EVOLUTION OF THE STING APPARATUS IN THE MYRMICINE ANTS.

Abstract

The morphology of the hymenopteran ovipositor and its descendant the sting apparatus has long been known to reflect major adaptive radiations within the order (reviewed in Oeser, 1961; Robertson, 1968; Smith, 1970; Maschwitz and Kloft, 1971), and for that reason it is used, in part, to define major subdivisions. But never has the taxonomic value and evolutionary significance of this structure been systematically analyzed at the generic level or in a still radiating group. Here I summarize the results of such a survey of the sting apparatus of the myrmicine ants and 1) show its potential for defining genera, 2) present an hypothesis of the phylogeny of the subfamily, and 3) attempt to show how the radiation of these ants is reflected in sting apparatus morphology, and in turn, how these changes in the sting may account for aspects of myrmicine biology. In the primitive ants of the subfamily Ponerinae, the sting apparatus is used for subduing live prey and for personal and colony defense. It is probable that the Myrmicinae evolved from the Ponerinae (Brown, 1954; Eisner, 1957; Hermann, 1969, p. 132; dissenting viewpoint in Robertson, 1968). Since the Oligocene, the myrmicines have radiated to become the largest, most dominant subfamily of ants. Some genera, particularly Crematogaster and Pheidole are still radiating and replacing genera of the Dolichoderinae in their advance (Brown, 1973). These and many other myrmicines are unable to sting. As is generally the case with newly evolving groups, the internal classification of this subfamily is confused. Most tribes and many genera are poorly defined, and the phylogenetic relationships among genera are completely unknown. New characters are needed to help remedy that situation, and earlier studies of the sting complex in ants led me to examine its taxonomic potential (Foerster, 1912; Robertson, 1968; Hermann, 1969). That potential seemed particularly great in the Myrmicinae, where the uncommon degree of variation in stinging ability suggested an underlying wide variation in sting morphology, and presented the opportunity to construct hypotheses of how and why the myrmicines radiated, why many lost their stinging ability, and how they compensated for the loss.