Bielawski, J. P. | bioRxiv Science

bioRxiv2020

MLS3: A New Type of Multilevel Selection

In most multispecies multilevel selection (MLS) models, offspring communities are generated by random assembly of individuals in numbers reflecting sizes of parental communities releasing them (MLS1), or by differential community dispersal based on a community-level trait such as size (MLS2). In both, offspring communities colonize vacant spaces: different communities never compete for the same space. Here we propose a third MLS type (MLS3) where multispecies communities disperse (migrate) into already-occupied spaces, larger communities more frequently. Conspecific variants compete, often opposing selection for community size against fitness within species. This makes the outcome of MLS3 less apparent than MLS1 and MLS2 where such tension is absent. Our simulations show that, if community size depends strongly on reduction in the fitness of individual community members, such a reduction (comprising a sort of "inter-species altruism") will evolve. The framework we present represents a step toward conceptualizing community coalescence in the context of metacommunities.

evolutionary biology↗

bioRxiv2020

The ups and downs of amino acid co-evolution: evolutionary Stokes and anti-Stokes shifts

The most fundamental form of epistasis occurs between residues within a protein. Epistatic interactions can have significant consequences for evolutionary dynamics. For example, a substitution to a deleterious amino acid may be compensated for by replacements at other sites which increase its propensity (a function of its average fitness) over time - this is the evolutionary Stokes shift. We discovered that an opposite trend -the decrease in amino acid propensity with time-can also occur via the same epistatic dynamics. We define this novel and pervasive phenomenon as the evolutionary anti-Stokes shift. Our extensive simulations of three natural proteins show that evolutionary Stokes and anti-Stokes shifts occur with similar frequencies and magnitudes across the protein. This high-lights that decreasing amino acid propensities, on their own, are not conclusive evidence of adaptive responses to a changing environment. We find that stabilizing substitutions are often permissive (i.e., expand potential evolutionary paths) whereas destabilizing substitutions are restrictive. We show how these dynamics explain the variations in amino acid propensities associated with both evolutionary shifts in propensities.

evolutionary biology↗