Parthenogenesis is common in invertebrates but relatively rare in vertebrates. Among birds, reptiles, sharks, and now rays, parthenogenesis is thought to be triggered by an unfertilized egg absorbing a sister cell called the polar body that is nearly genetically identical to the egg. This results in an offspring that has roughly half the genetic diversity of its mother. In many cases these offspring are malformed or die early.
The smalltooth sawfish (Pristis pectinata) is one of five species of sawfish, a group of large rays known for their long, tooth-studded rostrum that is used to subdue small fish. Sawfish may be the first entire family of marine animals to become extinct because they are all critically endangered as a result of overfishing and coastal habitat loss.
Today, smalltooth sawfish are mainly found in a handful of locations in southern Florida, including the Caloosahatchee and Peace rivers. It was here that scientists have discovered that these critically endangered ocean giants are sometimes breeding without sex.
“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,” said the study’s lead author, Andrew Fields, a Ph.D. 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.”
“There was a general feeling that vertebrate parthenogenesis was a curiosity that didn’t usually lead to viable offspring,” said Dr. Gregg Poulakis of the Florida Fish and Wildlife Conservation Commission, who led field collections of the sawfish. “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.”
The parthenogen sawfish were all tagged and released back into the wild as part of an ongoing study of sawfish biology and ecology.
Upcoming in Current Biology.
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