Sawfish DNA reveals startling reproductive strategy

Sawfish DNA reveals startling reproductive strategy

This amazing fish was observed giving "virgin birth," though this could mean disaster for its rapidly shrinking population.

The smalltooth sawfish, commonly found in the coastal estuaries of Florida, has come up with a unique defense against its rapidly dwindling population. According to National Geographic, the smalltooth sawfish has developed the ability to deliver its young via a “virgin birth,” without having mated with another individual.

A DNA analysis of smalltooth sawfish, published this Monday in the journal Current Biology, identified seven juvenile sawfish that were likely born as a result of their mother’s asexual reproduction.

Parthenogenesis, or asexual reproduction in complex mammals, is extremely uncommon, though it is observed in certain species of sharks, snakes, and birds. Typically, it is a response to the lack of available mates after being held in captivity for an extended period of time, but the baby sawfish are the first animals observed in the wild to have been conceived asexually.

The smalltooth sawfish can grow up to 20 feet in length and is critically endangered in the United States, largely due to its bizarre tooth-covered snout getting tangled in fishing lines. It’s unclear how many individuals there are in the US, though scientists believe that the current population is about 5 percent of historical levels.

The female sawfish is able to fertilize her own eggs to produce offspring by fusing with another egg called a polar body. The sawfish pups aren’t genetically identical to the mother, but all of the genetic information comes from her. The one-sided genome alerted researchers that there may be something unique about the way these sawfish were reproducing.

The virgin births observed in this population of smalltooth sawfish is extremely troubling to scientists. It suggests that there already aren’t enough viable male mates to go around, so females are taking responsibility for reproduction themselves. Splitting the genetic diversity of a population in half means that future generations will be more susceptible to disease and will be less likely to exhibit advantageous traits in the wild.

Scientists are now wondering if they’ve missed more wild virgin births. While it certainly is not a good sign for the critically endangered smalltooth sawfish, there may be species out there that have figured out a way to use parthenogenesis to their advantage.

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