In Nature, Virgin Births Are Pretty Common

Fish do it, bugs do it, even some species of snakes do it

virgin snake
This yellow-bellied watersnake gave birth without male contact in the last eight years. Candice Davis, courtesy Missouri Department of Conservation

The Virgin Mary belongs to a club that is slightly less exclusive than some might think. For years scientists have documented all sorts of virgin births in nature. Although animals that are fully asexually do exist, as Melissa Hogenboom writes for the BBC, it is also entirely possible for some creatures that normally require both a female and male to reproduce to still do so even without the presence of a male.  

Scientists have known for some time that certain species of insects, fish and lizards are capable of reproducing asexually, but it’s still rare in the rest of the animal kingdom, Elahe Izadi reported for the Washington Post. Back in September, however, a captive female yellow-bellied watersnake made headlines by giving birth for the second year in a row, despite the fact that she hadn’t had any contact with a male of her species in eight years. Although the snake’s new babies didn’t survive, that development indicated that there’s more to virgin births than scientists once thought.

“For many years, it was believed that such birth in captivity was due to sperm storage,” Missouri Department of Conservation herpetologist Jeff Briggler said in a news release. “However, genetics is proving a different story.”

In this case, the watersnake had been isolated for much longer than she would have been capable of storing sperm for. But it’s possible that the isolation itself is what triggered her to undergo parthenogenesis, or asexual reproduction in which offspring develop from unfertilized eggs. In a similar case documented this year, an unrelated team of researchers in Indiana witnessed a female copperhead snake lay four unviable eggs and one stillborn baby after almost a decade of isolation from males. But while such cases show that it was possible for some snakes to reproduce in this way, it’s far from ideal, Hogenboom writes.

"These snakes are half clones of their mother, so they are highly inbred," lead author Mark Jordan tells Hogenboom. "When parthenogenesis happens, there's a lot of mortality or lack of development."

As such, parthenogenesis might be a last-ditch effort to reproduce in the case that populations get too low. Although scientists still aren’t sure how virgin births originated, some suspect that it is a leftover strategy developed in early vertebrates, which may have found it more advantageous to clone themselves rather than spending time seeking out a mate. There’s no way to know for sure how many species are capable of having virgin births without conducting extensive genetic testing, but recent research indicates that scientists still have plenty more to learn about the phenomenon.

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