Sean O'Donnell, Ph.D. - US grants

The first endocrinological regulating mechanism for plasticity in division of labor identified in a eusocial insect, the honey bee (Apis mellifera), is juvenile hormone (JH). The evolution of JH as a regulator of division of labor by age-based task performance (age polyethism) in advanced eusocial insects will be examined in this research. What will be sought are correlative and causal relationships between JH titer and age polyethisms in workers of two species exhibiting independently- evolved advanced eusocial behavior: the stingless bee Melipona favosa and the swarm-founding wasp Polybia occidentalis. Field studies in Panama are to encompass three topics: (a) association of JH titer with behavioral differences, by examination of correlations between endogenous JH titer (assessed by radio-immunoassay) and rate of age polyethisms in workers from unmanipulated colonies, (b) effects of increased JH on behavior, by application of JH topically to M. favosa workers and then testing for dose-dependency effects on age polyethism, (c) correlation of JH titer with plasticity of behavioral role, to be studied by removal of workers from foraging and nest working tasks, then gauging the JH titers of behaviorally altered individuals compared with non-responsive ones. Results will elucidate patterns of the evolution of division of labor, a central component of insect colony integration of advanced eusocial insects. %%% Insect societies are complex, self-organizing entities that are useful as models for other systems such as nervous systems and organismal development. This study will augment our knowledge of rules governing colony function by enhancing understanding of how the behavior of individual components of the system are regulated physiologically. Comprehending mechanisms by which individual behavior is translated into colony function is a central focus of insect sociobiology. Such information is critical to discovering the elements responsible for evolutionary success and ecological impact of eusocial insect in contemporary terrestrial ecosystems, especially tropical ones such as these Hymenopterans inhabit.

This project will investigate how aggressive (dominance) interactions among animal society members can influence coordination at the group level. Social wasps are ideal subjects for this work, given their complex colonies and the ease with which one can experimentally manipulate their social structure. Dr. O'Donnell will assess how variation in physiology and genetic background lead to individual differences in dominance status among workers, and govern the development of dominance. In addition he will experimentally alter colony conditions, and assess the role of dominance in maintaining efficient task performance at the colony level.
Animal societies of hundreds or more interacting individuals may be self-organizing entities. The society's labor force is non-hierarchically structured, and workers rely on communication with other workers to regulate their task-performance decisions. The proposed research will enhance our understanding of the regulation of division of labor in a well-studied, complex animal society. Furthermore, this research will yield general insight into how social coordination may be achieved in large, decentralized social groups. The proposed studies of social dominance will expand upon recent findings of physiological and genetic constraints on individual behavior, by examining the ways in which an individuals' behavior may be integrated into a functioning colony.

Social insects are among the most ecologically dominant terrestrial animals. Their success is largely attributed to division of labor among the workers that make up their colonies. Individual differences in worker behavior are governed by physiological and anatomical changes in the nervous system, particularly in the brain. However, the dynamic properties of brain neurons that influence worker behavior are poorly understood. The goal of this project is to study how changes in brain neurons are associated with division of labor among social insect workers, focusing on neural plasticity in the mushroom bodies (MB). MB are structures in insect forebrains that are involved in learning and sensory integration, and the MB may play an important role in regulating division of labor.
As a first step toward understanding the evolution of MB effects on behavior, the relationships of MB neuroanatomy and worker behavior will be compared between a wasp species with small, simple societies (Mischocyttarus mastigophorus) and a species with larger, more complex colonies (Polybia aequatorialis). Three main approaches will be used. In the first study, MB neurons that are associated with individual differences in task performance will be identified. In the second study the effects of age on MB neuron plasticity and worker behavior will be measured. In the third study, colonies will be manipulated to induce changes in worker behavior, and associated neural changes will be measured.
The proposed projects include graduate and undergraduate training opportunities, and will provide inter-institutional training experiences. They will also promote education for Americans and local residents in Costa Rica, including biology guides (Monteverde Cloud Forest Reserve), and students on graduate and undergraduate field courses. Ongoing investigations in Monteverde will enhance the visibility of basic investigation at this important tropical research and conservation site. The research findings may also have relevance to the control/management of social insect pests and beneficial insects.

The evolution of social behavior can affect brain size: social species of animals tend to have larger brains than their solitary relatives. The goal of this project is to further our understanding of how changes in species' social structure can affect the architecture of their brains. The research will use social insects - paper wasps - as subjects. All species of paper wasps are social, but they show a wide range of colony sizes, they are diverse in social complexity, and they differ in nest architecture. Different anatomical regions of the wasp brain serve distinct cognitive functions - some regions are dedicated to vision, others to smell and touch. The researchers will measure the sizes (volumes) of these brain regions as a way of estimating how much tissue is invested in each region, and they will test whether the details of a species' social behavior (for example, large versus small colonies) predict the relative size of each brain region. The researchers will use information on how wasp species are related to each other to trace the evolution of associations between brain structure and behavior. By comparing selected species of paper wasps with different behavioral characteristics, the researchers will determine which elements of social behavior have impacted the investment in each brain region. The project will also explore how evolutionary changes in the immature development of the wasp brain have led to the observed patterns of adult brain region investment. The research will further our understanding of how changes in social complexity can influence brain architecture, and the findings will indicate which social cognitive challenges can affect the amount of investment in different brain regions. It will also contribute to our understanding of how adult brain architecture is generated by the developmental processes that occur during immature stages. The project includes employment and training opportunities for graduate and undergraduate students at two universities, and it will foster collaboration across universities. It also involves both local elementary school and international outreach and education efforts.