Seasonal Dynamics in the Chemistry and Structure of the Fat Bodies of Bumblebee Queens

PLoS One. 2015 Nov 11;10(11):e0142261. doi: 10.1371/journal.pone.0142261. eCollection 2015.

Abstract

Insects' fat bodies are responsible for nutrient storage and for a significant part of intermediary metabolism. Thus, it can be expected that the structure and content of the fat body will adaptively change, if an insect is going through different life stages. Bumblebee queens belong to such insects as they dramatically change their physiology several times over their lives in relation to their solitary overwintering, independent colony foundation stage, and during the colony life-cycle ending in the senescent stage. Here, we report on changes in the ultrastructure and lipid composition of the peripheral fat body of Bombus terrestris queens in relation to seasonal changes in the queens' activity. Six life stages are defined and evaluated in particular: pharate, callow, before and after hibernation, egg-laying, and senescence. Transmission electron microscopy revealed that the fat body contained two main cell types-adipocytes and oenocytes. Only adipocytes reveal important changes related to the life phase, and mostly the ration between inclusion and cytoplasm volume varies among particular stages. Both electron microscopy and chemical analyses of lipids highlighted seasonal variability in the quantity of the stored lipids, which peaked prior to hibernation. Triacylglycerols appeared to be the main energy source during hibernation, while the amount of glycogen before and after hibernation remained unchanged. In addition, we observed that the representation of some fatty acids within the triacylglycerols change during the queen's life. Last but not least, we show that fat body cell membranes do not undergo substantial changes concerning phospholipid composition in relation to overwintering. This finding supports the hypothesis that the cold-adaptation strategy of bumblebee queens is more likely to be based on polyol accumulation than on the restructuring of lipid membranes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / physiology*
  • Animals
  • Bees / physiology*
  • Cell Membrane / metabolism
  • Fat Body / metabolism*
  • Fatty Acids / metabolism
  • Hibernation
  • Seasons*

Substances

  • Fatty Acids

Grants and funding

This work was supported by the Czech Science Foundation (14-04291S); http://www.gacr.cz/; IV OK AV, Institute of Organic Chemistry and Biochemistry (61388963); http://www.uochb.cz/web/structure/31.html; IV AT EK MK PJ, Internal Grant Agency of Faculty of Forestry and Wood Sciences (20134359); http://www.fld.czu.cz/cs/; JS, and Agricultural Research, Ltd. The funder provided support in the form of salaries for authors [A.V., O.K.], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.