Two cases of virgin birth have been observed in wild snakes, the first time the phenomenon has ever been recorded among vertebrates living in their natural habitat.
Genetic analysis of the litters born to a sample of pregnant North American pit vipers revealed that two had reproduced without the help of a male – a feat which had only previously been observed in captivity.
The findings suggest that virgin births may be more common among animals which usually need to have sex to reproduce than previously thought, scientists said.
Although asexual reproduction is common among many species, such as bees and insects, it is rare among vertebrates – animals which have a backbone – like birds, mammals and lizards.
A small number of virgin births have been seen among domestic chickens and some species of shark, snake, lizard and bird but only among animals which were captive and isolated from the opposite sex.
Researchers from the University of Tulsa, Oklahoma, captured 22 copperhead and 37 cottonmouth pit vipers, all of which were already pregnant, from areas where males were also present.
After the snakes gave birth, the researchers studied the genes of their litters and found that one female of each species had offspring which bore only the mother's genetic material.
It meant the mothers must have reproduced through a process called parthenogenesis, or virgin birth, when a female's egg develops without having been fertilised.
Prof Warren Booth, who led the study published in the Biological Letters journal, told the BBC: "I think the frequency is what really shocked us.
"Between 2.5 and five per cent of litters produced in these populations may be resulting from parthenogenesis. That's quite remarkable for something that has been considered an evolutionary novelty."
