Mechanisms of Thermal Stability during Flight in the Honeybee Apis Mellifera

Thermoregulation of the Thorax Allows Honeybees (Apis Mellifera) to Maintain the Flight Muscle Temperatures Necessary to Meet the Power Requirements for Flight and to Remain Active Outside the Hive Across a Wide Range of Air Temperatures (T(A)). to Determine the Heat-Exchange Pathways through Which Flying Honeybees Achieve Thermal Stability, We Measured Body Temperatures and Rates of Carbon Dioxide Production and Water Vapor Loss between T(A) Values of 21 and 45°C for Honeybees Flying in a Respirometry Chamber. Body Temperatures Were Not Significantly Affected by Continuous Flight Duration in the Respirometer, indicating that Flying Bees Were at Thermal Equilibrium. Thorax Temperatures (T(Th)) during Flight Were Relatively Stable, with a Slope of T(Th) on T(A) of 0.39. Metabolic Heat Production, Calculated from Rates of Carbon Dioxide Production, Decreased Linearly by 43% as T(A) Rose from 21 to 45°C. Evaporative Heat Loss Increased Nonlinearly by over Sevenfold, with Evaporation Rising Rapidly at T(A) Values above 33°C. at T(A) Values above 43°C, Head Temperature Dropped Below T(A) by Approximately 1-2°C, Indicating that Substantial Evaporation from the Head Was Occurring at Very High T(A) Values. the Water Flux of Flying Honeybees Was Positive at T(A) Values Below 31°C, But Increasingly Negative at Higher T(A) Values. at All T(A) Values, Flying Honeybees Experienced a Net Radiative Heat Loss. Since the Honeybees Were in Thermal Equilibrium, Convective Heat Loss Was Calculated as the Amount of Heat Necessary to Balance Metabolic Heat Gain Against Evaporative and Radiative Heat Loss. Convective Heat Loss Decreased Strongly as T(A) Rose Because of the Decrease in the Elevation of Body Temperature above T(A) Rather Than the Variation in the Convection Coefficient. in Conclusion, Variation in Metabolic Heat Production is the Dominant Mechanism of Maintaining Thermal Stability during Flight between T(A) Values of 21 and 33°C, But Variations in Metabolic Heat Production and Evaporative Heat Loss Are Equally Important to the Prevention of overheating during Flight at T(A) Values between 33 and 45°C

The Flight Physiology of Reproductives of Africanized, European, and Hybrid Honeybees (Apis mellifera)

Neotropical African honeybees (Apis mellifera scutellata), in the process of spreading throughout tropical and subtropical regions of the Americas, hybridize with and mostly replace European honeybees (primarily Apis mellifera mellifera and Apis mellifera ligustica). To help understand this process, we studied the effect of lineage (African, European, or hybrid) on the flight physiology of honeybee reproductives. Flight metabolic rates were higher in queens and drones of African lineage than in European or hybrid bees, as has been previously found for foraging workers. These differences were associated with higher thorax/body mass ratios and higher thorax‐specific metabolic rates in African lineage bees. Queens were reared in common colonies, so these metabolic and morphological differences are likely to be genetic in origin. African drones had higher wing beat frequencies and thorax temperatures than European or hybrid bees. Hybrids were intermediate for many parameters, but hybrid queen mass‐specific flight metabolic rates were low relative to Africans and were nonlinearly affected by the proportion of African lineage, consistent with some negative heterosis for this trait

Allometry of Kinematics and Energetics in Carpenter Bees (Xylocopa Varipuncta) Hovering in Variable-Density Gases

We Assessed the Energetic and Aerodynamic Limits of Hovering Flight in the Carpenter Bee Xylocopa Varipuncta. using Normoxic, Variable-Density Mixtures of O2, N2 and He, We Were Able to Elicit Maximal Hovering Performance and Aerodynamic Failure in the Majority of Bees Sampled. Bees Were Not Isometric Regarding Thorax Mass and Wing Area, Both of Which Were Disproportionately Lower in Heavier Individuals. the Minimal Gas Density Necessary for Hovering (MGD) Increased with Body Mass and Decreased with Relative Thoracic Muscle Mass. Only the Four Bees in Our Sample with the Highest Body Mass-Specific Thorax Masses Were Able to Hover in Pure Heliox. Wingbeat Frequency and Stroke Amplitude during Maximal Hovering Were Significantly Greater Than in Normodense Hovering, Increased Significantly with Body Mass during Normodense Hovering But Were Mass Independent during Maximal Hovering. Reserve Capacity for Wingbeat Frequency and Stroke Amplitude Decreased Significantly with Increasing Body Mass, Although Reserve Capacity in Stroke Amplitude (10-30%) Exceeded that of Wingbeat Frequency (0-8%). Stroke Plane Angle during Normodense Hovering Was Significantly Greater Than during Maximal Hovering, Whereas Body Angle Was Significantly Greater during Maximal Hovering Than during Normodense Hovering. Power Production during Normodense Hovering Was Significantly Less Than during Maximal Hovering. Metabolic Rates Were Significantly Greater during Maximal Hovering Than during Normodense Hovering and Were Inversely Related to Body Mass during Maximal and Normodense Hovering. Metabolic Reserve Capacity Averaged 34% and Was Independent of Body Mass. Muscle Efficiencies Were Slightly Higher during Normodense Hovering. the Allometry of Power Production, Power Reserve Capacity and Muscle Efficiency Were Dependent on the Assumed Coefficient of Drag (CD), with Significant Allometries Most Often at Lower Values of CD. Larger Bees Operate Near the Envelope of Maximal Performance Even in Normodense Hovering Due to Smaller Body Mass-Specific Flight Muscles and Limited Reserve Capacities for Kinematics and Power Production

Cold Rearing Improves Cold-Flight Performance in Drosophila Via Changes in Wing Morphology

We Use a Factorial Experimental Design to Test Whether Rearing at Colder Temperatures Shifts the Lower Thermal Envelope for Flight of Drosophila Melanogaster Meigen to Colder Temperatures. D. Melanogaster that Developed in Colder Temperatures (15°C) Had a Significant Flight Advantage in Cold Air Compared to Flies that Developed in Warmer Temperatures (28°C). at 14°C, Cold-Reared Flies Failed to Perform a Take-Off Flight ∼47% of the Time Whereas Warm-Reared Flies Failed ∼94% of the Time. at 18°C, Cold- and Warm-Reared Flies Performed Equally Well. We Also Compared Several Traits in Cold- and Warm-Developing Flies to Determine If Cold-Developing Flies Had Better Flight Performance at Cold Temperatures Due to Changes in Body Mass, Wing Length, Wing Loading, Relative Flight Muscle Mass or Wing-Beat Frequency. the Improved Ability to Fly at Low Temperatures Was Associated with a Dramatic Increase in Wing Area and an Increase in Wing Length (After Controlling for Wing Area). Flies that Developed at 15°C Had ∼25% More Wing Area Than Similarly Sized Flies that Developed at 28°C. Cold-Reared Flies Had Slower Wing-Beat Frequencies Than Similarly Sized Flies from Warmer Developmental Environments, Whereas Other Traits Did Not Vary with Developmental Temperature. These Results Demonstrate that Developmental Plasticity in Wing Dimensions Contributes to the Improved Flight Performance of D. Melanogaster at Cold Temperatures, and Ultimately, May Help D. Melanogaster Live in a Wide Range of Thermal Environments

Downloading for PC Users; Part I: The U.S. Government Experience

Downloading for PC Users; Part I: The U.S. Government Experienc

Developmental changes in hypoxic exposure and responses to anoxia in Drosophila melanogaster

© 2015. Published by The Company of Biologists Ltd. Holometabolous insects undergo dramatic morphological and physiological changes during ontogeny. In particular, the larvae of many holometabolous insects are specialized to feed in soil, water or dung, inside plant structures, or inside other organisms as parasites where they may commonly experience hypoxia or anoxia. In contrast, holometabolous adults usually are winged and live with access to air. Here, we show that larval Drosophila melanogaster experience severe hypoxia in their normal laboratory environments; third instar larvae feed by tunneling into a medium without usable oxygen. Larvae move strongly in anoxia for many minutes, while adults (like most other adult insects) are quickly paralyzed. Adults survive anoxia nearly an order of magnitude longer than larvae (LT50: 8.3 versus 1 h). Plausibly, the paralysis of adults is a programmed response to reduce ATP need and enhance survival. In support of that hypothesis, larvae produce lactate at 3× greater rates than adults in anoxia. However, when immobile in anoxia, larvae and adults are similarly able to decrease their metabolic rate, to about 3% of normoxic conditions. These data suggest that Drosophila larvae and adults have been differentially selected for behavioral and metabolic responses to anoxia, with larvae exhibiting vigorous escape behavior likely enabling release from viscous anoxic media to predictably normoxic air, while the paralysis behavior of adults maximizes their chances of surviving flooding events of unpredictable duration. Developmental remodeling of behavioral and metabolic strategies to hypoxia/anoxia is a previously unrecognized major attribute of holometabolism

A Comparative Study of Dragonfly Flight in Variable Oxygen Atmospheres

i ABSTRACT One hypothesis for the small size of insects relative to vertebrates, and the existence of giant fossil insects, is that atmospheric oxygen levels have constrained body sizes because oxygen delivery would be unable to match the needs of metabolically active tissues in larger insects. This study tested whether oxygen delivery becomes more challenging for larger insects by measuring the oxygen-sensitivity of flight metabolic rates and behavior during hovering for 11 different species of dragonflies that range in mass by an order of magnitude. Animals were flown in 7 different oxygen concentrations ranging from 30% to 2.5% to assess the sensitivity of their behavior and flight metabolic rates to oxygen. I also assessed the oxygen-sensitivity of flight in low-density air (nitrogen replaced with helium), to increase the metabolic demands of hovering flight. Lowered atmosphere densities did induce higher metabolic rates. Flight behaviors but not flight metabolic rates were highly oxygen-sensitive. A significant interaction between oxygen and mass was found for total flight time, with larger dragonflies varying flight time more in response to atmospheric oxygen. This study provides some support for the hypothesis that larger insects are more challenged in oxygen delivery, as predicted by the oxygen limitation hypothesis for insect gigantism in the Paleozoic. ii ACKNOWLEDGEMENT

The Broadband XMM-Newton and NuSTAR X-ray Spectra of Two Ultraluminous X-ray Sources in the Galaxy IC 342

We present results for two Ultraluminous X-ray Sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by $\sim$7 days. We observe little spectral or flux variability above 1 keV between epochs, with unabsorbed 0.3--30 keV luminosities being $1.04^{+0.08}_{-0.06} \times 10^{40}$ erg s$^{-1}$ for IC 342 X-1 and $7.40\pm0.20 \times 10^{39}$ erg s$^{-1}$ for IC 342 X-2, so that both were observed in a similar, luminous state. Both sources have a high absorbing column in excess of the Galactic value. Neither source has a spectrum consistent with a black hole binary in low/hard state, and both ULXs exhibit strong curvature in their broadband X-ray spectra. This curvature rules out models that invoke a simple reflection-dominated spectrum with a broadened iron line and no cutoff in the illuminating power-law continuum. X-ray spectrum of IC 342 X-1 can be characterized by a soft disk-like black body component at low energies and a cool, optically thick Comptonization continuum at high energies, but unique physical interpretation of the spectral components remains challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot (3.8 keV) accretion disk, or a Comptonized continuum with no indication of a seed photon population. Although the seed photon component may be masked by soft excess emission unlikely to be associated with the binary system, combined with the high absorption column, it is more plausible that the broadband X-ray emission arises from a simple thin blackbody disk component. Secure identification of the origin of the spectral components in these sources will likely require broadband spectral variability studies.Comment: 12 pages, 11 figures, 5 Tables, Accepted for publication in The Astrophysical Journa

The Unique a4(1)/(2)a4 Agonist Binding Site in (a4) 3 (b2) 2 Subtype Nicotinic Acetylcholine Receptors Permits Differential Agonist Desensitization Pharmacology versus the (a4) 2 (b2) 3 Subtype s

ABSTRACT Selected nicotinic agonists were used to activate and desensitize high-sensitivity (HS) (a4) 2 (b2) 3 ) or low-sensitivity (LS) (a4) 3 (b2) 2 ) isoforms of human a4b2-nicotinic acetylcholine receptors (nAChRs). Function was assessed using 86 Rb 1 efflux in a stably transfected SH-EP1-ha4b2 human epithelial cell line, and twoelectrode voltage-clamp electrophysiology in Xenopus laevis oocytes expressing concatenated pentameric HS or LS a4b2-nAChR constructs (HSP and LSP). Unlike previously studied agonists, desensitization by the highly selective agonists A-85380 [3-(2(S)-azetidinylmethoxy)pyridine] and sazetidine-A (Saz-A) preferentially reduced a4b2-nAChR HS-phase versus LS-phase responses. The concatenated-nAChR experiments confirmed that approximately 20% of LS-isoform acetylcholine-induced function occurs in an HS-like phase, which is abolished by Saz-A preincubation. Six mutant LSPs were generated, each targeting a conserved agonist binding residue within the LS-isoform-only a4(1)/(2)a4 interface agonist binding site. Every mutation reduced the percentage of LS-phase function, demonstrating that this site underpins LS-phase function. Oocyte-surface expression of the HSP and each of the LSP constructs was statistically indistinguishable, as measured using b2-subunit-specific [ 125 I]mAb295 labeling. However, maximum function is approximately five times greater on a "per-receptor" basis for unmodified LSP versus HSP a4b2-nAChRs. Thus, recruitment of the a4(1)/(2)a4 site at higher agonist concentrations appears to augment otherwisesimilar function mediated by the pair of a4(1)/(2)b2 sites shared by both isoforms. These studies elucidate the receptor-level differences underlying the differential pharmacology of the two a4b2-nAChR isoforms, and demonstrate that HS versus LS a4b2-nAChR activity can be selectively manipulated using pharmacological approaches. Since a4b2 nAChRs are the predominant neuronal subtype, these discoveries likely have significant functional implications, and may provide important insights for drug discovery and development