Phylogeny of the army ant genus Dorylus: the status of the subgenera and the evolution of foraging stratum use
Caspar Schöning, Daniel Kronauer, and Jacobus Boomsma. Department of Population Biology, University of Copenhagen, Universitetsparken 15, Copenhagen, 2100, Denmark
Army ants of the genus Dorylus are keystone species for many ecosystems in the Old World tropics. While the monophyly of the genus is well supported, the internal phylogeny and thus the status of the six currently recognized subgenera are unresolved. One of the major problems in army ant taxonomy is that males have often been collected and described independently of workers and vice versa, which has resulted in two parallel classification systems. In order to reconstruct the phylogeny of the group and to overcome the problem of missing male–worker associations, we sequenced one nuclear (wingless) and two mitochondrial genes (cytochrome oxidase I, II) for 25 Dorylus species and three outgroup taxa. A Bayesian analysis of the data supports the contention that the monotypic subgenus Dichthadia is sister to all other extant species in the genus and that the subgenera Rhogmus, Alaopone, and Typhlopone are monophyletic. However, although the subgenera Doryluss.s. and Anomma form a clade together, neither of these subgenera is monophyletic. While D. (Dorylus)spininodis is the sister taxon to all other species in the clade (Dorylus s.s. + Anomma), the remaining species in the subgenus Dorylus form a monophyletic group nested within a clade containing all Anomma species hunting in the leaf-litter. This latter clade in turn is the sister to all Anomma species hunting aboveground (the fierce and famous species commonly referred to as driver ants). We therefore conclude that the evolution of foraging stratum use in African army ants has been more complicated than previously thought, with most species of the subgenus Dorylus representing a reversal from leaf-litter to subterranean foraging. The implications of our findings for the classification into subgenera are discussed.