The effect of migration and variation on populations of Escherichia coli adapting to complex fluctuating environments

Migration, a critical evolutionary force, can have contrasting effects on
adaptation. It can aid as well as impede adaptation. The effects of
migration on microbial adaptation have been studied primarily in simple
constant environments. Very little is known about the effects of migration
on adaptation to complex, fluctuating environments. In our study, we
subjected replicate populations of Escherichia coli, adapting to
complex and unpredictably fluctuating environments to different
proportions of clonal ancestral immigrants. Contrary to the results from
simple/constant environments, the presence of clonal immigrants reduced
all measured proxies of fitness. However, migration from a source
population with a greater variance in fitness resulted in no change in
fitness w.r.t the no-migration control, except at the highest level of
migration. Thus, the presence of variation in the immigrants could counter
the adverse effects of migration in complex and unpredictably fluctuating
environments. Our study demonstrates that the effects of migration are
strongly dependent on the nature of the destination environment and the
genetic makeup of immigrants. These results enhance our understanding of
the influences of migrating populations, which could help better predict
the consequences of migration.