Abstract
BackgroundParasitoid wasps have fascinating life cycles and play an important role in trophic networks, yet little is known about their genome content and function. Parasitoids that infect aphids are an important group with the potential for biological control. Their success depends on adapting to develop inside aphids and overcoming both host aphid defenses and their protective endosymbionts.ResultsWe present the de novo genome assemblies, detailed annotation, and comparative analysis of two closely related parasitoid wasps that target pest aphids: Aphidius ervi and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae). The genomes are small (139 and 141 Mbp) and the most AT-rich reported thus far for any arthropod (GC content: 25.8 and 23.8%). This nucleotide bias is accompanied by skewed codon usage and is stronger in genes with adult-biased expression. AT-richness may be the consequence of reduced genome size, a near absence of DNA methylation, and energy efficiency. We identify missing desaturase genes, whose absence may underlie mimicry in the cuticular hydrocarbon profile of L. fabarum. We highlight key gene groups including those underlying venom composition, chemosensory perception, and sex determination, as well as potential losses in immune pathway genes.ConclusionsThese findings are of fundamental interest for insect evolution and biological control applications. They provide a strong foundation for further functional studies into coevolution between parasitoids and their hosts. Both genomes are available at https://bipaa.genouest.org.
Highlights
Parasitoid wasps have fascinating life cycles and play an important role in trophic networks, yet little is known about their genome content and function
Bio) sequences, and were assembled with different strategies (Supplementary Tables 1 and 2). This produced two high quality genome assemblies (N50 in A. ervi: 581 kb, in L. fabarum: 216 kb) with similar total lengths (A. ervi: 139Mbp, L. fabarum: 141Mbp) but different ranges of scaffold-sizes (Table 1, Supplementary Table 3). The length of these assemblies is in range of that predicted by a kmer analysis with the K-mer Analysis Toolkit (KAT) (Supplementary Figure 1) [60], which predicted A. ervi at 142.83Mbp and L. fabarum at 99.26Mbp
The L. fabarum assembly is larger than the estimate from KAT; we suspect that this may be due to duplications in the assembly, and future work should address these duplications
Summary
Parasitoid wasps have fascinating life cycles and play an important role in trophic networks, yet little is known about their genome content and function. Parasitoids that infect aphids are an important group with the potential for biological control. Their success depends on adapting to develop inside aphids and overcoming both host aphid defenses and their protective endosymbionts. Parasites are ubiquitously present across all of life [1, 2]. Their negative impact on host fitness can impose strong selection on hosts to resist, tolerate, or escape potential parasites. Parasitoids are a special group of parasites whose successful reproduction is fatal to the host [3, 4]. Parasitoid radiations appear to have coincided with those of their hosts [11], and there is ample evidence that host-parasitoid relationships impose strong reciprocal selection, promoting a dynamic process of antagonistic coevolution [12,13,14]
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