Navigation Links
Genome duplication responsible for more plant species than previously thought
Date:8/12/2009

BLOOMINGTON, Ind. -- Extra genomes appear, on average, to offer no benefit or disadvantage to plants, but still play a key role in the origin of new species, say scientists from Indiana University Bloomington and three other institutions in this week's Proceedings of the National Academy of Sciences.

Plant biologists have long suspected polyploidy -- the heritable acquisition of extra chromosome sets -- was a gateway to speciation. But the consensus was that polyploidy is a minor force, a mere anomaly that accounts for 3 or 4 percent of the world's flowers and ferns.

The first direct, comprehensive survey of polyploid speciation in plant evolution severely challenges that notion.

"In the present paper, we make it clear that it is a common process," said evolutionary biologist and lead author Troy Wood, who began the research during graduate training at IU Bloomington. "Fifteen percent of flowering plant species and almost a third of fern species are directly derived from polyploidy."

Wood is now a research scientist at University of Muenster in Germany.

Could polyploidy provide plants with a powerful advantage over their chromosome-challenged peers? Not necessarily. The scientists' exhaustive survey of published phylogenetic and genomic data also shows that plant lineages starting with a polyploid ancestor appear to be no more successful at spawning species than diploid plants, which have two sets of chromosomes.

"The fact that polyploidy seems to have no effect on diversification rates should reduce the number of enthusiastic commentaries about the 'advantages of polyploidy,'" said IU Bloomington evolutionary biologist and paper coauthor Loren Rieseberg, who supervised the research. "However, our diversification rate analyses only examined recent polyploids. A future area of research should be to ask whether more ancient polyploidy events have increased diversification rates."

Rieseberg holds joint appointments at the University of British Columbia and IU Bloomington.

"The present study developed out of an ongoing project to write a book about plant speciation," Rieseberg said. "I felt that recent estimates of the polyploid speciation rate were too conservative because they did not take genealogical history into account. Troy began compiling chromosome number data and phylogenetic trees so that we could generate a more accurate estimate of the frequency of polyploid speciation."

While the variation that leads to new species is usually a glorious accident, evolutionary biologists are beginning to identify the biological properties of organisms that make those accidents stick around long enough for new species to become established. If whatever separates the new breed from its original population is tenuous, it's possible the new and old populations will comingle, negating the possibility of a new species. Geographic separation or "reproductive isolation" is crucial.

Mechanisms of reproductive isolation are almost as vast and varied as the species they make possible.

In some animals, sudden, heritable changes in the size and shape of genitalia have the potential to prevent some individuals of a population from mating with most of the others. Even though sexually reproducing plants do not rely on this sort of "lock and key"-type of sex matching, they have equivalent, more subtle systems for preventing the wrong pollen from fertilizing their eggs.

Polyploidy can also result in speciation, as polyploid individuals often cannot produce viable offspring with their diploid (two sets of chromosomes) relatives. While the polyploid and diploid individuals may appear more-or-less identical to one another, their genetics make sexual reproduction unlikely or impossible.

Some animals can handle polyploidy, but for most vertebrate species, an extra chromosome set is a death sentence. Humans, for example, can barely tolerate the presence of even one extra chromosome out of the total set of 23. Most human "trisomies," as these are called, result in natural abortion, or miscarriage. Non-lethal human trisomies result in developmental disorders, such as Down Syndrome. Human zygotes with three full sets of chromosomes do not develop.

Plants are pretty special. Not only can many species tolerate extra chromosome sets, but polyploidy appears to be a recurring theme throughout plant evolution. The question is why.

"Recent data reveal evidence of polyploidy in an array of plants, like grapes, poplar trees, corn, and many others," Wood said. "In most of these cases the evidence points to ancient polyploid events. Some species of flowering plants have more than 400 chromosomes and some fern species more than 1,000 due to repeated instances of polyploidy during their evolution. While these examples might seem remarkable, given the high frequency of polyploidy speciation documented here, the bigger surprise would be if plant lineages were found in which polyploidy was absent."

One implication of the PNAS paper is that Wood, Rieseberg, and their coauthors may be getting close to solving the mystery. If extra genomes provide no special advantage over relatives, the ubiquity of polyploidy in plants could simply be because polyploid mutants are commonly produced. Evolutionary change that doesn't involve the plus-or-minus forces of natural selection is called "neutral" in evolutionary biology parlance.

"I really thought we would find evidence that polyploids have an advantage," Wood said. "The idea that the large number of polyploid species and the attending high chromosome numbers might be simply due to a neutral process is intriguing."


'/>"/>

Contact: David Bricker
brickerd@indiana.edu
812-856-9035
Indiana University
Source:Eurekalert  

Related biology news :

1. Unravelling new complexity in the genome
2. Conquest of land began in shark genome
3. One species entire genome discovered inside anothers
4. Genome study shines light on genetic link to height
5. First individual genome sequence published
6. Ultraconserved elements in the genome: Are they indispensable?
7. $10 million gift to support cutting-edge epigenome center at USC
8. Fungus genome yielding answers to protect grains, people and animals
9. Which came first, the chicken genome or the egg genome?
10. Researchers expand efforts to explore functional landscape of the human genome
11. Genome update defines landscape of breast and colon cancers
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Genome duplication responsible for more plant species than previously thought
(Date:12/15/2016)... , Dec. 14, 2016 "Increase in ... biometrics market" The mobile biometrics market is expected to ... 49.33 billion by 2022, at a CAGR of 29.3% ... factors such as the growing demand for smart devices, ... transactions. "Software component is expected to grow ...
(Date:12/8/2016)... , Dec. 8, 2016 Market Research Future published ... Market. The global Mobile Biometric Security and Service Market is expected ... to 2022. Market Highlights: ... , , Mobile Biometric ... due to the increasing need of authentication and security from unwanted ...
(Date:12/7/2016)... PUNE, India , December 7, 2016 According to ... NLP, Machine Learning), Software Tool (Facial Expression, Voice Recognition), Service, Application Area, End ... size is estimated to grow from USD 6.72 Billion in 2016 to USD ... Continue Reading ... ...
Breaking Biology News(10 mins):
(Date:1/16/2017)... , Jan. 16, 2017  Eurofins Genomics today ... will allow more customers to receive their primers in ... or compromise in quality found with other providers. Express ... United States at no additional fee. ... routine genetic studies, including DNA sequencing, genotyping, site-directed mutagenesis, ...
(Date:1/13/2017)... ... January 13, 2017 , ... Two Kalamazoo ... compound called fulvic acid that farms, greenhouses and hydroponics operations use to increase ... among the fastest growing segments of customers using this high grade fulvic acid ...
(Date:1/12/2017)... ... January 12, 2017 , ... ... times capable of performing routine electrochemical biosensing has increased dramatically. Primarily driven ... sensitive detection and quantification of various analytes in complex samples. ...
(Date:1/12/2017)... January 12, 2017 A new report published by Allied Market ... Global Opportunity Analysis and Industry Forecast, 2014-2022," projects that the global in vitro toxicity ... at a CAGR of 15.07% during the forecast period. ... ... ...
Breaking Biology Technology: