AP Biology class blog for discussing current research in Biology

Odd Little Species Survives Without Sex

Of the two million know species on Earth, only about two thousand reproduce entirely asexually. Scientists think this is because organisms that reproduce without sex – which provides healthy genes from one parent that act as a template to repair mutated genes, leading to “theoretically healthier offspring” – are unable to mitigate the deleterious effects of gene mutation, which leads to their extinction. The bdelloid, a tiny, all-female, sea creature with a name that means “leechlike” for the way it moves, however, has survived for tens of millions of years without sex. In fact, they have diversified into more than four hundred species.

Researchers at the Marine Biology Laboratory in Woods Hole, MA wanted to find out why the bdelloid had avoided extinction, so they zapped some of the creatures with gamma radiation, which breaks up DNA. Oddly, the bdelloids did not succumb to the exposure even as the scientists pushed the radiation levels far past what would naturally occur on earth. When the mystified biologists examined the bdelloids’ DNA, they discovered that an early mutation had copied the entire genome, giving each organism four copies as opposed to the common two, which allowed it to repair severely damaged DNA. This mutation turned out to be beneficial for the aquatic creatures because it allows them to survive desiccation, a danger for bdelloids because of their transient underwater habitats.

More recently, scientists at the University of Cambridge published a paper in the journal PLoS Genetics recounting their discovery that about ten percent of the bdelloid’s genome is composed of alien DNA amassed through the consumption of bacteria, fungi, and algae. These foreign genes become active when a bdelloid dries out, and are thought to be partly responsible for the creature’s incredible ability to survive dehydration. Those same genes might also be behind “powerful antioxidants that protect bdelloids from the by-products of drying out”.

Evolutionary biologists are hopeful that a better grasp of the mechanisms that allow bdelloids to survive will lead to much greater discoveries such as how sex evolved. Matthew Meselson, a geneticist at Harvard University, said in an interview with LifeScience that “being able to understand how animal cells can be so resistant to radiation may be of some interest in understanding how [cancer, aging, and inflammation, of which DNA damage and repair are factors] might be inhibited in human cells.” Further experimentation could uncover new treatments that prolong life or fight cancer.

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  1. rawgdog

    I agree with sciencegirl025, cool post! It’s amazing how these bdelloids survive such strong radiation. I find it amusing how these small, relatively insignificant creatures have essentially found the key to immortality! This article reminded me of another one about a species of bacteria that can also survive strong radiation by packing its DNA into a small, incredibly dense ring formation (look at image in link below). Another thought that came to my mind is that these creatures could eventually be the only representatives for life on earth given that they can essentially travel through space without being affected by radiation. Just some food for though:)

    Here is the link to the article:

  2. sciencegirl025

    Great article! I especially find it interesting that the bdelloid has developed the capabilities to survive dehydration and desiccation. Its really fascinating how it can repair its’ DNA as a means of repairing its DNA and saving the specie from extinction! I read an article that explains how mutations happen rarely with asexual reproducing organisms so with new generations they become extinct because they didn’t have the means of adapting to new factors in the environment. You should check it out!

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