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June 4, 2008 13:24

Bdelloid rotifers

Russian scientists, currently employed in Harvard University and Josephine Bay Paul Centre in comparative molecular biology and evolution, made a fantastic discovery. They proved that tiny freshwater animals bdelloid rotifers permanently borrow genes from bacteria, fungi and even plants. Moreover, these animals make alien genes work.

Bdelloid rotifers are among numerous mysteries of Mother Nature, since they propagate by means of virgin birth or parthenogenesis (which is an asexual form of reproduction found in females where growth and development of embryos or seeds occurs without fertilization by males). This fact is not the only one that makes these animals so wonderful. After spending 40 million years on out planet bdelloid rotifers belong to over than 360 various species having no sexual reproduction, which has always been considered to be the key to genetic variability.

This discovery is a real bomb, an evolutional scandal, since gene recombination of two parents appeared to be needless for successful development of a whole class of living beings.

The secret seems to be revealed soon. Biologists detected massive horizontal gene transfer in bdelloid rotifers, which enrich their own genome with DNA fragments, taken form fungi, plants and bacteria! Previous facts of horizontal gene transfer were noted only in bacteria. Animals exchanged genes only in case of a parasite or an endosymbiont interacting with its host.

Researchers claim that adopted genes work in new conditions. Well, definitely not all of them, but they work, and this explains excellent ability of bdelloid rotifers to adapt to various ecological niches and their species formation. When animals are able to absorb and adapt genes of other living beings, they may exchange genes between each other, which is evolutional equivalent to sexual reproduction.

However, scientists do not have clear view of how these animals do their trick. Possible explanation of such incredible ability is bdelloid rotifers skill to survive droughts. Hot weather dries these animals, and their vital activities almost stop. Dried like chips, bdelloid rotifers can wait for years until water brings them back to life.

Horizontal gene transfer
Well, biologists know that these animals have a special mechanism for repairing DNA and cell membranes, damaged during the dry season. Moreover, bdelloid rotifers are able to recover after powerful irradiation, and biologists claim recovery mechanism is the same like in case of a drought.

When a bdelloid rotifer is dried as a raisin, its DNA is open for attachment of alien genes. Most of such inclusions were found near telomeres (regions of repetitive DNA at the end of chromosomes, which protect the end of the chromosome from destruction). Dry weather makes chromosome ends more open for insertions. Central parts of chromosomes also had foreign genes, but much less than ends. Chromosomes we are talking about are inside germline cells. When drought is over, happy bdelloid rotifer repairs its DNA with all newcomer genes, and its progeny will differ from parent organism.



Science Magazine

Kizilova Anna


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