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AP/Dave Thompson
Flora, a komodo dragon, was able to concieve without the help of a mate, only the second time
that the phenomenon of parthenogenesis has been seen in a komodo dragon.

Parthenogenesis: When Animals Reproduce Without a Mate

March 25, 2010
by Haley A. Lovett
In the wild, some female animals are able to create offspring without the help of a mate, a process known as parthenogenesis.

How Does Parthenogenesis Work?

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Parthenogenesis happens when an unfertilized egg produces an offspring. According to MSN Encarta, the term “parthenogenesis” comes from Greek terms meaning “virgin creation.”

Depending on the species, parthenogenesis happens for different reasons. Some species that normally reproduce sexually will sometimes reproduce asexually, either for lack of males, for population sex control, or in some cases because of an abundance of resources.

How the cell division happens during reproduction in each species determines if the resulting offspring from parthenogenesis will be an exact clone of the mother or not. Parthenogenesis occurs in lower animals such as insects, and in only about .1 percent of vertebrate species, according to Scientific American.

Swiss scientist Charles Bonnet discovered the phenomenon of parthenogenesis in the 1700s through his studies of aphids.

What Animals Are Capable of “Virgin Births?”

While there are a number of species that are capable of parthenogenesis, below are a few of the more interesting cases.

The New Mexico whiptail is one of few species that has only female members. This animal, which is also the state reptile of New Mexico, reproduces solely through parthenogenesis, and males have become obsolete. According to the Daily Texan, the females do continue mating behaviors, though. If two of the females are placed together in a cage, their ovulation cycles will synchronize oppositely and one will act more male during the ovulation of the other. The animals are even known to mount each other as if mating.

In 2006 two different cases of virgin births by Komodo dragons were discovered in England. In the first, a group of eggs hatched in April from a Komodo dragon named Sungai at the London Zoo. The second set of eggs hatched from a Komodo dragon named Flora at the end of the same year, according to National Geographic. Scientific American reported that some female reptiles are able to store sperm for years after copulation, so initially some scientists believed the hatchlings might actually have a father, but DNA testing proved that the baby lizards were in both cases the product of parthenogenesis. 

Komodo dragons are one species with the WZ chromosome makeup, so all of the parthenogenesis offspring are male. What this means, explains LiveScience, is that a female could become isolated from her population—as might happen in the island areas where Komodo dragons originate—and she could create an entire population of her own by mating with her male offspring.

Sharks are another animal not known, until recently, to be able to reproduce by parthenogenesis. In December of 2001, according to New Scientist, in a tank of three female hammerhead sharks, a shark pup suddenly appeared. Scientists argued for years about how the baby had appeared, and in 2007, after analyzing the pup’s DNA, they found that it was the product of only one animal, its mother.

In 2008, after a blacktip shark died, an autopsy revealed that she had been pregnant with a pup resulting from parthenogenesis. As reported by LiveScience, the shark, named Tidbit, had been in captivity for eight years and had no contact with male sharks during that time. DNA confirmed the parthenogenesis hypothesis. All shark pups resulting from parthenogenesis will be female.

Honey bees are also able to reproduce without fertilization, although the purpose of the parthenogenesis reproduction is slightly different than in other animals. The queen bee only mates once during her lifetime (although she may mate with many male bees during that time). According to MSN Encarta, the sperm is used to fertilize some of her eggs, which will become female worker bees. Her unfertilized eggs will grow into bees via parthenogenesis and will all be male drones.

The Myth: All Offspring Created Through Parthenogenesis Are Female

In animals whose sex is determined by chromosomes as opposed to incubation temperature, all offspring created due to parthenogenesis will be the same sex. However, what sex that will be depends on the sex chromosome setup of the individual animal. Scientific American explains that for many species that use a similar sex chromosome setup as humans—XX for females, XY for males—all of the offspring of parthenogenesis will be female, as the mother has no Y chromosome to give.

In some species, however, the like pairing of chromosomes, WW as it is called for these animals, creates a male, and the unlike pairing, WZ, creates a female. In parthenogenesis, each egg contains only one type of chromosome. This means that the only viable offspring created from parthenogenesis in these species will be male, as any ZZ embryos would not survive.
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