Within-Ejaculate Sperm Selection and Its Implications for Assisted Reproduction Technologies

In most animals, males produce large numbers of sperm in each ejaculate, but only very few end up fertilising an egg. This bottleneck in sperm numbers from ejaculation to fertilisation offers an intuitive opportunity for selection to act and improve the fitness of the next generation. However, the general view that sperm phenotype is not linked to its haploid sperm genotype stalled further research into this idea until recently. Two studies in zebrafish Danio rerio now suggest that selection among sperm within the ejaculate of male may have far-reaching consequences for the following generation(s). Selection for longer lived sperm resulted in offspring that showed higher survival during embryo development and a reduced number of abnormally developed larvae, as well as increased reproductive success during adulthood. These effects have been linked to the haploid genotypes in the sperm. We here discuss the possible benefits of refined sperm selection based on sperm haplotypes in the use of artificial reproduction technologies. Understanding the genetic processes occurring after meiosis until syngamy may provide insights that may help improve the existing methods and with that their success rates.