Alternative reproductive tactics, sperm mobility, and oxidative stress in Carollia perspicillata (Seba's short-tailed bat)

In social systems with alternative reproductive tactics, sneakers face a stronger sperm competition than harem males, and hence are predicted to allocate more resources to ejaculates. Antioxidants can protect sperm against oxidative stress, and thus their allocation to the ejaculate may depend on social status. In this study on the frugivorous bat Carollia perspicillata, we assessed for harem and sneaker males, four sperm mobility traits, blood and ejaculate markers of the redox balance, and the ejaculate to blood ratios of the redox markers. Under higher sperm competition, sneaker males should allocate proportionally more antioxidant resources to the protection of sperm than harem males. In contrast, harem males should favour pre-copulatory functions, which comprise the protection of blood. We found significantly higher sperm velocity and sperm survival in sneakers. There was no correlation between sperm mobility and sperm enzymatic antioxidant activity or ejaculate levels of lipid peroxidation (oxidative damage). Ejaculate levels of lipid peroxidation and sperm survival showed a significantly positive correlation, which could be attributed to the role of reactive oxygen species for sperm capacitation. Harem and sneaker males showed similar levels of
redox balance markers in ejaculate and blood. However, harem males showed a higher ratio of oxidized over reduced glutathione in blood, which may indicate higher cellular stress due to higher metabolism. Overall, our findings suggest that sneakers of C. perspicillata compensate for a stronger sperm competition by higher sperm mobility.