Why do we even need men? Female shark reproduces without male contact for years

Guys – who needs ‘em, right ladies?

Well, apparently not the female zebra shark (Stegostoma fasciatum), which was recently found to be capable of reproducing without any male contact for a period of years.

According to a new paper published in the journal Scientific Reports, a female zebra shark named Leonie was introduced to a male partner at an aquarium in 1999, and the two had more than two dozen offspring together. The male was transferred to another tank in 2012, leaving Leonie without male contact. And yet, in 2016, she had three more offspring.

The study team said one likely scenario involved Leonie saving sperm from her partner for years and eventually using it to fertilize her eggs. However, genetic analysis revealed the babies only took DNA from their mother, implying they were conceived through asexual means.

Asexual by Necessity

Several vertebrate species have the capacity reproduce asexually even though they commonly reproduce sexually, including some sharks, turkeys, lizards, and rays.

However, most known incidents have involved females who never once had a male partner. There have been some reports of asexual reproduction taking place in females with a sexual past. An eagle ray and a boa constrictor, both living in captivity, are the only other known female animals to have switched from sexual to asexual reproduction.

Christine Dudgeon, biologist with the University of Queensland, told CNN that sharks do often lay eggs when a male isn’t around.

“It’s much like a chicken — they lay eggs whether they are fertilized or not, if the conditions are good,” she said.

Hamish Tristram, a senior aquarist with the Reef HQ aquarium where Leonie was living, said the shark’s new pups came as quite a surprise.

“She had been mating successfully for several years, and there was nothing much published about such large animals switching reproductive strategy so quickly,” Tristam said.

The Australian aquarist noted that there are several theories about why animals switch from sexual to asexual reproduction.

“One theory is that in the wild, if for some reason males can’t have contact with the females for one breeding season, they can keep their lineage going for one or two seasons [through asexual reproduction], until they can reproduce the traditional way,” Tristam said.

“The genetic diversity of animals gets greatly reduced using this reproductive method,” Dudgeon also noted. “Long term, they need to diversify to help them adapt to their environment.”

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Image credit: Thinkstock

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