Eric C. Toolson

Diffusion of water through the arthropopd cuticle: Thermodynamic consideration of the transition phenomenon☆

Abstract 1. |The justification for the use of saturation deficit to correct measured cuticular permeabilities for thermally-induced changes in diffusion gradients is shown to be specious. 2. (2)|Thermodynamic considerations reveal that diffusion gradients are linearly increasing functions of temperature under the conditions used in cuticular permeability studies. 3. (3)|At temperatures below the melting point of the epicuticlar lipids, thermally-induced changes in cuticular permeability are accurately described by a simple Boltzmann temperature function. 4. (4)|Abrupt transitions in the physical state of arthropoid cuticular lipids that have been reported for many specieis are probably artifacts.

Temperature Effects on Epicuticular Hydrocarbons and Sexual Isolation in Drosophila mojavensis

Drosophila mojavensis is found in several geographically separate regions of the Sonoran Desert of North America. Within each area, it utilizes different host plants as its primary breeding site. When flies from two of these regions, Baja California and Sonora (including southern Arizona) are raised in the laboratory and then placed together to mate, a significant degree of sexual isolation is observed (Zouros and D’Entremont, 1980; Koepfer, 1987a, b). This isolation is due largely to a failure of Baja males to mate with Sonora females. The factors responsible for the observed isolation have not yet been identified, but they have been demonstrated to have a genetic component by the selection experiments of Koepfer (1987a, b), which makes D. mojavensis a particularly attractive subject for studies of speciation. We have been interested in both the proximate and ultimate causes underlying the sexual isolation between these populations. Our approach to this problem has been to first identify where the behavioral breakdown occurs and then to seek the characters involved. Our long term goal is to understand the evolutionary forces which caused the responsible characters to diverge in the first place.

Seasonal effects on cuticular permeability and epicuticular lipid composition inCentruroides sculpturatus ewing 1928 (Scorpiones: Buthidae)

SummaryThe epicuticular lipids of the scorpion,Centruroides sculpturatus (Buthidae), are composed mostly of hydrocarbons and cholesterol, with free fatty acids and alcohols being present in smaller proportions. Hydrocarbons of summer scorpions are predominantly long-chain branched alkanes. The fatty acid component is composed primarily of saturated and unsaturated sixteen- and eighteen-carbon molecules, while the aliphatic alcohols are primarily evenchain length molecules containing 18–32 carbon atoms. Hydrocarbons of scorpions collected during fall, winter and early spring are characterized by higher proportions of shorter n-alkanes, especially n-heptacosane and n-nonacosane. Transcuticular water loss rates of freshly-killed, sealed scorpions and total water loss rates of live scorpions are significantly higher in specimens collected in winter than in scorpions collected during summer months. The functional relationship between seasonal changes in cuticular permeability and epicuticular lipid composition is discussed.

The Refugee Health Screener-15 (RHS-15): development and validation of an instrument for anxiety, depression, and PTSD in refugees.

OBJECTIVE Screening for emotional distress in newly arrived refugees is not a standard practice due to multiple barriers, one being the absence of a valid screening instrument for multiple refugee populations. The Refugee Health Screener-15 (RHS-15) was empirically developed to be a valid, efficient and effective screener for common mental disorders in refugees. METHOD Development followed published methods. Two hundred fifty-one refugees from three countries were screened at their public health visit with a pilot instrument, and 190 were administered diagnostic proxy instruments (DPs). Data analyses using multiple methods selected the best items for classification on DPs. Follow-up clinical service data were obtained. RESULTS Post hoc analyses of the developed RHS-15 showed good sensitivity(range .81 to .95) and specificity (range .86 to .89) to DPs in two of three ethnic groups. Seventy-four percent of positive cases accepted treatment services. Of those, 79% engaged in treatment, and 92% continued treatment more than 3 months. CONCLUSIONS The RHS-15 is a screener for common mental disorders in newly-arrived refugees in public health. The RHS-15appears to be effective, but further prospective research in a broad range of refugee groups is required to establish generalizability. Strengths, limitations, methods to apply the RHS-15 for optimal performance, and future directions for research and implementation are discussed.

Electron paramagnetic resonance spectroscopy of spin-labelled cuticle of Centruroides sculpturatus (Scorpiones: Buthidae): Correlation with thermal effects on cuticular permeability

Abstract Cuticular phase transitions and molecular dynamics have been studied in the buthid scorpion Centruroides sculpturatus using the techniques of thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR). TGA studies of the cuticular permeability reveal discontinuous changes in thermal dependence of transcuticular water loss rates (transitions). The first transition occurs between 30–40 C and results in a small increase in water loss rate, whereas the second transition begins near 55 C and is accompanied by a large increase in water loss rate. EPR spectra of spin-labelled cuticle indicate that the epicuticular lipids are very mobile at ambient temperature, with the translational diffusion coefficient being about 5 × 10−6 cm2 sec at 22 C. and that the low-temperature transition is associated with an increase in mobility of the hydrocarbon chains of the epicuticular lipids. The high-temperature transition probably results from melting of the epicuticular lipids. The results of this study are discussed with reference to current models of the structure of the arthropod cuticle.

Epicuticular hydrocarbons of Drosophila pseudoobscura (Diptera; Drosophilidae) Identification of unusual alkadiene and alkatriene positional isomers

Epicuticular hydrocarbons of Drosophila pseudoobscura were analyzed by gas chromatography and mass spectrometry. Methyl-branched alkanes and alkadienes were the predominant hydrocarbons, with lesser amounts of monoenes (14%) and trienes (9%) also present. Alkanes (49%) were mostly odd carbon number 2-methylalkanes (C25–C31). Alkadienes (27%) were odd carbon number components (C25–C33), with the (Z,Z)-5,9-isomer predominating. Monounsaturated hydrocarbons were a mixture of 5-, 7-, 9-, 11-, 13-, 14- and 15-isomers containing 25–33 carbon atoms. The major alkatriene components contained 29–31 carbon atoms and were either 5,19,17- or 5,9,19-isomers. Sodium[1-14C]acetate was incorporated into each class of hydrocarbon and into each of the major alkadienes.

Thermodynamic and kinetic aspects of water flux through the arthropod cuticle

Abstract 1. 1. Irreversible thermodynamics theory is used to justify the use of chemical potential gradients in analysis of temperature effects on arthropod water loss rates. 2. 2. A kinetic derivation of Fisks first law is used to demonstrate difficulties in the use of saturation deficit in water loss studies in which temperature is a variable. 3. 3. Calculated values for the enthalpy of activation for transcuticular water flux indicate that the vaporization of water is not the rate-limiting step in most arthropods examined to date.

Eicosanoids mediate control of thermoregulatory sweating in the cicada, Tibicen dealbatus (Insecta: Homoptera)

Cicadas prevent body temperature from exceeding tolerable levels by a combination of behavioral responses and sweating. Sweating is activated when body temperature reaches a critical set-point temperature. We investigated control of sweating in the cicada, Tibicen dealbatus, by chemically manipulating biosynthesis of prostaglandins and other eicosanoids. Injecting prostaglandins in amounts equal to those that induce behavioral fever in scorpions and crustaceans resulted in only a small increase in set-point temperature. Blocking prostaglandin biosynthesis with cyclo-oxygenase inhibitors such as aspirin produced significant changes in set-point temperature, confirming that prostaglandins are involved in control of sweating. However, the effect of cyclo-oxygenase inhibitors was not the opposite of the effect of prostaglandins. Instead, the effect of cyclo-oxygenase inhibitors depended strongly on the value of setpoint temperature prior to treatment. Results of biochemical manipulations of other steps in eicosanoid biosynthetic pathways corroborated the results of cyclo-oxygenase inhibition and indicated that eicosanoids other than prostaglandins may be involved in control of body temperature in normothermic T. dealbatus. The effect of cyclo-oxygenase inhibitors on a given set-point temperature depended on the ambient temperature experienced by cicadas during the experiment. Surprisingly, cicadas exposed to ambient temperatures ≥40°C delayed activation of sweating until body temperature exceeded values normally recorded from T. dealbatus in the field. Control of body temperature in normothermic cicadas is thus complex, involving inputs from body temperature sensors, ambient temperature sensors, and at least two cyclo-oxygenase-dependent regulatory pathways.

Effective Screening for Emotional Distress in Refugees: The Refugee Health Screener.

Abstract Screening for emotional distress is important, but not widely available. This study assesses the utility of the Refugee Health Screener 15 (RHS-15) in a public health setting. Refugee Health Screener 15 and diagnostic proxy (DP) instruments assessing anxiety, depression, and posttraumatic stress disorder were administered to refugees from 3 countries at their public health examination. Properties of the RHS-15 and its components were evaluated utilizing appropriate methods. Scale Cronbach &agr; was 0.95, and a factor analysis identified 1 factor accounting for 66% of scale variance. Refugee Health Screener 15 scores and cases discriminated between refugee groups similar to DPs. Refugee Health Screener 15 case sensitivity and specificity to DPs were acceptable (≥0.87/0.77). A shorter, 13-item component had acceptable metric properties. The RHS-15 appears to be a valid screener for emotional distress of refugees. The 13-item scale may be more efficient and as efficacious for case identification. The critical public health need and recommendations for implementation are discussed.

Evaporative cooling and endothermy in the 13-year periodical cicada, Magicicada tredecem (Homoptera: Cicadidae)

SummaryThe thermobiology of a cicada, Magicicada tredecem, from a warm, high humidity environment was investigated. Thoracic temperature (Tth) of M. tredecem in the field was strongly dependent on, and consistently higher than, ambient temperature (Tam), averaging 33.0±0.19°C on warm sunny days (Tam=28–29°C, rh=60–75%). Laboratory studies documented cuticle water fluxes high enough (≈ 5mg · cm−2 · h−1 in dry air at 40°C) to result in a significant degree of passive evaporative cooling, but the ability of M. tredecem to actively facilitate evaporative water loss during thermal stress is comparatively limited: water loss rates (WLR) of live M. tredecem at 40°C (dry air) were only 35–45% greater than those of dead cicadas. The limited ability of M. tredecem to facilitate transcuticular WLR is associated with limited surface distribution of the cuticular ducts through which water is actively extruded during evaporative cooling. In the laboratory, active extrusion of water had no appreciable effect on Tth, demonstrating that evaporative cooling was due largely to passive water flux through the highly permeable cuticle. The location of the abdominal pore tracts is such that extrusion of water through the ducts may preferentially cool the heart and perhaps other abdominal tissues. Long-term climatological data indicate that M. tredecem rarely encounters Tam levels high enough (i.e., above its apparent Tth setpoint of 34–35°C) to require evaporative cooling. Inactive M. tredecem can endothermically increase Tth. An hypothesis is proposed to account for the diversity of body temperature setpoints in cicadas.