A lowly shark has given a U.K. aquarium double cause for celebration: She has laid two viable eggs, all without the apparent help of a male. Due to hatch in nine months’ time, this will be an example of a phenomenon called parthenogenesis, or a “virgin birth.”
Reported by the Guardian, the female is a white-spotted bamboo shark that has been without male contact since she arrived at her current home in the Great Yarmouth Sea Life Centre more than two years ago. While sharks reproduce in a variety of ways, including giving birth to live young, this species is an egg-layer. It’s not uncommon for such animals to lay eggs in the absence of males, but they’re usually assumed to be infertile. In this case, however, the eggs were found to contain viable embryos.
How precisely the shark achieved this is unknown, but the process of parthenogenesis is different to self-fertilization by an animal with both reproductive parts, or a hermaphrodite. Rather, these births can be achieved in one of two different ways. Often seen in plants, apomictic parthenogenesis involves the creation of an exact clone of the parent through normal cell division, or mitosis.
Automictic parthenogenesis, which likely explains the shark’s situation, involves the creation of half-clones, either by somehow doubling an egg’s chromosome number or fusing it with a leftover cell from egg formation, something called a polar body. During this process, called meiosis, four different cells are produced, but only one becomes the egg, while the rest turn into polar bodies. These extras, which contain genetic material, typically degrade, but in this type of parthenogenesis they can fuse with the egg and provide it with the extra DNA it needs to form an embryo.
Parthenogenesis gives animals an opportunity to survive in the absence of mates. Lukiyanova Natalia / frenta/Shutterstock
This phenomenon has actually been described in a range of species, from reptiles to birds, yet scientists aren’t really sure why animals do this. For a while, it was assumed to be the result of a lack of males in the environment, and thus a means to ensure species survival. However, it’s also been documented in animals when plenty of male suitors have been around, adding to the curiosity.
While this particular shark has been a spinster for two years, if she had contact with a male prior to her relocation to this particular aquarium, it’s possible that her births are also the result of sperm storage. Just over a year ago, a closely related species, a brownbanded bamboo shark, broke records by producing an egg after being isolated for an impressive 45 months.
We’ll have to wait a while to find out the eggs’ fate, but there is reason to be hopeful. The news comes shortly after a shark of the same species, which herself was the result of parthenogenesis, gave birth in this way in Germany.
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