Abstract:
Populations with a history of living in fluctuating environments are
predicted to be successful invaders. Enhanced invasive abilities can stem from
capacity to inhabit novel environments. A recent study has shown that bacterial
populations selected under fluctuating temperatures perform better when confronted
with novel environments. But experimental evidence for evolution of better
competitors/invaders, however, is still sparse. Moreover, the question as to how the
nature of selection regime, i.e. complexity and predictability, affects the potential to
respond to novel environments is largely unexplored. Here I compare the invasive
ability of replicate E. coli populations – selected in a randomly fluctuating complex
environment – with control populations that have not experienced such
environmental fluctuations. For this purpose, relative fitness was assessed in three
different biotic scenarios: (a) separate competition with two different bacteria,
Serratia, and Staphylococcus; (b) the ability to infect Drosophila melanogaster (fruit
fly). Results show that selected populations are better than the controls when
competed against Serratia, without any disadvantage in any of the other novel biotic
challenges. In the second part of the study, I checked whether the observed
advantage in the competition with Serratia exhibits a correlation with an improvement
in fitness in any of the component environments, i.e. environmental variables which
were part of the selection. To answer this, I compared the fitness of control and
selected populations over the duration of selection in all the three component
environments. The results of these fitness assays in the component environments
reveal absence of adaptation over time for selected populations. Therefore, my
results suggest that complex randomly fluctuating environments can select for
populations which can potentially be better invaders/competitors in some novel
environments, and evolution of this ability need not be correlated with the adaptation
to the component environments.
