野生蛇中首次发现单性生殖
A form of virgin birth has been found in wild vertebrates for the first time.
野生脊椎动物界首次发现单性生殖案例。
A virgin female and her son
Researchers in the US caught pregnant females from two snake species and genetically analysed the litters.
That proved the North American pit vipers reproduced without a male, a phenomenon called facultative parthenogenesis（兼单性生殖） that has previously been found only in captive species.
Scientists say the findings could change our understanding of animal reproduction and vertebrate evolution.
It was thought to be extremely rare for a normally sexual species to reproduce asexually.
First identified in domestic chickens, such "virgin births" have been reported in recent years in a few snake, shark, lizard and bird species.
Crucially though, all such virgin births have occurred in captivity, to females kept away from males.
Virgin births in vertebrates in general have been viewed as "evolutionary novelties", said Warren Booth, from the University of Tulsa, Oklahoma, US.
Professor Booth is lead author of a paper published in the Royal Society's Biological Letters that challenges this label.
He and his collaborators investigated virgin births in wild populations of two geographically separated and long-studied species of snake.
They captured pregnant copperhead and cottonmouth female pit-vipers from the field, where males were present.
The snakes gave birth, allowing the scientists to study the physical and genetic characteristics of the litters.
Of the 22 copperheads（铜斑蛇）, the scientists found one female that must have had a virgin birth.
Another single virgin birth occurred within the 37 cottonmouth litters.
"I think the frequency is what really shocked us," said Prof Booth.
"That's between 2.5 and 5% of litters produced in these populations may be resulting from parthenogenesis.
"That's quite remarkable for something that has been considered an evolutionary novelty," he said.