Some female members of a critically endangered species of sawfish are
reproducing in the wild without sex. The discovery marks the first time
living offspring from 'virgin births' have been found in a normally
sexually reproducing vertebrate in the wild, the researchers say.
Earlier evidence that vertebrates might sometimes reproduce via a
process called parthenogenesis had primarily come from isolated examples
of captive animals--including 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, researchers 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.
Demian Chapman of Stony Brook University in New York and his
colleagues from the Priztker Laboratory at the Field Museum of Chicago
and Florida Fish and Wildlife Conservation Commission 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. The researchers' DNA analyses show that about 3% of the
sawfish in their studies are products of this unusual form of
reproduction.
Smalltooth sawfish are one of five species of sawfish, a group of
large rays known for their long, tooth-studded rostrum that they use to
subdue small fish. The researchers say that sawfish could be the first
family of marine animals to be driven to extinction due to overfishing
and coastal habitat loss. Smalltooth sawfish are mainly found today in a
handful of locations in southern Florida, including the Caloosahatchee
and Peace Rivers.
"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," says lead author of the
study, Andrew Fields, a PhD candidate at the Stony Brook University's
School of Marine and Atmospheric Science. "What the DNA fingerprints
told us was altogether more surprising: female sawfish are sometimes
reproducing without even mating."
Parthenogenesis is common in invertebrates but rare in vertebrate
animals, the researchers explain. 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," says Gregg
Poulakis of the Florida Fish and Wildlife Conservation Commission, who
led field collections of the sawfish.
And yet the seven parthenogens the researchers found appeared to be
in perfect health. All of the animals were tagged and released back into
the wild as part of an ongoing study of sawfish movements.
"Occasional parthenogenesis may be much more routine in wild animal
populations than we ever thought," says Kevin Feldheim of the Pritzker
Laboratory at the Field Museum of Chicago, where the DNA fingerprinting
was conducted.
It's possible that this form of reproduction occurs mainly in small
or dwindling populations. The researchers are now encouraging others to
screen their DNA databases in search of other hidden instances of
vertebrate parthenogens living in the wild.
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.
"This should serve as a wake-up call that we need serious global efforts to save these animals," Feldheim says.
This story is taken from Science Daily
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