RT Journal Article
SR Electronic
T1 Non-linear tradeoffs allow cooperation to evolve from Prisoner’s Dilemma to Snow Drift
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 091041
DO 10.1101/091041
A1 Lin Chao
A1 Santiago F. Elena
YR 2016
UL http://biorxiv.org/content/early/2016/12/06/091041.abstract
AB The existence of cooperation or the production of public goods is a major evolutionary conundrum. Restricting the goods to kin or to reciprocating individuals is promoted as a solution, but that is inappropriate because the benefits are no longer public. Without kinship or reciprocation, the evolution of cooperation is limited by the Prisoner’s Dilemma (PD) game, which drives cooperators to extinction and selects for defectors that produce fewer public goods. Here we use existing molecular and genetic information on RNA viruses to create a mathematical model for the evolution of cooperation as a function of group size. While diffusible gene products are public goods, group size is represented by the number of virions co-infecting a host cell. Our results show that if a virus’ investment into replication versus making gene products conforms to a linear tradeoff, the viruses evolve into a monomorphic population that remains trapped by PD. However, if the tradeoff is non-linear and group size exceeds a threshold, selection is diversifying and the population bifurcates into a dimorphic state with lineages of ultra-defectors and ultra-cooperators. The modeling of a non-linear tradeoff and ultra-defectors was motivated by the existence of viral defective interfering (DI) particles, which are contracted viral genomes that lack coding regions and therefore gain an extra advantage by being smaller than defectors that make some public goods. If group size is further increased, the ultra-cooperators evolve to produce public goods at a maximum rate that matches the production evolved by kin selection. The emergence of ultra-defectors and ultra-cooperators in our model creates the Snow Drift (SD) game, which is the most advanced form of cooperation. Thus, our model shows that evolution can easily transition from PD to SD via the increase of group size. Although formulated for viruses, our model is easily adaptable to most biological systems.