Wild and Sexless

Scientists find snakes give “virgin birth” in the wild for the first time

Sep 17, 2012
Beth Marie Mole

Two wild female pit-viper snakes—a copperhead and a cottonmouth—gave birth to fatherless litters, according to researchers at the University of Tulsa in Oklahoma.

The phenomenon of spawning without male contribution—known as parthenogenesis—is common in invertebrates, such as ants. Scientists have also observed it in vertebrates before, including fish, lizards, birds, and snakes, but it’s rare and only seen when animals are captive or when no males are present.

Yet, the two virgin mother snakes were not only wild, but found in populations with males, researchers reported in the study published last week (September 12) in Biology Letters. Further, scientists found the virgins in relatively small collections of pregnant females—just 22 copperheads and 37 cottonmouths—hinting that parthenogenesis may be more common than previously thought.

“I think the frequency is what really shocked us,” Tulsa biologist and lead author Warren Booth told BBC News. “That's quite remarkable for something that has been considered an evolutionary novelty.”

It’s still unclear, however, whether the offspring will survive and reproduce. Fatherless snakes born in captivity have not been viable, but Booth and colleagues recently found a garter snake that produced viable male offspring parthenogenicly.

Some snakes, including pit-vipers, can produce males during parthenogenesis because they have ZW sex determination. In this system, males are homozygous for the sex chromosomes Z (ZZ), while females are heterozygous (ZW). Thus, during parthenogenesis, when a ZW female’s eggs likely fuse to make offspring, there is the possibility of forming ZZ males.

Researchers will know in 2 to 3 years if such males and the females from the pit-vipers’ litters are viable.

“If they cannot survive and reproduce, then this is a reproductive dead-end,” Booth told the BBC. “However, if they are healthy and can reproduce, that opens an entirely new avenue for research.”