With a long flat nose covered in spikes and beady little eyes, it’s a face only a mother could love. It would seem that might actually be the case, as new research has found that sawfish females have viable virgin births in the wild – no fathers required.
After analyzing samples collected from smalltooth sawfish (Pristis pectinata) young in Florida, researchers working at Stony Brook University discovered to their amazement that some of the samples appeared to be the result of virgin births, also known as parthenogenesis (“virgin creation”). This is the first time that young produced through parthenogenesis in a species that normally reproduces sexually have been found to be living and surviving in the wild.
Whilst some species of lizard reproduce exclusively through parthenogenesis, it was thought to be very rare for a normally sexual species to reproduce asexually. “There was one case where the researchers took a [wild] pregnant female [snake] and looked [at] what her litter was in utero, and found that they were [from] parthenogenesis,” Andrew Fields, lead author of the study, told IFLScience. “But since they hadn’t been birthed, we don’t know what would have happened to them.”
The samples in the new study were taken from one- and two-year-old sawfish pups in the mangroves of southern Florida, where they live naturally. They found that around 3% of them were the result of virgin births and, based on their genetic signature, think that these probably came from only three mothers. “So this is the first time that we have a free living individual [that] looks normal, behaves normal, but it was parthenogenetic,” says Fields.
One of the juvenile sawfish caught in Florida. Credit: Florida Fish and Wildlife Conservation Commission
Virgin births in vertebrates have been known to occur in a number of different species, from chickens to sharks, but reports of this event in the wild are extremely scarce, and many of these events in captivity don’t lead to viable young. Normally, they’ve happened after females have been isolated, and they were presumed to be the result of the animals not having access to males. So to discover parthenogenesis in a free-living wild population of animals is quite surprising.
Why some animals choose to reproduce in this way in the wild is unclear at this stage, but since it has been documented in a range of organisms, Fields thinks it's likely that many vertebrates could be capable of parthenogenesis but don't practise it when sexual reproduction is available. However, in certain conditions, such as a colonization event or extremely low population density, certain species may resort to it.
Once commonly found up the coast as far north as New York, best estimates suggest that smalltooth sawfish numbers are at just 5% of those from 1900 and the species is now considered critically endangered, restricted only to the estuaries of the Everglades. With their numbers decimated by hunting, their saws caught in fishing nets, and the destruction of their costal habitat, Fields is unsure what the future holds for the sawfish.
So are virgin births an oddity, or the norm for more species of vertebrates and we just don’t know it yet? Fields thinks that it’s definitely worth looking into: “We think it’s important for scientist to start scanning their databases, and seeing well, do they have individuals that come from parthenogenesis as well?”