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Is this fish the beginning of the end for men?

The small sawfish is critically endangered. Source: Getty.

The small sawfish is critically endangered. Source: Getty.

An endangered species of fish can produce offspring without mating, report US researchers.

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The discovery, published in Cell Biology, shows ‘Virgin births’ in the smalltooth sawfish (Pristis pectinata) may be triggered by the population’s dwindling numbers, report the researchers.

The smalltooth sawfish is a large, critically endangered ray that is estimated to have declined to 1-5 per cent of its population size since 1900. It is currently found mainly in southwest Florida.

The small sawfish is critically endangered. Source: Getty.

The small sawfish is critically endangered. Source: Getty.

Between 2004 and 2013, 190 individuals ranging in total length from 67.1 centimetres to 3.81 metres were sampled, tagged, and released in the Caloosahatchee River, Peace River and Ten Thousand Islands regions.

Routine testing of the fish’s DNA showed several markers that would normally contain a lot of variability were homozygous, or contained the same DNA sequence, says lead author Andrew Fields, a doctoral student at Stony Brook University’s School of Marine and Atmospheric Science.

“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 Fields.

“What the DNA fingerprints told us was altogether more surprising: female sawfish are sometimes reproducing without even mating.”

Seven of the sample fish – or 3 per cent – were found to be produced through parthenogenesis.

Vertebrate parthenogenesis is thought to occur when an unfertilised egg absorbs a genetically identical sister cell.

The resulting offspring have about half of the genetic diversity of their mothers, so the genetic diversity of the wild population is reduced, says Fields.

Parthenogenesis is common in invertebrates but rare in vertebrate animals, the researchers say in the paper.

Fields says this unusual reproductive process has been known to occur in captive animals, including birds, reptiles, and sharks who gave birth despite the fact that they’d had no opportunity to mate.

The ‘virgin birth’ smalltooth sawfish are all female and appeared to be healthy and the appropriate length for their age, which was estimated around one year.

Fields says this suggests individuals produced in this way can survive in the wild. Previously it was thought these offspring would be unviable.

The discovery suggests that parthenogenesis does occur “at a low frequency in nature”, says Fields.

“We normally do not see it because females mate and then there is no chance for this process to occur,” he says.

“However when individuals are at low density — for example endangered or in an aquarium by itself — and cannot find a mate, maybe parthenogenesis has the opportunity to take place.”

– ABC

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