Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists Confirm Second-Ever Case of Virgin Birth by Shark

13.10.2008
Scientists have confirmed the second-ever case of a “virgin birth” in a shark, indicating once again that female sharks can reproduce without mating and raising the possibility that many female sharks have this incredible capacity. This compelling new study will be published today in the latest issue of the Journal of Fish Biology, a leading international journal.

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

Kathryn Cervino | Newswise Science News
Further information:
http://www.stonybrook.edu
http://www.oceanconservationscience.org
http://www.virginiaaquarium.com

More articles from Studies and Analyses:

nachricht The personality factor: How to foster the sharing of research data
06.09.2017 | ZBW – Leibniz-Informationszentrum Wirtschaft

nachricht Europe’s Demographic Future. Where the Regions Are Heading after a Decade of Crises
10.08.2017 | Berlin-Institut für Bevölkerung und Entwicklung

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>