Mitogenome of a stink worm (Annelida: Travisiidae) includes degenerate group II intron that is also found in five congeneric species

Abstract

Mitogenomes are useful for inferring phylogenetic relationships between organisms. Although the mitogenomes of Annelida, one of the most morphologically and ecologically diverse metazoan groups have been well sequenced, those of several families remain unexamined. This study determined the first mitogenome from the family Travisiidae (Travisia sanrikuensis), analyzed its mitogenomic features, and reconstructed a phylogeny of Sedentaria. The monophyly of the Terebellida + Arenicolida + Travisiidae clade is supported by molecular phylogenetic analysis. The placement of Travisiidae is unclear because of the lack of mitogenomes from closely related lineages. An unexpected intron appeared within the cox1 gene of T. sanrikuensis and in the same positions of five undescribed Travisia spp. Although the introns are shorter (790–1386 bp) than other group II introns, they can be considered degenerate group II introns due to type II intron maturase open reading frames, found in two of the examined species, and motifs characteristic of group II introns. This is likely the first known case in metazoans where mitochondrial group II introns obtained by a common ancestor are conserved in several descendants. Insufficient evolutionary time for intron loss in Travisiidae, or undetermined mechanisms may have helped maintain the degenerate introns.

First mitochondrial genome of a lugworm (Annelida: Arenicolidae) and its phylogenetic position

“…This is the first study to determine the mitogenome sequence of Arenicolidae using Abarenicola claparedi oceanica and perform phylogenetic analyses using closely related families registered in GenBank. Using previously published mitogenome data (Bolbat et al, 2021;Nam et al, 2021;Kobayashi et al, 2022aKobayashi et al, , 2022b, mitogenomic phylogenetic trees were reconstructed with the most inclusive taxon sampling of the part of the Sedentaria families (oligochaetes, hirudineans, echiurans and some polychaetes). Analyses based on the nucleotide sequences confirmed the monophyly of Terebellidae, which was paraphyletic in analyses based on the amino acid sequences and previous mitogenomic phylogenies.…”

“…A previous study on the mitogenomic phylogeny indicated a close relationship between Travisiidae and the Terebellida and Arenicolida clade (Kobayashi et al ., 2022 a ). However, the phylogenetic position was not sufficiently clarified as the position of Travisiidae was poorly supported.…”

“…Although a robust phylogenetic framework is established, the phylogenetic positions of some families in this clade remain unclear. The mitogenomic phylogeny might provide implications for the phylogenetic relationships in this clade, although the position of Travisiidae and Terebellidae are unknown in the previous analyses based on mitogenomes (Zhong et al ., 2011; Nam et al ., 2021; Kobayashi et al ., 2022 a , 2022 b ). The intra-familial relationship of Arenicolidae was also not entirely understood by phylogenetic analyses based on 16S or 18S rRNA sequences (Bleidorn et al ., 2005; Darbyshire, 2017).…”

“…Arenicolida clade(Kobayashi et al, 2022a). However, the phylogenetic position was not sufficiently clarified as the position of Travisiidae was poorly supported.…”

Confirmation of the first intronic sequence in the bivalvian mitochondrial genome of Macoma balthica (Linnaeus, 1758)

“…Such taxonomic distribution is often used as empirical support for mutational-pressure hypothesis explaining lack of introns in fast-evolving mtDNA [34]. Up to this point, the only bilaterian animals where mitochondrial intronic sequences have been identified are several species of annelids [35][36][37][38].…”