Figure 2.

Intrinsic postzygotic reproductive isolation can evolve rapidly across many types of taxonomic groups. The rate of evolution of different types of intrinsic postzygotic reproductive isolation across nine different taxonomic groups. Scatterplots display the rate of accumulation of either hybrid inviability (V), sterility (F) or an index of both (I) for species pairs of differing divergence times, with the first species pair to achieve complete reproductive isolation (greater than 99.5% reproductive isolation) highlighted in red boxes. Note that the units of the X-axis differ among panels, as genetic distance was measured using different methods in each study (the statistic calculated as well as the markers used are listed as individual panel X-axis labels). References for the data are as follows: Birds [112], Drosophila [9], centrarchid fishes [117], Helianthus and Madiie [115], Streptanthus [116], Lepidoptera [111], Nolana [114], toads [113]. For both Nolana and Streptanthus, multiple components of intrinsic postzygotic reproductive isolation were measured. Here, we display reproductive isolation conferred by the number of viable seeds produced, as it is one of the earliest acting barriers. (Online version in colour.)