THE EFFECT OF ORDERED CHARACTERS ON PHYLOGENETIC RECONSTRUCTION

Area of Science:

• Evolutionary Biology
• Systematics
• Phylogenetics

Background:

• Morphological evolution often involves multiple changes, resulting in common multistate characters in systematic studies.
• The treatment of multistate characters as ordered (additive) versus unordered (non-additive) significantly impacts phylogenetic analyses.

Purpose of the Study:

• To review criteria for ordering character states and their underlying assumptions.
• To examine the effects of ordered multistate characters on phylogenetic reconstruction.
• To evaluate whether ordering character states enhances phylogenetic informativeness and resolution.

Main Methods:

• Review of criteria and assumptions for ordering multistate characters.
• Analysis of 27 datasets to assess the impact of ordered versus unordered characters on phylogenetic trees.
• Examination of effects on the number of equally parsimonious trees and tree resolution.

Main Results:

• Ordered characters can result in more, fewer, or an equal number of equally parsimonious trees compared to unordered characters.
• The impact on tree resolution varies: it can increase, decrease, or remain unchanged.
• Hypotheses of order can alter character polarities and outgroup topology, especially with multiple outgroups.

Conclusions:

• The assumption that ordered characters consistently improve phylogenetic resolution or restrict parsimonious trees is not supported.
• Ordered characters yield different topologies only when they conflict with the cladogram's hierarchy.
• If congruence with other characters is the primary criterion, ordering multistate characters may be inappropriate for assessing character evolution.