Hemolymph ecdysteroids do not affect vitellogenesis in the lubber grasshopper

The role of hemolymph ecdysteroids in the reproduction of non-dipteran insects is unclear. We examine the role(s) of hemolymph ecdysteroids during egg production in the lubber grasshopper, Romalea microptera. In all individuals, hemolymph ecdysteroids rose to a sharp peak with similar maxima and then fell to undetectable levels. The time from the adult molt to the maximum ecdysteroid titer (E(max) titer) varied in response to food availability, whereas the time from E(max) titer to oviposition was unrelated to food availability. Because both the timing of egg production and the timing of E(max) responded similarly to environmental changes, ecdysteroids may be involved in egg production. We hypothesized that this role is the stimulation of vitellogenesis. Ovariectomized females had vitellogenin but no ecdysteroids, so ecdysteroids are not necessary for vitellogenin production. In addition, treatment of females with ecdysteroids altered neither Vg titers nor ovarian growth. Ovarian ecdysteriods increased at the same age in development as hemolymph ecdysteroids. In contrast to hemolymph ecdysteroids, ovarian ecdysteroids persisted until oviposition. Despite this, [(3)H]ecdysone injected into the hemolymph was detected later only at very low levels in the ovary, suggesting that hemolymph ecdysteroids are not sequestered by the ovary. In summary, our studies indicate that hemolymph ecdysteroids in adult females of the lubber grasshopper are associated with the timing of egg production, but they neither regulate vitellogenesis nor act as a source of ecdysteroids for the ovary.     

Plasticity and canalization in the control of reproduction in the lubber grasshopper

The ability to change reproductive tactics during adult developmentin response to environmental variation is predicted to enhancefitness. Many organisms show phenotypic plasticity early innon-embryonic development, but later exhibit phases of developmentalinflexibility (=canalization). Therefore, we studied reproduction-relatedhormones and proteins and their relationships to plasticityin the Eastern lubber grasshopper. Diet-switching experimentsdemonstrated plasticity early in the egg production cycle, buta switch to canalization late in the cycle. We measured developmentaltiters of 4 hemolymph compounds from single individuals fromadult molt until first oviposition. These 4 compounds were theegg-yolk precursor protein vitellogenin, juvenile hormone (thecentral regulator of insect reproduction), major hemolymph proteins,and ecdysteroids (the arthropod molting hormone that ultimatelyis stored in the egg). Using diet manipulations, we investigatedhow these developmental titers relate to the switch from plasticto canalized egg production. All 4 hemolymph compounds reachedtheir peak levels during the canalized phase, about 12 day beforeoviposition. Diet switches after these peak levels did not affectthe timing to oviposition. Therefore, these peak titers werephysiological events that occurred after the individual committedto laying. We compared these patterns in reproduction to thedevelopment toward adult molt, another major life-history eventin insects. We observed an extended canalized phase before theadult molt. This canalized phase always included a peak of ecdysteroids.The similar patterns in the physiology of these life-historyevents suggested that common limitations may exist in majordevelopmental processes of insects that are directed by hormones.     

Tests of the mouse visual system

To apply the approach of forward genetics (e.g., gene identification with mutagenesis and screening, followed by positional cloning) to the mouse, it is necessary to have available screening tests that can be applied rapidly to individual mice and that give a reliable assessment of visual function. This paper reviews the strengths and limitations of two anatomical tests related to visual function, fundus examination and retinal histological examination. Two tests that do not depend on behavior of a conscious animal are reviewed: the electroretinogram and the visual evoked potentials of the cortex. Eight behavioral tests are also summarized: maze-based tests, cued fear conditioning, tests based on conditioned suppression, visual placing, optokinetic nystagmus, pupillary reflex, and light-induced shifts in circadian phase. It is recommended that retinal histology, the electroretinogram, and visual-evoked potentials be used at the present time for screening because they assess the function and structure of the visual system rapidly and reliably. In fact, the electroretinogram (or visually evoked potentials) can be recorded from several animals simultaneously in response to the same stimulus. It is also recommended that efforts be made to develop more appropriate, automated, behavioral tests of visual perception than are now available, particularly tests that rely solely on rewarding visually evoked behavior. Two other promising behavioral tests are cued fear conditioning and variants of maze tests. Received: 17 December 1999 / Accepted: 17 December 1999     

Primary structure of an analog of crustacean pigment-dispersing hormone from the lubber grasshopper Romalea microptera

An octadecapeptide capable of inducing pigment dispersion in the chromatophores of the fiddler crab Uca pugilator has been isolated from lyophilized heads of the lubber grasshopper Romalea microptera. This pigment-dispersing factor (PDF) was purified by gel filtration, ion-exchange chromatography, partition chromatography, and reversed-phase high performance liquid chromatography. Automated gas-phase sequencing, followed by the identification of the carboxyl-terminal amide, established the primary structure of this PDF as Asn-Ser-Glu-Ile-Ile-Asn-Ser-Leu-Leu-Gly-Leu-Pro-Lys-Leu-Leu-Asn-Asp-Ala- NH2. This structure was confirmed by chemical synthesis and by demonstrating that the synthetic and native PDF displayed identical chromatographic behavior and biological activity. The Romalea PDF is structurally related to the crustacean pigment-dispersing hormones (PDHs), which are also octadecapeptides. The sequence of grasshopper PDF shows 78% homology with beta-PDH (from the crabs U. pugilator and Cancer magister) and 50% homology with alpha-PDH (from the prawn Pandalus borealis). This study provides the first direct chemical evidence for the structural relatedness of insect PDF to the crustacean PDHs, thus identifying them as an authentic family of arthropod peptides.     

Sequence analyses of two neuropeptides of the AKH/RPCH-family from the lubber grasshopper, Romalea microptera

Two neuropeptides with adipokinetic activity in Locusta migratoria and hypertrehalosaemic activity in Periplaneta americana were purified by high-performance liquid chromatography from the corpus cardiacum of the lubber grasshopper, Romalea microptera. The sequences of both peptides, designated Ro I and Ro II, were determined by gas-phase sequencing employing Edman degradation after the N-terminal pyroglutamate residue was enzymatically deblocked, as well as by fast atom bombardment mass spectrometry. Ro I was found to be a decapeptide with the primary structure: pGlu-Val-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2, whereas Ro II is an octapeptide with the structure: pGlu-Val-Asn-Phe-Ser-Thr-Gly-Trp-NH2. Ro II is identical with AKH-G isolated from the cricket Gryllus bimaculatus. Synthetic materials having the assigned structures were found to be chromatographically, mass spectrometrically, and biologically indistinguishable from the natural peptides, confirming the sequences and establishing the Romalea peptides as members of the AKH/RPCH-family of peptides.     

Allatotropin regulation of juvenile hormone synthesis by the corpora allata from the lubber grasshopper, Romalea microptera

The in vitro synthesis of juvenile hormone (JH) by corpora allata (CA) from the lubber grasshopper (Romalea microptera) was stimulated by low concentrations of brain extract and this effect was reduced at higher concentrations, suggesting the presence of allatotropin (AT) and allatostatin (AST) factors in the brain. The AT activity of brain extracts caused a rapid and reversible stimulation and appeared to be a peptide(s). Reversed phase (C18) HPLC analysis of brain extracts disclosed two peaks of AT activity but no significant AST activity. Manse-AT, Schgr-NPF, and Locmi-FLRF had no effect on JH synthesis by lubber CA, indicating that the Rommi-AT factors are distinct from these peptides. High concentrations of Dippu-AST-7 and Grybi-AST-1 inhibited JH synthesis, implying that AST factors might be present in lubber grasshoppers. CA response to AT activity of brain extracts varied during the oviposition cycle ( approximately 35 days), with the maximum response occurring on days 16-18. AT activity of brain extracts also varied during the cycle, being highest on day 25. Our data suggest that the lubber CA is largely regulated by AT activity, and that JH synthesis reflects both CA response to AT activity and the level of AT activity in the brain.     

Sex-based divergence in head shape and diet in the Eastern lubber grasshopper (Romalea microptera)

Biologists are becoming increasingly aware of sex-based differences in ecologically important traits (locomotor performance, feeding morphology, thermoregulatory behavior). Yet, the overwhelming majority of these studies have been performed on vertebrates, despite often striking examples of sexual size dimorphism among the insects. Here, I tested whether adult male and female Eastern lubber grasshoppers differ in size/shape and feeding ecology. The morphological data clearly showed sex-based differences in several aspects of head and body size, with females being significantly larger in all aspects. Moreover, the sexes also differed in two aspects of size-adjusted morphology: head width and pronotum width, with females having relatively wider heads and thoraxes than males. Multiple regression analysis indicated that width of consumed foliage was positively related to pronotum width and foliage thickness was positively related to pronotum width, head width, and size-adjusted head width. Females consumed wider and thicker foliage (primarily smooth cord grass, Spartina alterniflora) than males, which most frequently consumed the narrow-leafed forb hemp sesbania (Sesbania macrocarpa). Therefore, the sex-based differences in size and shape in this grasshopper are correlated with differences in consumed foliage shape.     

Development of a toxic bait for control of eastern lubber grasshopper (Orthoptera: Acrididae)

This study assessed baits for eastern lubber grasshopper, Romalea guttata (Houttuyn). When offered a choice among several grain-based baits (rolled oats, wheat bran, oat bran, yeast, corn meal, cornflakes) and vegetable oils (canola, corn, peanut, soybean), eastern lubber grasshopper adults preferred bait consisting of wheat bran carrier with corn oil as an added phagostimulant. Other carriers were accepted but consumed less frequently. Discrimination by eastern lubber grasshoppers among oils was poor. Similarly, addition of flavorings (peppermint, anise, lemon, banana) resulted in few significant effects. The carbaryl, wheat bran, and oil bait developed in this study was effective at causing eastern lubber grasshopper mortality in field-cage studies. Significant mortality occurred even though grasshoppers had to locate dishes of bait in a large cage, and could feed on daylilies, or grass growing through the bottom of the cage, rather than on the bran flakes. Consumption of as little as a single carbaryl-treated bran flake could induce mortality, although individuals varied greatly in their susceptibility. The bait matrix developed in this study was readily consumed when in the presence of some plant species. We expect that wheat bran and corn oil bait would be most effective as protection for less preferred plants (tomato, pepper, eggplant, leek, parsley, fennel, daylily, lily of the Nile, and canna lily) because baits were readily consumed in the presence of these plants. Plants that are readily consumed in the presence of bait (preferred plants) included butter crunch lettuce, carrot, yellow squash, cauliflower, collards, green onion, chive, cucumber, cabbage, cantalope, endive, red leaf lettuce, society garlic, caladium, and amaryllis. Baits are likely to be less effective in the presence of such plants. On average, vegetables in Solanaceae (i.e., tomato, pepper, and eggplant) and Apiaceae (i.e., fennel and parsley) elicited high levels of bait-feeding activity, indicating that these vegetables were not highly preferred. The plants tested from Liliaceae, Cucurbitaceae, Asteraceae, and Brassicaceae elicited an intermediate-to-low level of bait feeding.     

The resolution and discrimination of images in the visual system

We analysed the conformity of optic and retinal cones anatomy factors by the two-point test. Obtained by F. Campbell and R. W. Gubish, the point spread function has a width of about 1 arc min. Cones sizes are equal to 0.5 arc min in the fovea. Functional pixel consists of 3-5 cones under the point spread function. Such an organisation in very useful in decreasing the samping noise of receptors. We carried out psychophysical investigations to show a consensus among the optic, receptors', and neuronal levels. In experiments we studied changes of the two-point pattern perception in respect to the points separation, measured the orientation threshold of small size stimuli. Data were compared with optical point-spread function, the hexagonal mosaic of cones, and line spread function of spatial elements, which form spatial frequency channels at the cortical level.     

Sensitivity variations in the visual system,contrast resolution and eye movements

Attention is drawn to the fact that under normal visual conditions the sensitivity of the receptor units of the visual system are subject to spatial and temporal variations, and that consequently in performing pattern recognition the visual cortex has to discriminate between external luminance structure and internal sensitivity structure. It is suggested that eye movements are the method by which this discrimination is performed. In a simplified model analysis it is shown that eye movements are a suitable mechanism for this discrimination. Implications of this model for detection threshold and stabilized retinal images are discussed. A new interpretation of the adaptation to sine wave grids is given.     

The B-chromosome system of the grasshopper Melanoplus femur-rubrum

In a sample of 85 males of the grasshopper Melanoplus femur-rubrum, three different supernumerary chromosomes (B-chromosomes) were observed: a medium-sized metacentric, B^M, present in 12.9% of the males and two small telocentrics, B^T and B^t, present in 8.2% and 3.5% of the males, respectively. The B^M element is mitotically stable, while the B^T and B^t elements are mitotically unstable, exhibiting numerical variation among testicular follicles. The mean number of B's per male (testis) is 1.00, 1.62, and 1.38 for the B^M, B^T, and B^t elements, respectively. A study of chiasma frequency among A-chromosomes revealed that there are no significant differences among the zero B and various B classes either for chiasma frequency or for the variation in chiasma frequency between individuals. There was, however, evidence for a higher within-individual variation in B-containing males when these were pooled. Cells with two B^t-chromosomes were regularly missing the smallest pair of A-chromosomes, suggesting that the B^t element induces non-disjunction of a pair of A-chromosomes and, possibly, that the B^t-chromosome is derived from the missing A-chromosome.Portions of this study were submitted by R. T. Stephens in partial fulfillment of the requirements for the degree of Master of Arts, Department of Biology, State University College, New Paltz, New York.     

Temperature compensation in the nervous system of the grasshopper

Abstract The wind-sensitive head hair neurones of the grasshopper Schistocerca americana (Drury) are influenced by temperature, increasing the number of spikes fired in response to a given hair deflection as temperature increases. Because these neurones show similar increases in spike output for greater hair deflections, an interneurone which receives their input would not be able to distinguish changes in stimulus strength from changes in temperature, unless the effects of temperature were compensated or independently measured. This study examines the effects of temperature on the output of the tritocerebral commissure giant (TCG), an interneurone that receives wind hair input. Some wind hairs provide excitatory input to the TCG, while others are inhibitory (Bacon & Möhl, 1983). Temperature variations similar to those measured in freely moving animals were applied to the wind hairs and TCG while the interneurone's spike output was recorded. Two manipulations resulted in temperature compensated outputs from the TCG: (1) When both excitatory and inhibitory hair fields were stimulated simultaneously, the temperature sensitivity of the interneurone's spike output was significantly lower than when the excitatory hairs alone were stimulated. (2) The spike output of the TCG showed very little sensitivity to temperature changes which occurred only at its wind hair inputs, the temperature of the interneurone itself remaining constant. It is therefore possible for the output of a neural circuit to be temperature compensated even though the circuit itself may be composed of temperature-sensitive units. Possible mechanisms by which temperature compensation may be produced in the TCG are discussed, and the behavioural relevance of the conditions under which TCG output is temperature compensated is considered.     

The reactions of three species of grasshopper to simple visual stimuli at different temperature-humidity conditions

The effect of the temperature-humidity factor on the reaction of two different visual stimuli has been investigated with Chorthippus brunneus (Thunb.) (= Chorthippus bicolor Charp.), Chorthippus longicornis (Latr.) (= Ch. parallelus Zett.) and Mecostethus grossus (L.). At low and high temperatures (high and low relative humidities), the three species show a greater preference for surroundings with vertical stripes than for white surroundings. At medium temperature and relative humidity, the preference for white surroundings is greater than for surroundings with vertical stripes. In a comparison between the three species at high temperature, they show regarding their intensity of preference for surroundings with vertical stripes a ranking order which is identical with that of their preference for dense grass vegetation in natural environments. In a comparison between and at high temperature, show a greater preference for surroundings with vertical stripes than .

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zusammenfassung Die Wirkung des Temperatur-Luftfeuchtigkeits-Faktors auf die Reaktion gegenüber zwei optischen Reizen wurde bei Chorthippus brunneus (Thunb.) (= Chorthippus bicolor Charp.). Chorthippus longicornis (Latr.) (= Ch. parallelus Zett.) und Mecostethus grossus (L.) untersucht. Bei niederen und hohen Temperaturen (hoher und niederer relativer Luftfeuchtigkeit) zeigen die drei Arten eine größere Bevorzugung für Umgebungen mit vertikalen Streifen als für weiße Umgebungen. Bei mittlerer Temperatur und relativer Feuchtigkeit ist die Bevorzugung weißer Umgebung größer als für Umgebungen mit vertikalen Streifen. Bei einem Vergleich der drei Arten bei hoher Temperatur ergibt sich hinsichtlich der Stärke ihrer Bevorzugung für vertikal gestreifte Umgebung eine Rangfolge, die mit der ihrer Bevorzugung dichter Grasvegetation in natürlicher Umgebung identisch ist. Bei einem Vergleich zwischen und bei hoher Temperatur zeigen die eine größere Präferenz für Umgebung mit Vertikalstreifung als die .

     

Effect of refractive error in visual tests with sinusoidal gratings

While sinusoidal grating stimuli are finding increasing application in clinical tests for visual disturbance, the possible effects on the test results of simple defocus of the retinal image, due to refractive or accommodative error, are not always acknowledged. Theoretical considerations and experimental measurements emphasize that the degradation in visual performance due to such defocus effects is minimal when the eye pupil is small and the spatial frequency of the grating test objects is low.     

Neuronal determination during embryonic development of the grasshopper nervous system

We have examined the roles of cell lineage and interactions in the determination of individual identified neurons in the grasshopper embryo by selective ablations of individual cells and/or their neighbors at successive stages following their birth. The neurons in the grasshopper central nervous system (CNS) are produced by two types of identifiable neuronal precursor cells: neuroblasts (NBs), which generate most of the neurons, and midline precursors (MPs), which generate only a few. NBs divide asymmetrically in a stem cell fashion to generate a chain of ganglion mother cells (GMCs) which then divide once more symmetrically to produce pairs of sibling neurons: MPs cleave once to generate a single pair of sibling neurons. We analyzed the determination of (1) the pair of sibling progeny produced by midline precursor 3 (MP3) and the determination of (2) the pair of sibling progeny produced by the first GMC from neuroblast 1-1 (NB 1-1); in each case the siblings normally differentiate into morphologically distinct neurons. Our results indicate that both pairs of neuronal progeny (1) are born equivalent, (2) become determined by cell interactions early in their development before axonogenesis, and (3) demonstrate a hierarchy of fates with one fate dominant over the other. These results suggest a common pattern of neuronal determination in the grasshopper and possibly all insect embryos.