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Hammerhead Sharks Reproduce Asexually

HammerheadAn international team of scientists surprised the world by reporting that female hammerhead sharks can reproduce without males through parthenogenesis, or "virgin birth". It was previously believed that sharks reproduced only sexually.

Researchers from Ireland and the United States performed genetic tests on a baby hammerhead born in an Omaha, Nebraska aquarium in 2001. The three occupants of the tank were all females who were captured as babies and had never been introduced to a male in captivity, which is what prompted the curiosity. The genetic tests proved that there was no "DNA of male origin" in the baby hammerhead.

Female sharks are able to store sperm for months, if not years, so there was some suspicion that the mother had mated prior to be taken into captivity, but the repeated DNA tests apparently ruled out this possibility.

While useful at times, reproduction through parthenogenesis carries risks for the species, as it reduces the genetic diversity of offspring and makes them more prone to being wiped out by disease. Given this new data, scientists speculate that parthenogenesis occurs in sharks only rarely -- when male mates are hard to find.

The new discovery poses a dilemma: mammals are now the only major vertebrate group where parthenogenesis has not been observed. Are they (we) incapable, or have scientists just not looked?

Source: Telegraph via Wired
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