title: Breeding for QX disease resistance negatively selects one form of the defensive enzyme, phenoloxidase, in Sydney rock oysters.
abstract: QX disease in Sydney rock oysters (Saccostrea glomerata) is caused by the paramyxean protozoan, Marteilia sydneyi. Disease outbreaks occur during summer (January to May) and can result in up to 95% mortality. The New South Wales Department of Primary Industries has been selectively breeding S. glomerata for resistance to QX disease since 1996. Previous work suggests that this breeding program has specifically affected the defensive phenoloxidase enzyme system of oysters. The current study more thoroughly characterises the effect of selection on the different forms of phenoloxidase found in oyster populations. Native polyacrylamide gel electrophoresis (native-PAGE) identified five discrete types of phenoloxidase in non-selected (wild type) and fourth generation QX disease resistant (QXR4) oysters. One electrophoretically distinct form of phenoloxidase, POb, is significantly less frequent in resistant oysters when compared to the wild type population. The frequency of POb also decreased in both the wild type and QXR4 populations over the course of a QX disease outbreak. This suggests that possession of POb makes oysters susceptible to QX disease and that breeding for resistance has resulted in negative selection against this form of phenoloxidase.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.
authors.forename: Britt
authors.initials: B
authors.lastname: Bezemer
authors.forename: Daniel
authors.initials: D
authors.lastname: Butt
authors.forename: John
authors.initials: J
authors.lastname: Nell
authors.forename: Robert
authors.initials: R
authors.lastname: Adlard
authors.forename: David
authors.initials: D
authors.lastname: Raftos
mesh_terms: D000818:Animals; D017756:Aquaculture / Q000379:methods; D001947:Breeding / Q000379:methods; D004591:Electrophoresis, Polyacrylamide Gel; D007113:Immunity, Innate / Q000235:genetics* / Q000276:immunology; D014442:Monophenol Monooxygenase / Q000235:genetics* / Q000276:immunology; D009517:New South Wales; D010125:Ostreidae / Q000201:enzymology / Q000235:genetics / Q000276:immunology* / Q000469:parasitology*; D012641:Selection, Genetic
chemical_list: D014442:Monophenol Monooxygenase