Recent Advances in Insect Research Involving Metabolic Rate Measurements Using Respirometry

Disparate regulation of IMD singaling drives sex differences in infection pathology in Drosophila melanogaster. Crystal, M.V. and Dionne M.S. (2021) PNAS August 10, 2021 118 (32)https://doi.org/10.1073/pnas.2026554118

Metabolic and physiological outputs were measured in Drosophila melanogaster with wild-type and mutant immune responses to determine if the sexes were differentially impacted by various sources of pathology. The sexes showed differential immune activity but similar bacteria-derived metabolic pathology. Expression of PGRP-LB, a female-specific, immune-inducible, negative regulator of the immune deficiency (IMD) pathway, enabled females to reduce immune activity in response to reductions in bacterial numbers. Females were more resistant to infection in the absence of PGRP-LB. The heightened regulation of the IMD signaling pathway by female, but not male, Drosophila melanogaster reduces the cost of immune activity at the expense of resistance to bacterial infection.

Metabolic rate, heat shock protein 70 (Hsp70) expression, antioxidant capacity, and oxidative damage in lipids were measured in males and females of the dung beetle Euoniticellus intermedius exposed to a sublethal dose of ivermectin – an antiparasitic drug used in livestock. Metabolic rates were higher in ivermectin-treated males and females. Ivermectin-treated females increased their expression of Hsp70, whereas males increased their antioxidant capacity. Neither sex showed changes in the levels of oxidative damage to lipids. A process of hormesis is suggested, with exposure to ivermectin inducing a protective mechanism against oxidative stress that is different in males and females. Ivermectin in dung from livestock represents a threat to dung beetles and other fauna, which may be mitigated by heat-shock proteins and antioxidants providing resistance.

Muscle function and homeostasis require cytokine inhibition of AKT activity in Drosophila. Kiedorf, K. et al. (2020) eLife 2020; 10.7554/eLife.51595

The immune system has a role in controlling metabolism. In Drosophila, a high-fat diet can trigger the immune system resulting in insulin resistance and a shorter lifespan. Kierdorf’s research investigated how the immune system and metabolism work together, revealing complex interactions. This involved stopping the activity of the dome receptor in the muscles of healthy flies, leading to an increase in the activity of AKT, a protein critical in relaying insulin-type signals inside the cell. This caused hyperactivation of insulin signaling, decreased muscle function, deleterious changes in energy storage and expenditure, and a shorter life for the insects. Qubit’s RP1LP was used to monitor the Drosophila’s metabolic rate.

Different amplitudes of temperature fluctuation induce distinct transcriptomic and matabolomic response in the dung beetle Phanaeus vindex. Sheldon, K.S. et al. (2020) J Exp Biol (2020) 223 (23) https://doi.org/10.1242/jeb.233239

The thermal sensitivity of metabolic rate and energetic reserves was investigated in dung beetles exposed to constant (20°C), low fluctuation (20±5°C), or high fluctuation (20±12°C) temperature treatments using respirometry (Qubit RP1LP) assessment of energetic reserves and HPLC-MS-based metabolomics. No significant differences in metabolic rate or energetic reserves were found, suggesting increased fluctuations were not energetically demanding. A de novo transcriptome was assembled and annotated, revealing non-overlapping transcriptomic and metabolomic responses of beetles exposed to different fluctuations, which was associated with post-translational modifications to histones. Thus, acclimation to different temperature fluctuations is distinct and related to increasing transcriptional plasticity. Histone modifications may underlie rapid acclimation to temperature variation.

The Q-Box RP1LP Low Range Respirometry Package ($10,000 US)

The Q-Box RP1LP Low Range Respiration Package is designed to measure the metabolic rate of small animals such as insects, reptiles, amphibians, other invertebrates, and small mammals in an open-flow or stop-flow gas exchange system. The Q-Box RP1LP can even be used for measurements of CO2 and O2 exchange in colonies of fungi and microorganisms. When combined with Qubit’s Gas Switching Systems, measurements of metabolic rates and RQ are possible on up to 7 organisms (8 channel systems including reference).

Learn more about the Q-Box RP1LP HERE.

COMPONENTS:

• Q-P103 Gas Pump (1L/min no load) in the standard package
• Q-P651 Gas Pump (3L/min no load) when used with GSS
• G117 Variable volume Flow-through Chamber (1.9cm ID)
• G115 Flow-through Chamber (3.8cm ID, user-specified length)
• Optional Custom chambers are available
• G122 Large Gas Bags (2 x 30L)
• Q-G266 Flow Monitor (1L/min)
• Q-S102 O2 Analyzer (0-25%)
• S132 Stainless Steel Temperature Probe
• Q-S151 CO2 Analyzer (0-2000ppm) (Includes CO2 and H2O scrubbers)
• C200 Digital Control Unit (DCU)
• A380 Two-Solenoid Assembly (redirects the gas flow from ref. to anal.)
• C610 two integrated LabQuest Mini data interfaces (6 analog, 4 digital ports)
• C901 Logger Pro Software
• C404 Customized Experimental Setup Files for Open flow and Stop flow measurements
• Q-Box Accessory Kit (tubing, connectors, filters)
• Rugged weather-proof case housing all analyzers and sensors
• Manual
• individual power supplies for stand-alone use of the analyzers and sensor

Optional Components:

• A249 Li-ion 3 Battery Pack (for use in the field)
• Gas Switching System (for 4 or 8 channels)