Ecology of slave-making ants
Joan Herbers Laboratory - Current Research
Current Research Projects at The Ohio State University - Ecology, Evolution & Organismal Biology
Obligate socially-parasitic ant species are incapable of surviving alone; instead they exploit the social behaviors of other ant species. The slave-maker, or dulotic, ant species are typically specialized for raiding nests of other species for their brood. Pupae and sometimes larvae are brought back to the natal nest, where they mature and become contributing members of the slave-maker colony, laboring on behalf of the slave-makers. Social parasites have long intrigued layman and biologists alike, primarily because of the imposed servitude of another species and the mechanisms that allow for such exploitation to occur. The population dynamics of host and social parasite furthermore offer evolutionary biologists insight into coevolutionary processes.
Our laboratory is currently researching the ecology of two species of slave-makers that occur in Ohio, around the greater Columbus area. With the help of John O'Meara, Executive Director of Metro Parks, and OSU emeritus faculty John Kraus*, our collecting forays into several of the Metro Parks and Kraus Woods Reserve have resulted in the discovery of both Temnothorax duloticus and Protomognathus (=Harpagoxenus) americanus slave-makers and their primary host species in the region, Temnothorax curvispinosus. These three species are just a few of the ant species nesting in second-year, hollowed acorn and hickory nuts and twigs that have been inhabited previously by various species of beetle larvae. Using behavioral observation, colony mapping, and microsatellite DNA analysis, we hope to ascertain the relative impact of the two slave-makers on the host population when they occur in sympatry vs in allopatry. Examination of host colony social structure in parasitized and unparasitized populations may aid us in identifying host tactics to counter colony decimation by slave raiders.
Classification: Formicidae: Myrmicinae: Formicoxenini: Temnothorax (formerly Leptothorax Myrafant group), Protomognathus (=Harpagoxenus)
A rare inquiline, Temnothorax minutissimus
Upon returning from our collecting trips, we open fully the ant-bearing acorns and hickories we've collected and brush the inhabitants into Fluon-coated nest boxes. Once the ants have settled into the glass slide-nests that we've provided, we count the number of workers, queens, winged reproductives, and pupae often with the aid of dissecting scope as they are quite small and difficult to see with the naked eye. We can also determine whether we've collected T. duloticus, which looks superficially like the host T. curvispinosus. On one occassion, however, our microscopic examination yielded an unexpected surprise. We not only found at least two species of ants in the nest but multiple queens of both species. The behavior and positive identification by Stefan Cover in the Department of Entomology at the Museum of Comparative Zoology revealed that we had had collected the rare inquiline (workless social parasite), Temnothorax minutissimus (Smith 1942).This relatively little known species is a social parasite of T. curvispinosus that produces mostly reproductive females (queens) and every so often males. Apparently, only the dominant parasite queen lays eggs and typically is the individual 'riding' or flanking the sides of the host queen, licking her head. We collected two colonies, a small one containing about 14 T. minutissimus queens and 1 live host queen (there was an abdomen of another) and a large one with about 32 T. minutissimus queens. In the larger nest there are about 8 host queens, but not all of them are flanked by the parasite. Only one or two queens are harassed, usually by two T. minutissimus queens. We've dissected a few of the T. minutissimus to determine whether all are mated and if perhaps more than one is laying eggs. With our very small sample size, it seems that more than just one is mated, but it is yet unclear whether more than one individaul is laying eggs. In the spring of 2004, we found new nests of T. curvispinosus with only a single, presumably founding, T. minutissimus queen. Even more astonishing was our finding of single T. minutissimus queens in two nests of the slave-maker T. duloticus! Interestingly these T. duloticus nests were devoid of T. duloticus queens. Even so, eventually after having been brought into the lab, T. minutissimus queens were mutilated.
Classification: Formicidae: Myrmicinae: Formicoxenini: Temnothorax
Citations:
Smith, M. R. 1942. A new, apparently parasitic ant. Proc. Entomol. Soc. Washington 44: 59-61.
The stealth predator Smithistruma*
Although Smithistruma ants may be found on every continent in the world, encounters with Smithistruma are often infrequent due to the small size of the ant - between 2 to 4 mm in length, its relatively slow and innocuous movement, its somewhat cryptic coloration and its often well-concealed nesting sites. Many Smithistruma species are predators of small arthropods such as Collembola (Dejean 1982). Other species apparently exploit nectar and aphid honeydew secretions (Dejean 1991). An interesting characteristic of Smithistruma (and the closely related Strumigenys) is the hardened spongiform growth that appears to ooze from the petiole and post-petiole. Dejean (1985) suggests that this structure may contain an allomone that attracts Collembola to foraging Smithistruma.
Little is known about Smithistruma social structure, although there is often more than one dealate queen within most nests. In our laboratory, we are beginning an examination into the social structure of a local species of Smithistruma collected from hickories.
Classification: Myrmicinae: Dacetini: Strumigeniti, Smithistruma*
Citations:
Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). Journal of Natural History 33: 1639-1689.
Dejean, A. 1982. Etude Èco-Èthologique de la prÈdation chez les fourmis du genre Smithistruma I. Effect du milieu sur le choix de proies chez Smithistruma truncatidens Brown. Insect Science Application 3: 245-249.
Dejean, A. 1985. Etude Èco-Èthologique de la prÈdation chez les fourmis du genre Smithistruma II. Attraction des proises principales (Collemboles). Insectes Sociaux, Paris 32: 158-172.
Dejean, A. 1991. Gathering of nectar and exploitation of Aphidadae by Smithistruma emarginata. Biotropica 23: 207-208.
On the web:
Pyramica of Autstralia http://www.ento.csiro.au/science/ants/myrmicinae/pyramica/pyramica_tax_cat.htm
Smithistruma of Costa Rica http://www.evergreen.edu/ants/genera/pyramica/old.genera/smithistruma/Smithistruma.html#Key
Smithistruma of Japan http://taxa.soken.ac.jp/ANT.WWW/Taxo_E/F424--.html
*Note: Pyramica Roger was recently made the senior synonym of Smithistruma and 16 other dacetonine genera (Bolton 1999). They have not yet been changed here.
Past Research Projects