If you think explaining the "birds and the bees" to a curious child is difficult, just imagine trying to tell a shark about it. A shark can be born three different ways, including live birth, hatching from an egg, and an egg-and-live-birth combination. Plus, in some shark species, you have to survive gestation without being eaten by your developing siblings. Not that you could tattle to Mom once you're out of the womb -- after birth, shark pups are pretty much on their own.
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The male shark sets a romantic mood by biting the female.
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We'll get to that in a minute, but first, let's look at how sharks get pregnant. As opposed to other fish, sharks use internal fertilization. Courtship between sharks often appears violent to humans. To get the female to stay in place, the male bites her fins or her back. The male positions the female shark so that he can align their reproductive organs, and then he inserts his clasper into her cloaca. The clasper, which in some species is spiny and barbed so that it stays in place, transfers sperm into the female.
At that point, the male shark, the ultimate deadbeat dad, exits the story, never to be seen again. In fact, the only time a shark pup may ever meet his or her father again is if the adult tries to eat the pup. The female is left to nourish the embryos growing inside. Find out how shark pregnancy works next.
In 2001, a Nebraska zoo welcomed a hammerhead shark pup into its aquarium. The fishy thing was that the aquarium only held female hammerhead sharks, none of whom had been exposed to male hammerheads in three years of captivity. At first, researchers thought the female had mated shortly before her capture and had stored the sperm. DNA tests, however, revealed that the only DNA in the shark pup was that of the mother and that no male DNA was present. This marked the first documented case of shark parthenogenesis, or asexual reproduction. Scientists think parthenogenesis could explain some observations of females who reproduce in the wild without contact with males [source: Queen's University Belfast]. Conversely, some sharks use many males to father one litter. DNA analysis of one litter of nurse shark pups found that at least four males had fathered some 32 pups [source: Saville et al.]. Other shark species may require multiple inseminations as well. |
