Dating the arthropod tree based on large-scale transcriptome data.

Area of Science:

• Evolutionary Biology
• Molecular Phylogenetics
• Paleontology

Background:

• Discrepancies exist between fossil records and molecular clock estimates for early animal phyla divergence.
• The Cambrian explosion (less than 540 million years ago) is a key period for multicellular animal origins.

Purpose of the Study:

• To reconcile molecular clock estimates with fossil data for arthropod and metazoan evolution.
• To determine more accurate divergence times for major animal lineages using a large molecular dataset.

Main Methods:

• Utilized a large multiple sequence alignment of 129 genes from 117 taxa, including 101 arthropods.
• Applied relaxed Bayesian clock models with various priors and calibration points, selecting a log-normal autocorrelated model via cross-validation.

Main Results:

• Estimated arthropod emergence around 600 million years ago.
• Calculated key splits: Onychophorans/euarthropods (~590 mya), Pancrustacea/Myriochelata (~560 mya), Myriapoda/Chelicerata (~555 mya), 'Crustacea'/Hexapoda (~510 mya), and Endopterygote insects (~390 mya).
• Obtained divergence times younger than previous molecular estimates, showing better agreement with the fossil record.

Conclusions:

• The study provides refined molecular clock estimates for arthropod evolution, supporting a Precambrian origin for many metazoan phyla.
• Large datasets of random nuclear sequences are effective for approximating the timing of early animal evolution.