Who needs men? A female shark separated from her long-term mate has developed the ability to have babies on her own.
Leonie the zebra shark (Stegostoma fasciatum) met her male partner at an aquarium in Townsville, Australia, in 1999. They had more than two dozen offspring together before he was moved to another tank in 2012.
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From then on, Leonie did not have any male contact. But in early 2016, she had three baby sharks.
Intrigued, at the University of Queensland in Brisbane, Australia, and her colleagues began fishing for answers.
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One possibility was that Leonie had been storing sperm from her ex and using it to fertilise her eggs. But genetic testing showed that the babies only carried DNA from their mum, indicating they had been conceived via asexual reproduction.
Some vertebrate species have the ability to reproduce asexually even though they normally reproduce sexually. These include certain sharks, turkeys, Komodo dragons, snakes and rays.
However, most reports have been in females who have never had male partners.
There are very few reports of asexual reproduction occurring in females with previous sexual histories, says Dudgeon. An eagle ray and a boa constrictor, both in captivity, are the only other female animals that have been documented switching from sexual to asexual reproduction.
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鈥淚n species that are capable of both reproductive modes, there are quite a few observations of switches from asexual to sexual reproduction,鈥� says at the University of New South Wales in Sydney. 鈥淗owever, it鈥檚 much less common to observe switches in the other direction.鈥�
In sharks, asexual reproduction can occur when a female鈥檚 egg is fertilised by an adjacent cell known as a polar body, Dudgeon says. This also contains the female鈥檚 genetic material, leading to 鈥渆xtreme inbreeding鈥�, she says. 鈥淚t鈥檚 not a strategy for surviving many generations because it reduces genetic diversity and adaptability.鈥�
Nevertheless, it may be necessary at times when males are scarce. 鈥淚t might be a holding-on mechanism,鈥� Dudgeon says. 鈥淢um鈥檚 genes get passed down from female to female until there are males available to mate with.鈥�
It鈥檚 possible that the switch from sexual to asexual reproduction is not that unusual; we just haven鈥檛 known to look for it, Dudgeon says.
Bonduriansky agrees. 鈥淚t would seem to be highly advantageous,鈥� he says. 鈥淚t could be much more common than we currently realise.鈥�
Scientific Reports
