Jumeirah announces the successful reproduction of a shark through parthenogenesis…

Parthenogenic zebra shark pup

Parthenogenic zebra shark pup hatched and reared by the Burj Al Arab Aquarium Team

Zebedee may have never met a male of her species, but that hasn’t stopped the nine-year-old female zebra shark from reproducing on a recurring basis.

In a phenomenon that has defied everything science ever knew about the zebra shark, Zebedee, who lives in an aquarium at the Burj Al Arab Hotel, has been giving birth for the past four years, a first-ever for her species, reveals Warren Baverstock, Aquarium Manager at Burj Al Arab and co-author of an article featured in the Journal of Fish Biology.

Baverstock and co-author, marine biologist and assistant aquarium manager David Robinson explained the reason the news wasn’t brought to public attention was because tests had to be carried out, DNA had to be sampled, research conducted and theories approved, before making a statement that could potentially change the way we view zebra sharks forever.

For the scientifically inclined, the process is called parthenogenesis. To the rest of us, it’s when an egg cell is triggered to develop as an embryo without the addition of any genetic material from a male sperm cell.

Perhaps even more surprising than the fact that Zebedee does not need a male to reproduce, is the possibility of her spawning an entire breed of pups who will grow into full-blown adults capable of parthenogenesis themselves, perhaps eradicating the need for the male altogether.

“It’s not quite that simple,” says Robinson. “All 21 pups are still young, with the eldest being one and a half years old and the youngest just a few months.

“We have approximately six years of waiting before we find out whether Zebedee’s offspring will reproduce exclusively through parthenogenesis, or would mate with a male if the opportunity arose, or would be able to alternate between the two styles of reproduction.”

For now, all these possibilities are just theories.

And as is the case with theories, they come attached with a lot of scepticism, with critics saying that the pups may not be able to display the same ability as the mother, or, since the pups are clones of the mother, sexually, they have no ability of their own.

“Parthenogenes are not clones of their mother,” explains Robinson. “They’re genetically different to each other and to her as well. They are parthenogenes, not clones [who are unable to reproduce on their own]. There is no reason why they can’t be reproductively viable. They have a normal reproductive system that we’ve seen and learnt about through post-mortems of the pups that didn’t survive.”

In layman’s terms, sexual reproduction results in offspring with two versions of every gene (one from each parent) while asexual reproduction leads to offspring with only one version of every gene.

“Sharks continue to inspire and amaze us with their remarkable adaptability,” adds Baverstock. “There is no wonder that sharks have been such an evolutionary success story. A lot of hard work has been put into this project by the Burj Al Arab aquarium team and I am glad to see the effort and research are successful.”

Although “virgin births” are known among invertebrates and some vertebrates such as hammerhead, black tip and bamboo shark, it was unheard of for a zebra shark to display this ability. “At first we had to eradicate all doubt of the possibility of her having had intercourse with a male shark of a different species,” says Robinson. “We tested her, we tested the male hammerhead shark and we tested all her pups to find out if the babies carried any DNA that didn’t match the mother’s. Our result showed no paternal DNA at all.”

Moreover, when examined, Zebedee had none of the bite marks that are usually inflicted on her gender during mating. Nor was it possible for her to store the male sperm in her body for future use (sharks have that ability), since her six years in captivity would have made the sperm redundant.

“Working closely with Dr Khazanehdari of the Central Veterinary Research Laboratory, we have confirmed that parthenogenesis took place through the DNA analysis of Zebedee’s offspring. This discovery is extremely exciting for us as researchers and raises further questions about what we thought we knew about shark reproduction.”

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VISION Magazine Publication – Small Wonders by Nikki Schreiber

photographs by warren baverstock - article by Nikki Schriber - copyright VISION Managazine

photographs by warren baverstock – article by Nikki Schriber – copyright VISION Managazine

The aquarium at the Burj Al Arab hotel in Dubai is small; in fact you could be forgiven for not knowing it’s there. The only indication that anything aquatic is going on behind the scenes are the mesmerizing tanks of tropical fi sh that line each side of the escalator from the lobby to the first floor; that and a round tank in the Al Mahara restaurant which contains so many different brightly coloured fish in a reef-like environment, that trying to hold a conversation with anyone in there is like trying to talk to a child playing a computer game. Should you ever find yourself in Al Mahara look carefully into the tank and you’ll see two greyish white sharks covered in black spots with a cylindrical body shape, a broad head at one end and a rudder-like tail fi n at the other. They are zebra sharks (also known as leopard sharks), mother and daughter; the subject of an astonishing discovery by the Burj Al Arab’s team of marine biologists and the focus of their scientific paper on parthenogenesis or asexual reproduction. This may be a small team of marine biologists working in a small aquarium but they are punching above their weight with the discovery that the female zebra shark reproduced without a mate. Parthenogenesis has only been confirmed in a few other species of shark, namely blacktip and bonnethead sharks, which both give birth to live young (livebearing – ie not egg-laying), and the egg-laying bamboo shark.

The phenomenon has never been observed in the egg-laying zebra shark before, making this finding an international fi rst for a genetically confirmed parthenogenic birth for this type of shark and only the fourth time it has been seen in sharks at all. “This is the only aquarium in the world that has managed to [observe and] exhibit a parthenogen pup,” points out Warren Baverstock, the aquarium’s Operations Manager. “Breeding zebra sharks is hard in itself. Even without the parthenogenesis this would be interesting,” adds David Robinson, Assistant Operations Manager and principal author of the scientific paper. Back in 2007 a scientific paper was published in the US confirming that a bonnethead shark which had been kept in isolation from a mate had given birth to a pup. Genetic analysis proved the pup to be a clone of the mother. The zebra shark at the Burj Al Arab had also been kept in isolation from a possible mate and so when she produced eggs in 2006, the marine biologists didn’t think anything of it and discarded them. However, the publication of the paper on the bonnethead shark prompted Baverstock and Robinson to keep the eggs their zebra shark produced in 2007. “It was a bit of a long shot,” says Robinson, “because that was a live-bearing shark, completely evolutionarily distant from our shark which is egg-laying.” But the long shot worked out and the aquarium has been producing live pups since those first eggs were kept in 2007. It has not been easy, though, and the fact that asexual reproduction is an extreme form of inbreeding meant that there were many abnormalities, as Robinson explains: “When a shark releases an egg, it splits into four polar bodies; in parthenogenesis one of the polar bodies fuses back with the mother so that all the offspring are genetically identical to the mother but not to each other. It depends which part of the egg fuses back. If the mother is carrying a bad allele [one of the alternative forms of a gene, found at the same place on a chromasone] and mates sexually it may well be overridden, but if she reproduces asexually it’s amplified.”

Even with the tender care of Abdulkareem Vettan, who is in charge of the husbandry of the pups, there have been problems with nutrition. It’s difficult for the team to know whether these problems are genetic or developmental, and the data collection and research are ongoing. The findings of this research are important for marine biologists all over the world who are interested in understanding shark reproduction and evolution. As Robinson points out: “It shows that evolutionarily speaking, when they move back to a common ancestor, it is probable that all sharks across the whole range of sharks can do this.” Dr Aaron Henderson from the department of Marine Science and Fisheries at Sultan Quaboos University in Oman, says: “It also elicits a number of interesting questions such as, do females only revert to parthenogenesis when there are no males available? What are the implications for genetic diversity and fitness? What are the physiological processes giving rise to parthenogenesis? The questions are endless.” As are the future research possibilities, the next stage of which is discovering whether these parthenogen pups can reproduce. The scientific community is particularly excited by the fact that this shark has produced litters of pups parthenogenetically over successive years, because up until now they didn’t know this was possible. It means that this species can reproduce without the input of a male if it has to and suggests that rather than being a one-off response to isolation when in captivity, sharks could, potentially, be doing this in the wild. Most importantly, it means that this shark is able to keep its genes within the genome in an effort to survive. Jennifer Schmidt, Associate Professor of Biological Sciences at the University of Illinois, Chicago points out: “As shark numbers continue to decline there may be more and more populations facing breeding pressures of this type. An increasing rate of parthenogenesis could have both helpful and harmful effects on a dwindling population, maintaining the number of individuals in the short term, while altering sex ratios and reducing genetic diversity in the long run.” With this exciting discovery, the marine biologists at the Burj Al Arab are keen to work with others and share their research. Baverstock and Robinson say they can see a point in the future when they will be twinning with aquariums around the world, sharing knowledge, and continuing to contribute to the global understanding of fish biology.

photographs by warren baverstock - article by Nikki Schriber - copyright VISION Managazine

photographs by warren baverstock – article by Nikki Schriber – copyright VISION Managazine

article by Nikki Schriber - copyright VISION Managazine

article by Nikki Schriber – copyright VISION Magazine

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