Figure 1

From: Speedy speciation in a bacterial microcosm: new species can arise as frequently as adaptations within a species

Figure 1

The expected trajectory of the MT:LT ratio (r) over time, under three models. (a) The null model, where strains are of equal fitness and in the same ecotype. Here, the initial r ratio is maintained indefinitely. (b) The single-ecotype community model. Here, the ratio stays at its initial value during a ‘wait time’ (tw), to be estimated, until the ratio starts changing at a slope (m), to be estimated, leading to elimination of one of the markers. (c) In the multi-ecotype community model, there is a wait time, to be estimated, with no change in ratio, followed by a change in the ratio at a slope, to be estimated, followed by stabilization at a new end ratio (r), to be estimated. (d, e) Each box represents an ecotype; each circle or triangle represents an individual organism within an ecotype; the different colors indicate the selectable markers MT and LT; an asterisk indicates a mutant strain that is adaptive within its ecotype’s niche. (d) Interpretation of the events observed in (b), where an adaptive mutant within one marker moiety (LT in this case) becomes fixed in the original ecotype, and thereby eliminates the other marker from the single-ecotype community. (e) One likely explanation for the events in (c) is that an ecotype formation event occurs within one marker, and a periodic selection event occurs in the original ecotype, stemming from an adaptive mutation in a genome with the other marker. We note that this method will not detect all cladogenesis events, especially if new ecotypes do not reach appreciable frequencies. In the absence of periodic selection, a new low-frequency ecotype would go unnoticed.