Washington: Biologists from the California Academy of Sciences have found a shark egg case dropped by an adult bamboo shark that has signs of healthy development.
The scientists had good reason for surprise as the Steinhart Aquarium's female shark adults had spent nearly four years - 45 months - in complete isolation from males!
The young shark most likely inherited this "mystery" genetic material from its father - an unknown male from the aquarium.
"Long-term sperm storage - where a female can delay fertilisation for months or even years after mating - is a remarkable adaptation that helps promote genetic diversity," said Luiz Rocha, curator at ichthyology department of California Academy of Sciences.
This is the first documentation of long-term sperm storage in brown banded bamboo shark (Chiloscyllium punctatum).
After mating, some female sharks can store sperm in the tubules near their oviduct - reproductive area that helps produce the jelly-like substance surrounding fertilised shark eggs.
This type of genetic diversity is a boon for wild populations.
There are two possibilities: Either a female adult shark reproduced asexually in a process called "parthenogenesis" or it had stored sperm from its last mating event several years before the fertilized egg appeared in the lagoon.
Diversity is key in maintaining the health of fishes - particularly those pared down by overfishing, environmental threats, and a lack of potential reproductive partners.
Fish that lack diversity are susceptible to widespread die-off in the face of significant threats.
"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," said Moises A. Bernal, a researcher in the academy's ichthyology department.
"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," Luiz Rocha said.
The results were published in the Journal of Fish Biology.