Wednesday, December 20, 2006

The evolution of robustness

Genomic robustness is just one of those things that seems almost counter-intuitive. For evolution to take place, one needs to have imperfect replication of the genetic material to generate diversity. At the same time mutations are a danger to fitness as the chance that they will be beneficial is slim. And so most organisms have mechanisms to protect against deleterious mutations such as proofreading enzymes, DNA repair enzymes, apoptosis, and redundant genes. And so there is a fine balance in the evolvability rate, where a less stable genome permits higher diversity and presumably a better chance to evolve fast enough to cope with changing environments, versus robustness to make sure the species doesn't go the way of the dodo. A nice article in PLOS asks this question: "And if robustness has evolved to maintain performance, what prevents systems from becoming ever more robust?"

The articles then goes into more details, one of which might interest you virus people:
"Populations evolving at high mutation rates may settle in regions of genotypic space where mutations are less deleterious, on average, than those regions that attract populations that experience low mutation rates. The idea is that evolution at low mutation rates favors populations that achieve high fitness peaks, even if they are surrounded by steep cliffs, because mutations that push progeny off those cliffs are rare. By contrast, at high mutation rates, most offspring carry mutations, and selection favors populations that find lower fitness peaks surrounded by less precipitous mutational chasms. Experiments with digital organisms (self-replicating computer programs) provide direct support for “survival of the flattest” at high mutation rates [8]. RNA viruses also have very high mutation rates, and a recent experiment implicated the importance of mutational robustness for them, in this case, by showing the loss of robustness in viruses that evolved at high multiplicities of infection, where co-infecting particles guaranteed redundancy and allowed their native robustness to decay [9]."

Very interresting stuff. Darwin would be proud. He was rich bitch.


Bayman said...

Thought-provoking article, although their flippant abuse/overuse of the term "robustness" made it a bit tough to follow.

rob said...

it's pronounced Rob - ustness. As in that paper it quite good, it shows good Robustnes.