title: Molecular evolution of globin genes in Gymnotiform electric fishes: relation to hypoxia tolerance.
abstract: Nocturnally active gymnotiform weakly electric fish generate electric signals for communication and navigation, which can be energetically taxing. These fish mainly inhabit the Amazon basin, where some species prefer well-oxygenated waters and others live in oxygen-poor, stagnant habitats. The latter species show morphological, physiological, and behavioral adaptations for hypoxia-tolerance. However, there have been no studies of hypoxia tolerance on the molecular level. Globins are classic respiratory proteins. They function principally in oxygen-binding and -delivery in various tissues and organs. Here, we investigate the molecular evolution of alpha and beta hemoglobins, myoglobin, and neuroglobin in 12 gymnotiforms compared with other teleost fish.
  
  
  
  The present study identified positively selected sites (PSS) on hemoglobin (Hb) and myoglobin (Mb) genes using different maximum likelihood (ML) methods; some PSS fall in structurally important protein regions. This evidence for the positive selection of globin genes suggests that the adaptive evolution of these genes has helped to enhance the capacity for oxygen storage and transport. Interestingly, a substitution of a Cys at a key site in the obligate air-breathing electric eel (Electrophorus electricus) is predicted to enhance oxygen storage of Mb and contribute to NO delivery during hypoxia. A parallel Cys substitution was also noted in an air-breathing African electric fish (Gymnarchus niloticus). Moreover, the expected pattern under normoxic conditions of high expression of myoglobin in heart and neuroglobin in the brain in two hypoxia-tolerant species suggests that the main effect of selection on these globin genes is on their sequence rather than their basal expression patterns.
  
  
  
  Results indicate a clear signature of positive selection in the globin genes of most hypoxia-tolerant gymnotiform fishes, which are obligate or facultative air breathers. These findings highlight the critical role of globin genes in hypoxia tolerance evolution of Gymnotiform electric fishes.
authors.affiliation: Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, 210046, China.|Department of Integrative Biology, The University of Texas, Austin, TX, 78759, USA.
authors.forename: Ran
authors.initials: R
authors.lastname: Tian
authors.affiliation: Department of Integrative Biology, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Losilla
authors.affiliation: Department of Integrative Biology, The University of Texas, Austin, TX, 78759, USA.|Department of Neuroscience, The University of Texas, Austin, TX, 78759, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, 210046, China. gyang@njnu.edu.cn.
authors.forename: Guang
authors.initials: G
authors.lastname: Yang
authors.affiliation: Department of Integrative Biology, The University of Texas, Austin, TX, 78759, USA. h.zakon@austin.utexas.edu.|Department of Neuroscience, The University of Texas, Austin, TX, 78759, USA. h.zakon@austin.utexas.edu.
authors.forename: Harold
authors.initials: H
authors.lastname: Zakon
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D005075:Biological Evolution; D004555:Electric Fish / Q000235:genetics* / Q000502:physiology; D019143:Evolution, Molecular; D005914:Globins / Q000235:genetics* / Q000378:metabolism; D006454:Hemoglobins / Q000235:genetics; D000860:Hypoxia / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics; D000078787:Neuroglobin; D010100:Oxygen
chemical_list: D006454:Hemoglobins; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D005914:Globins; D010100:Oxygen
keywords: Adaptive evolution; Globin; Gymnotiformes; Hypoxia tolerance; Positive selection