Morphometric discrimination among sibling species in the fulva–rudis–texana complex of the ant genus Aphaenogaster (Hymenoptera: Formicidae)

Abstract

The fulva–rudis–texana complex of the ant genus Aphaenogaster includes A. fulva, A. rudis, A. texana, and morphologically similar species. Morphometric and other morphological investigations were conducted on colony representatives of 10 forms (4 likely representing undescribed species) that were previously identified using cytogenetic and electrophoretic markers. In workers, most qualitative characters exhibit such a high degree of size-associated intraspecific variation relative to interspecific differences that they are not reliable for identification. Linear discriminant analysis and canonical variate analysis on 12 morphometric measurements were used to optimize classification and define a morphometric habitus for each form. Two-variable scatterplots clarify the nature of morphometric variation in the complex and provide simple characters that will reliably separate numerous pairs of forms. Indices appear to be of little taxonomic value in this complex. A preliminary key to the workers of the complex summarizes the most important taxonomic characters. This key substantially improves the ability to recognize morphologically most members of the complex, but sometimes only genetic evidence is definitive.