title: Mitochondrial divergence between slow- and fast-aging garter snakes.
abstract: Mitochondrial function has long been hypothesized to be intimately involved in aging processes--either directly through declining efficiency of mitochondrial respiration and ATP production with advancing age, or indirectly, e.g., through increased mitochondrial production of damaging free radicals with age. Yet we lack a comprehensive understanding of the evolution of mitochondrial genotypes and phenotypes across diverse animal models, particularly in species that have extremely labile physiology. Here, we measure mitochondrial genome-types and transcription in ecotypes of garter snakes (Thamnophis elegans) that are adapted to disparate habitats and have diverged in aging rates and lifespans despite residing in close proximity. Using two RNA-seq datasets, we (1) reconstruct the garter snake mitochondrial genome sequence and bioinformatically identify regulatory elements, (2) test for divergence of mitochondrial gene expression between the ecotypes and in response to heat stress, and (3) test for sequence divergence in mitochondrial protein-coding regions in these slow-aging (SA) and fast-aging (FA) naturally occurring ecotypes. At the nucleotide sequence level, we confirmed two (duplicated) mitochondrial control regions one of which contains a glucocorticoid response element (GRE). Gene expression of protein-coding genes was higher in FA snakes relative to SA snakes for most genes, but was neither affected by heat stress nor an interaction between heat stress and ecotype. SA and FA ecotypes had unique mitochondrial haplotypes with amino acid substitutions in both CYTB and ND5. The CYTB amino acid change (Isoleucine → Threonine) was highly segregated between ecotypes. This divergence of mitochondrial haplotypes between SA and FA snakes contrasts with nuclear gene-flow estimates, but correlates with previously reported divergence in mitochondrial function (mitochondrial oxygen consumption, ATP production, and reactive oxygen species consequences).
authors.affiliation: Iowa State University, Ecology, Evolution & Organismal Biology Department, Ames, IA 50011, USA.
authors.forename: Tonia S
authors.initials: TS
authors.lastname: Schwartz
authors.affiliation: Iowa State University, L. H. Baker Center for Bioinformatics & Biological Statistics, Ames, IA 50011, USA.
authors.forename: Zebulun W
authors.initials: ZW
authors.lastname: Arendsee
authors.affiliation: Iowa State University, Ecology, Evolution & Organismal Biology Department, Ames, IA 50011, USA. Electronic address: abroniko@iastate.edu.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Bronikowski
mesh_terms: D000375:Aging / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D017812:Colubridae / Q000235:genetics / Q000502:physiology*; D060146:Ecotype; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D053263:Gene Regulatory Networks / Q000502:physiology; D054629:Genome, Mitochondrial; D006239:Haplotypes; D018869:Heat-Shock Response / Q000235:genetics; D008136:Longevity / Q000235:genetics / Q000502:physiology; D008928:Mitochondria / Q000502:physiology*; D010641:Phenotype; D016415:Sequence Alignment; D013045:Species Specificity
keywords: Cytochrome B; Garter snake; Mitochondria; RNA-seq; Thamnophis elegans; Transcription initiation site; Transcriptional regulation