Background: Trichogrammatids are minute parasitoid wasps that develop within other insect eggs. They are less than half a millimeter long, smaller than some protozoans. The Trichogrammatidae are one of the earliest branching families of Chalcidoidea: a diverse superfamily of approximately half a million species of parasitoid wasps, proposed to have evolved from a miniaturized ancestor. Trichogramma are frequently used in agriculture, released as biological control agents against major moth and butterfly pests. Additionally, Trichogramma are well known for their symbiotic bacteria that induce asexual reproduction in infected females. Knowledge of the genome sequence of Trichogramma is a major step towards further understanding its biology and potential applications in pest control. Results: We report the 195-Mb genome sequence of Trichogramma pretiosum and uncover signatures of miniaturization and adaptation in Trichogramma and related parasitoids. Comparative analyses reveal relatively rapid evolution of proteins involved in ribosome biogenesis and function, transcriptional regulation, and ploidy regulation. Chalcids also show loss or especially rapid evolution of 285 gene clusters conserved in other Hymenoptera, including many that are involved in signal transduction and embryonic development. Comparisons between sexual and asexual lineages of Trichogramma pretiosum reveal that there is no strong evidence for genome degradation (e.g., gene loss) in the asexual lineage, although it does contain a lower repeat content than the sexual lineage. Trichogramma shows particularly rapid genome evolution compared to other hymenopterans. We speculate these changes reflect adaptations to miniaturization, and to life as a specialized egg parasitoid. Conclusions: The genomes of Trichogramma and related parasitoids are a valuable resource for future studies of these diverse and economically important insects, including explorations of parasitoid biology, symbiosis, asexuality, biological control, and the evolution of miniaturization. Understanding the molecular determinants of parasitism can also inform mass rearing of Trichogramma and other parasitoids for biological control.
Bibliographical noteFunding Information:
We thank Bob Schmitz for help with the whole genome bisulfite sequencing. We thank Hans Smid, Eric A. Smith, and three anonymous reviewers for feedback on earlier drafts of the manuscript. We thank the staff at the Baylor College of Medicine HGSC for their contributions, and we acknowledge Monica Poelchau and Christopher Childers for their contributions to the i5k workspace. This work was supported by the National Human Genome Research Institute (U54 HG003273 to RAG); the National Science Foundation (DEB 1501227 to ARIL, DEB 1257053 and IOS 1456233 to JHW, and MCB 1615664 to SVY); the United States Department of Agriculture (NIFA 194617 to RS and NIFA 2016-67011-24778 to ARIL); and Robert and Peggy van den Bosch Memorial Scholarships to ARIL. None of the funding bodies had any role in the design of the study; collection, analysis, and interpretation of data; or in writing of the manuscript
© 2018 Lindsey et al.
- Biological control
- Comparative genomics