Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Succulent plants waited for cool, dry Earth to make their mark

04.05.2011
Between 5 and 10 million years ago, the landscape on Earth changed dramatically.

Brown University biologists and colleagues have determined that cacti exploded onto the global scene then, about the same geologic time as other succulent plants and tropical grasses.

The trigger: A global period marked by cooling and increaed aridity, possibly with lowered atmospheric carbon-dioxide levels. Their findings appear in the Proceedings of the National Academy of Sciences.

The cactus, stalwart of the desert, has quite a story to tell about the evolution of plant communities found the world over.

In a paper published in the online edition of the Proceedings of the National Academy of Sciences, Brown University biologists and colleagues have discovered that the rapid speciation of cacti occurred between 5 and 10 million years ago and coincided with species explosions by other succulent plant groups around the world. The researchers propose that a prolonged dry spell and possibly lower levels of atmospheric carbon dioxide during that time, known as the late Miocene, opened habitat that contributed to the rise of these plants and a broad vegetative makeover on Earth.

“The cacti, as a group, have been around for a while, but most of the species diversity that we see today was generated really recently,” said Monica Arakaki, a postdoctoral researcher at Brown and the paper’s lead author.

The Brown team and colleagues from Oberlin College and the University of Zurich, Switzerland, were interested primarily in dating the origins of the cacti (scientific name Cactaceae). The team sequenced the chloroplast genomes (the organelles inside plant leaves that engineer photosynthesis) for a dozen cacti and their relatives and combined their new genomic data with existing genomes to build a phylogeny, or evolutionary tree, for angiosperms, the genealogical line of flowering plants that represents roughly 90 percent of all plants worldwide. From there, the scientists deduced that Cactaceae first diverged from its angiosperm relatives roughly 35 million years ago but didn’t engage in rapid speciation for at least another 25 million years.

“Cacti were actually present on the landscape for millions of years — looking like cacti and acting like cacti — before they began their major diversification,” said Erika Edwards, assistant professor of biology in the Department of Ecology and Evolutionary Biology at Brown and corresponding author on the paper.

The team then sifted through the literature on the timing of diversification in other succulents from regions around the globe. Succulents include aloes, the agaves of North America, the ice plants of South Africa and other lineages. Their comfort zone is in water-limited climates, and they have adapted physical characteristics to cope in those locales, such as shallow root systems, specialized water-storing tissue and exchanging gas at night, when it is cooler and less humid and so less water is lost. What struck the researchers was that all the succulent lineages, across habitats and continents, underwent major speciation between 5 and 10 million years ago, during roughly the same time period as the cacti.

C4 grasses, the tropical grasses that are now up to 20 percent of our planet’s vegetative covering, burst onto the scene as well during this same window of time.

This must be more than a coincidence, the researchers thought. “It isn’t overly surprising that most of the standing cactus diversity is relatively young. But when you put these species radiations in the context of all the other changes in plant communities that were happening at that very moment, all over the world, it begs some sort of global environmental driver,” Edwards said.

The most plausible causes, the scientists thought, were a drying out of the planet and lowering of atmospheric carbon-dioxide levels. A wealth of research involving oxygen isotopes from a deep-sea organism showed the Earth underwent a drop in temperature, which the researchers believe led to reduced rainfall and increased aridity worldwide.

The carbon-dioxide link is more nuanced and controversial. The authors highlight one study that inferred atmospheric CO2 levels spiraled downward beginning roughly 15 million years ago. Combined with global cooling, “a drop in CO2 concentration would therefore immediately expand the ecological space in which drought-adapted succulent plants, with their high photosynthetic water use efficiency, would be competitive,” the authors write.

“We suggest that a rapid expansion of available habitat (rather than any particular new ‘key’ innovation) during the late Miocene was a primary driver of the global diversification of plant lineages already possessing a preadapted succulent syndrome,” the researchers write. “Against a backdrop of increasing global aridity, a sharp CO2 decline is a plausible driver of the simultaneous expansion of C4 grasslands, the clustering of new C4 origins, and the diversification of succulent lineages.”

Contributing authors include postdoctoral research associate Pascal-Antoine Christin, graduate student R. Matthew Ogburn, and undergraduate student Elizabeth Spriggs, all of Brown; Reto Nyffeler and Anita Lendel from the University of Zurich; Urs Eggli from the Succulent Plant Collection in Zurich; and Michael Moore from Oberlin.

The U.S. National Science Foundation funded the research.

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

Richard Lewis | EurekAlert!
Further information:
http://www.brown.edu

More articles from Life Sciences:

nachricht New catalyst controls activation of a carbon-hydrogen bond
21.11.2017 | Emory Health Sciences

nachricht The main switch
21.11.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>