As editor, I found Turner et al.’s “Replaying Evolution” piece a well-crafted study to figure out why two long-coexisting ecotypes from their laboratory evolution experiment ceased to coexist. The authors carefully ruled out any kind of adaptive improvement in the surviving ecotype that may have driven the other ecotype to extinction. Moreover, they also ruled out a demographic cause of extinction. That is, the population sizes were too high for one of the populations to have randomly gone extinct. They concluded that some unidentified, one-time, random environmental change (maybe soap suds?) was most likely responsible for the demise of one ecotype. I saw this paper as a model for investigating the causes behind an extinction event in laboratory evolution, and I was glad to be a part of its publication in Plos One.

I was especially intrigued for what the results of this paper tell us about speciation theory (a point not pursued by the authors). Much has been found out recently about how easy it is for speciation to occur in bacteria, but little has been discussed about how difficult it is for newly divergent, ecologically distinct lineages to coexist indefinitely into the future. Certainly, to make it into the future, any newly divergent, ecologically distinct ecotypes must be ecologically distinct enough to be able to coexist indefinitely across the habitats where they occur now (Kopac et al., 2014). But the Turner et al. study alerts us that in addition, the ecotypes must be different enough such that when their environments change, they must always be able to find a way to partition resources. Indefinite coexistence requires that as the world changes, perhaps with unforeseen climate changes or invasions of pathogens or competitors, the newly divergent lineages must always be partitioning their resources.

Kopac, S., Wang, Z., Wiedenbeck, J., Sherry, J., Wu, M. & Cohan, F. M. (2014). Genomic heterogeneity and ecological speciation within one subspecies of Bacillus subtilis. Applied and Environmental Microbiology 80: 4842-4853.