Lead author Dr. Demian Chapman, shark scientist with the Institute for Ocean Conservation Science at Stony Brook University, Beth Firchau, Curator of Fishes for the Virginia Aquarium & Marine Science Center, and Dr. Mahmood Shivji, Director of the Guy Harvey Research Institute and Professor at Nova Southeastern University in Florida, have proven through DNA testing that the offspring of a female blacktip shark named “Tidbit” contained no genetic material from a father. Tidbit had lived at the Virginia Aquarium in the Norfolk Canyon Aquarium for eight years since shortly after her birth in the wild.
In May 2007, Chapman and Shivji were part of a team that made the groundbreaking scientific discovery confirming -– for the first time ever -- a virgin birth in a female shark. That shark was a hammerhead residing at an Omaha, Nebraska zoo and had not been in contact with male sharks for at least three years. That study was published in the journal Biology Letters and captured global media and scientific attention. The DNA-fingerprinting techniques used to prove both cases of virgin birth (scientifically known as “parthenogenesis”) are identical to those used in human paternity testing.
“It is now clear that parthenogenesis occurs in sharks other than just hammerheads,” Chapman said. “The first case was no fluke. It is quite possible that this is something female sharks of many species can do on occasion.”
Sharks’ ability to reproduce alone should not be viewed as an adequate replacement for normal sexual reproduction, Chapman cautioned. For one, the blacktip and hammerhead sharks that reproduced without mating both only produced one pup, rather than an entire litter. Shark litters can contain anywhere from a few to more than a hundred shark pups, depending upon the species. “The revelation that female sharks can reproduce alone shouldn’t stop us from worrying about driving shark populations to very low levels through overfishing,” said Chapman. “It is very unlikely that a small number of female survivors could build their numbers up very quickly by undergoing virgin birth.”
The new paper is entitled “Parthenogenesis in a large-bodied requiem shark, the blacktip Carcharhinus limbatus.” Tidbit was an Atlantic blacktip shark whom Virginia Aquarium biologists believe had only just reached sexual maturity.
“We have never observed her in reproductive behavior or showing typical signs of having been bred,” said Firchau. Scientists did not even know that Tidbit was pregnant until after she unfortunately died and an autopsy (called a necropsy for animals) was performed. “Sadness turned to surprise during the necropsy when we found that she was pregnant,” Firchau said. “There were no male blacktips in the tank for the past eight years!”
The phenomenon of “virgin birth” occurs when a baby is conceived without male sperm having first fertilized the female’s eggs, and has been proven in some bony fish, amphibians, reptiles, and birds. In the type of parthenogenesis seen in these sharks, known as automictic parthenogenesis, the newly forming pup acquires one set of chromosomes when the mother's chromosomes split during egg development. But instead of uniting with similarly split chromosomes from sperm, as occurs in sexual reproduction, the mother’s set is paired with a copy of itself. This results in offspring of reduced genetic diversity who may be at a disadvantage for surviving in the wild.
“The finding of parthenogenesis in blacktip sharks, which are close relatives of some of the larger predatory sharks in the ocean including the tiger, bull and dusky sharks, raises intriguing questions about how frequently parthenogenesis may occur in the wild in this group of heavily fished sharks,” said Shivji. “It is possible that parthenogenesis could become more common in these sharks if population densities become so low that females have trouble finding mates.” Populations of all of these sharks have declined in the past twenty years due to overexploitation, mainly to supply the shark fin markets.
There have been nearly a dozen reports of suspected virgin births in sharks in recent years, but scientists largely assumed these cases were the result of long-term sperm storage by females after mating with males. Virgin birth is now the more probable explanation, and DNA testing is underway to confirm it in additional sharks. Chapman is currently analyzing the DNA of yet another shark species with Dr. Kevin Feldheim of the Field Museum in Chicago.
The Institute for Ocean Conservation Science conducts scientific research about critical threats to oceans and their inhabitants, providing the foundation for smarter conservation policy. The Institute is a major research program of Stony Brook University's School of Marine and Atmospheric Sciences and was founded as the Pew Institute for Ocean Science in 2003. Visit us online at http://www.oceanconservationscience.org and http://www.somas.stonybrook.edu.
Virginia Aquarium is an AZA-accredited institution that takes pride in the care of its animal collections and works to educate the public and further scientific understanding about wild populations. Visit http://www.virginiaaquarium.com.
The Guy Harvey Research Institute (GHRI) is a scientific research and graduate education organization based at the Oceanographic Center of Nova Southeastern University, Florida, USA. The GHRI conducts marine fish biology and ecosystem function on a global scale to provide the knowledge required for more effective management, conservation and policy practices. For more information, please visit http://www.nova.edu/ocean/ghri.
For additional information contact Kathryn Cervino at 347.439.1816
New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)
Reusable carbon nanotubes could be the water filter of the future, says RIT study
30.03.2017 | Rochester Institute of Technology
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
24.04.2017 | Physics and Astronomy
24.04.2017 | Materials Sciences
24.04.2017 | Life Sciences