Ecological collapse and the emergence of traveling waves in transitional turbulence
How a laminar flow
becomes turbulence has been a long-standing problem in fluid dynamics
and is important in various industrial applications. As Reynolds number
increases, a single turbulent puff in a long pipe undergoes spontaneous relaminarization and spatiotemporal intermittency
and can expand into turbulent slugs, exhibiting non-trivial statistics
in transient times that have been found in experimental observation and
hydrodynamics simulations. I am studying transitional turbulence by
connecting it to spatially-extended ecosystems. We have found the extinction event and the formation and propagation of spatial patterns in predator-prey systems can be interpreted as the instabilities in fluid systems. I am also studying such connection in other hydrodynamics systems.
Nature Physics 12, 245 (2016), Journal of Statistical Physics (2016).
Collective co-evolution of cyanobacteria and cyanophages mediated by horizontal gene transfer
Horizontal gene transfer is a powerful driving force for accerlerating evolution. We study a model for how antagonistic predator-prey coevolution can lead to mutualistic adaptation to an environment, as a result of horizontal gene transfer. Our model is a simple description of ecosystems such as marine cyanobacteria and their predator cyanophages, which carry photosynthesis genes. These genes evolve more rapidly in the virosphere than the bacterial pan-genome, and thus the bacterial population could potentially benefit from phage predation. By modeling both the barrier to predation and horizontal gene transfer, we study this balance between individual sacrifice and collective benefits. The outcome is an emergent mutualistic coevolution of improved photosynthesis capability, benefiting both bacteria and phage. This form of multi-level selection can contribute to niche stratification in the cyanobacteria-phage ecosystem.
Rapid evolution
One of the important questions in ecology is how evolution affects ecological systems. Conventionally,
the evolutionary time scale is usually assumed to be too long, such
like millions of years, when compared with the life time of species. However,
how exactly the evolutionary process occurs and changes ecological
systems to become the contemporary structures is unknown. Moreover, the
evolution time scale could be comparable to the ecology, such that
antibiotic resistance keeps emerging rapidly in the treatment for
bacterial infections. In fact, anomalous dynamics of ecosystems under
evolution has been observed in lab experiments, which is so-called
"rapid evolution". Rapid evolution may arise from fast response to
strong selection among distinct strains. By applying statistical
mechanics approach and stochastic simulation to a generic simple model
based on the
individual-level behaviors, we find the intrinsic stochastic nature of
the system can lead to the emergence of rapid evolution. We also worked
out the phase diagram where fluctuation-determined extinction is
considered.
Phys. Rev. E 90, 050702(R) (2014).
Evolution of phenotypic fluctuations
Phenotype fluctuations are pervasive, and can be important in various scenarios in evolution. Phenotypic fluctuations have been conjectured to be beneficial characteristics to protect against fluctuating selection from environmental changes, the so-called “bet-hedging” strategy. However, it is not well-understood how phenotypic fluctuations shape the evolutionary trajectories of organisms. To address these questions we have performed directed evolution experiments and modeling on the speed of migration phenotype of chemotactic bacteria. We present a theoretical model that recapitulates the observed reduction of phenotypic fluctuations in experiment. Our stochastic modeling on the evolution of migration fronts suggests that whether or not phenotypic fluctuations grow or shrink during successive rounds of selection and growth is determined by both strength of selection and the existence of physical constraints.