Abstract
BackgroundButterflies 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 a de novo ovarian transcriptome of the Speckled Wood butterfly Pararge aegeria (L.), and compared the results with known model organisms such as Drosophila melanogaster and Bombyx mori.ResultsA total of 17306 contigs were annotated, with 30% possibly novel or highly divergent sequences observed. Pararge aegeria females expressed 74.5% of the genes that are known to be essential for D. melanogaster oogenesis. 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.
Highlights
Butterflies are popular model organisms to study physiological mechanisms underlying variability in oogenesis and egg provisioning in response to environmental conditions
As a first step in determining the conserved and divergent elements of the butterfly oogenesis Gene Regulatory Network (GRN), we investigated which of the genes known to play an essential role in D. melanogaster or B. mori oogenesis were transcribed by P. aegeria
The main aim of this study was to identify the genes expressed in the ovaries involved in oocyte formation, establishing oocyte polarities and the RNA transcripts transferred into the eggs by the mother, which either regulate early embryogenesis or are needed during early embryogenesis
Summary
Butterflies are popular model organisms to study physiological mechanisms underlying variability in oogenesis and egg provisioning in response to environmental conditions. The exact nature of the maternal effects and the contribution of a female to the phenotype (and fitness) of her offspring are not static, but to a large extent depend on her own internal state, resource availability [12,30] and in general the environmental conditions she experienced during her life (both biotic and abiotic) [31,32,33,34]. As such maternal effects constitute a form of non-genetic transmission of environmental conditions across generations. Lepidoptera are ideal candidates to undertake such ecological evolutionary developmental (eco-evo-devo) studies given the vast amount of physiological data on oogenesis [8], as well as very detailed information, for butterflies in particular, on reproductive variability in relation to environmental variability [10,11,43,44,45,46]
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