Mapping characters on a tree with or without the outgroups

Area of Science:

• Evolutionary Biology
• Phylogenetics
• Systematics

Background:

• Character optimization on phylogenetic trees often involves the use or exclusion of outgroups.
• The choice to retain or remove outgroups is frequently based on how well they represent character state diversity, rather than analytical rigor.
• This practice can lead to inconsistencies in evolutionary analyses.

Purpose of the Study:

• To critically evaluate the justification for retaining or removing outgroups in phylogenetic analyses.
• To demonstrate how arbitrary outgroup selection impacts the reconstruction of evolutionary character states.
• To propose a more rigorous approach for selecting taxa in phylogenetic studies.

Main Methods:

• Analysis of a specific case study involving character optimization on a phylogenetic tree.
• Examination of the impact of outgroup sampling on the diversity of character states.
• Comparison of phylogenetic reconstructions with and without specific outgroup sets.

Main Results:

• Authors' decisions to retain or remove outgroups are often dictated by their sampling of character state diversity.
• Excluding outgroups that do not comprehensively sample character states can result in an incoherent analysis.
• Inconsistent evolutionary patterns for the same character can arise from different analytical steps when outgroups are removed post-hoc.

Conclusions:

• Phylogenetic analyses require deliberate selection of both ingroup and outgroup taxa.
• Taxa should be chosen based on their representation of the character states necessary for accurate evolutionary history reconstruction.
• Minimizing incoherence necessitates a unified approach to data matrix construction and analysis throughout the phylogenetic process.