Fast-evolving homoplastic traits are best for species identification in a group of neotropical wasps.

Biological characters can be employed for both taxonomy and phylogenetics, but is conscripting characters for double duty a good idea? We explore the evolution of characters designed for taxonomic diagnosis in Costa Rican heterospiline wasps, a hyperdiverse lineage of parasitoid Braconidae, by mapping them to a robust multi-locus molecular phylogeny. We discover a strong positive relationship between the amount of evolutionary change a character undergoes and how broadly useful the characters are in the context of an interactive identification key--e.g., how evenly the character states are distributed among taxa. The empirical finding that fast characters are the most useful for species identification supports the idea that characters designed for taxonomic diagnoses are likely to underperform--or be positively misleading--in phylogenetic analyses.