A zebra shark, also known as leopard shark in Australia, created a shocking surprise by becoming the first in the world to be a female having given birth without a male partner.
It happened in a Queensland aquarium where a zebra shark named Leonie had been living cut off from her male partner since 2013 after she had pups in another aquarium.
In April 2016, at the Townsville's Reef HQ aquarium, the zebra shark surprised all by hatching three eggs despite staying away from male sharks. A study confirmed there was no role of any male sperm in the fertilization of eggs.
The rare birth incident kicked off the interest of Christine Dudgeon of the University of Queensland who started studying the case right away.
"We thought she could be storing sperm but when we tested the pups and the possible parent sharks using DNA fingerprinting, we found they only had cells from Leonie," said Dudgeon, who led the study and serves on the faculty of School of Biomedical Sciences.
The case is unique as it is the first documented case of a female shark moving to parthenogenesis after a stage of normal reproduction without male support.
During the study, the researchers ruled out chances of Leonie storing sperm of her ex-partner for fertilizing the eggs after they duly tested the genetic composition of the pups that showed they had only DNA from their mother, confirming the asexual mode of conception.
The study has been published in Scientific Reports.
According to experts, a dual mode of reproduction depending upon circumstances has not been uncommon.
"In species that are capable of both reproductive modes, there are quite a few observations of switches from asexual to sexual reproduction," noted Russell Bonduriansky from the University of New South Wales.
However, he pointed out it is still rare to see such transitions happening in the other direction.
Dudgeon mentioned cases of asexual reproduction in some females who had previous histories of sexual production and cited an eagle ray and a boa constrictor, which transited from sexual to asexual reproduction as females.
How Does It Happen?
The asexual reproduction in sharks takes place when the egg gets fertilized by a nearby cell called a polar body that carries the genetic material of the female.
In the zebra shark's case, it produced 47 eggs during 2014-2015 but no pups were hatched. However, during the period of 2015-2016, it produced 41 eggs from where three pups hatched between February and April of 2016.
Extreme Form Of Inbreeding
"This is an extreme form of inbreeding, and the fact that these animals can survive, at least for short periods of time, with this highly reduced genetic diversity really challenges the way that we think about reproduction," Dudgeon said.
She said asexual reproduction may be a useful strategy to sustain the population and survive in extreme isolation.
This is good news as zebra sharks have been declared endangered species already. The unique reproduction mode has excited scientists as they expect it could offer clues to rebuild the declining population of these sharks.
Photo: Idibal | Flickr