Scientists at the Cala Gonone Aquarium, Sardinia, Italy, recently witnessed a rare case of “virgin birth” or parthenogenesis in the smoothhound shark species. The mother shark was kept in an all-female shark tank for a decade. She gave birth to her offspring without being fertilized by a male shark’s sperm. The baby shark has been named Ispera meaning “hope” in Maltese.
The mother shark was in a tank with another female and hadn’t been in contact with male sharks for a long period of time. According to scientists, this form of asexual reproduction might be the very first documented event for the smoothhound shark species.
Marine biologists have sent the DNA samples of the newly born shark pup to a lab to prove her birth through parthenogenesis. According to Christine Dudgeon, a biosciences researcher at the University of Queensland, Australia, said, “Mortality in young sharks is common” and it is not known as to why this happens. However, the baby shark is looking healthy to the team of scientists surrounding her. The scientists are also hoping that Ispera, the baby shark could be bred in captivity to live a normal life.
Parthenogenesis is a form of asexual reproduction in which a female’s egg develops into an embryo without being fertilized by a male’s sperm. The term parthenogenesis is derived from the Greek words; Parthenos which means ‘virgin’ and Genesis meaning ‘origin.’
This phenomenon of a female’s ability to self-fertilize her eggs in extreme environmental conditions is a rare occurrence in nature. This form of inbreeding is a female’s last resort to save her species in the absence of a male.
Among sharks and ray fish, about 15 species have so far shown the ability to give virgin births. Reportedly, parthenogenesis has been observed in carpet sharks, zebra sharks, and some more species. Both oviparous and viviparous sharks have given birth by parthenogenesis.
The Director of the sharks and rays conservation program at Mote Marine Laboratory & Aquarium in Florida, Demian Chapman, told that in the past it has been particularly difficult to document such an event for shark species in their natural habitat. Sharks are capable of parthenogenesis in extreme situations like overfishing, climate change, predation, diseases, etc. When isolated from males in the wild or captivity for long periods, then female sharks may choose to reproduce asexually.
Parthenogenesis in brief
The production of an embryo from an unfertilized female gamete is witnessed in lower organisms normally but is a rare phenomenon in higher animals. Parthenogenesis is seen in some plant species, some invertebrate animal species (nematodes, tardigrades, scorpions, bees, parasitic wasps), and about 80 vertebrate species (fish, reptiles, amphibians, and some bird species).
Parthenogenetic development can proceed via various routes depending on whether the egg develops via meiosis or mitosis. If meiosis has failed to occur, then the offspring would mostly be a female. Egg cells are normally haploid as a result of meiosis and only when fertilized by the sperm cells become diploid. But parthenogenic offspring have a diploid chromosome. Based on the method of development in restoring the diploid pair of chromosomes, they might either become full clones or half clones of the mother.
Apomictic parthenogenesis is the type of egg development where meiosis is absent and the egg develops into a diploid zygote. This leads to the production of offspring which are genetically identical modules of the same genet.
On the other hand, automixis is the restoration of diploidy due to the fusion of the egg with a second polar body. The second polar body might be produced at the same time as the egg and acts like a pseudo-sperm cell with one strand of DNA. The resultant offspring is not the exact clone of the mother.
Though the offspring has the same genetic constitution as the mother yet it isn’t the mother’s exact clone according to biosciences researcher, Christine Dudgeon. Gametes have a unique combination of genes randomly selected from the parent at the time of its formation. Thus, the genetic makeup of each gamete is different. Hence when an egg cell combines with a polar body, a genetically different offspring comes into existence.
Those species which use the XY sex-determination system have two X chromosomes and the parthenogenetic offspring is female. While those species that use the ZW sex-determination system have either two Z chromosomes (male offspring) or two W chromosomes (non-viable or female offspring). Sometimes, it is also possible that the offspring has one Z and one W chromosome (a female offspring).
The Cala Gonone Aquarium, Sardinia, Italy
The Cala Gonone Aquarium in Sardinia was inaugurated on July 10, 2010, in the Gulf of Orosei. It has access to more than three hundred marine species from the Mediterranean Sea. The group of 25 aquariums presents an unfathomable journey from the shore to the deep sea. Visitors can experience, sea urchins, jellyfish, stingrays, hermit crabs, sharks, starfish, and a lot more in this magnificent aquarium.