Ancient trans-Atlantic flight explains locust biogeography: molecular phylogenetics of Schistocerca.

The desert locust (Schistocerca gregaria) has been an important agricultural pest at least since biblical times. Although the ecology, physiology and behaviour of this insect species have been well characterized, its biogeographical origins and evolutionary history are more obscure. Schistocerca gregaria occurs throughout Africa, the Middle East and Western Asia, but all other species in the genus Schistocerca are found in the New World. Because S. gregaria has the capacity for extreme long-distance movement associated with swarming behaviour, dispersal may have played an important role in determining current distribution patterns. Some authors have argued that S. gregaria is the product of an eastward trans-Atlantic dispersal from North America to Africa; others consider it more likely that the New World taxa are the product of westward dispersal from Africa. Here, we present a mitochondrial DNA phylogeny of Schistocerca species that supports the monophyly of New World species (including the Galapagos endemic Halmenus) relative to S. gregaria. In concert with observed patterns of molecular divergence, and in contrast to previous morphological studies, our analysis indicates a single trans-Atlantic flight from Africa to South America, followed by extensive speciation and ecological divergence in the New World.

Acylthioxanthenes: agents which selectively reduce decerebrate rigidity in the cat.

A series of 2-acylthioxanthene-delta 9 (gamma)-propylamines was synthesized, and their effect of reducing the intercollicular decerebrate rigidity in the cat was evaluated. The compound exhibiting the greatest separation between the dosage that reduced rigidity and that which caused sedation was (Z)-2-propionyl-9-[3-(dimethylamino)propylidene]thioxanthene. The separation of Z and E isomers was monitored by 1H NMR spectroscopy, using an europium shift reagent.

Syntheses and biological activities of potent potassium channel openers derived from (+/-)-2-oxo-1-pyridin-3-yl-cyclohexanecarbothioic acid methylamide: new potassium channel openers.

The syntheses and biological activities of (+/-)-2-(cyanomethylene)-1-pyridin-3-ylcyclohexanecarbothioic++ + acid methylamide (6) and trans-(+/-)-2-(cyanomethyl)-1-pyridin-3-ylcyclohexanecarbothioic acid methylamide (14) derived from (+/-)-2-oxo-1-pyridin-3-ylcyclohexanecarbothioic acid methylamide (4) are reported. Compounds were tested for antagonism of potassium-induced contraction of de-endothelialized rat aorta. The effects of modification of 6 and 14 on in vitro K(+)-channel opening activity are presented. These new series of potassium channel openers so derived are best exemplified by (+/-)-2-[2-(phenylsulfanyl)ethylidene]-1-pyridin-3-ylcyclohexan ecarbothioic acid methylamide (13d, RP 66266) and trans-(+/-)-2-[2-[(phenylsulfonyl)amino]ethyl]-1-pyridin-3- ylcyclohexanecarbothioic acid methylamide (25a, RP 66784), which have IC90 values of 3 and 0.3 nM, respectively. The potency of the most active compounds indicates a possible interaction at an extra binding site. The compounds described herein are potential antihypertensive and antianginal agents.

Synthesis and biological activity of trans(+-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothiopyrancarbothioamide 1-oxide (RP 49356) and analogues: a new class of potassium channel opener.

The synthesis and biological activity of trans-(+-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothiopyrancarbothioamid+ ++ e 1-oxide (8a, RP 49356) and analogues is reported. These compounds constitute a new structural class of K(+)-channel opener. The effects of changes in pyridyl group, thioamide, and thiane ring on in vitro K(+)-channel opening reactivity are discussed. A 3-pyridyl or 3-quinolyl group, a small N-alkyl thioamide function, and a thiane oxide ring, in which the sulfoxide is in a trans relationship to the thioamide, are preferred for activity. Selected compounds were tested intravenously in the normotensive anaesthetized rat for hypotensive effects, and the activities reflect their in vitro K(+)-channel opening activity. This led to further evaluation of compound 8a and the selection of the (-)-enantiomer 8b (RP 52891) for development as an antihypertensive and antianginal agent.

Individual variation in response to altitude training.

Moderate-altitude living (2,500 m), combined with low-altitude training (1,250 m) (i.e., live high-train low), results in a significantly greater improvement in maximal O2 uptake (V(02)max) and performance over equivalent sea-level training. Although the mean improvement in group response with this "high-low" training model is clear, the individual response displays a wide variability. To determine the factors that contribute to this variability, 39 collegiate runners (27 men, 12 women) were retrospectively divided into responders (n = 17) and nonresponders (n = 15) to altitude training on the basis of the change in sea-level 5,000-m run time determined before and after 28 days of living at moderate altitude and training at either low or moderate altitude. In addition, 22 elite runners were examined prospectively to confirm the significance of these factors in a separate population. In the retrospective analysis, responders displayed a significantly larger increase in erythropoietin (Epo) concentration after 30 h at altitude compared with nonresponders. After 14 days at altitude, Epo was still elevated in responders but was not significantly different from sea-level values in nonresponders. The Epo response led to a significant increase in total red cell volume and V(O2) max in responders; in contrast, nonresponders did not show a difference in total red cell volume or V(O2)max after altitude training. Nonresponders demonstrated a significant slowing of interval-training velocity at altitude and thus achieved a smaller O2 consumption during those intervals, compared with responders. The acute increases in Epo and V(O2)max were significantly higher in the prospective cohort of responders, compared with nonresponders, to altitude training. In conclusion, after a 28-day altitude training camp, a significant improvement in 5,000-m run performance is, in part, dependent on 1) living at a high enough altitude to achieve a large acute increase in Epo, sufficient to increase the total red cell volume and V(O2)max, and 2) training at a low enough altitude to maintain interval training velocity and O2 flux near sea-level values.

"Living high-training low" altitude training improves sea level performance in male and female elite runners.

Acclimatization to moderate high altitude accompanied by training at low altitude (living high-training low) has been shown to improve sea level endurance performance in accomplished, but not elite, runners. Whether elite athletes, who may be closer to the maximal structural and functional adaptive capacity of the respiratory (i.e., oxygen transport from environment to mitochondria) system, may achieve similar performance gains is unclear. To answer this question, we studied 14 elite men and 8 elite women before and after 27 days of living at 2,500 m while performing high-intensity training at 1,250 m. The altitude sojourn began 1 wk after the USA Track and Field National Championships, when the athletes were close to their season's fitness peak. Sea level 3,000-m time trial performance was significantly improved by 1.1% (95% confidence limits 0.3-1.9%). One-third of the athletes achieved personal best times for the distance after the altitude training camp. The improvement in running performance was accompanied by a 3% improvement in maximal oxygen uptake (72.1 +/- 1.5 to 74.4 +/- 1.5 ml x kg(-1) x min(-1)). Circulating erythropoietin levels were near double initial sea level values 20 h after ascent (8.5 +/- 0.5 to 16.2 +/- 1.0 IU/ml). Soluble transferrin receptor levels were significantly elevated on the 19th day at altitude, confirming a stimulation of erythropoiesis (2.1 +/- 0.7 to 2.5 +/- 0.6 microg/ml). Hb concentration measured at sea level increased 1 g/dl over the course of the camp (13.3 +/- 0.2 to 14.3 +/- 0.2 g/dl). We conclude that 4 wk of acclimatization to moderate altitude, accompanied by high-intensity training at low altitude, improves sea level endurance performance even in elite runners. Both the mechanism and magnitude of the effect appear similar to that observed in less accomplished runners, even for athletes who may have achieved near maximal oxygen transport capacity for humans.

Degree of arterial desaturation in normoxia influences VO2max decline in mild hypoxia.

PURPOSE: Elite endurance athletes display varying degrees of pulmonary gas exchange limitations during maximal normoxic exercise and many demonstrate reduced arterial O2 saturations (SaO2) at VO2max--a condition referred to as exercise induced arterial hypoxemia (EIH). We asked whether mild hypoxia would cause significant declines in SaO2 and VO2max in EIH athletes while non-EIH athletes would be unaffected. METHODS: Nineteen highly trained males were divided into EIH (N = 8) or Non-EIH (N = 6) groups based on SaO2 at VO2max (EIH <90%, Non-EIH >92%). Athletes with intermediate SaO2 values (N = 5) were only included in correlational analyses. Two randomized incremental treadmill tests to exhaustion were completed--one in normoxia, one in mild hypoxia (FIO2 = 0.187; approximately 1,000 m). RESULTS: EIH subjects demonstrated a significant decline in VO2max from normoxia to mild hypoxia (71.1+/-5.3 vs. 68.1+/-5.0 mL x kg(-1) min(-1), P<0.01), whereas the non-EIH group did not show a significant deltaVO2max (67.2+/-7.6 vs. 66.2+/-8.4 mL x kg(-1) x min(-1)). For all 19 athletes, SaO2 during maximal exercise in normoxia correlated with the change in VO2max from normoxia to mild hypoxia (r = -0.54, P<0.05). However, the change in SaO2 and arterial O2 content from normoxia to mild hypoxia was equal for both EIH and Non-EIH (deltaSaO2 = 5.2% for both groups), bringing into question the mechanism by which changes in SaO2 affect VO2max in mild hypoxia. CONCLUSIONS: We conclude that athletes who display reduced measures of SaO2 during maximal exercise in normoxia are more susceptible to declines in VO2max in mild hypoxia compared with normoxemic athletes.

Expiratory flow limitation confounds ventilatory response during exercise in athletes.

INTRODUCTION: A significant number of highly trained endurance runners have been observed to display an inadequate hyperventilatory response to intense exercise. Two potential mechanisms include low ventilatory responsiveness to hypoxia and ventilatory limitation as a result of maximum expiratory flow rates being achieved. PURPOSE: To test the hypothesis that expiratory flow limitation can complicate determination of ventilatory responsiveness during exercise the following study was performed. METHODS/MATERIALS: Sixteen elite male runners were categorized based on expiratory flow limitation observed in flow volume loops collected during the final minute of progressive exercise to exhaustion. Eight flow limited (FL) (VO2max, 75.9+/-2.4 mL x kg(-1) x min(-1); expiratory flow limitation, 47.3+/-20.4%) and eight non-flow limited subjects (NFL) (VO2max, 75.6+/-4.8 mL x kg(-1) x min(-1); expiratory flow limitation, 0.3+/-0.8%) were tested for hypoxic ventilatory responsiveness (HVR). RESULTS: Independent groups ANOVA revealed no significant differences between FL and NFL for VO2max, VE max (136.2+/-16.0 vs 137.5+/-21.6 L x min(-1)), VE/VO2, (28.4+/-3.2 vs 27.6+/-2.9 L x lO2(-1)), VE/VCO2 (24.8+/-3.1 vs 24.4+/-2.0 L x lCO2(-1)), HVR (0.2+/-0.2 vs 0.3+/-0.1 L x %SaO2(-1)), or SaO2 at max (89.1+/-2.4 vs 86.6+/-4.1%). A significant relationship was observed between HVR and SaO2 (r = 0.92, P < or = 0.001) in NFL that was not present in FL. Conversely, a significant relationship between VE/VO2 and SaO2 (r = 0.79, P < or = 0.019) was observed in FL but not NFL. Regression analysis indicated that the HVR-SaO2 and SaO2-VE/VO2 relationships differed between groups. DISCUSSION: When flow limitation is controlled for, HVR plays a more significant role in determining SaO2 in highly trained athletes than has been previously suggested.

Development of phenotypic differences in sensillum populations on the antennae of a grasshopper, Schistocerca americana.

The development of diet-induced phenotypic differences in numbers of sensilla on the antennae of the grasshopper Schistocerca americana was studied using the exuviae produced at each molt. This made it possible to follow changes within an individual insect. In the first instar, insects had similar numbers of four sensillum types: uniporous trichoid sensilla, coeloconic sensilla, and large and small multiporous basiconic sensilla. Rearing on lettuce resulted in sixth instars with greater numbers of three sensillum types than siblings reared on an artificial diet. The first statistically significant differences between treatments in numbers of trichoid sensilla and large basiconic sensilla occurred in the third and fourth instars, respectively. No major reductions in sensillum numbers occurred at any time and the phenotypic differences resulted from differences in the numbers added at each molt.

Variability of gustatory responsiveness to phenylalanine in the generalist caterpillar, Grammia geneura (Lepidoptera, Arctiidae).

Electrophysiological recordings were made from maxillary taste sensilla of the caterpillar Grammia geneura, stimulated with the deterrent amino acid, phenylalanine. High levels of variability were noted and different potential causes examined. Little variation was detected with respect to standardized intra-individual tests, phenylalanine concentration, previous food type or time of day. Some changes were observed in relation to age, but could not account for the overall variation found. Major differences in responsiveness depended on cohort and the possibility of important genetic differences is discussed.

Exercise economy does not change after acclimatization to moderate to very high altitude.

For more than 60 years, muscle mechanical efficiency has been thought to remain unchanged with acclimatization to high altitude. However, recent work has suggested that muscle mechanical efficiency may in fact be improved upon return from prolonged exposure to high altitude. The purpose of the present work is to resolve this apparent conflict in the literature. In a collaboration between four research centers, we have included data from independent high-altitude studies performed at varying altitudes and including a total of 153 subjects ranging from sea-level (SL) residents to high-altitude natives, and from sedentary to world-class athletes. In study A (n=109), living for 20-22 h/day at 2500 m combined with training between 1250 and 2800 m caused no differences in running economy at fixed speeds despite low typical error measurements. In study B, SL residents (n=8) sojourning for 8 weeks at 4100 m and residents native to this altitude (n=7) performed cycle ergometer exercise in ambient air and in acute normoxia. Muscle oxygen uptake and mechanical efficiency were unchanged between SL and acclimatization and between the two groups. In study C (n=20), during 21 days of exposure to 4300 m altitude, no changes in systemic or leg VO(2) were found during cycle ergometer exercise. However, at the substantially higher altitude of 5260 m decreases in submaximal VO(2) were found in nine subjects with acute hypoxic exposure, as well as after 9 weeks of acclimatization. As VO(2) was already reduced in acute hypoxia this suggests, at least in this condition, that the reduction is not related to anatomical or physiological adaptations to high altitude but to oxygen lack because of severe hypoxia altering substrate utilization. In conclusion, results from several, independent investigations indicate that exercise economy remains unchanged after acclimatization to high altitude.

Entomology in the twentieth century.

A number of landmark events in applied entomology are listed together with some insect-related studies that have had a major impact on biology in general. In large part, however, advances in our understanding of insects have depended on technological advances, especially in the second half of the century. The exponential increase in the ease and extent of communication has been critical. Sometimes, as in the field of insect/plant relations, the ideas of a few individuals have been critical with technological advances having a facilitating role. Elsewhere, as in the study of olfaction, major changes in understanding have been directly dependent on new technology. Very brief accounts of the impacts on insect-related science of developments in the fields of radio, radioactivity, immunology, imaging techniques, and chemical analysis are given. Despite the importance of technology, the lovers of their insects continue to have a key role.

Contact chemoreception in feeding by phytophagous insects.

Gustatory receptors associated with feeding in phytophagous insects are broadly categorized as phagostimulatory or deterrent. No phytophagous insect is known that tastes all its essential nutrients, and the ability to discriminate between nutrients is limited. The insects acquire a nutritional balance largely "adventitiously" because leaves have an appropriate chemical composition. Sugars are the most important phagostimulants. Plant secondary compounds are most often deterrent but stimulate phagostimulatory cells if they serve as host-indicating sign stimuli, or if they are sequestered for defense or used as pheromone precursors. The stimulating effects of chemicals are greatly affected by other chemicals in mixtures like those to which the sensilla are normally exposed. Host plant selection depends on the balance of phagostimulatory and deterrent inputs with, in some oligophagous and monophagous species, a dominating role of a host-related chemical. Evolution of phytophagy has probably involved a change in emphasis in the gustatory system, not fundamentally new developments. The precise role of the gustatory systems remains unclear. In grasshoppers, it probably governs food selection and the amounts eaten, but in caterpillars there is some evidence that central feedbacks are also involved in regulating the amount eaten.

An odor discrimination model with application to kin recognition in social insects.

The problem of discriminating between a number of similar, nonspecific odors is discussed with special reference to the phenomenon of kin and nestmate discrimination in social insects. Guided by the basic physiological and anatomical features of the olfactory sensory receptors and neural pathways in insects, a model is presented for the process of odor discrimination. The model hypothesizes neural processing capabilities that include the logarithmic transformations of electrical potentials to generate a scalar quantity representing the "similarity" of two multivalued signals. The model thereby quantifies the notion of phenotype matching that appears in the kin recognition literature, and makes the concept of a recognition template more precise. The hypotheses underlying the model suggest a number of neurophysiological studies that should be undertaken, while the model itself provides a basis for integrating several areas of research pertaining to kin recognition in particular species of animals.

Electrophysiological responses of taste cells to nutrient mixtures in the polyphagous caterpillar of Grammia geneura.

In a normally feeding insect, the taste receptors are exposed to complex mixtures of chemicals, not single compounds. We investigate the responses of neurons in the galeal sensilla of the caterpillar of Grammia geneura to mixtures of nutrient compounds at concentrations occurring in plants. Compounds that stimulated the same neuron were generally additive in their effects in binary mixtures. Amino acids that did not stimulate usually had no effect in mixtures with a stimulating compound, but glutamic acid reduced the response to serine in the medial sensillum. Nutrient compounds that stimulated different cells in a sensillum acted independently of each other. Complex mixtures of amino acids resembling samples of free amino acids from three host plants were less stimulating than expected from their molar concentrations. In host plant selection, the response from the medial sensillum is probably dominated by sucrose; unless sucrose levels are low, amino acids will contribute little to sensory input because they stimulate the same cell as sucrose. In the lateral sensillum, amino acids act independently of sugars. The limited contact chemosensory array of caterpillars seems inadequate to allow them to make fine distinctions between plants on the basis of their free amino acids.

Taste cell responses in the polyphagous arctiid, Grammia geneura: towards a general pattern for caterpillars.

The caterpillars of Grammia geneura are polyphagous as individuals. Electrophysiological responses of its medial and lateral galeal styloconic sensilla to 21 amino acids, 6 carbohydrates, 10 chemically diverse plant secondary compounds and two inorganic salts were examined. In the medial sensillum, a single cell responded to 8 amino acids, 3 carbohydrates, and the iridoid, catalpol, which is present in a favored hostplant. In the lateral sensillum, one cell responded to amino acids and another to fructose. Two cells in each sensillum responded to secondary compounds and it is suggested that the same cells are stimulated by inorganic salts. There was no evidence of a separate salt-sensitive cell. Phenylalanine stimulated a deterrent cell in the medial sensillum and was behaviorally deterrent. Some essential amino acids did not stimulate any cells and it is suggested that a small number of amino acids (sometimes non-essential) may serve as indicators of nutrient quality. Sugars probably serve as the primary phagostimulants because they are in relatively high concentrations in plants. It is proposed that taste receptor cells should be categorized primarily by their behavioral effects as phagostimulatory or deterrent, rather than their specific ranges of responsiveness. This would emphasize the basic similarities across taxa.

Control of muscle degeneration following autotomy of a hindleg in the grasshopper, Barytettix humphreysii.

When the grasshopper, Barrytettix humphreysii, sheds a hindlimb during autotomy, certain thoracic muscles degenerate although they are neither directly damaged nor denervated. Muscle degeneration is induced when a leg nerve (N5) that does not innervate the thoracic muscles is severed. Together these results suggest that transneuronal mechanisms influence muscle survival. To further characterize this autotomy-induced process, we studied the degeneration of a thoracic tergotrochanteral muscle (M#133b,c) following autotomy or experimental manipulation in adult animals. Its degeneration is correlated with reduced activity of its neural input and occurs by programmed cell death (PCD). PCD onset is variable between individual muscle fibers, indicating that the trigger of degeneration is fiber specific. Muscle degeneration appears to be triggered by the loss of proprioceptive input from the autotomized limb, since severing of axons from proprioceptive organs, but not exteroceptive chemo- or mechanoreceptors, leads to muscle degeneration. Muscle disuse, neuronal degeneration, or changes in juvenile hormone titer do not appear to play a role in autotomy-induced degeneration. We propose that the loss of proprioceptive input from proximal campaniform sensilla on the tibia deafferents the thoracic muscle motor neurons and leads to a decrease in their activity. Muscle degeneration is ultimately triggered by the loss of normal neural activity.

Sensitivity to chemically diverse phagostimulants in a single gustatory neuron of a polyphagous caterpillar.

Caterpillars of the arctiid moth, Grammia geneura, are polyphagous, but species of Plantago are amongst their preferred food plants. A neuron in the medial styloconic sensillum on the galea has been shown to have a general phagostimulatory function. Experiments with binary mixtures and cross-adaptation have demonstrated that it responds to some sugars, to several amino acids, and also to catalpol. Catalpol is a plant secondary compound in Plantago and a phagostimulant for the caterpillars. The possible significance of combining sensitivity to nutrient compounds with sensitivity to a secondary compound is discussed.