[p2p-research] Cooperation and Experimental Evolution

[Ryan]

  Sent to you by Ryan via Google Reader: Cooperation and Experimental
Evolution via Oscillator on 1/24/10

Cooperation and altruism are widespread in biology, from molecules and
genes working together in a cell, to bacterial communities that require
coordinated behavior to survive in a tough environment, to human
relationships and societies. Our human cultural perspective (perhaps
even more specifically our American cultural perspective, focused as it
is on individuality, free markets, and the American Dream), however,
treats cooperation as an outright anomaly that has to be explained away
by science (or often, religion). If natural selection is about
the "survival of the fittest" how can a selfless gene be rewarded
evolutionarily, surviving to the next generation? If evolution is about
individuals locked in a battle for resources, why would anyone share
with a friend?

Many experiments have shown that cooperation may actually not be so
anomalous, and in fact may be a driving force for evolutionary change
and diversity. Using experimental evolution, a synthetic approach to
evolutionary theory where researchers try to observe evolutionary
changes in controlled populations in the lab, several groups have shown
that symbiotic, cooperative, and altruistic behaviors can rapidly
evolve in many different situations. A recent paper from PLoS
Biology, "Experimental Evolution of a Plant Pathogen into a Legume
Symbiont" (ht Coturnix!) applied this kind of synthetic approach to
plant/bacteria cooperation (in depth paper synopsis here). Many plants
and bacteria have evolved a complex mutualistic relationship, where the
plants will protect the bacteria from the harsh soil environment and
the bacteria will provide crucial nutrients to the plant. Rhizobia are
species of bacteria that invade the root tissue of legume plants and
form small nodules where the bacteria grow and provide nitrogen that
the host plant needs to grow. These species have coevolved to this
complex mutualistic relationship over millions of years, but the
authors found that after only a few generations pathogenic bacteria
developed many of the behaviors required for the root nodule symbiosis,
with many implications for evolutionary theory. From the paper's
conclusion:
Our results show that adaptive genomic changes indeed allow effective
dissemination of symbiotic traits over large phylogenetic and
ecological distances. The fact that a single gene played a major role
in the shift from extracellular pathogenesis to endosymbiosis
reinforces previous reports that global regulators are preferred
targets for evolution and supports fluid boundaries between parasitism
and mutualism.
Other researchers have found similar results in very different model
systems. Myxobacteria are single-celled organisms that live in large
populations. When food is scarce, the bacteria activate a complex
cascade of events where the population transforms itself from slime to
a complicated fruiting body, with individuals performing highly
specialized behaviors, including a huge number of individuals
sacrificing themselves to provide food for the remaining cells, the
ultimate altruistic behavior. Genetic mutations in a population of
myxobacteria will lead to "cheater" cells that won't go through the
same changes when they are on their own and starve, but will free-ride
on altruistic neighbors in a mixed population with the wild type
strain. A 2006 paper in Nature, "Evolution of an Obligate Social
Cheater to a Superior Cooperator", started with this "obligate cheater
strain" and allowed it to compete against the wild type in a laboratory
evolution setup. They found that a single mutation in a gene that had
previously not been identified as important for this process was able
to turn the cheater strain not only into a cooperator, but into a
cooperator that was able to outcompete all the ancestral strains.
Scientists don't fully understand the processes that underly many of
these cooperative interactions, but what is clear is that the evolution
of these behaviors seems to be faster and more likely to spontaneously
emerge than many people think.

There is a huge diversity of cooperative relationships in nature that
expand the ability of living things to inhabit all ecological niches,
but symbiosis has an even more central role in the evolution of life on
earth. It is now widely accepted that complex eukaryotic cells (cells
with a nucleus, like our own) evolved as the result of symbiosis
between different prokaryotic (no nucleus, like bacteria). Organelles
inside eukaryotic cells that provide energy, like chloroplasts in
photosynthetic organisms and mitochondria in almost every eukaryotic
cell, often have their own genetic material, left over from the time
when they were free-living organisms. When Lynn Margulis proposed this
serial endosymbiotic theory of eukaryotic evolution in the 1960's
(based on theories of Russian botanists in the late 1800's and early
1900's) she was ridiculed by the biological establishment. The dogma at
the time held not only that evolution must proceed through the
accumulation of only small incremental changes, but also that symbiosis
was a weird thing that only a few species of fungi did, not important
stuff to molecular biologists. To the scientists, the notion that
nature was cruel, that cooperation shouldn't exist was the norm, and
the idea that evolution could be driven by cooperation at such a large
scale was unthinkable. Margulis persevered, and eventually everyone
realized that she was right all along. Decades later however, the
marginal, "weird" status of cooperation in the biological literature
remains, and Margulis warns that we should be careful with the words we
use when discussing it, that we shouldn't color our understanding of
reciprocal biological relationships with how we think about economics,
politics, and other human constructions. Other synthetic biology
experiments will perhaps further show that cooperation may be
more "natural" than science currently allows it to be.
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