Experimental manipulation of reproductive tactics in Seba’s short-tailed bats: consequences on sperm quality and oxidative status

Abstract

To reproduce, males have to fertilize the female’s eggs, sometimes in competition with ejaculates of other males. In species where males display alternative reproductive tactics, whereby territorial males secure mating and non-territorial males have to sneak copulations, the latter might be expected to invest relatively more resources towards sperm quality compared with the territorial males. Sperm cells are especially vulnerable to oxidative stress, which reduces male fertility. Therefore, antioxidant resources are expected to modulate sperm quality, and might be allocated differently between reproductive tactics. To test the link between reproductive tactics, redox profile and sperm quality, we experimentally induced changes in the reproductive tactics of 39 captive males Seba’s short-tailed bats Carollia perspicillata. We monitored the blood and ejaculate oxidative balance, and the sperm quality before, 7 days and 21 days after the manipulation of reproductive tactic. Although ejaculates’ oxidative damage was negatively related to sperm velocity, males exhibited similar blood and ejaculates redox profiles and similar sperm quality, regardless of their reproductive tactic. Possibly, these results arise as a consequence of some constraints having been lifted during the experiment. Our results also suggest that, in Seba’s short-tailed bats, the expression of alternative reproductive tactics is not subjected to strong oxidative constraints. Furthermore, our results could reflect an absence of trade-off between pre- and post-copulatory traits in harem males, as they could be selected to invest both in female attraction and sperm quality, as a consequence of their inability to fully monopolize females.

Male alternative reproductive tactics and sperm competition: a meta‐analysis

“…Ejaculates were stripped from live males either by applying gentle pressure to the abdomen or testes, or by electrostimulation (e.g. Sasson, Johnson & Brockmann, 2015; Meniri et al ., 2019). After collection of the ejaculate, sperm quantity was estimated by counting the number or density of sperm cells in a given volume of ejaculate, calculating the volume of the ejaculate (e.g.…”

The role of oxidative stress in postcopulatory selection

“…In the bat Carollia perspicillata, sperm motility was unrelated to several antioxidant markers in the blood and whole ejaculate. OS also did not respond to experimental manipulation of the social context for SC [79]. However, sperm velocity was negatively correlated with levels of malondialdehyde (MDA: a product of oxidative lipid damage) in the ejaculate [79], showing ejaculate OS effects, whereas other studies did not [80,81].…”

“…OS also did not respond to experimental manipulation of the social context for SC [79]. However, sperm velocity was negatively correlated with levels of malondialdehyde (MDA: a product of oxidative lipid damage) in the ejaculate [79], showing ejaculate OS effects, whereas other studies did not [80,81]. Sperm swimming performance (using CASA) in the house sparrow, Passer domesticus, showed no effects of oxidants or antioxidants in semen (analysis by C.R.F.…”