The mitochondrial genome of Apion squamigerum (Coleoptera, Curculionoidea, Brentidae) and the phylogenetic implications

Mitogenomics of the Olive Seed Weevil, Anchonocranus oleae Marshall and Implications for Its Phylogenetic Position in Curculionidae

Simple Summary

Anchonocranus oleae is a southern African weevil that feeds on the seeds of the African Wild Olive, a close relative of the European cultivated olive tree. The species is known to occur in the Western Cape of South Africa, the main region of olive production in Southern Africa. We generated reference DNA barcodes and the complete mitogenome of A. oleae as part of our ongoing genetic cataloguing of insects associated with wild and cultivated olives in South Africa. The phylogenetic position of A. oleae in the family Curculionidae was inferred to be in the Curculioninae, Conoderinae, Cossoninae, Molytinae, and Scolytinae (CCCMS) clade but could not be precisely determined due to the paucity of genetic data for adequate taxonomic context, highlighting the need for further coverage of related tribes and genera. Nevertheless, the data generated in this study contribute to the enrichment of baseline information on olive-associated insects, in general, and on the genus Anchonocranus, in particular.

Abstract

Anchonocranus oleae Marshall (Coleoptera: Curculionidae) is a seed-feeding weevil native to southern Africa; its larvae are known to develop in the fruits of the African Wild Olive and, more rarely, cultivated olives. The species has been mainly found in the Western Cape province of South Africa, but it has remained in relative obscurity because it does not seem to represent a current threat to commercial olive production. As part of an ongoing effort to produce baseline genetic data for olive-associated entomofauna in South Africa, we generated reference DNA barcodes for A. oleae collected from wild and cultivated olives and sequenced its mitogenome for assessment of the phylogenetic position of the species in the family Curculionidae. The mitochondrial phylogeny estimate indicated that A. oleae shares a common ancestor with Elaidobius (tribe Derelomini), but a definite and close relationship to this tribe and the precise tribal placement of A. oleae in the subfamily Curculioninae could not be inferred due to the lack of representative mitogenomes of other relevant curculionine tribes and genera. This study will assist future work on the DNA-based species identification, genetic diversity, and phylogenetic position of the genus Anchonocranus and related taxa.

The complete mitogenome of Curculiochinensis (Chevrolat, 1878) (Coleoptera: Curculionidae: Curculioninae)

The mitogenome of Curculiochinensis (Chevrolat, 1878) was sequenced and annotated to better identify C.chinensis and related species. The mitogenome is 18,680 bp in length, includes the 37 typical mitochondrial genes (13 protein-coding genes, two ribosomal RNA genes and 22 transfer RNA genes) and two control regions (total length: 3,879 bp). Mitogenome organisation, nucleotide composition and codon usage are similar to the previously sequenced Curculio mitogenomes. All 13 protein-coding genes use ATN or TTG as start codon and end with TAA/G or incomplete stop codons (single T-). Twenty-one transfer RNA genes have the typical clover-leaf structure, while the dihydrouridine (DHU) arm of trnS1 is missing. In Curculio mitogenomes, the size of the control region is highly variable. Both ML and BI analyses, based on the 13 PCGs and two rRNAs from six species of Curculioninae, strongly supported the monophyly of Curculio. In Curculio, the relationships amongst included species were inferred as ((C.chinensis + Curculio. sp.) + (Curculiodavidi + Curculioelephas)), with C.chinensis and C. sp. forming a clade (BS = 100; PP = 1).

Nanopore Sequencing Resolves Elusive Long Tandem-Repeat Regions in Mitochondrial Genomes

Long non-coding, tandem-repetitive regions in mitochondrial (mt) genomes of many metazoans have been notoriously difficult to characterise accurately using conventional sequencing methods. Here, we show how the use of a third-generation (long-read) sequencing and informatic approach can overcome this problem. We employed Oxford Nanopore technology to sequence genomic DNAs from a pool of adult worms of the carcinogenic parasite, Schistosoma haematobium, and used an informatic workflow to define the complete mt non-coding region(s). Using long-read data of high coverage, we defined six dominant mt genomes of 33.4 kb to 22.6 kb. Although no variation was detected in the order or lengths of the protein-coding genes, there was marked length (18.5 kb to 7.6 kb) and structural variation in the non-coding region, raising questions about the evolution and function of what might be a control region that regulates mt transcription and/or replication. The discovery here of the largest tandem-repetitive, non-coding region (18.5 kb) in a metazoan organism also raises a question about the completeness of some of the mt genomes of animals reported to date, and stimulates further explorations using a Nanopore-informatic workflow.

Mitochondrial genomes of twelve species of hyperdiverse Trigonopterus weevils

Mitochondrial genomes of twelve species of Trigonopterus weevils are presented, ten of them complete. We describe their gene order and molecular features and test their potential for reconstructing the phylogeny of this hyperdiverse genus comprising > 1,000 species. The complete mitochondrial genomes examined herein ranged from 16,501 bp to 21,007 bp in length, with an average AT content of 64.2% to 69.7%. Composition frequencies and skews were generally lower across species for atp6, cox1-3, and cob genes, while atp8 and genes coded on the minus strand showed much higher divergence at both nucleotide and amino acid levels. Most variation within genes was found at the codon level with high variation at third codon sites across species, and with lesser degree at the coding strand level. Two large non-coding regions were found, CR1 (between rrnS and trnI genes) and CR2 (between trnI and trnQ), but both with large variability in length; this peculiar structure of the non-coding region may be a derived character of Curculionoidea. The nad1 and cob genes exhibited an unusually high interspecific length variation of up to 24 bp near the 3' end. This pattern was probably caused by a single evolutionary event since both genes are only separated by trnS2 and length variation is extremely rare in mitochondrial protein coding genes. We inferred phylogenetic trees using protein coding gene sequences implementing both maximum likelihood and Bayesian approaches, each for both nucleotide and amino acid sequences. While some clades could be retrieved from all reconstructions with high confidence, there were also a number of differences and relatively low support for some basal nodes. The best partition scheme of the 13 protein coding sequences obtained by IQTREE suggested that phylogenetic signal is more accurate by splitting sequence variation at the codon site level as well as coding strand, rather than at the gene level. This result corroborated the different patterns found in Trigonopterus regarding to A+T frequencies and AT and GC skews that also greatly diverge at the codon site and coding strand levels.