According to scientists at the University of New South Wales, this is because molecules in the seminal fluid of the first male mate are absorbed by the immature eggs of the female and then influence the development of the second male's offspring.
"Our discovery complicates our entire view of how variation is transmitted across generations. It also opens up exciting new possibilities and avenues of research," said lead study author Angela Crean.
To reach this conclusion, Crean and colleagues Anna Kopps and professor Russell Bonduriansky manipulated the size of male flies and then studied their offspring.
They found that the young tended to be around the size of the first male their mothers had mated with, not the second male who was their biological father.
"We found that even though the second male sired the offspring, offspring size was determined by what the mother's previous mating partner ate as a maggot," explained Crean.
It shows that various non-genetic inheritance mechanisms make it possible for maternal or paternal environmental factors to influence characteristics of a child, researchers noted.
The study appeared in the journal Ecology Letters.