‘Old’ sperm produce healthier offspring, study finds

Sperm that live for longer before fertilizing an egg produce healthier offspring, according to new research from the University of East Anglia and Uppsala University in Sweden.

The research, published in the journal Evolution Letters, shows that longer-lived sperm in an ejaculate of a zebrafish male produce offspring with longer and healthier lifespans—who in turn produce more and healthier offspring themselves—than the shorter-lived sperm in the same ejaculate.

The findings may have important implications for human reproduction and fertility, particularly in the context of assisted fertilization technologies, the researchers say.

“One male produces thousands to millions of sperm in a single ejaculate but only very few end up fertilizing an egg,” said lead researcher Dr. Simone Immler, from UEA’s School of Biological Sciences. “Until now, there was a general assumption that it doesn’t really matter which sperm fertilizes an egg as long as it can fertilize it. But we have shown that there are massive differences between sperm and how they affect the offspring.”

The research team performed in vitro fertilizations by collecting gametes from males and females. “We found that when we select for the longer-lived sperm within the ejaculate of male zebrafish, the resulting offspring is much fitter than their full siblings sired by the shorter-lived sperm of the same male,” Immler said. “More specifically, offspring sired by longer-lived sperm produce more and healthier offspring throughout their life that age at a slower rate. This is a surprising result, which suggests that it is important to understand how sperm selection may contribute to the fitness of the next generations.”

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