Scientists have confirmed that three babies produced by a female zebra shark in Townsville City, Australia, were conceived asexually. Although this shark, named Leonie, had shark babies with a male partner in the early 2000s, aquarium workers noticed Leonie was pregnant yet again in early 2016.
Sure enough, three baby sharks were birthed later this year. Although asexual reproduction is rare in sharks, scientists have known for awhile that many vertebrate species have the ability to reproduce both sexually and asexually.
Background On Leonie’s Case
Leonie was first put into the Reef HQ Aquarium in Townsville City in 1999. She had a male partner with her at the beginning. Over the years, Leonie had some two dozen babies with the male shark. Then, in 2012, the aquarium staff decided to move the male shark out of Leonie’s tank to give her some privacy. From 2012 until today, Leonie has had no male contact.
After these years of isolation, Leonie suddenly produced three shark offspring in early 2016. This quickly caught the attention of local researcher Christine Dudgeon, a professor at the University of Queensland in Brisbane, Australia.
At first, Dudgeon and colleagues thought that Leonie must have stored sperm from her male mate and only chose to use it to fertilize her eggs much later. However, after testing Leonie’s three new children, researchers discovered that they only contained the DNA of her mother. There were no traces of the father’s DNA in these three little sharks.
This discovery made it clear that Leonie must have reproduced these offspring asexually. As mentioned before, this isn’t the first time a vertebrate has been observed asexually producing children. Scientists have documented Komodo dragons, eagles, and boa constrictors doing the same thing.
The interesting thing about Leonie’s case is that she switched from sexual to asexual reproduction exactly when her external conditions demanded she make an adaptation. This leads many in the scientific community to wonder just how common asexual reproduction is in the wild.
What Scientists Are Learning From This Zebra Shark
Scientists note that Leonie’s case is the first time on record they’ve observed a female zebra shark making the switch from sexual to asexual reproduction so quickly. Researchers say this decision to reproduce asexually clearly shows the importance of external pressure.
It also proves many animals that reproduce with partners have the ability to reproduce on their own if they feel the need to.
The actual biological function that allows this sexual/asexual switch is still unknown to scientists, but Leonie’s case offers a few more clues into its evolutionary function.
Dudgeon argues that the asexual function in female zebra sharks might be “a holding-on mechanism” so that a mother’s “genes get passed down from female to female until there are males available to mate with.”
In addition to learning more about this asexual reproductive function, researchers now have a clearer sense of the evolution of zebra sharks over time. Over the course of the species’ history, there are many periods of sharp reductions in the zebra shark population.
These declines often occurred during ice ages. Dudgeon believes that during these periods of population decline females must have preserved the species by reproducing asexually.
Hope For The Survival Of Zebra Sharks
The news of Leonie’s asexual reproduction isn’t only helping scientists better understand this mysterious evolutionary adaptation, it’s also giving them hope for the future. Zebra sharks are now considered a vulnerable species. The main threat to their survival comes from inshore fisheries.
Still, if female zebra sharks adapt to their circumstances and can start reproducing asexually, many marine biologists are hopeful zebra sharks will make it into the future just fine.
Image source: pexels.com/photo/underwater-no-person-water-fish-108056/
