Pollen alters amino acid levels in the honey bee brain and this relationship changes with age and parasitic stress

Authors: Gage, Stephanie; Calle, Samantha; Jacobson, Natalia; Carroll, Mark; DeGrandi-Hoffman, Gloria

Submitted to: Frontiers in Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2020
Publication Date: 3/24/2020
Citation: Gage, S.L., Calle, S.N., Jacobson, N.N., Carroll, M.J., Hoffman, G.D. 2020. Pollen alters amino acid levels in the honey bee brain and this relationship changes with age and parasitic stress. Frontiers in Nutrition. 14. https://doi.org/10.3389/fnins.2020.00231.
DOI: https://doi.org/10.3389/fnins.2020.00231

Interpretive Summary: Pollen nutrition is necessary for adult honey bees, but it is unclear whether pollen affects the honey bee brain and behavior. All nutrients to an extent influence brain maturation, but protein, which is comprised of amino acids, appears most critical to the development of neurological functions. We measured amino acid levels in the brains of pollen-fed bees, and pollen-deprived bees, and then tested behavior. We found that the honey bee brain was highly responsive to pollen, and pollen continued to affect the brain long after consumption. We also tested this relationship in bees infected with prevalent parasite, Nosema ceranae. This parasite changed the connection between pollen and brain function. Pollen did not improve behavior in normal bees in this study, but infected bees did improve with pollen. A better understanding of how pollen affects the honey bee brain gives us insight into honey bee longevity, improving nutritional supplements, and methods to understand and prevent the harmful effects of parasitic stress.

Technical Abstract: Pollen nutrition is necessary for proper growth and development of adult honey bees. Yet, it is unclear how pollen affects the honey bee brain and behavior. We investigated whether pollen affects amino acids in the brains of caged, nurse-aged bees, and what the behavioral consequences might be. We also tested whether parasitic stress altered this relationship by analyzing bees infected with prevalent stressor, Nosema ceranae. We measured levels of 18 amino acids in individual honey bee brains using Gas Chromatography – Mass Spectrometry at two different ages (Day 7 and Day 11). We then employed the proboscis extension reflex (PER) to test odor learning and memory. We found that the honey bee brain was highly responsive to pollen. Many amino acids in the brain were elevated, and were present at higher concentration with age. The majority of these amino acids were non-essential. Without pollen, levels of amino acids remained consistent, or declined. Nosema-infected bees showed a different profile. Infection altered amino acid levels in a pollen-dependent manner. The majority of amino acids were lower when pollen was given, but higher when deprived. Odor learning and memory was not affected by feeding pollen to uninfected bees; but pollen did improve performance in Nosema-infected bees. Our results suggest that pollen in early adulthood continues to shape amino acid levels in the brain with age, which may affect neural circuitry and behavior over time. Parasitic stress by N. ceranae modifies this relationship revealing an interaction between infection, pollen nutrition, and behavior.