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Spermatophyta Molecular Clock: Time Drift and Recent Acceleration.

Soichi Osozawa1

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Summary

Flowering plant evolution shows two major radiation events: a mid-Cretaceous expansion and a Quaternary adaptive radiation of species like Asarum and Viola. Environmental changes likely drove these evolutionary bursts.

Keywords:
BEAST v1.10.4C4 plantsbase substitution ratecalibrationglacier periodradiation

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Area of Science:

  • Evolutionary Biology
  • Paleobotany
  • Phylogenetics

Background:

  • Angiosperm (flowering plant) evolution is typically dated to the mid-Cretaceous period.
  • Recent adaptive radiations, such as those of Asarum and Viola, occurred during the Quaternary.
  • Understanding plant evolution requires accurate molecular timetrees.

Purpose of the Study:

  • To construct a robust, well-calibrated timetree for Spermatophyta (seed plants).
  • To investigate the timing and drivers of Angiosperm evolutionary radiations.
  • To reconcile molecular clock estimates with geological and environmental events.

Main Methods:

  • Phylogenetic analysis using the Angiosperm Phylogeny Group (APG) system.
  • Molecular dating using Bayesian Evolutionary Analysis Sampling Trees (BEAST) v1.10.4 with an alternative dating function.
  • Analysis of base substitution rates over geological time.

Main Results:

  • A well-calibrated Spermatophyta timetree was constructed, with node dates differing from recent mega-trees.
  • An exponential increase in base substitution rates was detected in recent geologic time, preceded by a mid-Cretaceous increase.
  • These rate increases correlate with Angiosperm radiations at the species (Quaternary) and order (mid-Cretaceous) levels.

Conclusions:

  • Plant evolution, including Angiosperm radiations, is influenced by environmental factors.
  • Quaternary radiations may be linked to C4 grass proliferation, reduced atmospheric CO2, and glacial cycles.
  • The mid-Cretaceous radiation might involve co-evolution with herbivorous beetles.