The Wettstein tesseract: A tool for conceptualising species-rank decisions and illustrating speciation trajectories

Abstract

Genealogy-based species-delimitation approaches resting upon multilocus sequence data aim at arranging organisms into species taxa (the “grouping” step in a classification procedure), but provide no criteria for the subsequent decision of whether these taxa should be acknowledged as species in the Linnaean classification system (the “ranking” step). By integration of genealogical, morphological, ecological, and geographical patterns as proposed by von Wettstein (1898), species-rank decisions can be conceptualised in a reproducible manner and comprehensibly depicted in a four-dimensional hypercube (the herewith introduced “Wettstein tesseract”). Additionally, the Wettstein tesseract provides a tool for illustrating and teaching components and properties of speciation pathways realised in nature.