Males produce hundreds of thousands to hundreds of millions of sperms in one single ejaculation, depending on the species. Does it matter which one that actually fertilizes the egg? A recent paper published in in PNAS reveals that selection of long-lived sperms from the male ejaculation results in offspring with greater prospects of surviving early in life and superior characteristics as adults.
The study, led by Simone Immler (Uppsala University/SciLifeLab) and in collaboration with East Anglia University, UK, may be of great importance for adaptive evolution and research on assisted reproductive technology, such as IVF.
Until now, it has been assumed that all fertile sperms in one ejaculation from an animal are equally capable of engendering viable offspring. Limited efforts have been made to investigate the importance of selection, where environmental factors determine which types of organisms that get on better than others, of a sperm and the offspring it generates.
The present study uses externally conceived zebrafish, Danio rerio, to show that selection also between intact fertile sperms in the same ejaculation affects the fitness of the offspring and that these differences will also be carried on to the next generation. Consequently, it is possible to get rid of sperm of lower quality in an ejaculation by making the selection based on sperm features.
The results demonstrate that the genes of each sperm influence its characteristics, a notion that has previously been rejected.