1. Identify target genes differentially expressed in Harvester ant workers exhibiting different task behaviors.
2. 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.

Foraging

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).

Period

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.