Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Do you need sex to be a species? Speciation in asexual rotifers

20.03.2007
If you own a birdbath, chances are you’re hosting one of evolutionary biology’s most puzzling enigmas: bdelloid rotifers. These microscopic invertebrates—widely distributed in mosses, creeks, ponds, and other freshwater repositories—abandoned sex perhaps 100 million years ago, yet have apparently diverged into nearly 400 species.

Bdelloids have remained an enduring enigma in part because biologists are still debating whether the species actually exist as true evolutionary entities. And if they do, what forces determine how they diverge? In the traditional view of species diversification, interbreeding promotes cohesion within a population—maintaining the species—and barriers to interbreeding (called reproduction isolation) promote species divergence. With no interbreeding to maintain cohesion, the thinking goes, asexual taxa might not diversify into distinct species.

In a new study published in PLoS Biology , Diego Fontaneto, Timothy Barraclough, and colleagues developed new statistical techniques for combined molecular and morphological analyses of rotifers to test the notion that species diversification requires sex. The researchers show that, despite an ancient aversion for interbreeding, bdelloids display evolutionary patterns similar to those seen in sexually reproducing taxa. How they have avoided the pitfalls of a lifestyle widely regarded as evolutionary suicide remains an open question.

Fontaneto et al. predicted that if factors other than interbreeding, such as niche specialization, controlled species cohesion and divergence, then asexual taxa should diverge along the same lines as sexually reproducing organisms. And if this were the case, they would expect to find genetic and morphological cohesion within independently evolving populations and divergence between them.

To detect independently evolving populations, the researchers analyzed marker genes isolated from clones of bdelloids collected from diverse habitats around the world. They constructed evolutionary trees using these and also did a morphological analysis where they measured the size and shape of the rotifers’ jaws (called trophi). The morphological results largely fell in line with traditional taxonomic classifications for most bdelloid species. And species identified as related on the DNA trees typically had similar morphology.

The correspondence between the molecular and morphological results suggests that the majority of traditionally identified bdelloid species are what’s known as monophyletic: individuals in the same species assort together on the evolutionary tree and share a common ancestor. Using statistical models to determine the likely origin of the observed DNA tree branching patterns, the researchers show that these distinct monophyletic genetic clusters represent independently evolving entities (rather than variations within a single asexual population).

But what caused them to evolve independently? Are they geographically isolated populations that evolved under neutral selection, or did they evolve into ecologically discrete species as a result of divergent selection pressures on trophi morphology? If bdelloids have experienced divergent selection, the researchers explain, they would expect to see high variation in trophi traits between species, and low intraspecies variation (compared to neutral changes). And that’s what they found: bdelloids have experienced divergent selection on trophi size (and to a lesser degree, on trophi shape) at the species level.

Altogether, these results show that the asexual bdelloids have indeed experienced divergent selection on feeding morphology, most likely as they adapted to different food sources found in different niches. By showing that asexual organisms have diverged into “independently evolving and distinct entities,” the researchers argue, this study “refutes the idea that sex is necessary for diversification into evolutionary species.” They hope others use their approach to study mechanisms underlying species divergence in sexual taxa to clarify the hazy nature of species and biological diversity.

Andrew Hyde | alfa
Further information:
http://www.plosbiology.org
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050087

More articles from Life Sciences:

nachricht Cancer diagnosis: no more needles?
25.05.2018 | Christian-Albrechts-Universität zu Kiel

nachricht Less is more? Gene switch for healthy aging found
25.05.2018 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Powerful IT security for the car of the future – research alliance develops new approaches

The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.

Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...

Im Focus: Molecular switch will facilitate the development of pioneering electro-optical devices

A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.

The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...

Im Focus: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

In focus: Climate adapted plants

25.05.2018 | Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

 
Latest News

In focus: Climate adapted plants

25.05.2018 | Event News

Flow probes from the 3D printer

25.05.2018 | Machine Engineering

Less is more? Gene switch for healthy aging found

25.05.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>