Year

2019

Degree Name

Doctor of Philosophy

Department

School of Medicine

Abstract

This thesis aimed to use a social insect model to investigate the effect of membrane phospholipid composition on longevity. The two female castes of honeybees are genetically identical yet become either exceptionally long-lived queens (up to 8 years) or short-lived workers (typically 2-6 weeks). This distinction is based on dietary supply during the larval developmental stage where queens are immersed in liquid food (royal jelly) until metamorphosis (pupation) whereas workers get a restricted supply of royal jelly. After emergence, workers begin feeding on honey and pollen (‘bee bread’) with pollen containing a high level of polyunsaturated fatty acids (PUFA), whereas queens feed exclusively on royal jelly with negligible PUFA (assumed to be the same jelly they receive as larvae). PUFA are capable of significant levels of oxidation (i.e. peroxidation) whereas monounsaturated (MUFA) and saturated (SAT) fatty acids are very resistant to peroxidation. Therefore, this thesis investigated the role of dietary lipids (specifically PUFA) and its potential to determine longevity differences in female honeybees.

Membrane phospholipids of six different life-history stages, covering all developmental stages from little larva to old adults of the castes of the honey bees (Apis mellifera) were analysed using shotgun mass spectrometry lipidomics. The membrane phospholipids of workers and queens as larvae, pupae, and newly emergent adults all had low PUFA and high MUFA levels. However, queens continued to maintain low PUFA and high MUFA levels throughout their entire lives whereas, by day 4 of adult life, worker bees had increased their PUFA levels 5-fold, with a commensurate decrease in MUFA. This difference in membrane composition appears due to the difference in nutrition after adult emergence. The increase in PUFA in worker membranes occurred in all phospholipid classes but predominantly in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules. The low level of PUFA present in the membranes of queens was mostly found in phosphatidylinositol (PIn) molecules. Queens maintained a much higher abundance of phospholipid molecules containing SFA and MUFA (that are both resistant to peroxidation and protective of phospholipids that contain PUFA) compared to adult worker bees. Both female castes shared a similar level of total phospholipids. Adult queens also possessed a much higher abundance of their PUFA-containing phospholipids as plasmalogens (that limit lipid peroxidation) compared to worker bees. Overall, queen membranes appear to be far more resistant to peroxidation compared to worker membranes.

FoR codes (2008)

0601 BIOCHEMISTRY AND CELL BIOLOGY, 0606 PHYSIOLOGY, 0603 EVOLUTIONARY BIOLOGY, 1199 OTHER MEDICAL AND HEALTH SCIENCES

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.