what is all the fuss about sex?
No Sex For 40 Million Years? No Problem
That is the time since when rotifers do exist, a group of organisms that during all that time has never had sex. These tiny creatures multiply by producing eggs that are genetic clones of the mother — there are no males. Nevertheless they managed to evolve into distinct species, says new research published today. These findings challenge the dogma that sex is necessary for organisms to diversify. As such, whatever sex is about, it is not about avoiding extinction of the species…
Scanning electron micrographs showing morphological variation of bdelloid rotifers and their jaws, the “wheels” or rota. (Credit: Diego Fontaneto / Courtesy of PLoS Biology)
The research, published in PLoS Biology, provides scientists with new insight into why species evolve in the first place. Fossil records and molecular data show that bdelloid rotifers have been around for over 40 million years without sexually reproducing, and yet this new study has shown that they have evolved into distinct species.
Using a combination of DNA sequencing and jaw measurements taken using a scanning electron microscope, the research team examined bdelloid rotifers across the UK, Italy and other parts of the world. They found genetic and jaw-shape evidence that the rotifers had evolved into distinct species by adapting to differences in their environment.
“We found evidence that different populations of these creatures have diverged into distinct species, not just because they become isolated in different places, but because of the differing selection pressures in different environments”, says Dr. Tim Barraclough from Imperial College London’s Division of Biology. “Our results show that, over millions of years, natural selection has caused divergence into distinct entities equivalent to the species found in sexual organisms.”
What Are Rotifers?
Rotifers are small, mostly freshwater animals, and are amongst the smallest members of a group of multicellular animals which includes humans, and whose bodies are organized into systems of organs.
Most rotifers are about 0.5mm in length or less, and their bodies have a total of around a thousand cells. This means that their organ systems are a greatly simplified distillation of the organ systems found in the bodies of the higher animals.