Project #1: Task Specific Gene Expression: Development and Behavior of Social Insects
The main research focus of my laboratory is to use the Harvester ant (Pogonomyrmex sp.) as a model system to study one of the central questions concerning the integration of complex biological systems, i.e. how do individuals process local information and alter behavior in response? The advent of genomic technology and its application to non-model organisms has opened exciting research opportunities in behavioral genetics, particularly in comparative sociogenomics. We study the molecular basis of task allocation in Harvester ant colonies by assaying gene expression between castes and between workers exhibiting different task behaviors. This gene expression project has two main goals:
- Identify target genes differentially expressed in Harvester ant workers exhibiting different task behaviors.
- Design experiments to study modulation of task-specific gene expression using target genes via manipulation of environmental or social cues.Currently, we are focusing on two target genes, outlined below.
Currently, we are focusing on two target genes, outlined below.
We are currently using the target gene approach to study the unique task-specific expression of a gene called foraging (for) in harvester ants. We are exploring explanations for this unique expression pattern by studying workers of different ages (developmental differences) and tasks (behavioral differences). Foraging is a protein kinase gene associated with foraging behavior in D. melanogaster and the honey bee. Using quantitative RT-PCR, we found significant differences in the expression of the harvester ant homolog Pbfor in workers of different tasks. In both field colonies and laboratory colonies, callow worker brains have a higher expression of Pbfor than the brains of foragers (Ingram et al., 2005). This is the opposite pattern of expression of Amfor in honeybees. We are exploring explanations for this unique expression pattern by studying workers of different ages (developmental differences) and tasks (behavioral differences).
We have also characterized the circadian rhythm gene called period (per), in harvester ants. The behavior of harvester ant colonies is regulated by daily behavioral patterns of workers. Tasks that occur outside the nest are regulated by day length and temperature, but inside tasks are not. Because so much is known about the circadian clock regulation pathway in insects, this gene has exciting prospects for experimental studies of ant behavior. Regulation of the circadian clock can be affected by the expression of per, by the rate of decay of per mRNA, or (for some insects) by changes in the ratio of different per types. Our data from laboratory and field colonies show that workers within the nest have different daily patterns of per expression than workers with outside tasks (Ingram, K. K., M. LeRoux, S. Krummey, to be submitted). Thus, the period gene and the circadian clock mechanism play a role in evolution of task allocation in ants. The finding that ants and bees show a similar developmental pattern of the onset of circadian rhythms suggests that there has been conservation in the molecular mechanisms regulating the evolution of division of labor and social organization across eusocial insects.
An exciting recent discovery this year has added a new direction to our research. It was found that the honeybee clock is more mammalian like than insect-like. Thus, we are attempting to clone the other major genes (cryptochrome and clock) in the circadian pathway of ants to determine whether ants (which evolved eusociality independently of bees) have a mammalian-like clock as well, or have evolved complex colony organization using a novel clock mechanism. We aim to use the expression pattern of these clock genes in experimental studies to determine how ecological factors in the environment (such as food availability, day length) may provide cues for the regulation of behavioral genes.
Project #2: Genetic Biodiversity of Southeast Asian Fish and Birds
In my lab, we are also involved in two research projects with collaborators in Singapore to study patterns of genetic biodiversity in Southeast Asian taxa. We are conducting phylogenetic studies of widespread (SE Asia) species of fish and birds, examining patterns of speciation and genetic diversity, and identifying cryptic species. Our data will be combined with collaborators' data on butterflies, flies, mammals, and frogs to provide the first comprehensive dataset on biodiversity and speciation patterns in the Southeast tropics. Recently, two students traveled with me to Singapore for the summer to assist in this research.