Two 'virgin' births in two years for this yellow-bellied water snake

What does this yellow-bellied water snake have in common with turkeys, smalltooth sawfish, and Komodo dragons? All of these animals have produced live young without having sex.

The yellow-bellied water snake in question lives at the Cape Girardeau Conservation Nature Center in Missouri in the US – and she's no contact with a male snake for at least eight years. Despite this, she's now reproduced on her own twice, once in 2014 and again this summer. This is the first example of a "virgin birth" in this species, which is exciting for the centre.

“This is the way you make discoveries when you keep things in captivity. You learn things about what they’re capable of," says AJ Hendershott, the outreach and education supervisor for the local conservation department.

"Virgin" births like these are a rare and unusual form of asexual reproduction in animals. Known as parthenogenesis, it occurs in less than 0.1% of all vertebrates.

So how does it work? Let’s break this down. In normal sexual reproduction, sex cells (or gametes), which contain the genetic information of each parent, combine to form a fertilised egg, and the genetic information mixes. As a result, the offspring have traits from both parents.

In parthenogenesis, the females go it alone, without any contributions from a male. Instead, the egg is "fertilised" by a sort of sperm substitute, a cell that's produced by the female along with the egg. Known as the "polar body", it contains identical genetic material. As a result, the offspring get all of their genes from the mother – you could say they're semi-clones. 

The earliest well-publicised cases of parthenogenesis, going back as early as the 1800s, occurred in chickens and turkeys. More recently, the no-males-required phenomenon has also been observed in Komodo dragons and smalltooth sawfish. Scientists believe virgin births in the sawfish may be a last-ditch attempt at bolstering population numbers in a species that's in dangerous decline.

Although the yellow-bellied water snake’s most recent offspring didn’t survive, the two born last summer are alive and well (and on display). 

Top header image: Natalie McNear, Fiickr