Scientists were shocked to discover female brownbanded bamboo sharks store sperm for as long as four years.
The finding was made when an egg case dropped by a female shark that had been isolated from males four 45 months showed signs of healthy development, the California Academy of Sciences reported. The findings reveal the longest documented case of sperm storage in any species of shark.
"Long-term sperm storage -- where a female can delay fertilization for months or even years after mating -- is a remarkable adaptation that helps promote genetic diversity," said Luiz Rocha, Academy Curator of Ichthyology. "In contrast, asexual reproduction produces offspring with very little genetic variation. Exploring the bamboo shark's ability to store sperm gives us hope that wild sharks can help protect their population's genetic diversity when mates are scarce and serious threats arise."
To make their findings the researchers used advanced genetic tools; they collected DNA-rich slivers from the fins of shark pups and their mothers during their annual exam and ran them through a number of genetic tests. On one gene test a shark pup displayed comparable results with each female on a particular genetic test that looks at genetic variation within an individual. This finding made the possibility of the sharks being birthed through asexual production less likely because in this case the offspring would have shown less genetic variation than that of its mother. The shark pups also contained genetic material that could not be explained through DNA analysis of the mother, suggesting it was inherited from the father.
"Questions remain," said lead author Moisés A. Bernal, a Ph.D. candidate and researcher in the Academy's Ichthyology Department. "We know that several species of sharks have reproductive tricks like storing sperm or reproducing by parthenogenesis in the absence of males, but we need to know when and how these alternate techniques are triggered. Understanding these mechanisms -- and how they impact genetic diversity -- could be vital for the future of shark conservation."
The findings were published in a recent edition of the Journal of Fish Biology.
