AbstractBackgroundButterflies are popular model organisms to study physiological mechanisms underlying variability in oogenesis and egg provisioning in response to environmental conditions. Nothing is known, however, about; the developmental mechanisms governing butterfly oogenesis, how polarity in the oocyte is established, or which particular maternal effect genes regulate early embryogenesis. To gain insights into these developmental mechanisms and to identify the conserved and divergent aspects of butterfly oogenesis, we analysed ade novoovarian transcriptome of the Speckled Wood butterflyPararge aegeria(L.), and compared the results with known model organisms such asDrosophila melanogasterandBombyx mori.ResultsA total of 17306 contigs were annotated, with 30% possibly novel or highly divergent sequences observed.Pararge aegeriafemales expressed 74.5% of the genes that are known to be essential forD. melanogasteroogenesis. We discuss the genes involved in all aspects of oogenesis, including vitellogenesis and choriogenesis, plus those implicated in hormonal control of oogenesis and transgenerational hormonal effects in great detail. Compared to other insects, a number of significant differences were observed in; the genes involved in stem cell maintenance and differentiation in the germarium, establishment of oocyte polarity, and in several aspects of maternal regulation of zygotic development.ConclusionsThis study provides valuable resources to investigate a number of divergent aspects of butterfly oogenesis requiring further research. In order to fully unscramble butterfly oogenesis, we also now also have the resources to investigate expression patterns of oogenesis genes under a range of environmental conditions, and to establish their function.