Hammerhead shark has sex on its own

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Researchers from the USA and UK have confirmed that the hammerhead shark (Sphyrna tiburo) is capable of undergoing asexual reproduction.

Publishing their results in the latest issue of the journal Biology Letters, Demian Chapman, Mahmood Shivji, Ed Louis, Julie Sommer, Hugh Fletcher and Paulo Prodohl conducted genetic tests on three captive female sharks that were held in the Henry Doorly Zoo in Omaha, Nebraska.

One of the sharks gave birth to a normally developed, live female pup in the absence of any males in the aquarium for an extended period of time on 14 December 2001, and found convincing evidence that one of the three females gave birth parthenogenetically to the pup.

The researchers examined four microsatellite genotypes in all the individuals involved, and found a complete allelic match between the pup and one of the three females in the aquarium at the four loci.

The absence of any paternal genetic contribution was confirmed by amplified fragment length polymorphism (AFLP) fingerprinting.

According to the authors: "All three-candidate mothers had been held in the absence of males for 3 years, since they were wild caught in the Florida Keys as immature animals less than 1 year old.

"At least 2 years away from the age of first maturity, it is improbable that they were capable of sexual activity and sperm storage prior to capture...Moreover, the duration of sperm storage by adult female S. tiburo in the wild is relatively brief (five months...).

"None of the candidate mothers showed any sign of even rudimentary external male copulatory organs (claspers) that are typical of rare cases of intersexuality in sharks...eliminating the possibility of self-fertilization. These factors led us to consider the possibility of asexual reproduction."

Earlier this week, Practical Fishkeeping reported that a lone female Blacktip reef shark held at the Virginia Aquarium and Marine Science Center had also given birth to a pup in the absence of a male of the same species.

Tests are still ongoing to determine whether this was also an example of parthenogenesis, or whether the shark hybridised with another species present in its aquarium.

For more information, see the paper: Chapman, DD, MS Shivji, E Louis, J Sommer, H Fletcher and PA Prodhl (2007) Virgin birth in a hammerhead shark. Biology Letters 3, 425"427.