WHEELER, D.E.; Univ. of Arizona, Tucson: Molecular basis of caste determination in social Hymenoptera

Castes in social insects are a dramatic example of polyphenism. Polyphenic insects can develop into alternative forms, usually in response to environmental cues. We recently were successful in using suppressive subtractive hybridization (Clontech) to find >100 unique ESTs differentially expressed during development of queen and worker honey bees. We have extended the study to include soldier determination in Pheidole ants. As in queen determination in honey bees, the switch to soldier development in Pheidole is mediated by juvenile hormone. In contrast, the switch in Pheidole ants is inhibited by the presence of adult soldiers. Our approach includes construction of subtracted libraries for bipotential larvae and soldier larvae. Differentially expressed ESTs are used to probe time series of mRNA from developing larvae under various conditions, including those treated with juvenile hormone and exposed to adult soldiers. The results indicate gene expression patterns that can be attributed to nutritional and hormonal signals that constitute the developmental switching mechanism.