Endangered sawfish forestalling extinction through virgin births

Endangered sawfish are warding off the threat of extinction partly through virgin births, biologists have found.

In the first example of the phenomenon, known as parthenogenesis, observed in the wild, scientists found female smalltooth sawfish off Florida were giving birth without mating.

Although parthenogenesis has been recorded in many species of invertebrates and isolated occasions among birds, reptiles and sharks in captivity, it has never been seen to play a significant role in a wild population before.

Only five species of sawfish, which share a distinctive long nose crenellated with teeth that they use to attack their prey, survive around the world and most of these are at risk of dying out. They are in danger of becoming the first entire family of marine animals to be wiped out by overfishing and the gradual destruction of their coastal habitat.

The researchers believe that virgin births could be a strategy that some critically endangered species end up adopting to survive.

Andrew Fields, a PhD student at Stony Brook University, in New York, said he and his colleagues noticed the phenomenon while routinely collecting the DNA of the smalltooth sawfish to see whether their gene pool was shrinking through breeding with close relatives."What the DNA fingerprints told us was altogether more surprising,’’ he said. ‘‘Female sawfish are sometimes reproducing without even mating."

Writing in the scientific journal Current Biology, the scientists said that about 3 per cent of the smalltooth sawfish had been born without the intervention of a father. The process is poorly understood in vertebrates but it is thought to happen when one unfertilised egg ‘‘swallows’’ another. The offspring resulting from this unusual union usually miss half of their genetic diversity and struggle to survive.

Gregg Poulakis, of the Florida Fish and Wildlife Conservation Commission, who was in charge of collecting the sawfish whose DNA was sequenced, said most biologists had previously agreed that parthenogenesis was a dead end for vertebrates. Nevertheless, the seven sawfish trapped by the researchers who were found to be the products of virgin births did not seem to have much wrong with them. This suggests that parthenogenesis may be happening much more often in the wild than biologists previously realised.

The next step is for geneticists to revisit collections of DNA taken from wild populations and look for tell-tale signs of parthenogenesis.

Speaking at The Times Cheltenham Science Festival, Adam Hart of the University of Gloucestershire, said it was ‘‘amazing’’ that this observation had only just been made after decades of conservation programmes. ‘‘We might think we know a lot about the world, but discoveries like this show that we are just scratching the surface.’’

The phenomenon is rare enough that it is not likely to be much of a shield against extinction for the sawfish.

Kevin Feldheim, a molecular manager who oversaw the DNA analysis in the Pritzker Laboratory at the Field Museum of Natural History, in Chicago, said that the finding should be ‘‘a wakeup call that we need serious efforts to save these animals’’.