The Timetree of Prokaryotes: New Insights into Their Evolution and Speciation

The increasing size of timetrees in recent years has led to a focus on diversification analyses to better understand patterns of macroevolution. Thus far, nearly all studies have been conducted with eukaryotes primarily because phylogenies have been more difficult to reconstruct and calibrate to geologic time in prokaryotes. Here, we have estimated a timetree of 11,784 'species' of prokaryotes and explored their pattern of diversification. We used data from the small subunit ribosomal RNA along with an evolutionary framework from previous multi-gene studies to produce three alternative timetrees. For each timetree we surprisingly found a constant net diversification rate derived from an exponential increase of lineages and showing no evidence of saturation (rate decline), the same pattern found previously in eukaryotes. The implication is that prokaryote diversification as a whole is the result of the random splitting of lineages and is neither limited by existing diversity (filled niches) nor responsive in any major way to environmental changes.