Age-related changes in male ant sperm quality

Sperm cells age during storage in the male reproductive organs, which can lead ejaculate quality to decline dramatically over time. Such may pose a particular concern in species with constrained sperm supplies, where adult males cannot replenish their sperm reserves. In eusocial hymenopterans (i.e. ants, bees and wasps with permanent castes), males typically reach adulthood with a limited quantity of sperm, and their testes deteriorate shortly thereafter. In adult life, both sexes mate during a single reproductive event. While males die quickly after copulation, they persist posthumously via sperm stored in their mates' spermatheca, sometimes for decades. As a result of this mating system, males should experience intense selection pressure to produce and transfer high-quality sperm. Using the black garden ant (Lasius niger) as a model system, we investigated whether the duration of storage in the accessory testes before copulation affected sperm quality. We found that there was no impact of male age on sperm number or viability and that sperm DNA fragmentation decreased rather that increased with age. These results highlight the extent to which male ants, and possibly other taxa with constrained sperm supplies, have evolved extremely specialized strategies to ensure reproductive performance.