ABSTRACT
Locusts have been reported to elevate metabolic rate in response to high carbohydrate diets; this conclusion was based on metabolic rates calculated from CO2 production, a common practice for insects. However, respiratory exchange ratio (RER, CO2 production divided by O2 consumption) can rise above 1 as a result of de novo lipid synthesis, providing an alternative possible explanation of the prior findings. We studied the relationship between macronutrient ingestion, RER and lipid synthesis using South American locusts (Schistocerca cancellata) reared on artificial diets varying in protein:carbohydrate (p:c) ratio. RER increased and rose above 1 as dietary p:c ratio decreased. Lipid accumulation rates were strongly positively correlated with dietary carbohydrate content and ingestion. RERs above 1 were only observed for animals without food in the respirometry chamber, suggesting that hormonal changes after a meal may drive lipid synthesis. Schistocerca cancellata does not elevate metabolic rate on low p:c diets; in fact, the opposite trend was observed.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: S.T., A.C., H.E.M., J.R., J.H.; Software: S.T.; Validation: S.T., A.C., R.F., J.H.; Formal analysis: S.T., R.F.; Investigation: S.T., A.C., R.F., H.E.M., J.R., J.H.; Writing - original draft: S.T., A.C., J.H.; Project administration: A.C., J.H.
Funding
This work was supported by National Science Foundation (NSF) IOS-1826848 and United States - Israel Binational Agricultural Research and Development Fund (BARD) FI-575-2018 grants.
Supplementary information
Supplementary information available online at https://jeb.biologists.org/lookup/doi/10.1242/jeb.240010.supplemental
- Received October 26, 2020.
- Accepted January 13, 2021.
- © 2021. Published by The Company of Biologists Ltd
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