title: Positive selection on panpulmonate mitogenomes provide new clues on adaptations to terrestrial life.
abstract: Transitions from marine to intertidal and terrestrial habitats resulted in a significant adaptive radiation within the Panpulmonata (Gastropoda: Heterobranchia). This clade comprises several groups that invaded the land realm independently and in different time periods, e.g., Ellobioidea, Systellomatophora, and Stylommatophora. Thus, mitochondrial genomes of panpulmonate gastropods are promising to screen for adaptive molecular signatures related to land invasions.
  
  
  
  We obtained three complete mitochondrial genomes of terrestrial panpulmonates, i.e., the ellobiid Carychium tridentatum, and the stylommatophorans Arion rufus and Helicella itala. Our dataset consisted of 50 mitogenomes comprising almost all major panpulmonate lineages. The phylogenetic tree based on mitochondrial genes supports the monophyly of the clade Panpulmonata. Terrestrial lineages were sampled from Ellobioidea (1 sp.) and Stylommatophora (9 spp.). The branch-site test of positive selection detected significant non-synonymous changes in the terrestrial branches leading to Carychium (Ellobiodea) and Stylommatophora. These convergent changes occurred in the cob and nad5 genes (OXPHOS complex III and I, respectively).
  
  
  
  The convergence of the non-synonymous changes in cob and nad5 suggest possible ancient episodes of positive selection related to adaptations to non-marine habitats. The positively selected sites in our data are in agreement with previous results in vertebrates suggesting a general pattern of adaptation to the new metabolic requirements. The demand for energy due to the colonization of land (for example, to move and sustain the body mass in the new habitat) and the necessity to tolerate new conditions of abiotic stress may have changed the physiological constraints in the early terrestrial panpulmonates and triggered adaptations at the mitochondrial level.
authors.affiliation: Senckenberg Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325, Frankfurt am Main, Germany. pedro.romero@senckenberg.de.|Institute for Ecology, Evolution & Diversity, Faculty of Biological Sciences, Goethe University Frankfurt, Max-von-Laue-Straße 13, 60438, Frankfurt am Main, Germany. pedro.romero@senckenberg.de.|Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Av. Arenales 1256, Apartado 14-0434, Lima 14, Peru. pedro.romero@senckenberg.de.
authors.forename: Pedro E
authors.initials: PE
authors.lastname: Romero
authors.affiliation: Aquatic Ecosystem Research, University of Duisburg-Essen, Universitätsstraße 5, 45141, Essen, Germany.|Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen, Universitätsstraße 2, 45117, Essen, Germany.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Weigand
authors.affiliation: Senckenberg Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325, Frankfurt am Main, Germany.|Institute for Ecology, Evolution & Diversity, Faculty of Biological Sciences, Goethe University Frankfurt, Max-von-Laue-Straße 13, 60438, Frankfurt am Main, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Pfenninger
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D049851:Gastropoda / Q000145:classification / Q000235:genetics*; D054629:Genome, Mitochondrial; D010802:Phylogeny
keywords: Codon models; Land invasion; Mitogenomics; Panpulmonata; Positive selection