Autapomorfia

Autapomorfia is a term used in cladistics to describe a derived character state that is unique to a single taxon. It is a trait that sets that lineage apart from its closest relatives and does not occur in other, related taxa. Autapomorfias arise on the branch leading to a particular species or lineage after it has diverged from its sister group, often due to genetic, developmental, or phenotypic changes.

In phylogenetic analysis, autapomorphies are useful for diagnosing and identifying a taxon, but they provide limited information about the relationships among different groups beyond that lineage. They are contrasted with synapomorphies, which are shared derived characters that define a clade, and with pleisiomorphies, which are ancestral traits present in a broader group and may be shared across several lineages.

Autapomorfia can be observed in both morphological and molecular data. Examples include a species-specific mutation in a gene, a unique protein variant, or a distinctive behavioral or physiological trait that is not found in closely related species. Detecting autapomorphies typically involves comparing character states across many taxa and inferring which traits originated on the terminal branch leading to the taxon in question.

Limitations include the possibility that autapomorphies result from limited sampling or convergent evolution, and their primary value lies in species diagnosis rather than revealing deeper evolutionary relationships.