Evolutionary Rescue from Extinction is Contingent on a Lower Rate of Environmental Change

Natural selection is defined as the method that allows species to persist and survive in an ever changing world.  But natural selection is a very long and slow process, so rapidly changing environments will hinder the ability of natural selection to keep species alive.  Lindseyet al. 2013 used the bacteria Escherichia coli to prove that rapid climate change will hinder the process of natural selection and may therefore cause extinction.  Although some experiments have shown that slower rates of environmental change have led to more adapted populations or fewer extinctions.  Lindsey et al. used different concentrations of the antibiotic, rifampicin with E. coli over different time periods to simulate slow, intermediate and rapid environmental change.  They then genetically created all possible combinations of mutations that can result from slow rates of environmental change.  The assessment of the engineered strains show that certain genotypes are evolutionarily inaccessible under rapid environmental change, and that rapid change could eliminate entire sets of mutations as options.  They further speculated that intermediate levels of change might enhance expressions of genes, then there could be more endpoints as a result.  This could have an effect on rates of adaptation that could among other things, increase rate of development of antibiotic resistance. —Cameron Lukos

Lindsey, H.A., Gallie, J., Taylor, S., Kerr, B., 2013. Evolutionary rescue from extinction is contingent on a lower rate of environmental change. Nature 494, 463–467.

                  The experiment was carried out by propagating 1,255 populations of E. coli.  The experimenters also created mutants to add the secondary factor of selective accessibility.  These populations were then placed under increasing amounts of the antibiotic rifampicin.  The treatments had different rates of change, ranging from sudden to gradual.  The populations all started in an antibiotic free environment and ended at a maximum concentration of 190µg/ml.  The populations that were subject to rapid change were exposed to the maximum rifampicin concentration after the first transfer and remained at that level for the rest of the experiment.  Populations exposed to moderate change received the maximum amount of rifampicin halfway through the experiment and the populations exposed to gradual changed experienced the full amount of rifampicin on the last transfer of the experiment.
                  The results indicate that as the rate of environmental change increased the number of populations that survived the whole experiment decreased.  Populations exposed to gradual change were able to become resistant to the antibiotic because there was more time for mutations to occur and spread.  They also found that there were significant differences in growth rates of the populations exposed to gradual and sudden change, indicating that different mutations occurred in different treatments.  For instance, in the case of the sudden populations only one mutation was detected, while in the moderate and gradual populations many different mutations were discovered.  Lindsey et al. found a clear historical contingency for mutations that occurred in the intermediate environments.  It suggests that the mutations allow for the lineage to gain other mutations, a historical contingency.  From this, the results suggest the high rates of climate change will cause problems for species resulting in higher extinction rates.  Not only will it wipe out genetic diversity but it may also result in the loss of potential mutations that could occur under less extreme conditions.
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