Who are my Neighbours? Selection Targets Robustness to Full Replication Events, Not to Individual Mutations

The theory suggests that populations should develop mutational robustness, the ability to maintain a constant phenotype despite mutations. However, selection does not focus on individual mutations, but on entire replication events, which can involve different numbers of mutations. To clarify this, researchers distinguish between mutational robustness and replicative robustness.

While the two concepts may appear similar at first glance, an evolutionary simulation model reveals that they can be selected for in different ways.

Genomes with high redundancy and/or large amounts of non-coding DNA are mutationally robust, meaning they maintain a constant phenotype even with mutations. Yet, these same genomes are replicatively fragile because their size leads to a higher number of mutations per replication event. This becomes particularly important when genomes are vulnerable to severe disruption from chromosomal rearrangements.

The fitness landscape metaphor, often used to explain robustness evolution, proves to be limiting. Neutral plateaus in this metaphor can be mutationally robust but replicatively unstable, making them less favored by selection. Conversely, narrow peaks resulting from densely encoded genomes can replicate more reliably, despite potentially being less mutationally robust.

In conclusion, the study identifies replicative robustness as a separate target of selection, not just concerned with tolerance to individual mutations, but also with the overall likelihood of those mutations occurring.