Longest-ever case of sperm storage in brownbanded bamboo sharks

The brownbanded bamboo shark, Chiloscyllium punctatum, is a near-extinct bamboo shark residing in the Indo-West Pacific from Japan to northern Australia. The major threats to these sharks are the loss of their habitat, pollution, and hunting (both for aquarium trade and food).

However recent findings give hope for this near-threatened shark species. Steinhart Aquarium biologists at the California Academy of Sciences have showed that this shark species has a capacity for incredible sperm storage. Female animals cunningly maintain sperm in their bodies, from spiders to mammals such as marsupials, frogs and reptiles. But this shark holds the record of storing sperm at least, 45 months after capture. The female shark concerned produced 2 eggs in a mermaids purse. One of them produced a healthy pup-shark that lives on to demonstrate the remarkable event. Their results, published in the Journal of Fish Biology, mark the longest documented case of sperm storage in any species of shark, and highlight a bright bit of news for the future of wild sharks threatened by overfishing and habitat loss.

To rule out the possibility of parthenogenesis (has been observed in four different shark species), the scientists used modern genetic tools. They analysed the genetic profile of the pups and the potential mothers. They found that the shark pup displayed comparable results with each female on a particular genetic test that looks at genetic variation within an individual. If the mother had reproduced asexually through parthenogenesis, the offspring would have shown less genetic variation than that of its mother. The pup also displayed genetic material–in the form of 32 alleles, or parts of genes–absent from all three adult females. Study authors concluded that the young shark most likely inherited this “mystery” genetic material from its father, a completely unknown male.

The experts think that ability to store sperm offers females the power to produce young regardless of whether or not they are ovulating when mating occurs. Moreover a potential pup would have unique genetic contributions from both the parents. This type of genetic diversity is a huge advantage for wild populations, because diversity is critical in maintaining the health of populations, especially those pared down by overfishing, environmental threats, and a lack of potential reproductive partners. Furthermore populations that lack diversity are susceptible to widespread die-off in the face of significant threats, like a monoculture crop is completely destroyed by a single pest species.

Understanding these mechanisms–and how they impact genetic diversity–could be vital for the future of shark conservation, which is vital to marine ecosystems of all types and this discovery gives some hope for many species.

 

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Arunima Maiti

Arunima Maiti

Biomedical scientist with special interest in reproductive biology.

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