2015 Annual Science Report
University of Illinois at Urbana-Champaign Reporting | JAN 2015 – DEC 2015
Project 9: Metapopulation Structure
Although often modeled as a single well mixed populations, microbes in terrestrial systems likely exist as metapopulations, isolated but connected by infrequent migration. This can change the evolution of complexity, increasing the effect of genetic drift and decreasing the effect of selection. It can increase diversity and the rate at which complexity evolves. We have argued that metapopulation structure may have existed in early life and been responsible for the rapid evolution of LUCA and diversification across the tree of life. We investigate microbial genome evolution in metapopulations in Yellowstone National Park. We find that indeed they represent evidence for both natural selection and genetic drift shaping these populations.
To address the Darwinian Transition question, we built a quasi-species model of interacting organisms that includes HGT. We ran the simulation in an environment which exhibited a “Mount Fuji” fitness landscale. We discovered that for early times, the system exhibited a progenote phase, with rampant HGT and no unique species. After some time, a transition occurred and HGT switched off, leading to tree-like vertical evolution. It is important to emphasize that the transition is spontaneous and occurs after the population of organisms have evolved their fitness. HGT is still operative, but the actual effect of it becomes minimal because the population has a whole is now near the fitness peak and the likelihood of an improved gene being transferred becomes correspondingly smaller. In other words, HGT drives itself into a regime where it is ineffective. The Darwinian Transition occurs without fine tuning or external factors being adjusted. This result contrasts with earlier theories for the Darwinian Transition which put in by hand the down-regulation of HGT as the organismal complexity increased. In summary, this calculation shows how the Darwinian Transition emerges naturally from HGT dynamics.
PROJECT INVESTIGATORS:Rachel Whitaker
PROJECT MEMBERS:Isaac Cann
RELATED OBJECTIVES:Objective 3.2
Origins and evolution of functional biomolecules
Origins of cellularity and protobiological systems
Production of complex life.
Adaptation and evolution of life beyond Earth