EVOLUTION: Adding Less or Substrating More?

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Science  29 Aug 2008:
Vol. 321, Issue 5893, pp. 1134c-1135c
DOI: 10.1126/science.321.5893.1134c

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Calibrating robust molecular phylogenies of clades of extant species against time offers a means of characterizing the tempo and mode of evolutionary radiations. Often, net diversification is rapid early in the history of a clade and declines later on. This “explosive-early” pattern could be produced either by a fall in speciation rates over time or by a rise in extinction rates—alternatives that support distinct ecological explanations for diversification.

Rabolsky and Lovette present an analytical model, based on the birth-death process, in which speciation and extinction rates vary continuously over time. They apply their framework to three published phylogenies (Australian agamid lizards, Australo-Papuan pythons, and North American wood warblers), and they use simulations to fit features of lineage accumulation curves to different modes of declining net diversification. They find that the explosive-early pattern can be explained only by declining speciation rates and is not observed in scenarios with high ratios of extinction rates to speciation rates. Their results also show that an apparent excess of recently diverged lineages in lineage-through-time plots (typically seen as the result of increasing diversification or high relative extinction rates) can be produced when declining net diversification is driven by increasing speciation rates. — ShJS

Evolution 62, 1866 (2008).

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