title: Mitogenomics reveals high synteny and long evolutionary histories of sympatric cryptic nematode species.
abstract: Species with seemingly identical morphology but with distinct genetic differences are abundant in the marine environment and frequently co-occur in the same habitat. Such cryptic species are typically delineated using a limited number of mitochondrial and/or nuclear marker genes, which do not yield information on gene order and gene content of the genomes under consideration. We used next-generation sequencing to study the composition of the mitochondrial genomes of four sympatrically distributed cryptic species of the Litoditis marina species complex (PmI, PmII, PmIII, and PmIV). The ecology, biology, and natural occurrence of these four species are well known, but the evolutionary processes behind this cryptic speciation remain largely unknown. The gene order of the mitochondrial genomes of the four species was conserved, but differences in genome length, gene length, and codon usage were observed. The atp8 gene was lacking in all four species. Phylogenetic analyses confirm that PmI and PmIV are sister species and that PmIII diverged earliest. The most recent common ancestor of the four cryptic species was estimated to have diverged 16 MYA. Synonymous mutations outnumbered nonsynonymous changes in all protein-encoding genes, with the Complex IV genes (coxI-III) experiencing the strongest purifying selection. Our mitogenomic results show that morphologically similar species can have long evolutionary histories and that PmIII has several differences in genetic makeup compared to the three other species, which may explain why it is better adapted to higher temperatures than the other species.
authors.affiliation: Marine Biology Section Biology Department Faculty of Science University of Ghent Krijgslaan 281 (S8) 9000 Gent Belgium.
authors.forename: Tara
authors.initials: T
authors.lastname: Grosemans
authors.affiliation: Department of Biochemistry and Molecular Biology Hubbard Center for Genome Studies University of New Hampshire 35 Colovos Road Durham New Hampshire 03824.
authors.forename: Krystalynne
authors.initials: K
authors.lastname: Morris
authors.affiliation: Department of Biochemistry and Molecular Biology Hubbard Center for Genome Studies University of New Hampshire 35 Colovos Road Durham New Hampshire 03824.
authors.forename: William Kelley
authors.initials: WK
authors.lastname: Thomas
authors.affiliation: Marine Biology Section Biology Department Faculty of Science University of Ghent Krijgslaan 281 (S8) 9000 Gent Belgium; CeMoFe University of Ghent Karel Lodewijk Ledeganckstraat 359000 Gent Belgium.
authors.forename: Annelien
authors.initials: A
authors.lastname: Rigaux
authors.affiliation: Marine Biology Section Biology Department Faculty of Science University of Ghent Krijgslaan 281 (S8) 9000 Gent Belgium.
authors.forename: Tom
authors.initials: T
authors.lastname: Moens
authors.affiliation: Marine Biology Section Biology Department Faculty of Science University of Ghent Krijgslaan 281 (S8) 9000 Gent Belgium; Royal Belgian Institute of Natural Sciences (RBINS) OD Taxonomy and Phylogeny Vautierstraat 291000 Brussels Belgium.
authors.forename: Sofie
authors.initials: S
authors.lastname: Derycke
keywords: Adaptation; Litoditis marina; Miocene; Wolbachia; cryptic speciation