title: Hypercapnia and low pH induce neuroepithelial cell proliferation and emersion behaviour in the amphibious fish Kryptolebias marmoratus.
abstract: Aquatic hypercapnia may have helped to drive ancestral vertebrate invasion of land. We tested the hypothesis that amphibious fishes sense and respond to elevated aquatic PCO2 by behavioural avoidance mechanisms, and by morphological changes at the chemoreceptor level. Mangrove rivulus (Kryptolebias marmoratus) were exposed to 1 week of normocapnic control water (pH 8), air, hypercapnia (5% CO2, pH 6.8) or isocapnic acidosis (pH 6.8). We found that the density of CO2/H(+) chemoreceptive neuroepithelial cells (NECs) was increased in hypercapnia or isocapnic acidosis-exposed fish. Projection area (a measure of cell size) was unchanged. Acute exposure to progressive hypercapnia induced the fish to emerse (leave water) at water pH values ∼6.1, whereas addition of HCl to water caused a more variable response with a lower pH threshold (∼pH 5.5). These results support our hypothesis and suggest that aquatic hypercapnia provides an adequate stimulus for extant amphibious fishes to temporarily transition from aquatic to terrestrial habitats.
authors.affiliation: Department of Integrative Biology, University of Guelph, 488 Gordon Street, Guelph, ON, Canada N1G 2W1 roberceg@mcmaster.ca.
authors.forename: Cayleih E
authors.initials: CE
authors.lastname: Robertson
authors.affiliation: Department of Integrative Biology, University of Guelph, 488 Gordon Street, Guelph, ON, Canada N1G 2W1.
authors.forename: Andy J
authors.initials: AJ
authors.lastname: Turko
authors.affiliation: Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Jonz
authors.affiliation: Department of Integrative Biology, University of Guelph, 488 Gordon Street, Guelph, ON, Canada N1G 2W1.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Wright
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000818:Animals; D001522:Behavior, Animal; D002245:Carbon Dioxide / Q000378:metabolism*; D003532:Cyprinodontiformes / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D046569:Neuroepithelial Cells / Q000166:cytology* / Q000502:physiology; D000068357:Saline Waters / Q000737:chemistry*
chemical_list: D002245:Carbon Dioxide
keywords: Chemoreceptor; PCO2; Phenotypic plasticity