Disrupted architecture and fast evolution of the mitochondrial genome of Argeia pugettensis (Isopoda): implications for
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RESEARCH ARTICLE
Open Access
Disrupted architecture and fast evolution of the mitochondrial genome of Argeia pugettensis (Isopoda): implications for speciation and fitness Jianmei An1* , Wanrui Zheng1†, Jielong Liang1†, Qianqian Xi1, Ruru Chen1, Junli Jia1, Xia Lu1 and Ivan Jakovlić2
Abstract Background: Argeia pugettensis is an isopod species that parasitizes other crustaceans. Its huge native geographic range spans the Pacific from China to California, but molecular data are available only for a handful of specimens from NorthAmerican populations. We sequenced and characterised the complete mitogenome of a specimen collected in the Yellow Sea. Results: It exhibited a barcode (cox1) similarity level of only 87–89% with North-American populations, which is unusually low for conspecifics. Its mitogenome is among the largest in isopods (≈16.5 Kbp), mostly due to a large duplicated palindromic genomic segment (2 Kbp) comprising three genes. However, it lost a segment comprising three genes, nad4L-trnP-nad6, and many genes exhibited highly divergent sequences in comparison to isopod orthologues, including numerous mutations, deletions and insertions. Phylogenetic and selection analyses corroborated that this is one of the handful of most rapidly evolving available isopod mitogenomes, and that it evolves under highly relaxed selection constraints (as opposed to positive selection). However, its nuclear 18S gene is highly conserved, which suggests that rapid evolution is limited to its mitochondrial genome. The cox1 sequence analysis indicates that elevated mitogenomic evolutionary rates are not shared by North-American conspecifics, which suggests a breakdown of cox1 barcoding in this species. Conclusions: A highly architecturally disrupted mitogenome and decoupling of mitochondrial and nuclear rates would normally be expected to have strong negative impacts on the fitness of the organism, so the existence of this lineage is a puzzling evolutionary question. Additional studies are needed to assess the phylogenetic breadth of this disrupted mitochondrial architecture and its impact on fitness. Keywords: Barcode, Speciation, Decoupling of nuclear and mitochondrial evolution, Branch length, Crustaceans, Inversion of the origin of replication
Background Eukaryotes are invariably characterised by the co-existence of two different genomes within a single organism: nuclear and mitochondrial. The maintenance of evolutionary coadaptation between the two genomes, necessary for the * Correspondence: [email protected] † Wanrui Zheng and Jielong Liang contributed equally to this work. 1 School of Life Science, Shanxi Normal University, Linfen 041000, PR China Full list of author information is available at the end of the article
interacting mitochondrial and nuclear components to reach their functional potential, called mitonuclear ecology, is an emerging topic in molecular biology [1–3]. There is accumulating evidence that mitochondrial DNA may have a disproportionately large role in generating Dobzhansky– Muller incompati
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