Ant Insights

- Research -

Adaptive radiation in ants Adaptive radiation is defined by a pattern of ecological and phenotypic diversification within a rapidly multiplying lineage. Divergent natural selection, established by contrasting ecology, is thought to drive this pattern. However, we know very little about this process in the ants. This is a group with over 11,000 extant species, with many lineages clearly having undergone major adaptive radiations. The main focus of my research is therefore to understand how ecological diversification has shaped the adaptive radiation of ant lineages. I am particularly interested in the ecological forces that shape the evolution of lineages with morphologically distinct and specialized 'castes'. So what do we know about specialized castes? First and foremost, we know that they are an important, recurrent theme in the phenotypic diversification of social insect lineages. Castes have evolved multiple times in the ants and aphids, and there are also independent origins in three other major insect lineages. Castes are also common in many of the most evolutionarily and ecologically successful ant taxa. From a developmental standpoint, specialized castes are usually the product of differential growth, not different genes. That is to say that within a species that has castes, all female larvae have the potential to develop into any female morph (e.g. queen, standard worker, or specialized soldier). The 'switch' that turns on the developmental pathways for the specialized caste is controlled by how much a larva is fed at different stages of their early life. Specialized castes are also a fascinating evolutionary puzzle because these individuals do not usually reproduce and are morphologically predisposed or limited to a single job throughout their lives. If they do not reproduce, how are the genes that code for their special form and function transmitted from generation to generation? Kin selection provides a powerful explanation for how specialized castes can evolve because while they do not reproduce, they are helping raise sisters and brothers that carry copies of the same genes (remember that all female larvae have the genes to potentially develop into a specialized caste). We also understand that the evolution of specialized castes may be inhibited by developmental constraints (i.e. the potential for caste evolution are not boundless), intra-colonial conflict, and various life history characters. However, in cases where these barriers have been relaxed or lifted, we know very little about the ecological forces that have driven the origin and subsequent adaptive diversification of specialized castes within radiating lineages. This is where my interests are focused. In my Ph.D. research, I studied the role of dietary changes in the evolution of a specialized transport caste or 'submajor' in the army ant genus Eciton. I also studied the evolution of an unusual and extreme behavioural specialization in the army ant Eciton burchellii, which I call 'plugging'. My ongoing work is on the role of nesting ecology in the adaptive radiation of the arboreal ant genus Cephalotes. I am particularly focused on understanding the role of ecological specialization, defined in terms of nesting ecology, in the evolution of the remarkable soldier caste seen in this lineage. I am also investigating the role of ecology in other aspects of phenotypic diversification in Cephalotes, including the evolution of morphological diversification in standard workers, independent origins of 'information parasitism' and mimicry, and queen dimorphism. For more information on this work please see my publications page and navigate to my ants page.
Resource Use, Competition, & Diversity in Arboreal Ant Communities Evolved patterns of resource use can interact with the local distribution of resources to shape the structure and diversity of communities. My work with Cephalotes has firmly established that most members of this genus are highly specialized in their use of nesting resources, which allows as many as six species to coexist on individual trees only three meters tall. This work further suggests that each Cephalotes species interacts with a set of equally specialized nest-site competitors. So how does specialized nesting ecology affect the structure and diversity of the hyper-diverse arboreal ant communities of the Neotropics? To investigate this issue, I am working with Heraldo Vasconcelos and students at the Universidade Federal de Uberlândia (UFU), Brazil. Specifically, we are currently addressing the importance of resource availability, resource heterogeneity, and competition on patterns of diversity in canopy ant community of the cerrado biome. This work is being conducted at the Panga Ecological Reserve near the the city of Uberlândia, and with generous funding from The National Geographic Society, we have been able to substantially renovate and triple the size of the research station. This improvement has been vital for our project, but we also hope that it is amounts to an important and lasting contribution to research in the cerrado. Already, this new station has stimulated more research at the reserve by students and faculty at UFU.
The Mechanisms of Social Organization An early and persistent interest of mine is the underlying mechanisms of the highly organized division of labour seen in ant colonies. This is a old and hotly debated topic in the study of social insects and the only certainty is that the underlying mechanisms of social organization are complex and multi-layered. My particular interests lie with understanding the possible evolutionary origins of ant organizational mechanisms. Put another way, given the likely social environment in the ancestral ant societies, what social interactions might have been co-opted as the mechanistic basis of a simple yet robust colony organization? The best option for addressing this question in ants are various members of the Ponerinae subfamily. Some of these ants have retained what appears to be an ancestral social structure, with relatively small colonies, limited morphological differentiation between workers and queens, and high levels of intra-colonial conflict. My work with ponerines has focused on the role of dominance interactions, a common feature of "primitive" societies, as a mechanism for establishing spatial structure and task organization within the work environment of the colony. In simple terms, I have found that dominance interactions determine the location of individuals with respect to the brood within the nest, and location determines the jobs that they interact with and thus perform. Moreover, changes in the pattern of dominance interactions results in changes to the movement patterns of colony members and the job they specialize in. I argue, therefore, that dominance interactions could have served as the mechanistic foundation for a flexible and dynamic in division of labour in ants, and indeed does in some extant ponerines. My published work on this topic is currently limited to one paper and my Masters thesis, but this will change when I eventually get around to publishing the studies from my Masters thesis in widely available journals!
Ants, ants, & more ants Outside of my main research, my fascination with ants has led to work on a diversity of different projects with ants over the years. These projects include the following: Predator-prey interaction between the army ant Nomamyrmex esenbeckii and Atta leaf-cutting ants [PDF] [Photos] Army ant diversity, activity, and raid impact [Request PDF...more to come] Army ant mating biology [Request PDFs] Ant running speed [Request PDF]