Sperm storage in Apis mellifera, proteomics, genomics and technology
Anita M. Collins, BRL, USDA, ARS, 10300 Baltimore Ave., Bldg 476, Beltsville, MD 20705 and Jay Evans, BRL, USDA, ARS,, 10300 Baltimore Ave., Bldg 476 BARC-East, Beltsville, MD 20705.
The honey bee is an important model social insect for understanding evolution of social behavior. Because the queens mate with many males and store sperm for their lifetimes, they represent an extreme of reproductive behavior. Honey bees have also been included in a program for animal germplasm preservation, so technology to store semen and embryos needs to be developed. Using biochemical assays, protein identification and genome databases, we have determined that several antioxidants are at high levels in the queen’s spermatheca (sperm storage organ) after mating, some from the male. Honey bee semen contains metabolic enzymes related to glycolysis but few from the Kreb’s cycle. We found no orthologs of Drosophila male accessory gland proteins in honey bee semen, which may reflect the differences in mating behavior or rapid evolution of this class of proteins. Sperm in diluted semen samples do not show directional swimming behavior like mammalian sperm, instead they coil. However, sperm will show directional swimming for short distances if moving from an area of high concentration (whole semen) to low (extender), and will swim faster at a pH of 9 (spermatheca) than ph of 7 (semen). Honey bee semen is unusual in that it will remain viable for at least nine weeks at ambient temperature, as determined by dual fluorescent staining. A minimum of 50 % viable sperm used in artificial insemination will result in queens that lay normal amounts of fertilized eggs (worker bees) for at least one year, thus setting a threshold for semen preservation. A protocol for freezing semen in liquid nitrogen has been designed that meets this threshold. Ambient temperature storage up to eight weeks is also successful, but must be supplemented with an extender prior to insemination for sperm to reach the spermatheca.