Abstract:
Population size influences various evolutionary outcomes. However, we have a very
limited understanding of the effects of population sizes on niche evolution. In this study,
we investigate how population sizes influence the utilization of an unaccustomed niche
present alongside a habitual niche. We subjected Escherichia coli populations of two
different population sizes to selection in a mixture of an unaccustomed and a habitual
niche for approximately 480 generations. The selection environments consisted
constant lines experiencing only one habitual niche and fluctuating lines experiencing all
the habitual niches in four possible combinations in terms of predictability and speed of
fluctuations, along with a constantly present unaccustomed niche. We found that all
populations adapted to the unaccustomed niche with large populations adapting
significantly greater than the small populations. Interestingly, the identity of the selection
environment did not influence the adaptation to the unaccustomed niche. Moreover,
large populations even adapted to their habitual niche better than the small populations
in both the constantly selected and fluctuating lines. Also, predictability and speed of
fluctuations did not affect the adaptation to the habitual niche. Therefore, our findings
suggest that population size is an important parameter which must be taken into
account when studying the ecological processes like niche utilization and expansion.
