lunes, 21 de septiembre de 2015

Scientists astonished after snake has virgin birth





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A female yellow-bellied water snake in Missouri has amazed scientists by giving birth to offspring without the presence of a male.
The snake, which was at Cape Girardeau Conservation Nature Center, gave birth via a process called parthenogenesis, which essentially means a virgin birth, according to a UPI report.

It’s the second time such a virgin birth has been witnessed in Missouri in as many summers. Unfortunately, none of this year’s brood survived, but two snakes from the last one did make it.

This particular yellow-bellied water snake lives at Cape Girardeau Conservation Nature Center in its own enclosure, so scientists are confident she hasn’t been in contact with any males for a very long time. And yet, they found her again this summer with snake eggs filling her cage. In fact, her caretakers initially thought it was a joke, according to the report.

Not only that, but this type of snake doesn’t give birth to eggs, but rather has live births.

Parthenogenesis is the term for the production of unfertilized eggs, which is rare but not unheard of in nature. It’s actually fairly common in insects, but reptiles, birds, and fish only rarely do it. Mammals don’t do it at all.

And there is more than one type of parthenogenesis, which simply refers to a mode of asexual reproduction where females produce offspring without any genetic contribution from a male.

Unfortunately for this mother snake, there are risks involved with this reproductive method. The offspring didn’t survive probably because of defective chromosome combining, which wouldn’t have been a problem had there been genetic input from a male.

However, sometimes the eggs successfully hatch if the mother has a dissimilar sex chromosome compared to a male.

The yellow-bellied water snake belongs to the Colubridae family of non-venomous snakes, and to the order Squamata, which includes lizards and snakes. It’s a heavy-bodied, medium-sized snaked that is primarily darkly colored along its back, and with a plain yellow baby, hence its name. The snake does not have any pattern, although its young have a brown dorsal and some lateral blotches.

This species of snake can grow to length of about 30 to 48 inches. It prefers to hang out in swamps, lakes, and ponds where the waters are calm, often basking on logs or branches, or on the shore itself.
Although the snake is non-venomous, it will bite if cornered, as most water snakes will.

The snake prefers to eat fish, toads, crayfish, and salamanders. It can be found along the Mississippi river. It is most active in the spring to summer months, mostly March through October, with courtship happening in the spring months.
The snake gives birth to live young, but as has been seen in this one individual snake, sometimes through parthenogenesis it can give birth to eggs without a sexual partner.

Parthenogenesis is seen most often in insects, crustaceans, flatworms, and rotifers, but they are also seen in squamata, which includes lizards and snakes. One of the most well known squamata to produce asexually is the Komodo dragon, but there are certainly plenty of other examples. Whiptails, geckos, and rock lizards also go through parthenogenesis from time to time.

In 2012, researchers in the United States found a pregnant copperhead snake and female cottonmouth pit-vipers that had become impregnated via parthenogenesis.

Essentially, reptiles use a ZW chromosome system, where males have the ZZ chromosome and females the ZW chromosome. Most scientists had though that the creation of a WW offspring was impossible in the ZW chromosome system, but scientists in 2010 found a boa constrictor that had done just that.

Scientists have studied this phenomenon in the New Mexico whiptail. Its genus, Cnemidophorus, has 15 species that reproduce via parthenogenesis exclusively.
Bizarrely, there is still a mating ritual often involved in parthenogenesis in squamata, but it is often a role played by the female. The female will mount the other female that is about to lay eggs. Scientists think this has to do with the hormonal cycle of females that cause them to behave like males. This sexual behavior stimuli seems to help with reproductive results.

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