Browsing by Author "Harrison, Jon F."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Correlated patterns of tracheal compression and convective gas exchange in a carabid beetle
    Socha, John J.; Lee, Wat-Keat; Harrison, Jon F.; Waters, James S.; Fezzaa, Kamel; Westneat, Mark W. (Company of Biologists Ltd., 2008-11-01)
    Rhythmic tracheal compression is a prominent feature of internal dynamics in multiple orders of insects. During compression parts of the tracheal system collapse, effecting a large change in volume, but the ultimate physiological significance of this phenomenon in gas exchange has not been determined. Possible functions of this mechanism include to convectively transport air within or out of the body, to increase the local pressure within the tracheae, or some combination thereof. To determine whether tracheal compressions are associated with excurrent gas exchange in the ground beetle Pterostichus stygicus, we used flow-through respirometry and synchrotron x-ray phase-contrast imaging to simultaneously record CO(2) emission and observe morphological changes in the major tracheae. Each observed tracheal compression (which occurred at a mean frequency and duration of 15.6 +/- 4.2 min(-1) and 2.5 +/- 0.8 s, respectively) was associated with a local peak in CO(2) emission, with the start of each compression occurring simultaneously with the start of the rise in CO(2) emission. No such pulses were observed during inter-compression periods. Most pulses occurred on top of an existing level of CO(2) release, indicating that at least one spiracle was open when compression began. This evidence demonstrates that tracheal compressions convectively pushed air out of the body with each stroke. The volume of CO(2) emitted per pulse was 14 +/- 4 nl, representing approximately 20% of the average CO(2) emission volume during x-ray irradiation, and 13% prior to it. CO(2) pulses with similar volume, duration and frequency were observed both prior to and after x-ray beam exposure, indicating that rhythmic tracheal compression was not a response to x-ray irradiation per se. This study suggests that intra-tracheal and trans-spiracular convection of air driven by active tracheal compression may be a major component of ventilation for many insects.
  • Thumbnail Image
    Effects of load type (pollen or nectar) and load mass on hovering metabolic rate and mechanical power output in the honey bee Apis mellifera
    Feuerbacher, Erica N.; Fewell, Jennifer H.; Roberts, Stephen P.; Smith, Elizabeth F.; Harrison, Jon F. (2003)
    In this study we tested the effect of pollen and nectar loading on metabolic rate (in mW) and wingbeat frequency during hovering, and also examined the effect of pollen loading on wing kinematics and mechanical power output. Pollen foragers had hovering metabolic rates approximately 10% higher than nectar foragers, regardless of the amount of load carried. Pollen foragers also had a more horizontal body position and higher inclination of stroke plane than measured previously for honey bees (probably nectar foragers). Thorax temperatures ranked pollen > nectar > water foragers, and higher flight metabolic rate could explain the higher thorax temperature of pollen foragers. Load mass did not affect hovering metabolic rate or wingbeat frequency in a regression-model experiment. However, using an analysis of variance (ANOVA) design, loaded pollen and nectar foragers (mean loads 27% and 40% of body mass, respectively) significantly increased metabolic rate by 6%. Mean pollen loads of 18% of body mass had no effect on wingbeat frequency, stroke amplitude, body angle or inclination of stroke plane, but increased the calculated mechanical power output by 16–18% (depending on the method of estimating drag). A rise in lift coefficient as bees carry loads without increasing wingbeat frequency or stroke amplitude (and only minimal increases in metabolic rate) suggests an increased use of unsteady power-generating mechanisms.
  • Thumbnail Image
    Isometric spiracular scaling in scarab beetles—implications for diffusive and advective oxygen transport
    Wagner, Julian M.; Klok, C. Jaco; Duell, Meghan E.; Socha, John J.; Cao, Guohua; Gong, Hao; Harrison, Jon F. (eLife Sciences, 2022-09-01)
    The scaling of respiratory structures has been hypothesized to be a major driving factor in the evolution of many aspects of animal physiology. Here, we provide the first assessment of the scaling of the spiracles in insects using 10 scarab beetle species differing 180× in mass, including some of the most massive extant insect species. Using X-ray microtomography, we measured the cross-sectional area and depth of all eight spiracles, enabling the calculation of their diffusive and advective capacities. Each of these metrics scaled with geometric isometry. Because diffu-sive capacities scale with lower slopes than metabolic rates, the largest beetles measured require 10-fold higher PO2 gradients across the spiracles to sustain metabolism by diffusion compared to the smallest species. Large beetles can exchange sufficient oxygen for resting metabolism by diffusion across the spiracles, but not during flight. In contrast, spiracular advective capacities scale similarly or more steeply than metabolic rates, so spiracular advective capacities should match or exceed respiratory demands in the largest beetles. These data illustrate a general principle of gas exchange: scaling of respiratory transport structures with geometric isometry diminishes the potential for diffu-sive gas exchange but enhances advective capacities; combining such structural scaling with muscle-driven ventilation allows larger animals to achieve high metabolic rates when active.
  • Thumbnail Image
    Microfluidic Flow Creation in the Insect Respiratory System
    Garrett, Joel Frederick (Virginia Tech, 2021-01-07)
    In this dissertation, we examine how advective and diffusive flows are created in the insect respiratory system, using a combination of direct biological studies and computational fluid dynamics simulations. The insect respiratory system differs significantly from the vertebrate respiratory system. While mammals use oxygen-carrying molecules such as hemoglobin, insects do not, favoring the direct delivery of oxygen to the tissues. An insect must balance advective flow with diffusive flux in order to sustain the appropriate oxygen concentrations at the tissue level. To better understand flow creation mechanisms, we studied the Madagascar hissing cockroach. In Chapter One, we used x-ray imaging to identify how tracheal tube compression, spiracular valving, and abdominal pumping coordinate to produce unidirectional flow during active respiration. In Chapter Two, we altered the environmental conditions by exposing the animals to various levels of hypoxia and hyperoxia, then examined how they changed their respiratory behaviors. In Chapter Three, we used our previous findings to construct a simulated insect respiratory system to parametrically study the effects of network geometry and valve timing on the creation of unidirectional advective flow and diffusive flux. These results can be used to inform future studies of the insect respiratory system, as well as act as the basis for bio-inspired microfluidic devices.