No sex for 40 million years? No problem.

New research shows that tiny asexual creatures have managed to evolve into different species<em> - news Release</em>

Imperial College London news release

Strictly embargoed for
17.00 hours Pacific Daylight Time Monday 19 March 2007
(00.00 hours GMT Tuesday 20 March 2007)

A group of organisms that has never had sex in over 40 million years of existence has nevertheless managed to evolve into distinct species, says new research published today. The study challenges the assumption that sex is necessary for organisms to diversify and provides scientists with new insight into why species evolve in the first place.

The research, published in PLoS Biology, focuses on the study of bdelloid rotifers, microscopic aquatic animals that live in watery or occasionally wet habitats including ponds, rivers, soils, and on mosses and lichens. These tiny asexual creatures multiply by producing eggs that are genetic clones of the mother – there are no males. 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 living in different aquatic environments 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.

Dr Tim Barraclough  from Imperial College London's Division of Biology explained: "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.

"One remarkable example is of two species living in close proximity on the body of another animal, a water louse. One lives around its legs, the other on its chest, yet they have diverged in body size and jaw shape to occupy these distinct ecological niches. Our results show that, over millions of years, natural selection has caused divergence into distinct entities equivalent to the species found in sexual organisms."

Previously, many scientists had thought that sexual reproduction was necessary for speciation because of the importance of interbreeding in explaining speciation in sexual organisms. Asexual creatures like the bdelloid rotifers were known not to be all identical, but it had been argued that the differences might arise solely through the chance build-up of random mutations that occur in the 'cloning' process when a new rotifer is born. The new study proves that these differences are not random and are the result of so-called 'divergent selection', a process well known to cause the origin of species in sexual organisms.

Dr Barraclough adds: "These really are amazing creatures, whose very existence calls into question scientific understanding, because it is generally thought that asexual creatures die out quickly, but these have been around for millions of years.

"Our proof that natural selection has driven their divergence into distinct species is another example of these miniscule creatures surprising scientists – and their ability to survive and adapt to change certainly raises interesting questions about our understanding of evolutionary processes."

-Ends-

For more information please contact:

Danielle Reeves, Imperial College London press office
Tel: +44 (0)20 7594 2198
Mob: +44 (0)7803 886248
Email: Danielle.reeves@imperial.ac.uk

*Please note – images of the bdelloid rotifers are available by email.

Notes to editors:

1. 'Independently evolving species in asexual bdelloid rotifers', PLoS Biology, Monday 19 March 2007.

Diego Fontaneto (1), Elisabeth A. Herniou (2,3), Chiara Boschetti (4), Manuela Caprioli (1), Giulio Melone (1), Claudia Ricci (1), Timothy G Barraclough (2,3,5).

(1) Dipartimento di Biologia, Università di Milano, Milan, Italy.
(2) Division of Biology, Imperial College London, Ascot, UK.
(3) NERC Centre for Population biology, Imperial College London, Ascot, UK.
(4) Institute of Biotechnology, University of Cambridge, Cambridge, UK.
(5) Jodrell Laboratory, Royal Botanic Gardens, Kew, UK.

2. About Imperial College London

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Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

With 62 Fellows of the Royal Society among our current academic staff and distinguished past members of the College including 14 Nobel Laureates and two Fields Medallists, Imperial's contribution to society has been immense. Inventions and innovations include the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of our research for the benefit of all continues today with current focuses including interdisciplinary collaborations to tackle climate change and mathematical modelling to predict and control the spread of infectious diseases.

The College's 100 years of living science will be celebrated throughout 2007 with a range of events to mark the Centenary of the signing of Imperial's founding charter on 8 July 1907.

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