The interdisciplinary study of chemical communication has developed into a cutting-edge field of science that can address key questions on the organization of life at both the cellular and the organismal level. The study of communication in insect societies and their social parasites has played a pivotal role in these developments. The genus Megalomyrmex comprises 38 described species and roughly ten are social parasites of fungus-growing ants while the other Megalomyrmex species are free-living predators. These fungus-growing ant associates infiltrate then consume the fungus garden and brood of the host colony. Megalomyrmex ants are chemical warriors, dispensing volatile venom alkaloids by waving their stings (i.e. gaster flagging) as they enter another ant species' nest as parasites or during competition (by predatory free-living species). Species of both lifestyles use gaster flagging as a 'warning shot', announcing their presence to hosts or competitors. If the host does not allow infiltration, the invader will attack and kill. Infiltration can be accomplished as just described (i.e. chemical weaponry) or through the alteration of cuticular hydrocarbons (i.e. surface chemistry) using chemical mimicry and/or insignificance. Our work will decipher the chemical code of communication and manipulation of Megalomyrmex ants, linking behaviors observed to their chemical ecology by 1) testing three infiltration strategy hypotheses with behavioral observations and chemical analysis, 2) identifying chemical compounds, and 3) examining the results in an evolutionary context with phylogenetic hypothesis testing.
Venom alkaloid characterization
Function of ant-derived pyrrolidines, pyrrolizidines, piperidines and pyrrolines has been studied in Solenopsis and Monomorium species where pyrrolidines function as heterospecific repellents and piperidines have antibiotic, insecticidal and repellency properties. We hypothesize that Megalomyrmex parasites are using their alkaloids as host colony disrupters, useful during host colony infiltration and integration. Behaviors such as gaster flagging and venom wiping, dispense these volatile and toxic alkaloids. Comparative work with other solenopsidines will allow us to determine if compounds have evolved convergently to satisfy similar functional needs.
Social parasitism in ants has evolved independently multiple times in various forms. The parasites successfully infiltrate host colonies, apparently defying nestmate discrimination that safeguards from colony invasion. Social parasites in the Megalomyrmex genus specialize in attacking fungus-growing ant species, harming the host by draining resources such as brood and fungus-garden. We investigate the behavioral interactions between fungus-growing ant hosts and their Megalomyrmex parasites, addressing questions surrounding the topics of infiltration strategies, host fitness costs, and symbiotic species networks.
The Solenopsidini tribe (Hymenoptera: Formicidae: Myrmicinae), first proposed in 1893, has challenged taxonomists for over a century. Not only has the monophyly of the tribe been called into question but there are also unsatisfactory generic delineations. Our work begins with an overview of the tribe then delves deeper into the three largest genera in the tribe, Solenopsis, Monomorium and Megalomyrmex. Using a phylogenetic approach we examine over 200 taxa testing the monophyly of Solenopsidini and the relationships between the included genera.
A typical social insect colony is made up of a reproductive queen or gyne and her sterile workers. Her body size is characteristically large and she initially has wings for dispersal and mating. She leaves her natal colony, mates in flight, and then searches for appropriate nesting habitat. As more ant species are studied it is becoming ever clearer that the above scenario is not always true. There are great costs associated with being a large winged female therefore it is not surprising that alternative strategies have evolved. For example, a reproductive female may mate in her natal nest or return to it after being mated. She may also "bud" from her natal colony taking a subset of her sisters, to ensure her success as a future queen. In these cases, large body size (needed for initial founding stages when she does not eat) and wings may no longer be necessary. The Megalomyrmex leoninus-group (10 species) consists of only wingless queens but still maintain a larger body size compared to the workers. Still, in the modestus-group, there are intermediate stages found where the queens no longer have wings but are the same size as workers. Clearly the reduction in body size and the presence, reduction, or absence of wings in queens appears to be a plastic morphological character. We are studying reproductive strategies of Megalomyrmex and other Solenopsidini tribe member using phylogenetic and morphometric methods.
Prof. Koos Boomsma
University of Copenhagen, Denmark
Dr. David Nash
University of Copenhagen, Denmark
Prof. Christian Peeters
Laboratoire d'Ecologie Université, Pierre et Marie Curie, France
Dr. Falko Drijfhout
Keele University, UK
North and South America
Prof. Roberto Brandão
Museu de Zoologia, Universidade de São Paulo, Brazil
Drs Ted Schultz and Sean Brady
Smithsonian Institution, USA
Prof. Ulrich Mueller
The University of Texas, USA
Dr. Tappey Jones
Virginia Military Institute, USA
Dr. John Longino
The Evergreen State College, USA