The effect of dilution rate and transfer interval on eco-evolutionary
dynamics of experimental microbial communities
Abstract
All organisms are susceptible to the environment and changing
environmental conditions can infer structural modifications in
predator-prey communities. A change in the environment can influence,
for example, the mortality rate of both the prey and the predator, or
determine how long the interaction between both partners is. This may
have a substantial impact on ecological, but also evolutionary dynamics.
Experimental studies, in which microbial populations are maintained by a
repeated dilution into fresh conditions after a certain period of time,
are able to dissipate underlying mechanisms in a controlled way. By
design, dilution rate (modifying mortality) and transfer interval
(determining the time of interaction) are crucial factors, but they
often receive little attention in experimental design. We study data
from a live predator-prey (bacteria and ciliates) system used to gain
insight into eco-evolutionary principles and apply a mathematical model
to predict how various dilution rates and transfer intervals would
affect such an experiment. We find the ecological dynamics to be
surprisingly robust for both factors. However, the evolutionary rates
are expected to be affected. Our work predicts that the evolution of the
anti-predator defence in the bacteria, and the evolution of the
predation efficiency in the ciliates, both decrease with higher dilution
rate, but increase with longer transfer intervals. Our results provide
testable hypotheses for future studies of predator-prey systems and we
hope this work will help improving our understanding how ecological and
evolutionary processes together shape composition of microbial
communities.