title: Convergent Evolution of Hemoglobin Function in High-Altitude Andean Waterfowl Involves Limited Parallelism at the Molecular Sequence Level.
abstract: A fundamental question in evolutionary genetics concerns the extent to which adaptive phenotypic convergence is attributable to convergent or parallel changes at the molecular sequence level. Here we report a comparative analysis of hemoglobin (Hb) function in eight phylogenetically replicated pairs of high- and low-altitude waterfowl taxa to test for convergence in the oxygenation properties of Hb, and to assess the extent to which convergence in biochemical phenotype is attributable to repeated amino acid replacements. Functional experiments on native Hb variants and protein engineering experiments based on site-directed mutagenesis revealed the phenotypic effects of specific amino acid replacements that were responsible for convergent increases in Hb-O2 affinity in multiple high-altitude taxa. In six of the eight taxon pairs, high-altitude taxa evolved derived increases in Hb-O2 affinity that were caused by a combination of unique replacements, parallel replacements (involving identical-by-state variants with independent mutational origins in different lineages), and collateral replacements (involving shared, identical-by-descent variants derived via introgressive hybridization). In genome scans of nucleotide differentiation involving high- and low-altitude populations of three separate species, function-altering amino acid polymorphisms in the globin genes emerged as highly significant outliers, providing independent evidence for adaptive divergence in Hb function. The experimental results demonstrate that convergent changes in protein function can occur through multiple historical paths, and can involve multiple possible mutations. Most cases of convergence in Hb function did not involve parallel substitutions and most parallel substitutions did not affect Hb-O2 affinity, indicating that the repeatability of phenotypic evolution does not require parallelism at the molecular level.
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America.
authors.forename: Chandrasekhar
authors.initials: C
authors.lastname: Natarajan
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America.
authors.forename: Joana
authors.initials: J
authors.lastname: Projecto-Garcia
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Moriyama
authors.affiliation: Department of Bioscience, Zoophysiology, Aarhus University, Aarhus, Denmark.
authors.forename: Roy E
authors.initials: RE
authors.lastname: Weber
authors.affiliation: Estación Biológica de Doñana-CSIC, Sevilla, Spain.|Conservation Genetics Group, Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany.
authors.forename: Violeta
authors.initials: V
authors.lastname: Muñoz-Fuentes
authors.affiliation: Estación Biológica de Doñana-CSIC, Sevilla, Spain.
authors.forename: Andy J
authors.initials: AJ
authors.lastname: Green
authors.affiliation: Centro de Ecología Aplicada del Litoral (CECOAL), Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET), Corrientes, Argentina.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Kopuchian
authors.affiliation: División Ornitología, Museo Argentino de Ciencias Naturales 'Bernardino Rivadavia' (MACN-CONICET), Buenos Aires, Argentina.
authors.forename: Pablo L
authors.initials: PL
authors.lastname: Tubaro
authors.affiliation: Institute of Arctic Biology and University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Luis
authors.initials: L
authors.lastname: Alza
authors.affiliation: Institute of Arctic Biology and University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Mariana
authors.initials: M
authors.lastname: Bulgarella
authors.affiliation: Institute of Arctic Biology and University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Smith
authors.affiliation: Institute of Arctic Biology and University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Wilson
authors.affiliation: Department of Bioscience, Zoophysiology, Aarhus University, Aarhus, Denmark.
authors.forename: Angela
authors.initials: A
authors.lastname: Fago
authors.affiliation: Institute of Arctic Biology and University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.|Department of Biology and Department of Marine Biology and Ecology, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Coral Gables, Florida, United States of America.
authors.forename: Kevin G
authors.initials: KG
authors.lastname: McCracken
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America.
authors.forename: Jay F
authors.initials: JF
authors.lastname: Storz
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000531:Altitude; D000818:Animals; D001717:Birds / Q000097:blood / Q000235:genetics / Q000502:physiology; D019143:Evolution, Molecular; D006454:Hemoglobins / Q000737:chemistry / Q000235:genetics*; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D010802:Phylogeny; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D055542:alpha-Globins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D055544:beta-Globins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D055542:alpha-Globins; D055544:beta-Globins; D010100:Oxygen