title: Introgression of mitochondrial DNA among Myodes voles: consequences for energetics?
abstract: BACKGROUND
  Introgression of mitochondrial DNA (mtDNA) is among the most frequently described cases of reticulate evolution. The tendency of mtDNA to cross interspecific barriers is somewhat counter-intuitive considering the key function of enzymes that it encodes in the oxidative-phosphorylation process, which could give rise to hybrid dysfunction. How mtDNA reticulation affects the evolution of metabolic functions is, however, uncertain. Here we investigated how morpho-physiological traits vary in natural populations of a common rodent (the bank vole, Myodes glareolus) and whether this variation could be associated with mtDNA introgression. First, we confirmed that M. glareolus harbour mtDNA introgressed from M. rutilus by analyzing mtDNA (cytochrome b, 954 bp) and nuclear DNA (four markers; 2333 bp in total) sequence variation and reconstructing loci phylogenies among six natural populations in Finland. We then studied geographic variation in body size and basal metabolic rate (BMR) among the populations of M. glareolus and tested its relationship with mtDNA type.
  
  
  RESULTS
  Myodes glareolus and its arctic neighbour, M. rutilus, are reciprocally monophyletic at the analyzed nuclear DNA loci. In contrast, the two northernmost populations of M. glareolus have a fixed mitotype that is shared with M. rutilus, likely due to introgressive hybridization. The analyses of phenotypic traits revealed that the body mass and whole-body, but not mass corrected, BMR are significantly reduced in M. glareolus females from northern Finland that also have the introgressed mitotype. Restricting the analysis to the single population where the mitotypes coexist, the association of mtDNA type with whole-body BMR remained but those with mass corrected BMR and body mass did not. Mitochondrial sequence variation in the introgressed haplotypes is compatible with demographic growth of the populations, but may also be a result of positive selection.
  
  
  CONCLUSIONS
  Our results show that the phenotypic traits vary markedly along the north-south axis of populations of M. glareolus. This variation may be related to adaptation to local environments and coincides with the gradient of genome reticulation between M. glareolus and M. rutilus, which was assessed by mtDNA introgression. Introgression of mtDNA may have affected morpho-physiological traits but do not show strong effects on either body mass or basal metabolic rate alone. We discuss the causes and biological meaning of our results and the means to clarify these questions in future research.
authors.affiliation: Centre of Excellence in Evolutionary Research, Department of Biological and Environmental Science, University of Jyväskylä, Finland. boratyns@gmail.com
authors.forename: Zbyszek
authors.initials: Z
authors.lastname: Boratyński
authors.forename: Paulo Célio
authors.initials: PC
authors.lastname: Alves
authors.forename: Stefano
authors.initials: S
authors.lastname: Berto
authors.forename: Esa
authors.initials: E
authors.lastname: Koskela
authors.forename: Tapio
authors.initials: T
authors.lastname: Mappes
authors.forename: José
authors.initials: J
authors.lastname: Melo-Ferreira
mesh_terms: D000818:Animals; D001110:Arctic Regions; D003411:Arvicolinae / Q000235:genetics* / Q000378:metabolism*; D001481:Basal Metabolism; D002467:Cell Nucleus / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics*; D005260:Female; D008297:Male; D010641:Phenotype
chemical_list: D004272:DNA, Mitochondrial