In January 2012, curators at the Steinhart Aquarium of the California Academy of Sciences got a surprise – the birth of a shark bamboo brownbanded in a tank that had the potential dads, only three possible mothers. How did it happen? Moisés A. Bernal and other scientists of the Academy wanted to find out, so they began to tease out the history of female sharks’ to understand how the shark child came to be. The results of their study were published December 28 in the Journal of Fish Biology.
The Steinhart Aquarium in San Francisco bought the three bamboo sharks brownbanded female in September 2007 from the Aquarium of the Pacific in Long Beach, Calif., Where they had been kept with males of their species. For a year, females have been living in a temporary structure and produced eggs that were discarded. Then the three females were moved to new facilities in Golden Gate Park, where their tank mates were female blacktip reef sharks and a lone male cownose ray Javanese. Sharks bamboo brownbanded still eggs and liquidators referred cases of eggs collected in January 2011. In November, two of these cases of eggs showed signs of embryonic development. A hatched January 21, 2012
The researchers considered three possible scenarios for how this shark pup came to be: The shark was the result of a hybridization between females and only Javanese cownose ray; the puppy result of parthenogenesis – a type of reproduction in which the offspring develops from an unfertilized egg; or mama shark stored sperm of the father for a long, long time.
The first option was rejected outright – the two species are so far apart that hybridization would be unlikely, the scientists concluded. But the other two, they decided, were worthy of consideration. Parthenogenesis had been documented in a similar species, the shark bamboo whitespotted. And several species of sharks are known to store sperm for periods of months or years. The strategy allows a female to mate successfully, even when his body is still ovulating and ready to start playing.
The team did not know which of the three female sharks had laid the egg, though, so compared the DNA markers of offspring and his three possible mothers. The analysis revealed that the puppy was more closely related to a shark labeled “Female A” in the document – its likely mom – but also had the genetic material of unknown origin. The verdict: The puppy has a father.
The coupling must have occurred in 2007, when the shark mama was still at the Aquarium of the Pacific, which means it has preserved his sperm for at least 45 months – a record in sharks. But who the father was, or where it is now is a mystery. “Unfortunately,” the researchers write, “there is no information about where the sharks who shared the enclosure with three females of this study.”