For the second time in history, newDNA evidence shows that a female blacktip shark in Virginia fertilized her ownegg without mating with a male shark. This is the second time scientists haveused DNA testing to verify shark parthenogenesis—the process that allowsfemales of some species to produce offspring without sperm. The female shark, dubbed Tidbit, died duringa routine physical exam before the pregnancy was identified. A necropsy—ananimal autopsy—after her death revealed she was carrying a near-term pup fetusthat was about 12 inches (30 centimeters) in length. Tidbit was caught in thewild when she was very young and reached sexual maturity in a tank at theVirginia Aquarium in Virginia Beach, where she lived for eight years.
Lead author Dr. Demian Chapman, whois a shark scientist with the Institute for Ocean Conservation Science at StonyBrook University, Beth Firchau, Curator of Fishes for the Virginia Aquarium& Marine Science Center, and Dr. Mahmood Shivji, Director of the Guy HarveyResearch Institute and Professor at Nova Southeastern University in Florida,have proven through DNA testing that the offspring of a female blacktip sharknamed “Tidbit” contained no genetic material from a father. Tidbit had lived atthe Virginia Aquarium in the Norfolk Canyon Aquarium for eight years sinceshortly after her birth in the wild. Chapman stated in the NationalGeographic article that there were no male blacktip sharks in the tank for theentire time of her captivity.
Chapman and his colleaguesgenerated a DNA fingerprint for the mother shark and her pup fetus with aprocedure identical to a human paternity test.
Ordinarily, a shark’s DNA containssome genetic material from its mother and some from its father. Tidbit’s pup,however, was not ordinary.
Sharks’ ability to reproduce aloneshould not be viewed as an adequate replacement for normal sexual reproduction,Chapman cautioned. For one, the blacktip and hammerhead sharks that reproducedwithout mating both only produced one pup, rather than an entire litter. Sharklitters can contain anywhere from a few to more than a hundred shark pups,depending upon the species. “The revelation that female sharks can reproducealone shouldn’t stop us from worrying about driving shark populations to verylow levels through overfishing,” said Chapman. “It is very unlikely that asmall number of female survivors could build their numbers up very quickly byundergoing virgin birth.”
Tidbit was an Atlantic blacktipshark whom Virginia Aquarium biologists believe had only just reached sexualmaturity.