With or Without You

Virgin motherhood by a copperhead snake. Sperm storage for more than five years by an eastern diamondback rattlesnake before fertilization and motherhood.

Reptile reproduction, to steal from Alice in Wonderland,  is getting curioser and curioser.

In a new paper, Dr. Warren Booth, an NC State postdoctoral researcher, and a colleague from Georgia State University show two remarkable snake “firsts” that flip conventional wisdom about snake reproduction on its belly.

Virgin births in snakes have been reported in only five other snake species – including findings in boa constrictors and Colombian rainbow boas reported by Booth earlier this year – making the copperhead virgin birth a relatively rare occurrence as reported in scientific literature. The copperhead was collected in August 2004 and placed in an aquarium exhibit with another female. Five years later, she produced a small and not completely healthy litter of babies – only two of 16 possible babies survived.

Meanwhile, so-called long-term sperm storage in reptiles – in which snakes hold sperm in the uterus with fertilization and motherhood coming some time later – has been more commonly reported. But this particular eastern diamondback rattler took long term to an extreme. Booth says the female was collected from the wild in January 2005 as a juvenile aged 16 or 17 months old and then housed in isolation from males. In August 2010, she gave birth to 10 females and nine males. It is the longest confirmed record of sperm storage in any vertebrate species to date.

Booth says new molecular genetics techniques have allowed him and other researchers to tease out snake parentage – in some cases a total lack of fatherhood and in some cases the delayed pregnancies involved with sperm storage – in ways previously unfathomable.

His findings suggest that the conventional wisdom in reptile reproduction – that sperm-storage births are much more common than virgin births and that immature snakes don’t mate – may need to be reexamined.

“You can’t always assume sperm storage in cases where there are no males around – you have to use molecular genetic markers to figure out if a male parent was involved,” Booth says.
He adds that there are conservation implications tied in with long-term sperm storage.

“In the case of the rattlesnake, the female was sexually immature when it mated, either by choice or by force,” he says. “So if you’re bringing an immature female from the wild to a zoo or aquarium, you can’t assume she hasn’t mated – she could be storing sperm. In this case, if the mother chose to mate and store the sperm – essentially hedging her bets – figuring out how and why the snake did this could lead us to important discoveries not only in how reproductive biology of snakes has evolved but also in how we can help conserve them in the future.”