Inconvenient hyperdiversity – the traditional concept of “Pheidole pallidula” includes four cryptic species (Hymenoptera: Formicidae)

Abstract

Results of a pilot study are presented suggesting that Edward Wilson’s guess of some 1500 species in the hyperdiverse genus Pheidole Westwood, 1839 is likely to turn out as rather moderate estimate. Investigation of 112 nest samples containing 287 major workers of Westpalaearctic ants currently named Pheidole pallidula (Nylander, 1849) was performed by the explorative data analyses NC-Ward and NC-k-means clustering in combination with cross-validated linear discriminant analysis. Seventeen primary morphometric data were recorded by high-resolution stereomicroscopy. Allometric variance of shape variables was removed. Four cryptic species, forming the Ph. pallidula complex, were resolved: Ph. pallidula, Ph. balcanica nov. sp., Ph. koshewnikovi Ruzsky, 1905 and Ph. cicatricosa Stitz, 1917. The classification error varied between 0 and 2.8 % in NC clustering of nest samples and between 1.6 and 3.7 % in cross-validated linear discriminant analysis of individuals.
Ph. cicatricosa has a North African distribution whereas Ph. pallidula, Ph. balcanica nov. sp. and Ph. koshewnikovi are Eurasian species with large sympatric ranges in the Balkans and Asia Minor. Colonization of urban regions north of the Alps and of offshore islands in the Mediterranean Sea indicates an invasive potential of the supercolonial social type of Ph. pallidula. There are no indications that any of these four taxa might represent an intraspecific polymorphism and signals for putative interspecific hybridization are not significant. The following synonymies were established: Ph. subdentata Mayr, 1853, Ph. pallidula var. obscura Santschi, 1936 and Xenoaphaenogaster inquilina Baroni Urbani, 1964 are junior synonyms of Ph. pallidula, Ph. pallidula var. arenarum Ruzsky, 1905 and Ph. pallidula ssp. orientalis Müller, 1923 are junior synonyms of Ph. koshewnikovi and Ph. pallidula var. recticeps Menozzi, 1932 is a junior synonym of Ph. cicatricosa. The senior synonymy of the following seven Westpalaearctic taxa with any member of the Ph. pallidula complex was excluded by type investigation and diagostic statements in the original descriptions: Ph. sinaitica Mayr, 1862, Ph. jordanica Saulcy, 1874, Ph. teneriffana Forel, 1893, Ph. laticeps Mayr, 1904, Ph. schmitzi Forel, 1911, Ph. obtusa Stitz, 1917 and Ph. pallidula selenia Özdikmen, 2010. Species delimitation in the less differentiated caste of minor workers was not tested but seems possible when accessory morphological characters are included.