After being isolated for four years, a female zebra shark gave birth to three healthy babies in 2016. Before she was moved in a separate tank in 2012, the shark lived for 12 years with a male with whom she had 24 babies.
Researchers were stunned to see that the female zebra shark was able to reproduce on its own after so much time spent in isolation, away from any male partners. A team of researchers from the University of Queensland located in Brisbane, Australia led by Professor Christine Dudgeon initially believed the female used some kind of technique to preserve her former partner’s sperm which she could have used to fertilize her eggs. However, the tests revealed that the offsprings carried only their mother’s DNA. Hence, the researchers had sufficient evidence to conclude that the female zebra shark achieved asexual reproduction.
According to the scientific community, sharks are not the only ones that can reproduce asexually.
“Some vertebrate species have the ability to reproduce asexually even though they normally reproduce sexually”, said the researchers.
Turkeys, snakes, Komodo dragons, and rays have been known to reproduce this way, as well, in order to ensure the survival of their species.
Nevertheless, asexual reproduction generally occurs in females with no prior sexual history. Once a mate is found, the female can switch from asexual to sexual reproduction. However, only two cases in which females switch from sexual to asexual reproduction have been recorded so far. In the past, similar behavior has been observed in a boa constrictor and an eagle ray.
University of South Wales’ Professor Russel Bonduriansky says that while switching from asexual to sexual reproduction in nothing new, it is extremely uncommon for the opposite to occur. Also, this particular form of inbreeding, especially among sharks could be exceptionally harmful to the species in the scheme of evolution. When asexual reproduction occurs, a polar body, which is an adjacent cell, fertilizes the female’s eggs with her own genetic material. Even though this ensures the survival of the species for a little longer, the strategy cannot be employed for many generations, since the technique drastically reduces genetic adaptability and diversity, says Christine Dudgeon. Researchers believe the ability only works as a temporary mechanism to ensure the survival of the species until a male partner is found.
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