The phylogeny and evolutionary ecology of hoverflies (Diptera: Syrphidae) inferred from mitochondrial genomes

Codon usage bias analysis in the mitochondrial genomes of five Rhingia Scopoli (Diptera, Syrphidae, Eristalinae) species

This study presents the sequencing and annotation of mitochondrial genomes from five Rhingia species of the family Syrphidae, focusing on codon bias. Each species possessed 22 tRNAs genes, 13 protein-coding genes, 2 rRNAs genes, and a control region, without any observed gene rearrangements. Nucleotide composition analysis revealed a higher AT content compared with GC content, indicating AT enrichment. Neutrality plot, Parity rule 2 bias, and effective number of codons plot analyses collectively indicated that natural selection primarily influences the codon usage bias in the five Rhingia species. Relative synonymous codon usage analysis identified the optimal codons for Rhingia binotata, R. fromosana, R. campestris, R. louguanensis, and R. xanthopoda as 10, 14, 10, 11, and 12, respectively, all ending with A/U and exhibiting AT preference. Phylogenetic analysis, based on maximum likelihood and Bayesian inference methods applied to three datasets, confirmed the monophyly of Rhingia. In conclusion, this research establishes a foundation for understanding the phylogenetic evolution and codon usage patterns in Rhingia, offering valuable for future studies.

Unusual rearrangements of mitogenomes in Diptera revealed by comparative analysis of 135 tachinid species (Insecta, Diptera, Tachinidae)

The Tachinidae is one of the most speciose families in Diptera, and the exclusively parasitoid species play an important role in regulating populations of many herbivorous insects in ecosystems, including many agricultural pests. To better comprehend the characteristics and evolution of the mitochondrial genome for the Tachinidae, we are adding a massive amount of new molecular data by assembling the mitogenomes for 71 genera and 135 species from all four tachinid subfamilies through next-generation sequencing, and we are presenting the most comprehensive mitogenomic phylogenetic analysis of this family so far. Extensive rearrangements observed in the mitogenome of Admontia podomyia (Exoristinae) are unique for the entire suborder Cyclorrhapha. The rearrangement pattern suggests that the process involved a tandem duplication of the complete mitogenome, followed by both random and nonrandom loss of one copy of each gene. Additionally, five minor mitogenome rearrangements are discovered and described in three subfamilies. We present the largest species-level phylogenetic hypothesis for Tachinidae to date, based on mitogenomes of 152 species of Tachinidae, representing all four subfamilies and with five non-tachinid outgroups. Our analyses support the monophyly of the Tachinidae and most tribes and genera were recovered with good support, but the higher-level phylogenetic relationships within Tachinidae were poorly resolved, indicating that mitogenome data alone are not enough to unambiguously resolve the deeper phylogenetic relationships within Tachinidae.

Episyrphus balteatus symbiont variation across developmental stages, living states, two sexes, and potential horizontal transmission from prey or environment

Introduction

Episyrphus balteatus is one representative Syrphidae insect which can provide extensive pollination and pest control services. To date, the symbiont composition and potential acquisition approaches in Syrphidae remain unclear.

Methods

Herein, we investigated microbiota dynamics across developmental stages, different living states, and two sexes in E. balteatus via full-length 16S rRNA genes sequencing, followed by an attempt to explore the possibility of symbiont transmission from prey Megoura crassicauda to the hoverfly.

Results

Overall, Proteobacteria and Firmicutes were the dominant bacteria phyla with fluctuating relative abundances across the life stage. Cosenzaea myxofaciens is dominant in adulthood, while Enterococcus silesiacus and Morganella morganii dominate in larvae and pupae of E. balteatus, respectively. Unexpectedly, Serratia symbiotica, one facultative endosymbiont commonly harbored in aphids, was one of the predominant bacteria in larvae of E. balteatus, just behind Enterococcus silesiacus. In addition, S. symbiotica was also surprisingly most dominated in M. crassicauda aphids (92.1% relative abundance), which are significantly higher than Buchnera aphidicola (4.7% relative abundance), the primary obligate symbiont of most aphid species. Approximately 25% mortality was observed among newly emerged adults, of which microbiota was also disordered, similar to normally dying individuals. Sexually biased symbionts and 41 bacteria species with pairwise co-occurrence in E. balteatus and 23 biomarker species for each group were identified eventually. Functional prediction showed symbionts of hoverflies and aphids, both mainly focusing on metabolic pathways. In brief, we comprehensively explored the microbiome in one Syrphidae hoverfly using E. balteatus reared indoors on M. morganii as the model, revealed its dominated symbiont species, identified sexually biased symbionts, and found an aphid facultative endosymbiont inhabited in the hoverfly. We also found that the dominated symbiotic bacteria in M. crassicauda are S. symbiotica other than Buchnera aphidicola.

Discussion

Taken together, this study provides new valuable resources about symbionts in hoverflies and prey aphids jointly, which will benefit further exploring the potential roles of microbiota in E. balteatus.