Sexual Calling Behavior in Highly Primitive Ants

In recent years an interesting mating pattern has been discovered in a number of socially parasitic and dulotic Myrmicine ants, including the related genera Leptothorax, Doronomyrmex, and Harpagoxenus, and in the guest ant Formicoxenus nitidulus (Buschinger, 1968, 1971a, 1971 b, 1974; 1975). Typically the alate or ergatoid young female leaves the parent colony, crawls to a prominent position, and settles there motionless for a long period sometimes amounting to hours with gaster raised, legs extended, and sting extruded. Sooner or later males assemble about the "calling" female, and mating takes place. Buschinger, who first observed it in these genera, has described the pattern in detail for the slave-making Harpagoxenus sublaevis (1968), and in the permanently socially parasitic Doronomyrmexpads, Leptothorax kutteri, and L. goesswaldi (1975). He also observed the pattern in fine detail in populations of F. nitidulus (1975) maintained in the laboratory as guests of Leptothorax acervorum, and found it generally similar to the others, though differing in detail in ways to which we will later allude. Buschinger was able to demonstrate that in all these forms a sex-attractant pheromone was released from the poison gland, as Holldobler (1971) had been the first to demonstrate in the Myrmicine ant Xenomyrmex floridanus. Recently Moglich, Maschwitz, and Holldobler (1974), in a particularly provocative study, have presented the results of detailed analyses of "tandem-calling" behavior in the independently-living Leptothorax acervorum, L. muscorum, and L. nylanderi, a pattern by which workers of these independently-living species recruit sisters to newly discovered food sources, one recruiter guiding only one follower to the source at a time. A component of the initial behavior of the recruiting worker is described as essentially identical with the "calling" behavior in Harpagoxenus females, and the authors call attention to the interesting hypothesis posited earlier by Holldobler (1971) that, in at least some Myrmicine ants, sex