Evolution and increasing information

[SteveF]

Interesting upcoming (and free access) paper in Biology Direct:

Takeuchi, N. and Hogeweg, P. (2008) Evolution of complexity in RNA-like replicator systems. Biology Direct, upcoming

Background

The evolution of complexity is among the most important questions in biology. The evolution of complexity is often observed as the increase of genetic information or that of the organizational complexity of a system. It is well recognized that the formation of biological organization---be it of molecules or ecosystems---is ultimately instructed by the genetic information, whereas it is also true that the genetic information is functional only in the context of the organization. Therefore, to obtain a more complete picture of the evolution of complexity, we must study the evolution of both information and organization.

Results

Here we investigate the evolution of complexity in a simulated RNA-like replicator system. The simplicity of the system allows us to explicitly model the genotype-phenotype-interaction mapping of individual replicators, whereby we avoid preconceiving the functionality of genotypes (information) or the ecological organization of replicators in the model. In particular, the model assumes that interactions among replicators---to replicate or to be replicated---depend on their secondary structures and base-pair matching. The results showed that a population of replicators, originally consisting of one genotype, evolves to form a complex ecosystem of up to four species. During this diversification, the species evolve through acquiring unique genotypes with distinct ecological functionality. The analysis of this diversification reveals that parasitic replicators, which have been thought to destabilize the replicator's diversity, actually promote the evolution of diversity through generating a novel "niche" for catalytic replicators. This also makes the current replicator system extremely stable upon the evolution of parasites. The results also show that the stability of the system crucially depends on the spatial pattern formation of replicators. Finally, the evolutionary dynamics is shown to significantly depend on the mutation rate.

Conclusions

The interdependence of information and organization can play an important role for the evolution of complexity. Namely, the emergent ecosystem supplies a context in which a novel phenotype gains functionality. Realizing such a phenotype, novel genotypes can evolve, which, in turn , results in the evolution of more complex ecological organization. Hence, the evolutionary feedback between information and organization, and thereby the evolution of complexity.

They introduce:

How complexity can increase through evolution has been one of the most important questions in biology. As is well recognized, the formation of biological organization—be it of protein complexes or of ecosystems—is ultimately instructed according to the genetic information, which is stored as the patterns of nucleotide sequences in genomes. Hence, the above question boils down to how genetic information increases through evolution. This is, however, a one-sided view. The patterns in nucleotide sequences are
biologically functional only in conjunction with the organization (e.g., consider the function of a regulatory gene). Thus, organization and information are mutually dependent, and this interdependence is, as this study will show, a key to understanding the evolution of biological complexity.

The conclusions are:

Complex ecological organization can evolve in a simple RNA-like replicator system, where parasitic replicators actually promote the evolution of diversity, rather than inhibit it.

Smaller mutation rates allow the evolution of complex ecological organization, while greater mutation rates inhibit it.

Extreme persistence is observed in the replicator system where the evolution at the individual level determines the system’s ecological organization, and vice versa.

This study demonstrates an evolutionary feedback between information and organization and, therewith, suggests a potential scenario for the evolution of biological complexity.

http://www.biology-direct.com/content/3/1/11

[espritch]

Smaller mutation rates allow the evolution of complex ecological organization, while greater mutation rates inhibit it.

That seems a little counter intuitive. I wonder if this might be due to a need for stability in host replicators to allow for evolution of parasitic replicators? They indicate that parasites promote diversity, but I imagine it would be difficult for parasites to develop if the host was changing too quickly since they have to adapt to match the host.

[RBH]

That seems a little counter intuitive. I wonder if this might be due to a need for stability in host replicators to allow for evolution of parasitic replicators? They indicate that parasites promote diversity, but I imagine it would be difficult for parasites to develop if the host was changing too quickly since they have to adapt to match the host.On a very fast scan of the paper itself, the "high" mutation rates appear to have been up close to the error catastrophe threshold, so that may have played into it. When I have time I'll read the paper more carefully.

[RBH]

OK, on a second fast reading, the high mutation rate with the consequent increased number of deleterious mutations inhibits the evolution of parasites. Apparently the parasites are 'fragile' early in their evolution and are easily disrupted by point mutations (the only kind of mutation in the study). Interestingly, parasites that evolved for some time in a lower mutation rate condition are thereafter robust in a high mutation rate condition.

[SAWells]

Evolution of increased information by duplications and point mutations:

The cat sat on the mat.

The cat sat on the mat, the cat sat on the mat.

The cat sat on the mat, the rat sat on the mat.

The cat sat on the mat, the rat sat on the cat. :)