title: Osmotic/ionic status of body fluids in the euryhaline cephalopod suggest possible parallel evolution of osmoregulation.
abstract: Acclimation from marine to dilute environments constitutes among the dramatic evolutionary transitions in the history of life. Such adaptations have evolved in multiple lineages, but studies of the blood/hemolymph homeostasis mechanisms are limited to those using evolutionarily advanced Deuterostome (chordates) and Ecdysozoa (crustaceans). Here, we examined hemolymph homeostasis in the advanced Lophotrochozoa/mollusc, the other unexplored taxa, and its possible regulation by the vasopressin/oxytocin superfamily peptides known to be implicated in fluid homeostasis in Chordata and Arthropoda. The hemolymph osmotic and ionic status in the euryhaline cephalopod (Octopus ocellatus) following transfer from 30-ppt normal seawater to 20 ppt salinity indicate hyperosmo- and hyperionoregulatory abilities for more than 1 week, as in crustaceans and teleost fish. While ventilation frequency decreased by 1 day, Na(+)/K(+)-ATPase activity, which has been generally implicated in ion transport, was induced in two of the eight posterior gills after 1 week. In addition, the octopuses were intravenously injected with 1 or 100 ng/g octopressin or cephalotocin, which are Octopus vasopressin/oxytocin orthologs. After 1 day, octopressin, but not cephalotocin, decreased the hemolymph osmolality and Ca concentrations, as well as urinary Na concentrations. These data provide evidence for possible parallel evolution in hyperionoregulatory mechanisms and coordination by conserved peptides.
authors.affiliation: Ushimado Marine Institute, Faculty of Science, Okayama University, Setouchi, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sakamoto
authors.affiliation: Ushimado Marine Institute, Faculty of Science, Okayama University, Setouchi, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ogawa
authors.affiliation: Ushimado Marine Institute, Faculty of Science, Okayama University, Setouchi, Japan.
authors.forename: Yudai
authors.initials: Y
authors.lastname: Nishiyama
authors.affiliation: Ushimado Marine Institute, Faculty of Science, Okayama University, Setouchi, Japan.
authors.forename: Chiaki
authors.initials: C
authors.lastname: Akada
authors.affiliation: Ushimado Marine Institute, Faculty of Science, Okayama University, Setouchi, Japan.
authors.forename: Hideya
authors.initials: H
authors.lastname: Takahashi
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Suntory Foundation for Life Sciences, Mishima, Osaka, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Minakata
authors.affiliation: Ushimado Marine Institute, Faculty of Science, Okayama University, Setouchi, Japan.
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Sakamoto
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001826:Body Fluids / Q000378:metabolism*; D049830:Cephalopoda / Q000502:physiology*; D005880:Gills; D006458:Hemolymph / Q000378:metabolism; D064587:Osmoregulation; D009995:Osmosis; D054712:Salinity; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase