Genome of the Parasitoid Wasp Diachasma alloeum, an Emerging Model for Ecological Speciation and Transitions to Asexual Reproduction.

Josefa Gonzalez,Hugh M Robertson,Andrew A Forbes,Glen R Hood,Kyle E Mcelroy,John M Logsdon,Jeffrey L Feder,John H Werren,Eric S Tvedte,Kimberly K O Walden

doi:10.1093/gbe/evz205

Abstract

Parasitoid wasps are among the most speciose animals, yet have relatively few available genomic resources. We report a draft genome assembly of the wasp Diachasma alloeum (Hymenoptera: Braconidae), a host-specific parasitoid of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae), and a developing model for understanding how ecological speciation can “cascade” across trophic levels. Identification of gene content confirmed the overall quality of the draft genome, and we manually annotated ∼400 genes as part of this study, including those involved in oxidative phosphorylation, chemosensation, and reproduction. Through comparisons to model hymenopterans such as the European honeybee Apis mellifera and parasitoid wasp Nasonia vitripennis, as well as a more closely related braconid parasitoid Microplitis demolitor, we identified a proliferation of transposable elements in the genome, an expansion of chemosensory genes in parasitoid wasps, and the maintenance of several key genes with known roles in sexual reproduction and sex determination. The D. alloeum genome will provide a valuable resource for comparative genomics studies in Hymenoptera as well as specific investigations into the genomic changes associated with ecological speciation and transitions to asexuality.

Highlights

The Hymenoptera may be the largest order of insects due to the immense diversity of parasitic wasps (i.e. “parasitoids”) that lay their eggs into or on other insect species (LaSalle & Gould, 1993; Austin & Dowton, 2000; Whitfield, 2003; Forbes et al, 2018)
We report the de novo genome assembly of the parasitoid wasp D. alloeum, adding to the genomic resources for parasitoid wasps, which are underrepresented among available hymenopteran genomes (Branstetter et al, 2017)
The likely bacterial contaminating scaffolds were removed from the D. alloeum assembly, and the remaining 3,313 scaffolds will be made available as genome assembly Dall2.0

Summary

Introduction

The Hymenoptera may be the largest order of insects due to the immense diversity of parasitic wasps (i.e. “parasitoids”) that lay their eggs into or on other insect species (LaSalle & Gould, 1993; Austin & Dowton, 2000; Whitfield, 2003; Forbes et al, 2018). The decay of genes involved in sexual traits has been observed in multiple asexual parasitoid wasps (e.g. Ma et al, 2014; Kraaijeveld et al, 2016), there is a dearth of comparative assessments of genomic molecular evolution between sexual and asexual Hymenoptera. We performed a series of descriptive analyses to assess the overall quality and content of the D. alloeum genome, and focused on annotation and evolutionary analyses of gene families with potential relevance to speciation and sex determination in Diachasma. The de novo genome assembly Dall1.0 (GenBank accession: GCA_001412515.1)

Results

Conclusion