(Press-News.org) Contact information: Richard Hund
rhund@botany.org
314-577-9557
American Journal of Botany
From one cell to many: How did multicellularity evolve?
The evolutionary path from unicellular life to multicellularity is varied, but all lead to complex organisms
In the beginning there were single cells. Today, many millions of years later, most plants, animals, fungi, and algae are composed of multiple cells that work collaboratively as a single being. Despite the various ways these organisms achieved multicellularity, their conglomeration of cells operate cooperatively to consume energy, survive, and reproduce. But how did multicellularity evolve? Did it evolve once or multiple times? How did cells make the transition from life as a solo cell to associating and cooperating with other cells such that they work as a single, cohesive unit?
Karl Niklas (Cornell University, Ithaca, NY), a plant evolutionary biologist, is interested in how plants have changed over the past few million years, in particular their size, shape, structure, and reproduction. As the first article in a series of Centennial Review papers celebrating 100 years of the American Journal of Botany, Niklas reviews the history of multicellularity and the changes that cells must have had to go through—such as aspects of their shape, function, structure, and development—in order to be able to functionally combine with other cells. He also explores the underlying driving forces and constraints (from natural selection to genetics and physical laws) that influence the evolution of multicellularity.
As a student, Niklas started out being interested in mathematics, but then turned to studying plants because of their "mathematical-like structure." "Multicellularity is a fundamental evolutionary achievement that is capable of mathematical description," comments Niklas, "and one that has occurred multiple times in different plant lineages."
Indeed, no matter how it is defined, scientists agree that multicellularity has occurred multiple times across many clades. Defined in the loosest sense, as an aggregation of cells, multicellularity has evolved in at least 25 lineages. However, even when defined more strictly—requiring that cells be connected, communicate, and cooperate in some fashion or another—it has still notably evolved once in animals, three times in fungi, six times in algae, and multiple times in bacteria.
Multicellularity could have been achieved numerous times based on the premise that selection acts on phenotypes and how well certain combinations of traits work. In other words, even if cells adhere together using different mechanisms, or via different developmental pathways, if the results are cooperative aggregations of cells that function well and thus are able to survive better and, critically, produce more offspring than their unicellular counterparts, then these various evolutionary pathways could all be possible.
"The curtail point," emphasizes Niklas, "is that the evolution of multicellular organisms occurred multiple times and involved different developmental 'motifs,' such as the chemistry of the 'glues' that allow cells to stick together."
Certainly, one of the themes that Niklas drives home in his review is that natural selection acts on functional traits, so multicellularity could have evolved many times via different mechanisms and modes of development, and using different aspects of cellular biology.
However, there are certain sets of requirements that must be met in order for multicellularity to evolve. These include that cells must adhere to, communicate with, and cooperate with each other, and that cells must specialize in their functions (i.e., that not all cells do exactly the same thing, otherwise they would just be a group of cells or a colony). In order to make these things happen, cells must not reject each other. In other words, they must be genetically compatible to some extent—analogous to how our human bodies reject foreign items that are not recognized by our cells. This first step is termed "alignment-of-fitness."
Interestingly, this "alignment-of-fitness" requires a "bottleneck" or unicellular stage when the organism consists of just one cell—a spore, zygote, or uninucleate asexual propagule. This is necessary so that all subsequent cells share similar genetic material.
The "export-of-fitness" stage is the second step necessary to the evolutionary process of multicellularity. This requires that cells work together for a common goal of reproducing more cohesive units, or individuals, like themselves and thereby work in a concerted way toward increasing their fitness. Once this is achieved, a distinct phenotype, or form, of organism exists.
How exactly steps such as cell-to-cell adhesion or communication were achieved in plants, animals, fungi, and algae differs among the major eukaryotic clades, yet an important aspect is that these multicellular organisms all went through a similar series of steps on their way to becoming multicellular, functional organisms.
As Niklas puts it: "This convergent evolution is well summarized by the saying 'There are many roads to Rome, but Rome is not what it used to be'."
In fact, these stages can be mapped on to theoretically possible body plans, illustrating the most plausible series of evolutionary steps—unicellular to colonial to multicellular—that is seen in algae, land plants, and animals. Niklas also posits a plausible alternate evolutionary route, starting with a single cell containing multiple nuclei (e.g., from a siphonous to multicellular form) and finds support for this in the observed forms of some fungi and algae.
"This review of the literature has now brought my attention to 'cooperation'" concludes Niklas, "because multicellularity requires cells to work together. Cheating cells cannot be tolerated over the long run because like a cancer they can gain the upper hand and kill a multicellular organism."
INFORMATION:
Niklas, Karl J. 2014. The evolutionary-developmental origins of multicellularity. American Journal of Botany 101(1):6-25. doi:10.3732/ajb.1300314
The Open Access full article is available at http://www.amjbot.org/content/101/1/6.full.pdf+html.
The Botanical Society of America is a non-profit membership society with a mission to promote botany, the field of basic science dealing with the study and inquiry into the form, function, development, diversity, reproduction, evolution, and uses of plants and their interactions within the biosphere. It has published the American Journal of Botany for nearly 100 years. In 2009, the Special Libraries Association named the American Journal of Botany one of the Top 10 Most Influential Journals of the Century in the field of Biology and Medicine. The AJB is celebrating 100 years of publication in 2014.
For further information, please contact the AJB staff at ajb@botany.org.
From one cell to many: How did multicellularity evolve?
The evolutionary path from unicellular life to multicellularity is varied, but all lead to complex organisms
2014-01-25
ELSE PRESS RELEASES FROM THIS DATE:
Carbon dioxide paves the way to unique nanomaterials
2014-01-24
In common perception, carbon dioxide is just a greenhouse gas, one of the major environmental problems of mankind. For Warsaw chemists CO2 became, however, something ...
Material developed could speed up underwater communications by orders of magnitude
2014-01-24
University of California, San Diego electrical engineering professor Zhaowei Liu and colleagues have taken the first steps in a project to develop fast-blinking ...
Scientists reveal why life got big in the Earth's early oceans
2014-01-24
Why did life forms first begin to get larger and what advantage did this increase in size provide? UCLA biologists working with an international team of scientists examined the ...
10 years on Mars leads to livable mud
2014-01-24
Some of the oldest minerals ever analysed by NASA's Mars Opportunity Rover show that around four billion years ago Mars had liquid water so fresh it could have supported life.
The findings were announced in a special 'Exploring ...
40 percent of parents learn how to use technology from their children
2014-01-24
Washington, DC (January 21, 2014) – Just how are adults learning to use technology? Chances are if ...
Biomarker for stress hormones in polar bears, wildlife affected by global climate change
2014-01-24
AMHERST, Mass. – Chemical analyses by neuroscientist Jerrold Meyer and colleagues at the University of Massachusetts Amherst are helping to establish hair ...
Landmark egg production study reveals reduction in environmental impact over past 50 years
2014-01-24
PARK RIDGE, Ill., (January 24, 2014) – A new study published ...
Do religious people love their neighbors? Yes -- some neighbors, Baylor study finds
2014-01-24
Most religions teach their followers to "Love thy neighbor" — including those of different races, nationalities or beliefs. But is religiousness really related to love of neighbors? ...
CWRU researchers find epileptic activity spreads in new way
2014-01-24
Researchers in the biomedical engineering department at Case Western Reserve University have found that epileptic activity can spread through a part of the brain in a new way, suggesting a possible ...
2-way street
2014-01-24
Scientists have called for data held in biobanks to be made accessible to the people donating material and data to them. In a paper published today in Science, ...
LAST 30 PRESS RELEASES:
GDF-15 and eGFRdiff: Predicting kidney risk and survival in diabetes mellitus
Detecting cancer cells in blood: the development of microchannel devices with microcone arrays
SLAS Discovery: Advancing tools for cancer fibrosis and drug discovery
Researchers create ‘virtual scientists’ to solve complex biological problems
AI-Powered brain stimulation at home could enhance concentration, new research finds
Carbon-based molecules open new pathways for quantum sensing
Immunotherapy for leukemia may affect the bone marrow environment, cancer researchers find
World’s largest tropical peatlands revealed to be more than 40,000 years old
Pick up the pace of your daily walk to boost longevity, experts say
Normal hormone levels trigger severe depression in some women; researcher discovers mechanism
Mexican neuroscientist identifies glutamate biomarker predicting schizophrenia treatment success
Living brain tissue reveals 80% of genes behave differently than assumed
How much time did our ancestors spend up trees? Studying these chimpanzees might help us find out
Discovery of role of gut hormone in chronic diarrhoea could aid development of new tests and treatments
New discovery reveals the spinal cord’s role in bladder control
Kākāpō decline reveals threat of parasite coextinction
Astrocytes identified as hidden culprit behind PTSD
Offering self-collection kits in routine GP appointments could prevent 1,000 women a year from developing cervical cancer
European study offers clearer picture of childhood brain tumor survival
The Lancet: Three in five liver cancer cases due to preventable risk factors; obesity-linked cases on the rise, new analysis suggest
Tiny artificial cells can keep time, study finds
How aging quiets lupus and brings relief to some older patients
Research alert: Synergistic treatment approach supercharges cancer immunotherapy
White veteran high users of online portal generate and exchange more messages than certain patient minorities in the Veterans Health Administration
Web-based tool helps Michigan physicians navigate diabetes coverage and prior authorization
Most primary care patients with opioid use disorder who start treatment stay engaged
U.S.-born Latinos have higher rates of obesity compared to foreign-born Latino and white youth
Study finds veterans experiencing homelessness who gain housing are more likely to get colorectal and breast cancer screenings
Body fat percentage beats BMI in predicting 15-year mortality risk among U.S. adults ages 20 to 49
Umbrella review summarizes family physicians’ experiences with clinical integration
[Press-News.org] From one cell to many: How did multicellularity evolve?The evolutionary path from unicellular life to multicellularity is varied, but all lead to complex organisms