Functional insights from the GC-poor genomes of two aphid parasitoids, Aphidius ervi and Lysiphlebus fabarum
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 biocontrol. Their success depends on adapting to develop inside aphids and overcoming both host aphid defenses and their protective endosymbionts.
We 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), highly syntenic, 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 also find that absence of some immune genes (Toll and Imd pathways) resembles similar losses in their aphid hosts, highlighting the potential impact of symbiosis on both aphids and their parasitoids.
These findings are of fundamental interest for insect evolution and beyond. This will provide a strong foundation for further functional studies including coevolution with respect to their hosts, the basis of successful infection, and biocontrol. Both genomes are available at https://bipaa.genouest.org.
or genomes of two aphid parasitoids, Aphidius ervi and Lysiphlebus fabarum
Dennis, A.B., Ballesteros, G.I., Robin, S. et al. Functional insights from the GC-poor genomes of two aphid parasitoids, Aphidius ervi and Lysiphlebus fabarum. BMC Genomics 21, 376 (2020).
New publication by Uli Ernst
In this article, Uli Ernst discusses the results of a study by Andrés E. Quiñones and colleagues that appeared in the journal Evolution. Eusociality, i.e. the division of labour between fertile individuals who reproduce and those who do not, is generally quite rare in the animal kingdom. However, it is more common in ants, bees and wasps, i.e. those state-forming insects in which there is a division of labour between queens, which have specialised in reproduction, and infertile workers, who as a rule do not lay eggs but perform all other work. It is striking that ants, bees and wasps all belong to the insect order of hymenopterans, which have a special genetic mechanism for determining the sex of the offspring. Males develop from unfertilized eggs and females hatch from fertilized eggs. It has been discussed for a long time whether this genetic mechanism ("haplodiploidy") could have led to the fact that in the hymenopteran order of insects, state-forming insects developed more frequently than in other insects. In the current study, mathematical models were used to show that there are two factors that initially facilitate the evolution of eusociality. One is an imbalance in the sex ratio between different nests (i.e. that some nests produce mainly males, while others produce mainly females), and the other is that workers within a nest can influence this sex ratio among the offspring by eliminating male offspring. In the long run this leads to different results. On the one hand, it can lead to a mixture of social nests (with female workers) and solitary nests (without female workers). On the other hand, it can also lead to exclusively social nests (with division of labour between infertile workers and fertile queens), where some nests specialise in the production of females, others in the production of males, and others in the production of both females and males.
Ernst, U.R. (2020), Digest: Evolution of eusociality favored by split sex ratios under worker‐control. Evolution, 74: 201-202. doi:10.1111/evo.13890
For the article that is discussed, please click here.
Quiñones, A.E., Henriques, G.J.B. and Pen, I. (2020), Queen–worker conflict can drive the evolution of social polymorphism and split sex ratios in facultatively eusocial life cycles. Evolution, 74: 15-28. doi:10.1111/evo.13844