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A revision of the Palaearctic members of the Formica rufa group, the famous mound-building red wood ants, is presented based on Numeric Morphology-Based Alpha-Taxonomy (NUMOBAT) and on genetic information from studies published in cooperation with others. Standardized morphological character systems were described numerically to allow objective hypothesis formation by exploratory data analyses and testing by hypothesis-driven data analyses. NUMOBAT data were recorded in a total of 1200 samples with 5500 worker individuals and 410 gynes. Comparative tables to workers and gynes of all species and the most frequent hybrids and a key to the workers are presented. Considering 54 available names, the survey recognized 13 good species, 32 junior synonyms and eight names not interpretable to species level (incertae sedis). The ratio of junior synonyms against the number of recognized species is elevenfold the ratio found in a revision of Palaearctic Lasius s.str. conducted by the same author in 2020 with basically the same methodology. Excessive name production in the F. rufa group is partly result of the big attention these eye-catching ants have received by naturalists but it also reflects the enormous difficulties to reasonably interpret a multitude of phenotypes. These difficulties are caused by extraordinary frequency of reticulate evolution, particular mechanisms for the evolution of deviating local populations, and intraspecific polymorphism with differences sometimes being larger than those between species. Hybridization and introgression were shown or made plausible in 46% of the 13 recognized species with regional hybridization frequencies of above 20% in three species. The author assumes that the evolutionary history of F. rufa group ants will turn out as extremely reticulate comparable with the situation in Heliconius butterflies or Darwin Finches once whole genome analyses will be available for all species. The 13 species of the F. rufa group were assigned to four species complexes: (a) the F. rufa complex with F. rufa Linnaeus, 1761 and F. polyctena Foerster, 1850; (b) the F. lugubris complex with F. lugubris Zetterstedt, 1838, F. helvetica sp.n., F. paralugubris Seifert, 1996, F. aquilonia Yarrow, 1955 and F. ussuriensis sp.n.; (c) the F. pratensis complex with F. pratensis Retzius, 1783 and F. kupyanskayae Bolton, 1995 and (d) the F. truncorum complex with F. truncorum Fabricius, 1804, F. dusmeti Emery, 1909, F. frontalis Santschi, 1919 and F. sinensis Wheeler, 1913. Formica yessensis Wheeler, 1913 is recognized as a new junior synonym of F. truncorum. Special sections describe the situation in six hybrid combinations. Comments on species incertae sedis and unavailable names are given in a final chapter. |
