Two female smoothhound sharks at the Cala Gonone aquarium give birth continuously despite living without males for the past 14 years.
Young sharks born at the aquarium. (Photo: Esposito et al/Scientific Reports).
The pair of female sharks kept in a zoo in Italy have been giving birth without the need for a male, highlighting a potentially critical survival mechanism, according to a study published in the journal Scientific Reports. In the research, scientists recorded repeated asexual reproduction in two smoothhound sharks (Mustelus mustelus), also known as dogfish sharks, which are classified as vulnerable by the International Union for Conservation of Nature (IUCN). This species is typically found in the Mediterranean Sea and other warm waters but is threatened by illegal fishing, as reported by Live Science on August 7.
The two female sharks at the Cala Gonone Aquarium in Italy have lived without a male companion for 14 years. Since 2020, they have begun reproducing asexually, revealing a phenomenon known as parthenogenesis. Parthenogenesis allows eggs to develop into offspring without fertilization. Although not common in vertebrates, this phenomenon has been observed in several reptile species such as crocodiles, water snakes, amphibians, and fish.
However, this is the first documented case of random parthenogenesis (organisms capable of switching between sexual and asexual reproduction) in smoothhound sharks. The research team discovered that the two female sharks could give birth via parthenogenesis once a year. This eliminates the possibility of sexual reproduction through stored sperm. Notably, the findings suggest that parthenogenesis could occur annually in sharks, alternating between the two females.
In total, the pair of female sharks have given birth to four offspring. The first pup was born in 2016 but did not survive. The remaining three pups were born in 2020, 2021, and 2023, respectively. Only the pup born in 2021 is still alive. All of them bore bite marks on their bodies, likely contributing to the deaths of the two pups born in 2020 and 2023.
To confirm the genetic origin of the newborn sharks, the research team collected DNA samples from the three pups and compared them with the adult sharks. They found that the young sharks had genes identical to their mother, demonstrating the importance of parthenogenesis as a survival mechanism in wild populations with decreasing male numbers. While the research focused on smoothhound sharks, parthenogenesis has also been documented in other shark species, including the white-spotted bamboo shark (Chiloscyllium plagiosum), zebra shark (Stegostoma tigrinum), and swell shark (C. ventriosum).
