Figure 2.

The taxonomic circle. The dotted lines that traverse the inner part of the circle indicate experimental routes that can be taken in taxonomic endeavour to accomplish corroboration of taxonomic hypotheses. The only way to delineate a new taxon is to break out of the circle (the solid arrows emanating from the circle). In our scheme, it only takes one traversal of the interior of the taxonomic circle where corroboration occurs in order for the taxonomist to ‘break out’ of the circle and designate a taxon. Examples of use of the taxonomic circle using hypothetical examples. A. Classical morphological taxonomy; a taxonomic hypothesis is established on the basis of organisms appearing to be similar at a particular geographic locality. The taxonomic hypothesis is tested with morphological information and corroborated with the morphological attributes. The morphological attributes then become diagnostic characters if they corroborate the geographical hypothesis. B. Cryptic species in taxonomy; a geographical hypothesis is posed and tested with morphology. The morphological attributes collected do not corroborate the geographical hypothesis and hence the taxonomist cannot ‘break out’ of the circle. Retaining the geographical hypothesis the taxonomist then examines the aggregates established using the geographical hypothesis with DNA sequence data and corroboration ensues with DNA sequence characters being diagnostic. C. Sympatric species in taxonomy; morphological differences are recognized among a group of organisms. A hypothesis of aggregation is posited based on the morphological information. When geographical distributions are used to test the aggregation patterns, there is no geographic pattern to the distribution of the different morphological types. The taxonomist then uses DNA sequence attributes to test the morphological hypothesis of aggregation and corroborates the morphological hypothesis and the taxonomist ‘breaks out’ of the circle. D. Failure to detect a new taxon; in this example, a geographic hypothesis is made and tested with morphological information. The morphological information fails and the geographical and any morphological hypotheses of aggregation are then tested with DNA sequence information. DNA sequence information fails to reject the hypothesis of no new taxa and, hence, the taxonomist cannot ‘break out’ of the circle and the inference is that there are no differentiable aggregates and hence only a single taxon.