Abstract: Ant and termite nests are long-term stable, semi-closed systems constantly producing conspecific worker populations of related individuals over many generations. Accordingly, nests of these eusocial insects, as they are found in nature, offer free of cost an analysis situation that has to be generated in other groups of organisms by controlled rearing experiments. A test system based on analyzing intranidal and large-scale phenotype distributions and comparing the observed distributions with predictions for different scenarios of heterospecificity and intraspecific dimorphism is introduced by a case study on ants. The test system, named Dimorph test, allows a taxonomist to distinguish if discrete character syndromes represent separate species or an intraspecific phenomenon. One of the most important parameters within the test system is the abundance and distribution of phenotypically mixed nest populations. Five biological explanations are possible for ant nests with a mixture of discrete phenotypes: They may represent (1) genetically determined intraspecific morphs, (2) intraspecific modifications induced by environmental factors, (3) the association of a temporary social parasite with a host species, (4) the association of a permanent social parasite with a host species, and (5) a parabiotic association of two basically independent (self-sustaining) species. The paper explains the biological background of the scenarios (1) to (5) and presents mathematical models and generalizations from empirical data to predict phenotype distributions for each scenario under variable conditions. Four cases of intraspecific dimorphism and five cases of taxonomically recognized pairs of cryptic or similar species are presented and analyzed. The observed intranidal phenotype distribution was most similar to the predicted scenario of intraspecific dimorphism in Camponotus lateralis (Olivier, 1792), Lasius umbratus (Nylander, 1846), Formica lugubris Zetterstedt, 1838, and Cardiocondyla elegans Emery, 1869. In three of these examples, intraspecific morphs had been considered previously as different species. Heterospecificity was confirmed for four pairs of cryptic species and one pair of closely related species: Formica pressilabris Nylander, 1846 vs. F. foreli Bondroit, 1918, Temnothorax crassispinus (Karavajev, 1926) vs. T. crasecundus Seifert & CSÖSZ, 2015, Temnothorax luteus (Forel, 1874) vs. T. racovitzai (Bondroit, 1918), two cryptic species of the Pheidole pallidula (Nylander, 1849) complex, and Myrmica vandeli Bondroit, 1920 vs. M. scabrinodis Nylander, 1846. The phenotype-based Dimorph test can be applied to the large worldwide collections of mounted museum material or private collections of ants independent from age or Dna degradation and can thus operate in fields where genetic investigation faces analytical and logistic problems and where controlled rearing experiments are not possible. The system can be adapted, with some modification, to other groups of eusocial organisms.

Preview not available.