A new study, led by Dr Demian Chapman from Stony Brook University, documents the first known cases of parthenogenesis – the ability of sexually reproducing species to sometimes produce offspring asexually – in a wild vertebrate, the smalltooth sawfish (Pristis pectinata).
The smalltooth sawfish (Pristis pectinata). Image credit: Forrest Samuels / U.S. Fish and Wildlife Service Headquarters / CC BY-NC-SA 2.0.
Earlier evidence that vertebrates might sometimes reproduce via parthenogenesis had primarily come from a range of ordinarily sexually reproducing vertebrates in captivity, including some birds, reptiles and sharks. In those instances, the animals in question surprised their keepers by giving birth despite the fact that they’d had no opportunity to mate.
In addition, scientists recently reported two free-living female snakes, each pregnant with a single parthenogen, but it was not known if these embryos would have lived in the wild. Therefore, no one really knew if this phenomenon took place to any significant extent in wild populations.
Dr Chapman’s team made the discovery that vertebrate parthenogens can and do live in the wild after conducting some routine DNA fingerprinting of smalltooth sawfish in a Florida estuary.
Their DNA analyses show that about 3 percent of the sawfish in the study are products of parthenogenesis.
“We were conducting routine DNA fingerprinting of the sawfish found in this area in order to see if relatives were often reproducing with relatives due to their small population size. What the DNA fingerprints told us was altogether more surprising: female sawfish are sometimes reproducing without even mating,” explained Andrew Fields of Stony Brook University, first author of results published online in the journal Current Biology.
“Parthenogenesis is common in invertebrates but rare in vertebrate animals. Vertebrate parthenogenesis is thought to occur when an unfertilized egg absorbs a genetically identical sister cell. The resulting offspring have about half of the genetic diversity of their mothers and often die.”
“There was a general feeling that vertebrate parthenogenesis was a curiosity that didn’t usually lead to viable offspring,” said co-author Dr Gregg Poulakis of the Florida Fish and Wildlife Conservation Commission.
And yet the seven parthenogens Dr Chapman and co-authors found appeared to be in perfect health. All of specimens were tagged and released back into the wild as part of an ongoing study of sawfish movements.
The scientists think it’s possible that facultative parthenogenesis occurs mainly in small or dwindling populations.
As for smalltooth sawfish, it’s possible this ability could keep them going for a little longer. But it won’t be enough to save them.
The researchers are now encouraging others to screen their DNA databases in search of other hidden instances of vertebrate parthenogens living in the wild.
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