"We were conducting routine DNA fingerprinting of the sawfish found in this area in order to see if relatives were often reproducing with relatives because of their small population size,” Andrew Fields, the study's lead author, said in a statement. “What the DNA fingerprints told us was altogether more surprising; female sawfish are sometimes reproducing without even mating.”
It's called facultative parthenogenesis, a phenomenon that is thought to be rare in vertebrates but has generally been observed in species, such as the Komodo dragon and several shark species in captivity. Females are able to switch between sexual and asexual reproduction, often depending on the availability of a mate.
With parthenogenesis, an egg absorbs a genetically identical cell to create offspring about half as genetically diverse as the mother. These offspring often don't survive.
But the sawfish produced through parthenogenesis that were caught by researchers, then tagged and released, were found to be not just viable, but perfectly healthy.
"This could rewrite the biology textbooks," study co-author Kevin Feldheim of the Pritzker Laboratory at the Field Museum of Natural History said in a statement. "Occasional parthenogenesis may be much more routine in wild animal populations than we ever thought."
And Fields — a PhD candidate at Stony Brook University’s School of Marine and Atmospheric Science — told the Miami Herald that five of the parthenogenetic sawfish were found to be siblings, suggesting that this reproductive process was able to produce multiple viable offspring for a single female.
“There was a general feeling that vertebrate parthenogenesis was a curiosity that didn’t usually lead to viable offspring,” said Gregg Poulakis, a researcher with the Florida Fish and Wildlife Conservation Commission, which led field collections of the sawfish in the Caloosahatchee and Peace rivers.
“The seven parthenogens we found looked to be in perfect health and were normal size for their age. This suggests parthenogenesis is not a reproductive dead end, assuming they grow to maturity and reproduce," he added.
The scarcity of mates prompts animals to sometimes do remarkable things to survive. But that shouldn't necessarily be a source of comfort.
Sawfish, which are characterized by a long, saw-like rostrum, are threatened by accidental entanglement during fishing and habitat loss thanks to humans. All five species of sawfish are classified as either endangered or critically endangered, and they could be the first of family of marine animals to be driven to extinction.
The findings should only accelerate efforts to save and preserve the species before it is too late, said Feldheim, whose lab conducted the DNA fingerprinting.
"Parthenogenesis could help endangered species like sawfish dodge extinction for a little while, but it should also serve as a wake-up call that we need serious global efforts to save these animals," Feldheim noted.
Want more science? Give these a click: