems

For both the intricate morphogenetic layout of the sensory cells in the ear and the elegantly radial arrangement of the sensory neurons in the nose, numerous signaling molecules and genetic determinants are required in concert to generate these specialized neuronal populations that help connect us to our environment. In this review, we outline many of the proteins and pathways that play essential roles in the differentiation of otic and olfactory neurons and their integration into their non-neuronal support structures. In both cases, well-known signaling pathways together with region-specific factors transform thickened ectodermal placodes into complex sense organs containing numerous, diverse neuronal subtypes. Olfactory and otic placodes, in combination with migratory neural crest stem cells, generate highly specialized subtypes of neuronal cells that sense sound, position and movement in space, odors and pheromones throughout our lives.

Useless hearing in male Emblemasoma auditrix (Diptera, Sarcophagidae)--a case of intralocus sexual conflict during evolution of a complex sense organ?

Sensory modalities typically are important for both sexes, although sex-specific functional adaptations may occur frequently. This is true for hearing as well. Consequently, distinct behavioural functions were identified for the different insect hearing systems. Here we describe a first case, where a trait of an evolutionary novelty and a highly specialized hearing organ is adaptive in only one sex. The main function of hearing of the parasitoid fly Emblemasoma auditrix is to locate the host, males of the cicada species Okanagana rimosa, by their calling song. This task is performed by female flies, which deposit larvae into the host. We show that male E. auditrix possess a hearing sense as well. The morphology of the tympanal organ of male E. auditrix is rather similar to the female ear, which is 8% broader than the male ear. In both sexes the physiological hearing threshold is tuned to 5 kHz. Behavioural tests show that males are able to orient towards the host calling song, although phonotaxis often is incomplete. However, despite extensive observations in the field and substantial knowledge of the biology of E. auditrix, no potentially adaptive function of the male auditory sense has been identified. This unique hearing system might represent an intralocus sexual conflict, as the complex sense organ and the behavioural relevant neuronal network is adaptive for only one sex. The correlated evolution of the sense organ in both sexes might impose substantial constraints on the sensory properties of the ear. Similar constraints, although hidden, might also apply to other sensory systems in which behavioural functions differ between sexes.

Application of synchrotron-radiation-based computer microtomography (SRμCT) to selected biominerals: embryonic snails, statoliths of medusae, and human teeth

Synchrotron-radiation-based computer microtomography (SRmicroCT) was applied to three biomineralised objects First, embryonic snails of the freshwater snail Biomphalaria glabrata, second, rhopalia (complex sense organs) of the medusa Aurelia aurita, and third, human teeth. The high absorption contrast between the soft tissue and mineralised tissues, i.e. the shell in the first case (consisting of calcium carbonate) and the statoliths in the second case (consisting of calcium sulphate hemihydrate), makes this method ideal for the study of biomineralised tissues. The objects can be non-destructively studied on a micrometre scale, and quantitative parameters like the thickness of a forming a snail shell or statolith crystal sizes can be obtained on a length scale of 1-2 mum. Using SRmicroCT, the dentin-enamel border can be clearly identified in X-ray dense teeth.

Ultrastructural Analysis of the Sensilla of Austroperipatus aequabilis Reid, 1996 (Onychophora, Peripatopsidae)

AbstractThe head of Austroperipatus aequabilis bears five types of sensilla. which were examined by electron microscopy. They differ from each other in position, shape of outer sensory elements and cuticular socket structures. Thus, we distinguish sensilla with sensory hairs, sensilla with sensory bulbs, cone‐shaped sensilla. sensilla with sensory bristles, and sensilla of the lips. They are composed of up to 15 cells, which can he separated into four cell types. The most frequent cell type is the bipolar receptor cell that occurs in all sensilla. The apical surface of this primary receptor cell is characterized by one or two partly branched cilia with a basal 9 × 2 + 0 pattern of microtubules. A modified bipolar receptor cell was found in all sensilla bearing a sensory peg except for the sensilla equipped with sensory bristles. The apical dendrite extends to a long pale process which exclusively contains mitochondria and single microtubules. In all sensilla examined in this study at least one supporting cell occurs which is characterized by parallel microvilli. An additional function of this cell type as a part of the stimulus‐conducting system is possible. In the sensillum with a sensory bulb two kinds of supporting cells occur. A unique cell type with an upside down position has regularly been found in all sensilla bearing a sensory peg. Apart from the sensilla they also occur within the labial epidermis. Since most sensilla contain several different receptor cells, they can be considered as complex sense organs. © 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All rights reserved

The locust tegula: significance for flight rhythm generation, wing movement control and aerodynamic force production

The tegula, a complex sense organ associated with the wing base of the locust, plays an important role in the generation of the flight motor pattern. Here its function in the control of wing movement and aerodynamic force production is described. The vertical component of forewing movement was monitored while recording intracellularly from flight motoneurones during stationary flight. First, in accordance with previous electrophysiological results, stimulation of hindwing tegula afferents was found to reset the wingstroke to the elevation phase in a well-coordinated manner. Second, recordings made before and after removal of fore- and hindwing tegulae were compared. This comparison demonstrated that the delayed onset of elevator motoneurone activity caused by tegula removal is accompanied by a corresponding delay in the upstroke movement of the wings. The consequences of this delayed upstroke for aerodynamic force production were investigated by monitoring wing movements and lift generation simultaneously. A marked decrease in net lift generation was observed following tegula removal. Recordings of wing pronation indicate that this decrease in lift is primarily due to the delayed upstroke movement - that is, to a delay of the wings near the aerodynamically unfavourable downstroke position. It is concluded that the tegula of the locust hindwing signals to the nervous system the impending completion of the wing downstroke and allows initiation of the upstroke movement immediately after the wings have reached the lower reversal point of the wingstroke. The functional significance of tegula feedback and central rhythm generation for locust flight control are discussed.

The Locust Tegula: Significance for Flight Rhythm Generation, Wing Movement Control and Aerodynamic Force Production

ABSTRACT The tegula, a complex sense organ associated with the wing base of the locust, plays an important role in the generation of the flight motor pattern. Here its function in the control of wing movement and aerodynamic force production is described. The vertical component of forewing movement was monitored while recording intracellularly from flight motoneurones during stationary flight. First, in accordance with previous electrophysiological results, stimulation of hindwing tegula afferents was found to reset the wingstroke to the elevation phase in a well-coordinated manner. Second, recordings made before and after removal of fore-and hindwing tegulae were compared. This comparison demonstrated that the delayed onset of elevator motoneurone activity caused by tegula removal is accompanied by a corresponding delay in the upstroke movement of the wings. The consequences of this delayed upstroke for aerodynamic force production were investigated by monitoring wing movements and lift generation simultaneously. A marked decrease in net lift generation was observed following tegula removal. Recordings of wing pronation indicate that this decrease in lift is primarily due to the delayed upstroke movement – that is, to a delay of the wings near the aerodynamically unfavourable downstroke position. It is concluded that the tegula of the locust hindwing signals to the nervous system the impending completion of the wing downstroke and allows initiation of the upstroke movement immediately after the wings have reached the lower reversal point of the wingstroke. The functional significance of tegula feedback and central rhythm generation for locust flight control are discussed.

Is the Physiology of Cutaneous Receptors Determined by Morphology?

Publisher Summary This chapter discusses the general morphological and physiological principles governing the sensory mechanisms of cutaneous receptors. The extent to which morphology determines physiology is analyzed. There is a focus on the organized mechanoreceptors—Pacinian and Golgi-Mazzoni corpuscles; hair follicle receptors; the Meissner corpuscle; Merkel touch-spot; the Ruffini ending in mammals and, the Herbst and Grandry corpuscles in birds. In each case, the distinctive morphology revealed by electron microscopy is associated with a specific physiological responsiveness, which may be evident as a selective sensitivity to certain parameters of the physical stimulus and/or in the output discharge code of impulses in the afferent nerve fibre. A complex sense organ, the sinus hair, is then considered to test the hypothesis that the general principles enunciated for individual kinds of mechanoreceptor can be applied to a more elaborate system.

The peripheral morphological basis of tactile sensibility in the beak of geese.

The distribution, form variability and organization of two types of encapsulated mechanoreceptors, the Grandry and the Herbst corpuscles, were studied in the beak of geese. (1) In the beak skin Grandry corpuscles were found 20 to 150 μ below the epidermis in the domestic goose (Anser anser) and 1 to 80 μ deep in the white-fronted goose (Anser albifrons). The Herbst corpuscles lay deeper beneath the base of the epidermis, 70 to 310 μ in the domestic goose and 10 to 120 μ in the white-fronted goose. (2) The number of both types of receptors increased towards the distal portions of the beak skin, the Grandry corpuscles being roughly ten times more numerous than the Herbst corpuscles. Grandry corpuscles are particularly numerous in the prominent dermal ridges of the beak skin. (3) In Anser anser and Anser albifrons the Grandry corpuscles displayed a complexity unusual for other birds. Up to twelve specialized Grandry cells in a single corpuscle were found, and over fifty percent of all corpuscles consisted of more than two specialized cells. The average number of specialized cells in Grandry corpuscles increased towards the distal beak skin. (4) Underneath the horny plate, covering the tip of the upper and lower bill, both kinds of receptors occur but the Grandry corpuscles are less frequent than the Herbst corpuscles. The Grandry corpuscles are strikingly associated with connective tissue strands that often link several corpuscles into chains of spindle-like formations. The Herbst corpuscles occur in large numbers deep beneath the horny plate and in bony lacunae. (5) In the tip of the upper and the lower bill a complex sense organ, the bill tip organ, was discovered. It consists of a large number of processes emerging from deep connective tissue, which contain various kinds of mechanoreceptors. These processes run in horny tubules towards the surface of the distal rim of the horny tip of the bill and probably are moved in their longitudinal axis on mechanical stimulation. (6) The morphological findings are discussed in respect to the problem of the structure and function of the mechanoreceptors in the beak of birds.