Effects of Male Age on Reproductive Success and Offspring Fitness in Zebrafish (Danio rerio)

Abstract

Many studies have observed that sperm quality decreases both in humans and other animals as individual’s age; however, the direct effects of age on reproduction and offspring fitness are not yet fully understood. A preliminary study in zebrafish has shown some survival advantages in offspring from old males despite reduced sperm quality. However, what effects, if any, this has on subsequent generations is not clear. Sperm samples from the offspring of old and young males (F1 generation) were collected and in-vitro fertilisations (IVFs) used to produce an F2 generation. Fitness parameters (e.g., fertilisation success, hatching success, and survival) and sperm traits (e.g., motility and swimming velocity; measured using computer assisted sperm analysis) of F1 from young and old males were compared. Results demonstrate a significantly higher proportion of fertilised embryos produced from IVFs using the sperm of the offspring of old males compared to the young males. But, we see no significant differences between the two groups in the proportion of fertilised embryos that hatch or survive. There was a significant difference in the semen volume expelled during sampling where the F1 of old males tended to produce more sperm than the F1 from young males. But, there was no difference in any other sperm traits and no sperm traits were significant predictors of fertilisation success. These data suggest that there is a reproductive advantage acquired from old males in the form of greater sperm production and increased rates of fertilisation. Overall, the data are consistent with previous findings suggesting that old males deliver fitness benefits.