Using RNA sequencing to characterize female reproductive genes between Z and E Strains of European Corn Borer moth (Ostrinia nubilalis)

Abstract

BackgroundReproductive proteins often evolve rapidly and are thought to be subject to strong sexual selection, and thus may play a key role in reproductive isolation and species divergence. However, our knowledge of reproductive proteins has been largely limited to males and model organisms with sequenced genomes. With advances in sequencing technology, Lepidoptera are emerging models for studies of sexual selection and speciation. By profiling the transcriptomes of the bursa copulatrix and bursal gland from females of two incipient species of moth, we characterize reproductive genes expressed in the primary reproductive tissues of female Lepidoptera and identify candidate genes contributing to a one-way gametic incompatibility between Z and E strains of the European corn borer (Ostrinia nubilalis).ResultsUsing RNA sequencing we identified transcripts from ~37,000 and ~36,000 loci that were expressed in the bursa copulatrix or the bursal gland respectively. Of bursa copulatrix genes, 8% were significantly differentially expressed compared to the female thorax, and those that were up-regulated or specific to the bursa copulatrix showed functional biases toward muscle activity and/or organization. In the bursal gland, 9% of genes were differentially expressed compared to the thorax, with many showing reproduction or gamete production functions. Of up-regulated bursal gland genes, 46% contained a transmembrane region and 16% possessed secretion signal peptides. Divergently expressed genes in the bursa copulatrix were exclusively biased toward protease-like functions and 51 proteases or protease inhibitors were divergently expressed overall.ConclusionsThis is the first comprehensive characterization of female reproductive genes in any lepidopteran system. The transcriptome of the bursa copulatrix supports its role as a muscular sac that is the primary site for disruption of the male ejaculate. We find that the bursal gland acts as a reproductive secretory body that might also interact with male ejaculate. In addition, differential expression of proteases between strains supports a potential role for these tissues in contributing to reproductive isolation. Our study provides new insight into how male ejaculate is processed by female Lepidoptera, and paves the way for future work on interactions between post-mating sexual selection and speciation.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-189) contains supplementary material, which is available to authorized users.

Molecular characterization of firefly nuptial gifts: a multi-omics approach sheds light on postcopulatory sexual selection

“…Moreover, to date, gene expression in those female reproductive tissues that receive and process male ejaculates has been examined for only a few taxa, including Drosophila spp 27,. the honeybee Apis mellifera 30, the corn borer moth Ostrinia nubilalis 25, and Pieris rapae butterflies26. In Photinus fireflies, after the male spermatophore is deposited in the female’s bursa copulatrix, it enters the spermatophore-digesting gland where it subsequently disintegrates over the next several days40.…”

“…Female peptidases and peptidase regulators are likely to be important mediators of postcopulatory sexual interactions, and these have also been identified from female reproductive tracts of other insects252627. In D. melanogaster , female peptidases and peptidase inhibitors interact with male SFPs and are required to process into their active forms at least three male proteins that induce egg-laying and reduce female receptivity to remating79.…”

“…Additionally, sexual selection research shows a recognized bias toward male reproductive traits24. Thus, despite the central role that females play in postcopulatory sexual interactions, remarkably little is known about the products of female reproductive glands252627282930. Understanding the role of nuptial gifts in the context of sexual selection will require comprehensive analyses interrogating the molecular composition of male nuptial gifts as well as secretions from female reproductive tissues that receive and process male gifts.…”

“…Importantly, this work is part of an expanding set of non-model organisms that lack a sequenced genome yet have biologically interesting reproductive molecules that can be identified using a combination of de novo transcriptomes, proteomics and RNA sequencing. Indeed, similar approaches have identified reproductive molecules in crickets53, moths25, and butterflies54, expanding our knowledge of nuptial gifts beyond existing model systems such as Drosophila and humans, and further shedding light on specific accessory gland functions and the molecular mechanisms of postcopulatory sexual selection.…”

Evaluating Cryptic Female Choice in Highly Promiscuous Tribolium Beetles

“…Another major missing link in understanding of postmating male-female interactions,-not only for Tribolium but also for most arthropods,-is a general lack of knowledge on the function of female reproductive glands (Al-Wathiqui et al 2014). In Tribolium, the close proximity of the spermathecal gland to the sites of sperm storage and fertilization suggest a possible role in female sperm choice.…”