title: Hagfish: Champions of CO2 tolerance question the origins of vertebrate gill function.
abstract: The gill is widely accepted to have played a key role in the adaptive radiation of early vertebrates by supplanting the skin as the dominant site of gas exchange. However, in the most basal extant craniates, the hagfishes, gills play only a minor role in gas exchange. In contrast, we found hagfish gills to be associated with a tremendous capacity for acid-base regulation. Indeed, Pacific hagfish exposed acutely to severe sustained hypercarbia tolerated among the most severe blood acidoses ever reported (1.2 pH unit reduction) and subsequently exhibited the greatest degree of acid-base compensation ever observed in an aquatic chordate. This was accomplished through an unprecedented increase in plasma [HCO3(-)] (>75 mM) in exchange for [Cl(-)]. We thus propose that the first physiological function of the ancestral gill was acid-base regulation, and that the gill was later co-opted for its central role in gas exchange in more derived aquatic vertebrates.
authors.affiliation: Department of Fisheries and Oceans, Vancouver Island University, Nanaimo, BC. Canada, V9R 5S5.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Baker
authors.affiliation: Department of Biological Sciences, California State University, Stanislaus, California, One University Circle, Turlock, CA, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Sardella
authors.affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, 1 James Cook Drive, Townsville, QLD 4811 Australia.
authors.forename: Jodie L
authors.initials: JL
authors.lastname: Rummer
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, B.C., Canada, V6T 1Z4.
authors.forename: Michael
authors.initials: M
authors.lastname: Sackville
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, B.C., Canada, V6T 1Z4.
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Brauner
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism*; D005880:Gills / Q000502:physiology*; D006196:Hagfishes / Q000502:physiology*; D010802:Phylogeny
chemical_list: D002245:Carbon Dioxide