A multigene timescale and diversification dynamics of Ciliophora evolution

Area of Science:

• Evolutionary Biology
• Protistology
• Paleontology

Background:

• Ciliophora represents a highly diverse lineage of unicellular eukaryotes.
• A robust evolutionary timescale for Ciliophora, calibrated with fossil evidence, has been lacking.
• Understanding ciliate diversification patterns is crucial for evolutionary studies.

Purpose of the Study:

• To infer a time-calibrated phylogeny for Ciliophora using multigene data and fossil calibrations.
• To investigate the rates and patterns of ciliate lineage diversification through time.
• To establish a more accurate evolutionary timescale for major ciliate lineages.

Main Methods:

• A two-step analytical approach was employed, optimizing both gene and taxon sampling.
• Multigene phylogenetic analysis was conducted to reconstruct evolutionary relationships.
• Fossilized ciliate specimens were used as primary calibration points for the molecular clock.

Main Results:

• The origin of Ciliophora is estimated at 1143 million years ago, significantly younger than previous estimates.
• A major diversity explosion occurred during the Paleozoic era.
• Spirotrichea diverged around 850 million years ago, while Protocruziea emerged around 56 million years ago.
• A significant rate shift in diversification was detected in a spirotrichean clade during the Ediacaran-Cambrian transition.
• Speciation rates generally declined through time across investigated lineages, with low and constant extinction rates.

Conclusions:

• The study provides a robust, fossil-calibrated timescale for Ciliophora evolution.
• Ciliate diversification dynamics reveal a significant acceleration in speciation during the Ediacaran-Cambrian transition.
• The findings contribute to a better understanding of the macroevolutionary history of unicellular eukaryotes.