Stylus of the odonate endophytic ovipositor: a mechanosensory organ controlling egg positioning

Using light and scanning electron microscopy, a sensory field consisting of 15-20 campaniform sensillae is described on the base of the stylus of the endophytic ovipositor of Odonata. It is hypothesised that two symmetric styli equipped with this number of sensillae can function as a mechanosensory organ responsible for control of precise egg positioning in plant stems during oviposition. In laboratory experiments with females of damselflies Lestes sponsa and Lestes barbarus (Lestidae), it was demonstrated that the distance between laid eggs is not dependent on the presence of styli. Removal of styli from both sides did not influence a shift of oviposition to one side. Females with one removed stylus shifted the clutch line in the opposite direction toward the removed stylus. Additionally, removal of styli influenced positions of single eggs in egg sets, and disturbed the capacity for complex oviposition. Thus, both morphological and experimental data support the hypothesis that styli participate in the control of egg line and egg patterning in the clutch.     

External proprioceptors of locust locomotor organs and their change in the course of early larval ontogenesis

This work studies topography and structure of such important insect external proprioceptors as campaniform sensillae (CS). These mechanoreceptors are essential components of insect posture and locomotion regulation and participate in control of various forms of insect motor behavior (walking, jump, flight). There are traced their quantitative changes as well as differences in distribution of groups of these leg receptors at consecutive stages (from the 1st to the 4th instar) of ontogenetic development of larva of the locust Locusta migratoria L. The presence of groups of CS in proximal parts of extremities has been noted as early as in the 1st instar larvae. The CS groups in the wing pads were revealed only in the 4th instar larvae. The presented data allow connecting changes in structure and distribution of these proprioceptors with differences in locomotion of imagoes and larvae. A possible effect of these insect larval proprioceptors on central generators of the locomotion rhythms is discussed.     

Fine structure of antennal mechanosensilla of adult Rhodnius prolixus stål (Hemiptera: Reduviidae)

Each antenna of both sexes of adult Rhodnius prolixus has approximately 570 mechanosensitive neurons that innervate five morphologic types of cuticular mechanosensilla: campaniform sensilla, tapered hairs, trichobothria, and type I and type II bristle sensilla. Each campaniform sensillum and tapered hair is presumably innervated by one mechanosensitive bipolar neuron and probably functions in proprioception. The campaniform sensilla being located at the base of the scape could monitor the position of the antenna. Tapered hairs are found at the distal margin of flagellar segment I and projecting laterally from the bases of the pedicel and scape. They probably provide information about the relative positions of the antennal segments. Seven trichobothrium are located on the pedicel and three on flagellar segment I. Each trichobothrium has a long filamentous hair inserted into the base of a socket that extends inwardly as a cuticular tube and is innervated by one bipolar neuron with a tublar body, a parallel arrangement of microtubules associated with electron-dense material. The trichobothria may respond to small variations in air currents. Type I bristles occur at the base of the antenna and are the most numerous type of mechanosensillum; an average of 452 occur on each antenna of females and 440 on males. The bristle is curved toward the antennal shaft and is serrated distally. Type II bristles are located distally and are the second most numerous type of mechanosensillum; an average of 88 were counted on each antenna of females and 94 on males. The type II bristle is straight with small, longitudinal, external grooves and projects laterally from the antennal shaft. Each type I and II bristle sensillum is innervated by a bipolar neuron whose dendrite is divided into an inner and outer segment. The outer segment is encased by a dendritic sheath which may be highly convoluted and distally contains a tubular body. Two sheath cells are associated with each sensillum. Both types of bristle sensilla have a tactile function. The tubular bodies of both types of bristle sensilla have a complex structure indicating that they are very sensitive. Variations in the amount and arrangement of the electron-dense material at the tip of the tubular bodies may reflect differences in viscoelastic properties that underlie functional characteristics.     

Features of the receptors of the alar system of locusts which have lost their ability to fly

Using two species of locusts, Romalia microptera Beavy and Podisma pedestris L., receptors of the wing apparatus are described: campaniform sensillas of the wing, hair receptors of the tegula, chordotonal organ and thorax stretch receptor. A comparative analysis of the receptors mentioned with the homologous sensitive organs, participating in the control of wing movements, is performed in well flying species (Locusta migratoria migratorioides and Schistocerca gregaria). Loss of ability to fly is accompanied with a sharp decrease in the wing campaniform sensillas and in the tegula proprioceptive hairs. Simultaneously, there is loss of connection between the thorax receptors and the wing elements that are present in good flyers. The thorax stretch receptor begins to innervate the longitudinal dorsal muscle, as it is observed in the abdominal segments. The data obtained make it possible to speak about homology of the tergal chordotonal organs and the thorax and abdomen stretch receptors and about the pathways of their evolution, when the insects obtain and loose their ability to fly.     

Wing receptors of the American cockroach Periplaneta americana]

Wing receptors of the cockroach have been studied using staining technique with methylene blue in living animals. Five types of the receptors were found: trychoid hairs, bristles, complaniform sensillae, chordotonal organs and multiterminal neurons. The majority of the receptors is located at the lower surface of the wing, especially along its ribs. Together with primitive features in the structure (polyneuronal origin of hairs and bristles, poor content of chordotonal organs, absence of distinct groups of companiform sensillae), some specialization of wing receptors with respect to flight function is noted (concentration of proprioceptors along the main mechanical axis of the wing and formation of distinct rows by the companiform sensillae).     

The effects of local application of retinoids to different positions along the proximo-distal axis of embryonic chick wings

Summary Two retinoids, all-trans-retinoic acid and a synthetic analog, TTNPB, were locally applied to different positions along the proximo-distal axis of embryonic chick wing buds using controlled release carriers. Truncations or limbs with duplicated structures across the antero-posterior axis develop after retinoid application to distal positions in buds from stage 20–24 embryos. Phocomelic limbs develop when the retinoids are applied more proximally to buds of stage 23–24 embryos. Duplications of the pattern of structures along the proximo-distal axis never occur.Using TTNPB that is relatively stable, the amount of retinoid in the wing tissue when phocomelia is induced was measured. There is twice as much retinoid per cell in the proximal half of the bud as in the distal half of the bud. The concentration of TTNPB in proximal tissue is estimated to be three times higher than in distal tissue in which pattern formation and cartilage morphogenesis are relatively normal.At early stages in the development of phocomelia, the shape of the bud changes and the indentation that marks the elbow does not arise. Neither retinoid-induced cell killing nor effects on the pattern of programmed cell death were detected.The induction of phocomelia by retinoids appears to be based on effects on proximal cells, whereas retinoids produce pattern changes by acting on distal cells. Furthermore, compared with pattern changes, higher concentrations of retinoid in the bud tissue are required to produce phocomelia.     

Spatial differences in patterns of modification: selection on hairy in Drosophila melanogaster wings

Artificial selection was carried out for over 45 generations to enhance and suppress expression of the mutation hairy on the Drosophila melanogaster wing. Whole chromosome mapping of X‐linked and autosomal modifiers of sense organ number displayed regional differences in magnitude and direction of their effects. Regional specificity of modifier effects was also seen in some interchromosomal interactions. Scanning electron microscopy allowed precise measurement of sense organ size and position along the L3 longitudinal wing vein. Sense organ size varied in a predictable fashion along the proximal–distal axis, and the dorsal pattern differed from the ventral pattern. The high and low selection lines differed most in the proximal portion of the L3 vein. Extra sense organs in the High line were often associated with vein fragments at locations predicted from ancestral vein patterns. Thus, regional specificity of polygenic or quantitative trait locus modifier effects was identified in several different parts of the wing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the Nature and Function of Polygenic Loci in Drosophila. III. Veinlet Modifiers Having Region-Specific Effects upon the Vein Pattern

Polygenic modifiers affecting the expression of the mutant veinlet were studied to determine whether each acts specifically upon one vein or wing region or whether they affect the venation pattern in some general way. Selection experiments showed that the L4 vein can be modified independently of the L2 and L3 veins. Similarly, the L2 vein can be shortened while the L3 is selected to be longer, although there is some interdependence between the L2 and L3 veins. Assays of heterozygous whole chromosome effects show that different chromosomes are involved in the responses of separate veins, and one polygenic locus causing a decrease in L4 vein length has been isolated. Substitutions of whole chromosomes from selection lines into unselected backgrounds of non-homologous mutants demonstrate that the selected modifiers have the same qualitative effects upon other mutants having similar phenotypes. These results support the hypothesis that the polygenic modifiers affecting veinlet expression function independently of the veinlet locus, presumably by influencing common steps in the developmental processes leading to the formation of individual veins.     

Interaction of directional and stabilizing selection for wing characteristics in Drosophila melanogaster

The effects of interaction of artificial directional and stabilizing selection were studied using a recessive mutation of Drosophila melanogaster radius incompletus which causes interruption of the second longitudinal wing vein (L2). The character under directional selection was the length of the proximal segment of L2; stabilizing selection was conducted for a complex of morphometric wing characters. Three experimental designs in three replications were used: 1) directional and stabilizing selection; 2) directional selection; 3) unselected controls. The dynamics and variation of the character under directional selection was shown to be different in the stabilized and unstabilized lines. Coefficient of variation which increased in the unstabilized lines remained at the same level in the stabilized lines and in the controls. The results are in agreement with those of the previous experiment, where directional selection was conducted for a behavioral trait, which suggests general character of the relationships observed.     

Reaction norms across and genetic parameters at different temperatures for thorax and wing size traits in Drosophila aldrichi and D. buzzatii

Reaction norms across seven constant and one fluctuating temperature of development were measured for thorax length and several wing size traits for up to 10 isofemale lines of each of the cactophilic Drosophila species, D. aldrichi and D. buzzatii, originating from the same locality. Maximum thorax length was reached at different low to intermediate temperatures for the two species, whereas wing length was highest at the lowest temperature in both species. Various ratio parameters showed pronounced species differences. The reaction norm for the wing loading index (wing length/thorax length) decreased monotonically with temperature in both species, but was much steeper and spanned a wider range in D. aldrichi than in D. buzzatii, suggesting either that wing loading is not a good characterization of flight capacity or, more likely, that flight optimization does not occur in the same manner in both species. The vein ratio (distal length/proximal length of the third vein) increased with temperature in D. buzzatii but decreased in D. aldrichi. Wing development in the two species thus is very different, with the proximal part of the wing in D. buzzatii more closely allied to the thorax than to the distal part. Among line variation was significant for all traits in both species, and most pronounced for thorax length and the ratio parameters. Coefficients of variation were significantly different between the species for all traits, with those in D. aldrichi higher than in D. buzzatii. Genetic variance in plasticity was significant for all traits in D. buzzatii, but only for seven out of 12 in D. aldrichi. Additive genetic variances for all traits in both species were significantly larger than zero. Genetic correlations between thorax length and several wing length parameters, and between these and wing area, were positive and generally significant in both species. The genetic correlation between the distal and the proximal length of the third vein was not significantly different from zero in D. aldrichi, but negative and significant in D. buzzatii. Heritabilites varied significantly among temperatures for almost all traits in both species. Phenotypic variances were generally higher in D. aldrichi than in D. buzzatii, and commonly highest at the extreme temperatures in the former species. At the high temperature the genetic variances also were usually highest in D. aldrichi. The data clearly suggest that the process of thermal adaptation is species specific and caution against generalizations based on the study of single species.     

Mosaic Drosophila wings reveal regional heterogeneity in the guidance of ectopic axons

In most studies of axon guidance in the peripheral tissues of insects, the ability of experimentally perturbed axons to pathfind was examined only along their normal pathways. This means that regions normally devoid of axons have not been sampled for their ability to influence axonal trajectories. To examine this question, we have induced the formation of single sensory neurons in a variety of abnormal locations in the developing wing of Drosophila and have examined the course taken by their axons. The axons of such ectopic neurons have a regionally varying tendency to grow in the normal, proximal direction. This proximal bias approaches 100% for neurons located in the distal part of vein L2 and 70% in distal vein L4 but falls to chance (50%) along vein L5. Thus, neurons forming in ectopic regions of the wing, especially those found near the normal axon pathways (veins L1 and L3), have a high probability of growing axons in the correct direction. We conclude that information relevant to axon outgrowth is not restricted to the normal pathways. Whether this information is intrinsic or extrinsic to the neurons, and why its strength shows such conspicuous regional variation, awaits further study.     

Change in the system of wing venation of Drosophila melanogaster under heat shock and selection

A change in the system of wing venation of Drosophila melanogaster appeared in response to heat shock and positive selection pressure directed to restoring the normal formation of wing radial vein, L2, that had been violated earlier by the recessive mutation of radius incompletes. Positive selection was effective, L2 having been formed correctly and completely to 35 generation. Besides, (+)-selection was accompanied by appearance of a small fragment of an additional vein at the wing tip. Selection directed to increase of size of this fragment resulted in the sufficient changes in the system of wing venation as a whole. It is suggested that, during evolution, transformation of wing venation of Drosophila was effected by the change of the way of prepattern realization, whereas the cells of wing plate continued to allow the formation of veins practically over a whole area.     

Functional role of leg receptors of the cockroach Periplaneta americana in the system of walking control

This work deals with study of role of the hairplate and of campaniform sensillae (CS) on legs of the cockroach Periplaneta americana in the system of walking control. Three receptors were shown to induce their regulatory, correctional effect on the rhythm of the cockroach steps depending on the external circumstances. These effects are mainly realized only at slow walking.     

Neural projection patterns from homeotic tissue of Drosophila studied in bithorax mutants and mosaics.

The central projection patterns of sensory cells from the wing and haltere of Drosophila, as revealed by filling their axons with cobalt, consist of dorsal components arising from small campaniform sensilla and ventral components arising from large campaniform sensilla and from bristles. All of the bristles of the wing are innervated, some singly and some multiply. All three classes of sensilla are strongly represented on the wing, but the haltere carries primarily small campaniform sensilla and has a correspondingly minute ventral projection. In bithorax mutants in which the haltere is transformed into wing, ventral components are added to the projection pattern, while the dorsal components appear as if haltere tissue were still present. Thus, the three classes of receptors not only produce different projection patterns when they develop in their native mesothoracic segment, but also behave differently in the homeotic situation. Consequently, different developmental programs are inferred for each class. When somatic recombination clones of bithorax tissue are generated in phenotypically wild-type flies, they also produce ventral projections. However, these projections of mutant fibers into wild-type ganglia differ in certain details from the projections of mutant fibers into mutant ganglia. Thus, homeotic changes are inferred to occur in the CNS of mutant flies, but these are not required for the execution of those developmental instructions carried in the genome of large campaniform and bristle sensory cells which specify that their axons should grow ventrad in the CNS.     

The polarity of axon growth in the wings of Drosophila melanogaster

We have analyzed the growth of axons in the wings of the mutants Hairy wing and hairy of Drosophila melanogaster. These mutants produce many supernumerary bristle organs and sensilla campaniformia, whose axons grow between the two wing epithelia and can be visualized in both pupal and adult stages. The sensory axons of wild-type animals follow two paths in the wing, within longitudinal veins L1 and L3, and always grow with a distal to proximal polarity. In the mutants, all axons following these two paths likewise grow with correct polarity. Axons elsewhere in the wing, however, are found to grow in many different directions, including from proximal to distal and hence directly away from the central nervous system. A variety of patterns of axon growth and fasciculation are seen in different individuals. Only if the supernumerary axons encounter the two normal paths do they reliably grow toward the base of the wing. We conclude that these two paths provide polarity information for axon growth, information which is either not used or not available elsewhere in the wing in spite of the obvious morphological polarization of every epithelial cell. The time course of neural differentiation suggests that the normal sensory cells of mutant wings, which grow axons relatively early, may be the source of polarity information for the later-differentiating supernumerary cells.     

Fine structure of antennal sensilla coeloconica of culicine mosquitoes

The sensilla coeloconica (pegs in pits) previously mis-identified as campaniform organs, at the tip of the antennae of female Aedes aegypti L. and Culexpipiens (L.) are described. Each sensillum is innervated by three bipolar neurons: the dendrites of two are unbranched whereas the distal portion of the third is folded into tightly packed lamellae. One unbranched dendrite extends to the tip of the peg and the other ends near the base of the peg. The lamellae-bearing dendrite terminates 4-5 μ beneath the base of the peg. Chemo- and thermoreception are the proposed functions for the sensillum.     

Effect of genotypic environment on phenotypic manifestation of radius incompletus mutation in Drosophila melanogaster

Genetic analysis of marked regions of Drosophila chromosome 3 was performed in order to localize the "effective factors" of the polygene system that controls the expression of the limiting mutation in radius incompletus, the major-effect gene. The marked homozygous strain with genotype th st ri sr ca was crossed with the "selection" riSN strain. Contributions of the marked regions of chromosome 3 to the expression of the proximal and distal fragments of the wing radial vein were estimated. It was demonstrated that the th-st region of the marked strain contained a polygene determining a large positive contribution to the lengths of both fragments, whereas the st-ri region contained a polygene determining a large negative contribution to the length of the distal fragment compared to the riSN strain. Crossings were performed between strains that contained Mendelian mutations of the ri, ve, and vn major-effect genes of the wing vein patterns. Unexpectedly, a strong, non-additive effect of the interaction between these mutations was found. This effect was expressed as a complete disarrangement of the wing vein pattern. Each participant gene may be regarded as a large-effect polygene relative to the other genes.     

Variability of the quantitative and qualitative traits of Aedes dorsalis mosquitoes from larval cultures of varying densities

Larvae of Aedes dorsalis Mg. were maintained at the density of 0.05 and 0.5 spec./ml. It was noted that mosquitoes from overpopulated cultures grew smaller in size. The wings became shorter and more narrow by 4 to 6%. The wing reduction occurred on account of its distal elements (veins r3 and m2). Despite the decrease in the value of characters their variability decreased too, having increased only for wing width and vein mcu. In overpopulated cultures the wing length connection with veins r3 and m2 grew weaker in males while in females only such tendency was observed. Wing bilateral asymmetry was noted: left wing of females became wider and those of males wider and shorter. Analysis of variability of qualitative wing characters, which were singled out according to the venation pattern, has shown that of 9 studied characters only two depended on density (arrangement of corners of radial and medial vectors) and only in females. The role of such wing changes for swarming, active escaping from danger, direction and distance of flight of mosquitoes is discussed.     

The effect of isogenization on the phenotypic manifestation of quantitative traits in Drosophila melanogaster

A comparative analysis of the phenotypic values of the proximal and distal fragments of the radial wing vein was carried out in heterogeneous lines of Drosophila melanogaster and in isogenic lines derived from them with the help of a balancer line. The mean values of the traits in the isogenic lines were shown to significantly differ from the corresponding values in the "parental" heterogeneous lines. Apparently, the change in the trait values was caused by a double recombination exchange between the inverted and the "normal" chromosomes, which suggests partial crossing over suppression in the balancer lines.