Sharks have been known to reproduce either sexually or asexually, but it's usually one or the other. Now, researchers have observed the first documented case of a zebra (or leopard) shark switching from sexual to asexual reproduction, which could have important repercussions for conservation of the sharks as an endangered species.
Named Leonie, the shark in question was caught in the wild in 1999 and now resides in the Reef HQ Aquarium in Queensland, Australia. Between 2008 and 2013, Leonie had pups each year with a male zebra shark, but after the two were separated, she stopped producing young, as expected.
"In April 2016 Leonie hatched three eggs, despite having no access to a mating partner for three mating seasons," explains Christine Dudgeon, lead author of the study.
Initially, the researchers thought that the most likely scenario was that the shark had been storing sperm since her last encounter. It's unknown how long female zebra sharks can store sperm, but the team points out that related species have been known to do so for up to 45 months, so this could have accounted for Leonie's later litter.
"But when we tested the pups and the possible parent sharks using DNA fingerprinting, we found they only had cells from Leonie," says Dudgeon.
With that possibility ruled out, Leonie has made the record books as the first known case of a shark with a sexual mating history swapping to asexual reproduction. This could be good news for the species, which was recently included on the IUCN Red List of Threatened Species.
"Leonie adapted to her circumstances and we believe she switched because she lost her mate," says Dudgeon. "This has big implications for conservation and shows us how flexible the shark's reproductive system really is. What we want to know now is could this occur in the wild and, if so, how often does it?"
The next steps for the team are to determine if the pups, produced asexually, can make the switch back to sexual reproduction when they themselves reach maturity.
"You lose genetic diversity with generations of asexual reproduction, so we'll be seeing if these offspring can mate sexually themselves," says Dudgeon.
The research was published in the journal Scientific Reports.
Source: University of Queensland