Looking for Darwin in Endosymbionts

ABSTRACT

Darwinian evolution has championed mechanistic models explaining the forces shaping species diversification. This principle however has been challenged by tantalizing observations in many organismal systems where selection seemed to have a minor role. One such a system is the case of endosymbiotic bacteria of insects that present evolutionary features only conceivable if stochastic variation over-weights selection. This is because these bacteria present proteomes with high rates of evolution that have driven the biological system to the edge of catastrophe error. In this review I discuss and demonstrate, based on recent emerging literature and other observations, that rather than a fact this stochasticity is only apparent. Most of the variation patterns can be explained if we introduce new variables in the equation that defines selection-drift balance such as translational robustness, functional divergence and epistasis. The main conclusion of this review is that, endosymbiotic bacterial proteomes have evolved an evolutionary complex proteome/interactome system robust to mutations.