title: Comparative mitogenomic analysis of three species of periwinkles: Littorina fabalis, L. obtusata and L. saxatilis.
abstract: The flat periwinkles, Littorina fabalis and L. obtusata, offer an interesting system for local adaptation and ecological speciation studies. In order to provide genomic resources for these species, we sequenced their mitogenomes together with that of the rough periwinkle L. saxatilis by means of next-generation sequencing technologies. The three mitogenomes present the typical repertoire of 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes and a putative control region. Although the latter could not be fully recovered in flat periwinkles using short-reads due to a highly repetitive fragment, in L. saxatilis this problem was overcome with additional long-reads and we were able to assemble the complete mitogenome. Both gene order and nucleotide composition are similar between the three species as well as compared to other Littorinimorpha. A large variance in divergence was observed across mitochondrial regions, with six- to ten-fold difference between the highest and the lowest divergence rates. Based on nucleotide changes on the whole molecule and assuming a molecular clock, L. fabalis and L. obtusata started to diverge around 0.8 Mya (0.4-1.1 Mya). The evolution of the mitochondrial protein-coding genes in the three Littorina species appears mainly influenced by purifying selection as revealed by phylogenetic tests based on dN/dSratios that did not detect any evidence for positive selection, although some caution is required given the limited power of the dataset and the implemented approaches.
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO, Laboratório Associado, Universidade do Porto, Campus Agrário de Vairão, 4485-661 Vairão, Portugal. Electronic address: joao.marques@cibio.up.pt.
authors.forename: João P
authors.initials: JP
authors.lastname: Marques
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO, Laboratório Associado, Universidade do Porto, Campus Agrário de Vairão, 4485-661 Vairão, Portugal. Electronic address: gsotelo.fdz@gmail.com.
authors.forename: Graciela
authors.initials: G
authors.lastname: Sotelo
authors.affiliation: University of Gothenburg, Department of Marine Sciences, Box 460, SE -405 30 Gothenburg, Sweden. Electronic address: tomas.larsson@marine.gu.se.
authors.forename: Tomas
authors.initials: T
authors.lastname: Larsson
authors.affiliation: University of Gothenburg, Department of Marine Sciences, Tjärnö, SE -452 96 Strömstad, Sweden. Electronic address: kerstin.johannesson@marine.gu.se.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Johannesson
authors.affiliation: University of Gothenburg, Department of Marine Sciences, Tjärnö, SE -452 96 Strömstad, Sweden. Electronic address: marina.panova@marine.gu.se.
authors.forename: Marina
authors.initials: M
authors.lastname: Panova
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO, Laboratório Associado, Universidade do Porto, Campus Agrário de Vairão, 4485-661 Vairão, Portugal; IBE, Institute of Evolutionary Biology (CSIC-UPF), Department of Experimental and Health Sciences, Pompeu Fabra University, Doctor Aiguader 88, 08003 Barcelona, Spain. Electronic address: rui.faria@upf.edu.
authors.forename: Rui
authors.initials: R
authors.lastname: Faria
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D003062:Codon / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D019143:Evolution, Molecular; D054629:Genome, Mitochondrial; D008297:Male; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D012908:Snails / Q000235:genetics*
chemical_list: D003062:Codon; D004272:DNA, Mitochondrial
keywords: Gastropoda; annotation; assembly; mtDNA divergence; selection