These sharks just keep getting pregnant!

27 06 2007

Because of my public school education, I have been trained to immediately think of the New Mexico Whiptail lizard (Cnemidophorus neomexicanus) whenever I hear the word “parthenogenesis.” What exactly parthenogenesis was or how it occurred was never covered, but the association between reproduction without a male and these lizards was certainly hammered in to my brain. Lately, however, there have been various cases of other animals exhibiting parthenogenic reproduction, including Komodo Dragons (Varanus komodoensis) and Bonnethead Sharks (Sphyrna tiburo).

The latest news deals with a Blacktip Reef Shark (Carcharhinus melanopterus) that had died after a physical had gone awry, the shark (named “Tidbit”) biting one of the aquarium staff before dying shortly thereafter. Upon autopsy, veterinarian Bob George discovered a near-term baby shark inside Tidbit, making this perhaps the second known case of shark parthenogenesis known. Tests still need to be done to confirm this, but Tidbit was not kept with any males of her species and sharks are not known to hybridize, so it is fairly certain that this is another case of parthenogenesis (it should also be noted that both bonnetheads and blacktip reef sharks belong to Order Charcharhiniformes, or the “Ground Sharks”).

In the case of the bonnethead shark, the parthenogenic offspring was female, and the CNN article linked above makes no mention of the sex of the offspring found in Tidbit (whatever I guessed, I’d have a 50/50 chance at being right). It is possible that in times of sexual isolation some sharks can produce offspring on their own, but if no males show up (or no males are produced through parthenogenesis, as komodo dragons apparently can achieve), then the population is no better off. I would also be interested to see if this particular ability exists across all shark groups or just in this particular order; are the “warm-bodied” lamniform sharks like Makos, Porbeagles, and Great White Sharks capable of this as well? Is this ability something new that evolved in this one group, or is it an ancestral condition that more derived sharks have lost? For now we’ll have to await Tidbit’s test results, but if nothing else aquarium curators should be keeping their eyes open for more instances of parthenogenesis going on right under their noses.



3 responses

27 06 2007
Zach Miller

It’s probably a lot more common than we think it is. It’s also been documented in Komodo dragons. One wonders if parthenogenesis occurs in mammals, seeing as all amniotes reproduce in basically the same way.
Now, if we find a case of mammalian parthenogenesis, I think that would have some implications for the beginnings of Christianity…

27 06 2007

Indeed Zach; I linked to the Komodo Dragon Nature paper in my post if you want to look at it. I’m doubtful as to parthenogenesis in mammals (we’re amniotes, but we’re pretty derived amniotes), and it may turn your stomach to hear this but DaveScot of Uncommon Descent actually came up with this same idea right around Christmas of last year. You can see his quote and my thoughts here.

If I remember correctly PZ even weighed in on the subject and why human parthenogenesis was unlikely, so you might want to check Pharyngula from around that time too.

27 06 2007
Zach Miller

Sure, we’re derived amniotes, but the method of fertilization seems basically similar (although I’m not biologist). I can dream about Christianity being shaken to its very core, can’t I? 🙂

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