Older sperm produce healthier offspring

Scientists from the University of East Anglia (UEA) and Uppsala University have released new research claiming that sperm that live for longer before fertilising an egg produce healthier offspring. And while the research was conducted in zebrafish, the findings may have important implications for human reproduction and fertility.

“One male produces thousands to millions of sperm in a single ejaculate but only very few end up fertilising 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 fertilises an egg as long as it can fertilise it.

“But we have shown that there are massive differences between sperm and how they affect the offspring.”

Writing in the journal Evolution Letters, the research team detailed how they performed in vitro fertilisations by collecting gametes from male and female zebrafish. They then split the ejaculate of a male into two halves.

They selected for shorter-lived sperm in one half and for longer-lived sperm in the other half. They added the sperm to two half clutches from a female to fertilise the eggs and reared the offspring into adulthood. They then monitored their lifespan and their reproductive output for two years.

“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,” Dr 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.”

Dr Immler noted that the sperm within an ejaculate vary not only in their shape and performance, but also in the genetic material that each of them carries. The researchers are currently in the process of identifying the genes underlying their findings.

“This research has important implications for evolutionary biology and potentially beyond into areas that use assisted fertilisation technologies, for example in livestock rearing or IVF in humans,” Dr Immler said.

Image credit: ©iStockphoto.com/Alexandr Mitiuc

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