Diapause in the Alfalfa Leafcutting Bee, Megachile rotundata: Environmental History Impact on Gene Expression

While similarities among diapausing insects are many, the molecular foundation for these similarities has been investigated under a limited number of environmental conditions. Diapausing insects are able to respond to changes in environmental conditions, which are regulated by changes in the underlying gene expression. The aim of this investigation was to clarify the degree to which environmental history effects gene expression during diapause development. Diapausing prepupae of the alfalfa leafcutting bee, Megachile rotundata were collected early in the nesting season (June 30 to July 19, 2010) and late in the season (September 1, 2010). All diapausing prepupae were maintained under field conditions until October 22, 2010 when the prepupae from each group were further subdivided into management types: laboratory (constant 4°C) or field (stored in open shelter). Thus we had four treatment groups for the prepupae: early laboratory, late laboratory, early field, and late field. Illumina libraries were constructed from samples taken from each group in November, January, March and May and 100bp paired-end sequencing was carried out using a HiSeq Illumina sequencer. Analysis of the results revealed that there were treatment specific gene expression patterns in each of the treatment groups. There were very few differentially regulated genes shared between all four treatment groups. The results demonstrated that environmental history has a major impact on gene expression during diapause development and thereby is a confounding factor in our understanding of the molecular regulation of diapause development.