No Sex Required

An all-female species, distantly related to flatworms, steals all of genetic material it needs to diversify its genome.

By Edyta Zielinska | November 19, 2012

Scanning electron micrograph of bdelloid rotifers.Wikimedia, Diego FontanetoA microscopic rotifer called a bdelloid, often studied as an interesting exemplar of asexual reproduction, has taken up to 10 percent of its genome from an estimated 500 other species in order to maintain genetic diversity, according to a new study published last week (November 15) in PLOS Genetics.

Animals that don’t swap genetic information through sex are often thought to eventually go extinct because their lack of genetic diversity prevents them from adapting to the changing environment and new niche opportunities. As a result, John Maynard Smith called bdelloids an “evolutionary scandal,” reported ScienceNOW. Despite this, these organisms, which live in aquatic environments, such as puddles, sewage treatment plants, or dew drops on soil, have lived for an estimated 80 million years.

Earlier studies have found that bdelloids have some foreign genetic material, but the extent of the borrowing was only studied in depth in the new study, which found that about one tenth of its DNA came from other species. Although it’s unclear how the microscopic organisms acquire the foreign DNA, it appears that they adopt many of the functions encoded within. Indeed, as much as 40 percent of the bdelloid’s enzymatic activity has a foreign component, the researchers found. “Its biochemistry is a mosaic in the same way,” Alan Tunnacliffe, a molecular biologist at the University of Cambridge in the United Kingdom and head author on the paper told ScienceNOW. “It's a real mishmash of activities.” The animal has sequences for the generation of enzymes that have only been seen in much simpler organism, for example, including two genes encoding enzymes that break down bezyl cyanide, and two others, apparently from a parasitic protozoan, that generate a compound involved in protection from cellular damage.

"We have a joke in the lab that every time you investigate these animals . . . they come out with something weird," Tunnacliffe told ScienceNOW. "It's like they're here to keep us entertained and surprised."

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Avatar of: James V. Kohl

James V. Kohl

Posts: 526

November 19, 2012

Excerpted from the article: "Although it’s unclear how the microscopic organisms acquire the foreign DNA, it appears that they adopt many of the functions encoded within."

From Kohl (2012) : "Among different bacterial species existing in similar environments, DNA uptake (Palchevskiy & Finkel, 2009) appears to have epigenetically ‘fed’ interspecies methylation and speciation via conjugation (Fall et al., 2007; Finkel & Kolter, 2001; Friso & Choi, 2002). This indicates that reproduction began with an active nutrient uptake mechanism in heterospecifics and that the mechanism evolved to become symbiogenesis in the conspecifics of asexual organisms (Margulis, 1998)."

If, acquisition of foreign DNA is not a receptor-mediated event consistent with nutrient chemical uptake (referenced above), how could asexual reproduction be controlled by the epigenetic effects of nutrient chemicals and pheromones as is required in all species (to avoid out-reproducing the nutrient chemical supply in the ecological niche required for social niche construction)?

Avatar of: Meganmiller


Posts: 1

December 5, 2012

That's kind of weird. I imagine it might be kind of frustrating to be leave without sex relationships.

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