Female shark became the first vertebrate to reproduce without mating with male. Scientists couldn't find male DNA in the new born baby hammerhead.
A baby hammerhead was born in December 2001 at Henry Doorly Zoo aquarium very unexpectedly. There were only three female sharks from Florida water, none of them had a chance to mate with a male. So this baby hammerhead was a dilemma for the scientists.
"The findings were really surprising because as far as anyone knew, all sharks reproduced only sexually by a male and female mating, requiring the embryo to get DNA from both parents for full development, just like in mammals,"Â said Dr Paulo Prodohl, of Queen's School of Biological Sciences, who headed the university's research team. "The discovery that sharks can reproduce asexually by parthenogenesis now changes this paradigm, leaving mammals as the only major vertebrate group where this form of reproduction has not been seen."
Scientists were thinking of two theories: the female shark could possibly mated before being brought to the aquarium, somehow stored the sperm for three years and then fertilized her eggs. The second theory is that maybe she had mated with any of the different species in the aquarium.
Scientists tested baby hammerhead's DNA to find out its genetic makeup. But they were really surprised, when they didn't find any male origin genes. They only found who's the mother from the three female sharks. This eliminated both of the previous theories.
Scientists were shocked, because only a few species of vertebrate have females, which can give birth to healthy baby without mating with male. This is a very unusual reproductive ability, known as parthenogenesis, and it occurs very rarely only in birds, reptiles, amphibians. But it has never been occurred in sharks.
"We may have solved a general mystery about shark reproduction - our findings suggest that parthenogenesis is the likely explanation behind the anecdotal but increasing observations of other species of female sharks reproducing successfully in captivity despite not having contact with males,"Â said Dr Mahmood Shivji, who led the Guy Harvey Research Institute team. "It now appears that at least some female sharks can switch from a sexual to a non-sexual mode of reproduction in the absence of males. Unfortunately, this occurrence is not benign because it results in reduced genetic diversity in the offspring since there is no new genetic variation introduced from the paternal side."
But this is not just a worry of scientists for this single case, this occasional case means a lot for the whole shark population. So the scientists expect similar cases if female sharks have difficulties with finding males.
By Ruzan Harutyunyan for HULIQ
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