Virgin birth: sharks’ secret survival trick


CAN’T find a mate? Try parthenogenesis. The type of asexual reproduction may be part of an extreme survival strategy for sharks.

In parthenogenesis, females’ eggs start dividing without being fertilised. This produces daughters that are genetically similar to the mother. It was first observed in a captive hammerhead shark in 2001, but this was an isolated incident, and the shark pup died after three days, making it difficult to say much about its evolutionary significance.

Kevin Feldheim at the Field Museum in Chicago, and an international team of colleagues, have now shown that the incident was not exceptional and sharks born from a virgin mother can survive for many years (Journal of Heredity, vol 101, p 374).

The team were inspired by the 2001 birth to keep eggs produced by a captive white-spotted bamboo shark at the Belle Isle Aquarium of the Detroit Zoological Institute. The female had never encountered a male during her adult life and biologists had assumed the eggs were infertile. To their surprise seven incubated eggs produced two pups that survived five years before they were transferred to another facility. Genetic analysis confirmed that they were parthenogens.

“This suggests that parthenogenesis is a viable shark survival strategy,” says Paulo Prodöhl of Queen’s University Belfast, UK, who is investigating a possible case of virgin birth in the whitetip reef shark.

Modern sharks have been on Earth for several hundred million years. One theory is that switching from sexual reproduction to virgin birth might have helped these ancient creatures survive so long. Prodöhl suggests virgin birth could have been a safeguard mechanism. Several shark species live in single-sex groups and he says parthenogenesis may have ensured that isolated populations of females could survive without males.

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