Temperature dependent lipid content in the red harvester ant, Pogonomyrmex barbatus

Authors: ROEDER, DIANE - South Dakota State University; REMY, SAMANTHA - Cameron University; Roeder, Karl

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2023
Publication Date: 6/10/2023
Citation: Roeder, D.V., Remy, S., Roeder, K.A. 2023. Temperature dependent lipid content in the red harvester ant, Pogonomyrmex barbatus. Journal of Insect Science. 23(3). Article 14. https://doi.org/10.1093/jisesa/iead040.
DOI: https://doi.org/10.1093/jisesa/iead040

Interpretive Summary: We often lack detailed information on if and how animal physiology tracks temperature over time. To address this knowledge gap, we tracked lipid content of harvester ants from 14 different colonies across their activity period during an annual cycle. In doing so, we found that lipid content of ants declined almost 70% from cool months to hot months. We next assessed if lipid levels of ants could also change in a shorter time period by placing individuals into chambers set at 10, 20, and 30°C. Temperature again had a significant impact as lipid content of ants in the hottest chamber (30°C) decreased more than 75%. Harvester ants clearly have the ability to mobilize energy stores to offset some of the physiological demands of stressful abiotic conditions. But how consistent is this across ants and other insects? As our world changes, understanding how traits and trait variation are associated with environmental stressors like temperature remains a fundamental goal towards predicting which taxa will increase or decrease in the coming years.

Technical Abstract: Temperature is one of the most important environmental conditions affecting physiological processes in ectothermic organisms like ants. Yet we often lack information on how certain physiological traits co-vary with temperature across time. Here, we test predictions on how one trait—lipid content—co-varies with long- and short-term fluctuations in temperature using a conspicuous, ground-dwelling harvester ant, Pogonomyrmex barbatus. From March to November, we collected and extracted lipids from 14 colonies while simultaneously recording ground temperature. We first assessed if lipid content was highest during cooler temperatures when ants were less active and less metabolically stressed. In doing so, we found that lipid content of ants declined almost 70% from cool months (November lipid content = 14.6%) to hot months (August lipid content = 4.6%). We next assessed if lipid levels of a single cohort of ants could change by placing individuals into growth chambers set at 10, 20, and 30°C (i.e. the approximate span of average temperatures experienced from March to November). Temperature again had a significant impact such that after 10 days, lipid content of ants in the hottest chamber (30°C) had decreased more than 75%. While intraspecific variation in physiological traits often follows seasonal patterns, our results suggest fluctuations in temperature alone can account for a large portion of the variance observed in traits like lipid content.