Branch length statistics in phylogenetic trees under constant-rate birth-death dynamics

Area of Science:

• Evolutionary biology
• Phylogenetics
• Mathematical modeling

Background:

• Phylogenetic trees depict evolutionary relationships among extant species.
• Extinct or unsampled lineages are typically excluded from phylogenetic trees.
• Birth-death models are used to simulate lineage diversification over time.

Purpose of the Study:

• To investigate the impact of sampling on branch lengths in phylogenetic trees.
• To extend existing birth-death models by analyzing branch length distributions.
• To compare the behavior of pendant and interior branches under varying sampling probabilities.

Main Methods:

• Derivation of branch length distributions for phylogenetic trees.
• Application of a constant-rate birth-death model.
• Analysis under two scenarios: fixed process age and fixed observation time.
• Examination of effects of random sampling of extant individuals.

Main Results:

• Pendant branches (connected to tree leaves) lengthen indefinitely as sampling probability decreases.
• Interior branches rapidly attain an asymptotic distribution independent of sampling probability.
• Sampling significantly impacts pendant branch lengths more than interior ones.

Conclusions:

• The length of branches in phylogenetic trees is highly sensitive to sampling strategies.
• Understanding sampling effects is crucial for accurate evolutionary relationship inference.
• Distinct behaviors of pendant and interior branches necessitate tailored analytical approaches.