Sorry cloning opponents: cloning is very, very natural…
No males? No problem. Smalltooth sawfish (Pristis pectinata) native to rivers in south-west Florida, appear to have given birth without sex – essentially cloning themselves.
The sawfish – a type of ray that grows up to 7 metres long – is a critically endangered species. Because of this, the females may turn to parthenogenesis – reproduction without fertilisation from a male – as a last resort to produce offspring and avoid extinction, says a team led by Andrew Fields of Stony Brook University in New York.
Plenty of plants and invertebrates reproduce this way. And several captive vertebrate species including sharks, birds and reptiles have been shown to clone themselves in captivity. But this sawfish is the first vertebrate known to do it successfully in the wild.
Wild snakes have been seen gestating parthenogenetic young, but it’s unknown if they would ever have produced viable offspring.
The researchers analysed telltale markers called microsatellites in 190 sawfish that reveal how related their parents are. In seven fish, the markers suggested their parents were identical to them. The analysis revealed that the seven fish came from three different mothers.
Getting back together
“The statistics say they’re extremely unlikely to have a father,” says Fields.
Parthenogenesis is thought to happen when an egg is fertilised by another of the animal’s cells called a polar body, says Fields. Polar bodies are small cells created and usually discarded when an egg is formed, with the egg receiving half the chromosomes and the polar body the other half.
“Right now, we don’t know what causes a female to reproduce parthenogenetically,” says Warren Booth of the University of Tulsa in Oklahoma. In captive bird species, however, it seems to be a heritable trait, he says.
“So if a female resulted from in-breeding, she might carry forward the mutations that cause her to reproduce parthenogenetically,” says Booth. “As such, when populations become small, the rate of in-breeding increases and this raises the likelihood that these genetic conditions will become evident.”