Previous Sexual Partner's Semen Can Influence Another Fly's Offspring

Russell Bonduriansky. Neriid flies.

If you think Facebook photos and holiday memories are harsh reminders of previous relationships, count yourself lucky you’re not a fly.  According to a new study, a mother’s previous sexual partner can influence certain characteristics in another male’s offspring. This newly discovered form of non-genetic inheritance means that, at least in flies, offspring can resemble previous sexual partners, rather than the fly that fertilized the female’s eggs. The study has been published in Ecology Letters.

The idea that males can leave lasting marks on female mates that influence her offspring to future partners isn’t new; telegony was actually first suggested in ancient Greek times by the philosopher Aristotle. However, as scientists started to learn about genetics and inheritance at the turn of the 20th century, the idea lost credibility and was swept under the carpet. But recent observations in the neriid fly (Telostylinus angusticollis) hinted that inheritance may not always be as black and white as long believed.

University of New South Wales researchers discovered that influencing a male’s body size by diet could in turn dictate progeny size. For example, males that were fed a nutrient-rich diet as maggots produced large offspring. While this hinted that males are able to pass on environmentally acquired conditions to offspring, the researchers didn’t know whether this was down to the male’s genes or another factor in the seminal fluid, such as a particular protein.

To find out more about what could be going on, the researchers devised a neat experiment. They produced both large and small male flies by feeding the larvae different diets. Once these males had reached maturity, they mated either a large or a small fly with a sexually immature female. When the females reached sexual maturity, they mated them again with either a small or a large male and measured the resulting offspring.

Even though the second partner fertilized the female’s eggs, they found that offspring body size was determined by the condition of the previous male, which was a reflection of what he ate as a maggot. According to the researchers, this suggests that something in the seminal fluid of the first male is being absorbed by the female’s immature eggs. Somehow, this unknown factor then goes on to influence the growth of offspring of later partners.

“Our discovery complicates our entire view of how variation is transmitted across generations, but also opens up exciting new possibilities and avenues of research,” lead author Angela Crean said in a news release. “Just as we think we have things figured out, nature throws us a curve ball and shows us how much we still have to learn.”

The researchers hasten to add that currently, we do not know if this new form of non-genetic inheritance is found in other species, and it would be virtually impossible to prove if this happens in humans. 

[Via University of New South Wales, Ecology Letters and PopSci]

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