The Complete Mitochondrial Genome of the Geophilomorph Centipede Strigamia maritima

Abstract

Strigamia maritima (Myriapoda; Chilopoda) is a species from the soil-living order of geophilomorph centipedes. The Geophilomorpha is the most speciose order of centipedes with over a 1000 species described. They are notable for their large number of appendage bearing segments and are being used as a laboratory model to study the embryological process of segmentation within the myriapods. Using a scaffold derived from the recently published genome of Strigamia maritima that contained multiple mitochondrial protein-coding genes, here we report the complete mitochondrial genome of Strigamia, the first from any geophilomorph centipede. The mitochondrial genome of S. maritima is a circular molecule of 14,938 base pairs, within which we could identify the typical mitochondrial genome complement of 13 protein-coding genes and 2 ribosomal RNA genes. Sequences resembling 16 of the 22 transfer RNA genes typical of metazoan mitochondrial genomes could be identified, many of which have clear deviations from the standard ‘cloverleaf’ secondary structures of tRNA. Phylogenetic trees derived from the concatenated alignment of protein-coding genes of S. maritima and >50 other metazoans were unable to resolve the Myriapoda as monophyletic, but did support a monophyletic group of chilopods: Strigamia was resolved as the sister group of the scolopendromorph Scolopocryptos sp. and these two (Geophilomorpha and Scolopendromorpha), along with the Lithobiomorpha, formed a monophyletic group the Pleurostigmomorpha. Gene order within the S. maritima mitochondrial genome is unique compared to any other arthropod or metazoan mitochondrial genome to which it has been compared. The highly unusual organisation of the mitochondrial genome of Strigamia maritima is in striking contrast with the conservatively evolving nuclear genome: sampling of more members of this order of centipedes will be required to see whether this unusual organization is typical of the Geophilomorpha or results from a more recent reorganisation in the lineage leading to Strigamia.

Complete mitochondrial genomes of two flat-backed millipedes by next-generation sequencing (Diplopoda, Polydesmida)

“…However, the arrangement of genes in mt genomes is remarkably variable in Strigamia maritima (Chilopoda: Geophilomorpha) and Symphylella sp. (Symphyla: Scolopendrellidae) (Gai et al 2008; Robertson et al 2015). All millipedes in which the mt genome has been sequenced, except Sphaerotheriida, have nad6 + cob placements that differ from that of Limulus Polyphemus and the nad6 + cob pattern was supposed to be sound molecular evidence supporting the Helminthomorpha clade.…”

“…Although taxon sampling is limited, gene synteny has supplied evolutionary evidence relating to Myriapoda phylogenetic and evolutionary history. Full mitochondrial genomes of sixteen myriapod species have hitherto been sequenced, however, this number is still far from sufficient considering the high species richness of this group (Sierwald and Bond 2007; Budd and Telford 2009; Dong et al 2012a; Robertson et al 2015). This lack of mitochondrial genome data is hampering phylogenetic and evolutionary studies within the subphylum Myriapoda.…”

“…Avoiding inadequate outgroups, selecting conserved amino acid alignment regions and bolstering taxon sampling are keys to phylogenetic reconstruction using mt genomes (Rota-Stabelli et al 2011; Chen et al 2014; Robertson et al 2015). However, complete representation of the four myriapod classes in many studies is not included (Rota-Stabelli et al 2011; Brewer et al 2013) and the mt genomes of class Pauropoda, the presumed sister lineage of millipedes, are available in Genbank but not included in previous studies (Brewer et al 2013).…”

“…However, complete representation of the four myriapod classes in many studies is not included (Rota-Stabelli et al 2011; Brewer et al 2013) and the mt genomes of class Pauropoda, the presumed sister lineage of millipedes, are available in Genbank but not included in previous studies (Brewer et al 2013). Relationships among the Myriapoda remain unresolved in Robertson et al (2015), including among the four classes.…”

Complete mitochondrial genome ofSellanucheza jaegeriGolovatch, 2013 by next generation sequencing (Polydesmida: Paradoxosomatidae) and phylogenetic analysis in Diplopoda

“…The rearrangement of genes in mitogenomes had remarkably occurred in Diplopoda. However, relationships among the Myriapoda remain unresolved in Robertson et al (2015), and owning to the lack of species sequences, the interordinal phylogenetic relationships within Diplopoda are one of the most debated issues.…”