HOMOPLASY AND THE CHOICE AMONG CLADOGRAMS

Area of Science:

• Phylogenetics
• Systematic Biology
• Computational Biology

Background:

• Cladistic analysis relies on phylogenetic trees to infer evolutionary relationships.
• The decisiveness of cladistic data is crucial for robust phylogenetic inference.
• Existing tree evaluation statistics may not fully capture data decisiveness.

Purpose of the Study:

• To investigate the relationship between cladistic data decisiveness and tree length variation.
• To derive formulas for calculating common phylogenetic indices in undecisive matrices.
• To propose and validate a new statistic for measuring data decisiveness.

Main Methods:

• Recursive generation of undecisive matrices for varying numbers of taxa.
• Derivation of formulas for consistency, rescaled consistency, and retention indices.
• Introduction of the Decisiveness Index (DD) using tree lengths (S, S̄) and observed variation (M).

Main Results:

• Undecisive matrices occur when all possible dichotomous trees have the same length.
• Traditional indices (CI, RCI, RI) do not directly correlate with data decisiveness.
• The proposed Decisiveness Index (DD) provides a direct measure of data decisiveness.
• Mean tree length (S̄) calculation is independent of character congruence.

Conclusions:

• Data decisiveness in cladistics is linked to the variation in possible tree lengths.
• The new Decisiveness Index (DD) offers a more direct measure of phylogenetic data support.
• Consistency Index remains a valid measure of homoplasy, while Retention Index is suitable for comparing tree fits.