Abstract
Evolutionary innovations allow populations to colonize new ecological niches. We previously reported that aerobic growth on citrate (Cit+) evolved in an Escherichia coli population during adaptation to a minimal glucose medium containing citrate (DM25). Cit+ variants can also grow in citrate-only medium (DM0), a novel environment for E. coli. To study adaptation to this niche, we founded two sets of Cit+ populations and evolved them for 2500 generations in DM0 or DM25. The evolved lineages acquired numerous parallel mutations, many mediated by transposable elements. Several also evolved amplifications of regions containing the maeA gene. Unexpectedly, some evolved populations and clones show apparent declines in fitness. We also found evidence of substantial cell death in Cit+ clones. Our results thus demonstrate rapid trait refinement and adaptation to the new citrate niche, while also suggesting a recalcitrant mismatch between E. coli physiology and growth on citrate.
Highlights
Evolutionary novelties are qualitatively new traits that allow populations to invade previously inaccessible ecological niches (Simpson 1953, Mayr 1960)
Our results show that genomic structural variation involving transposable elements and amplifications can provide a rich source of plasticity and potential for adaptation to novel niches
We used each of the six clones to found two populations that evolved in the citrate-only medium (DM0) for 2,500 generations and two populations that evolved for 2,500 generations in the medium containing both glucose and citrate (DM25) as a control
Summary
Evolutionary novelties are qualitatively new traits that allow populations to invade previously inaccessible ecological niches (Simpson 1953, Mayr 1960). Novel traits are important drivers of speciation and adaptive radiations that promote biodiversity and ecological complexity. We previously proposed a model in which novel traits evolve via three distinct phases (Blount et al 2012). Mutations accumulate in a lineage that make it possible to evolve the trait. Evolved traits are typically weak and ineffective. If the new trait confers even a slight advantage, it may spread through a population and, in the refinement phase, be improved by natural selection acting on subsequent mutations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
