Thursday, January 5, 2012

Zebra Shark Survival: could "virgin births" be a sign of nature's resilience?

Nature will find a way.

It's an amazing component of nature's dedication to survival that, when faced with conditions that impede propagation of a species, nature may choose another course other than to watch a population dwindle towards extinction. Parthenogenesis, or virgin birth, is just one such avenue. This is when an animal is able to produce viable offspring without the need for a traditionally fertilized egg, also known as asexual reproduction. No males around to breed with? Well, why wait?

Parthenogenesis is a somewhat rare occurrence, limited to a few reported cases, but one zebra shark that resides in the Burj Al Arab Hotel's aquarium in Dubai, has successfully produced eggs that brought forth healthy juvenile sharks. And she has done it each year for the past four years. The aquarium can verify that the shark has not had any contact with a male in all that time.

Interestingly, the juvenile sharks are all female - but not just clones of the female; their gene structure shows distinct differences. Could this also be another way that nature is trying to improve the odds, by generating more females? Scientists are not sure; the rarity of the event makes it a difficult subject to study.

David Robinson, the aquarium's operations manager, explained how the aquarium staff originally made the discovery, "
We were actually moving the eggs and one of the guys felt something move inside the egg. And we checked the eggs with light and there were babies inside. So, it was actually quite, I don't know...we went looking for it, but I don't think we were ever expecting to find it. So we're just awestruck."

Zebra sharks - which get their name because of the striking zebra pattern on the juvenile, which later gives way to a more leopard-like spotted pattern - will continually lay eggs several times throughout the year, fertilized or not. When I was a dive team leader at the Aquarium of the Pacific in Long Beach, CA, part of my team's responsibilities was to round up zebra shark eggs strewn about the Tropical Reef exhibit, deposited by either of the two large female zebra sharks in the exhibit.

Stuck to the artificial rocks and corals with mucus-like strands that could probably be bottled and sold as the next super glue - or at least that was what we thought as we would spend considerable effort getting the gunk off of our fingers - the eggs would be collected and set aside for disposal. With Dubai's reproductive zebra shark, named Zebedee, as an inspiration, the aquarists in Long Beach are probably now taking a long look at those eggs that the divers find.

BBC News reported on Zebedee's egg-laying abilities recently and the report includes an interesting video. Click here to view the video.

Nature has many fascinating ways of dealing with the natural or organic challenges it has had to contend with for eons. Evolution can be both an organized progression and an abrupt reaction to environmental changes. Unfortunately, man-made impacts seem to exceed even nature's formidable skills in perseverance and resiliency. But if we give it a break, nature can do wonders.

Sources:, BBC News.

No comments: