Estimating divergence times in large phylogenetic trees.

Area of Science:

• Phylogenetics
• Computational Biology
• Evolutionary Biology

Background:

• Estimating divergence times from phylogenetic trees is crucial for understanding evolutionary history.
• Existing methods for molecular clock calibration can be computationally intensive and struggle with large datasets.

Purpose of the Study:

• To introduce PATHd8, a novel computational method for estimating ultrametric trees.
• To provide a flexible and efficient tool for time-calibrating phylogenetic trees with varying molecular clock assumptions.

Main Methods:

• PATHd8 estimates node ages using mean path lengths to leaves, incorporating corrections for molecular clock deviations.
• It allows for arbitrary reference nodes with defined ages (absolute, min, or max) and handles incompletely resolved trees.
• The method locally smooths substitution rates, enabling analysis of very large phylogenetic trees.

Main Results:

• PATHd8 produces divergence times comparable to existing methods, with notable differences in crown group ages.
• While other methods yield smoother chronograms, PATHd8 preserves more of the original branch length heterogeneity.
• PATHd8 is significantly faster than other methods, handling trees with thousands of leaves efficiently.

Conclusions:

• PATHd8 is a computationally efficient and flexible tool for estimating ultrametric trees, particularly advantageous for large datasets.
• It offers a valuable alternative for molecular clock calibration, providing sensible results even for extreme datasets.
• The method's speed and ability to handle large trees make it a significant advancement in phylogenetic analysis.