I need to be putting some science up in this blog as I am a scientist, after all!
So to start here is a story about a virgin birth from a Hammerhead shark. Just wait until that makes it into the next Shark Attack movie!
Hammerhead Shark in Nebraska Gives Virgin Birth
Wednesday, May 23, 2007
DUBLIN, Ireland — Female sharks can fertilize their own eggs and give birth without sperm from males, according to a new study of the asexual reproduction of a hammerhead in a U.S. zoo.
The joint Northern Ireland-U.S. research, being published Wednesday in the Royal Society’s peer-reviewed Biology Letters journal, analyzed the DNA of a shark born in 2001 in the Henry Doorly Zoo in Omaha, Neb.
The shark was born in a tank with three potential mothers, none of whom had contact with a male hammerhead for at least three years.
Analysis of the baby shark’s DNA found no trace of any chromosomal contribution from a male partner. Shark experts said this was the first confirmed case in a shark of parthenogenesis, which is derived from Greek and means “virgin birth.”
Asexual reproduction is common in some insect species, rarer in reptiles and fish, and has never been documented in mammals.
The list of animals documented as capable of the feat has grown along with the numbers being raised in captivity — but until now, sharks were not considered a likely candidate.
“The findings were really surprising because as far as anyone knew, all sharks reproduced only sexually by a male and female mating, requiring the embryo to get DNA from both parents for full development, just like in mammals,” said marine biologist Paulo Prodahl of Queen’s University of Belfast, Northern Ireland, a co-author of the report.
Before the study, many shark experts had presumed that the Nebraska birth involved a female shark’s well-documented ability to store sperm for a lengthy period of time. Doing this for six months is common, while three years would be exceptional, they agreed.
The lack of any paternal DNA in the baby shark ruled out this possibility.
“We were all very skeptical about these reports, about the possibility of a so-called virgin birth in a shark, because sharks have this unusual ability to store sperm for months if not years. So this finding is new and definitely unexpected,” said Bob Hueter, director of the Center for Shark Research at the Mote Marine Laboratory in Sarasota, Fla., who wasn’t involved in the project.
He noted that sharks have been on Earth longer than other species higher up the evolutionary chain that have also demonstrated this ability, such as lizards and birds.
The report’s other co-author, Mahmood Shivji of the Guy Harvey Research Institute in Dania Beach, Fla., said the finding explained growing numbers of reports of mystery, male-free shark births in captivity.
Shivji said the research “may have solved a general mystery about shark reproduction,” because it suggests that sharks can “switch from a sexual to a non-sexual mode of reproduction.”
But he said this was not necessarily a positive ability because baby sharks produced only by the mother suffer from “reduced genetic diversity.”
Genetic diversity makes living creatures better able to adapt to threats, such as disease.
Remember that recently a female Komodo Dragon had a virgin birth as well, proving that their species could also. No word on if the komodo was a gigantic mutant komodo or if it fought a cobra.
Female Komodo Dragon Has Virgin Births
By Jeanna Bryner, LiveScience Staff Writer
posted: 20 December 2006 01:03 pm ET
Maybe females could live without males, at least for Komodo dragons. These behemoths of the reptile world can produce babies without fertilization by a male, scientists recently discovered.
Currently at London’s Chester Zoo, one mother-to-be named Flora [image] is waiting for her eight offspring to hatch, each one the result of a process called parthenogenesis–or a virgin conception.
“Parthenogenesis has never been documented in Komodo dragons before now, so this is absolutely a world first,” said co-researcher Kevin Buley of Chester Zoo.
No sperm needed
Parthenogenesis, in which an unfertilized egg develops to maturity, has been found in 70 species of vertebrates, including captive snakes and a monitor lizard species. In most of these reptile cases, this process is their only method of reproduction.
In some whiptail lizards, males have become somewhat of an accessory, and all individuals are female. The type of asexual reproduction in whiptail lizards generates all-female offspring.
The Komodo dragon, turns out, can do both: they can reproduce sexually or asexually depending on their environmental conditions. At most zoos, females live alone and are kept separate from other dragons.
Magic dragon
In May of this year, Flora laid 25 eggs, of which 11 were viable. The zookeepers knew Flora had played both mom and pop as soon as they confirmed her eggs were fertile. That’s because Flora had never come into contact with a male dragon while at the zoo.
Three of the developing eggs collapsed during incubation, providing embryonic material for testing this theory. The zoo staff worked with Phillip Watts of Liverpool University to carry out genetic analysis of the collapsed eggs.
“This paternity test confirmed that all the genetic material in the eggs had come from Flora and that she was indeed both the mother and the father of the developing eggs,” Buley told LiveScience.
Egg-cellent
Both males and females carry out meiosis in which cells divide to form the respective sex cells, sperm or egg. In females, meiosis produces four egg-progenitor cells, one of which becomes the egg while the other three typically get reabsorbed by the female’s body. For Flora, one of the extra cells acted like a surrogate sperm and fertilized the egg cell, explained Buley.
The one-parent event resulted in offspring containing the same genetic material as their mother. Flora’s infant dragons will not be her clones, however, because there is genetic shuffling going on during the egg production stage, Buley said.
For instance, not all copies of genes are identical and each gene has an alternate form. If a person has two “alleles” for blond hair she would show a head of sunny hair, but if one allele was for blond and the other for dark brown, the person could show up a brunette. The same shuffling process occurred in the Komodo dragon babies.
Family affairs
With the ability to reproduce without male mates, Komodo females could potentially found an entirely new colony on their own. “Theoretically, a female Komodo dragon in the wild could swim to a new island and then lay a fertile clutch of eggs,” Buley said.
The downside is that all hatchlings resulting from this type of parthenogenesis are males. “These would grow up to mate with their own mother and therefore, within one generation, there would potentially be a population able to reproduce normally on the new island,” Buley explained.
In the long-term this Oedipus-like practice could lead to health problems associated with inbreeding, as the entire colony would have such low genetic diversity.
The results also have implications for captive-breeding programs that have sprouted to ensure the survival of the threatened lizards. Fewer than 4,000 Komodo dragons are thought to remain in the wild, residing on just three islands in Indonesia.
Scientists wonder if the act of keeping males and females separate could cause them to switch from sexual to asexual reproduction, which could lead to decreased genetic diversity.
The discovery is detailed in the Dec. 21 issue of the journal Nature.
