Female sharks keep giving birth in the absence of males – and scientists say it is a bizarre ‘survival mechanism’
FEMALE sharks are having babies with no males in sight – and scientists say the bizarre behavior holds clues about TKTK
Captivesharks at the Cala Gonone Aquarium in Italy have repeatedly produced offspring without the involvement of males.
And scientists believe this virgin birth could be a purposeful effort to maximize their chances of survival.
A study published last month in the journal Scientific Reports notes the repeated asexual reproduction in two common smooth-hound sharks.
The creatures have spent more than a decade away from males of their species.
“Nonetheless, a nearly annual production of young was observed in the absence of males,” the paper reads.
Since 2020, the scientists believe the female sharks have undergone facultative parthenogenesis, the process by which unfertilized eggs develop into young.
While this type of reproduction is commonly thought to occur in fungi and bacteria, it has also been reported in vertebrates including several shark species.
However, the repeated delivery of young is what puzzled scientists.
One proposed theory is that this type of asexual reproduction is an “adaptive reproduction strategy” that kicks in when females have limited access to males.
The phenomenon is called facultative parthenogenesis, or asexual reproduction that occurs in females who usually reproduce sexually.
In a biological context, it ensures the species can continue no matter the constraints on population.
In the case of common smooth-hound sharks, it is easy to see how this strategy could be beneficial.
The sharks’ native range extends through the eastern Atlantic Ocean and the Mediterranean Sea, but they are increasingly at risk of illegal fishing.
The creatures are so threatened that the International Union for Conservation of Nature has classified them as endangered.
Researchers found that the two females could reproduce asexually roughly once a year, ruling out the possibility of sexual reproduction through stored sperm.
The Italian sharks have produced four pups, though only one born in 2021 was viable.
When reproducing sexually, they typically have a litter of between four and 15 pups.
The first pup born in 2016 died shortly after, and its remains were not studied, meaning scientists cannot definitively conclude how it was conceived.
Two other pups born in 2020 and 2023 respectively did not survive either.
And the appalling survival rate is not due to defects associated with low genetic diversity, contrary to what one may think.
All of the young had bite marks on their bodies, which scientists say was the likely cause of death for those born in 2020 and 2023.
Even the pup born in 2021 sustained a “cranial bite” at birth, according to the paper.
Researchers gathered DNA samples from the three remaining pups and compared them to the genetic profiles of the adult females.
Miraculously, the scientists discovered that the offspring shared unique genetic markers with their mothers.
“These findings greatly enhance our understanding of reproductive strategies in sharks and could inform conservation efforts for endangered species,” the authors wrote.
While further research must be done on the topic, scientists believe facultative parthenogenesis may serve as a corrective measure in populations with declining male numbers.
Animals that have 'virgin births'
Komodo dragon: Scientists first discovered that the Komodo dragon could have virgin births in 2006, when a female at the Chester Zoo in the UK delivered 25 eggs in the absence of males.
Sharks: In 2001, workers at Omaha’s Henry Doorly Zoo and Aquarium discovered a juvenile bonnethead shark in a tank containing three females. This marked the first genetically confirmed case of parthenogenesis.
Virgin births have also been witnessed in zebra sharks, smooth-hound sharks, and blacktip reef sharks.
California condor: Researchers at the San Diego Zoo housed critically endangered female condors with a male in hopes they would produce offspring. In 2021, genetic testing confirmed that two make chicks carried identical copies of their mother’s DNA – meaning the males weren’t necessary.
Stick insects: Creatures within the genus Timema have reproduced exclusively in this manner for a million years. To ensure genetic variability – and in turn, the survival of the species – the insects will sometimes divert to sexual reproduction.
Crocodiles: The first confirmed case of parthenogenesis in crocodiles occurred in 2023. After spending 16 years away from males, a female American crocodile in a Costa Rican zoo gave birth to 14 eggs.
Unfortunately, the eggs weren’t viable. Out of the 14, only seven developed when incubated. After incubation, only one egg had a fully formed fetus, but the baby crocodile was born dead.
Tardigrades: These tiny creatures are also known as the “water bear” due to their cuddly appearance under the microscope.
The aquatic creatures are revered for their ability to withstand extreme conditions – including space travel and life on the moon. They can reproduce both sexually and asexually, but parthenogenesis is common only in watery and terrestrial habitats.