Long-term survival of high quality sperm: insights into the sperm proteome of the honeybee Apis mellifera.

In the social bees, ants, and wasps, females (queens) mate only during a brief period early in their lives and afterward store a lifetime supply of sperm in a specialized organ, the spermatheca. In some species, stored sperm can remain viable for several decades and is used by queens to fertilize millions of eggs. The physiological adaptations that allow this prolonged survival are unknown. To unravel them, we conducted proteomic analyses on the sperm of the honeybee Apis mellifera to define proteins that are bee-specific or highly divergent from sequences in the sperm proteomes of flies or mammals and might therefore be associated with long-term sperm survival. We identified a honeybee sperm proteome of 336 members and defined the subset of proteins or protein networks that cannot be discerned in the sperm proteomes of fruit flies and humans. This subset contained a significant number of proteins that are predicted to act in enzyme regulation or in nucleic acid binding and processing. From our analysis we conclude that long-term survival of sperm in social insects could be underpinned by substantial changes in only a specific subset of sperm proteins that allow physiological adaptation to storage. The unexpected preponderance of proteins predicted to be involved in transcriptional processes and enzyme regulation suggest these are the primary targets of this adaptation.