title: Different flooding responses in Rorippa amphibia and  Rorippa sylvestris, and their modes of expression in F1  hybrids.
abstract: The river floodplain species Rorippa amphibia, Rorippa sylvestris, and their hybrid Rorippa x anceps were studied here, with the aim of identifying potential species differences with respect to flooding tolerance, and of assessing their expression in F1 hybrids. Parents and their F1 hybrids were subjected to three flooding treatments mimicking natural conditions, and growth-related and leaf morphological traits were compared. In contrast to R. sylvestris, R. amphibia responded to waterlogging by forming specialized roots, and its growth was not reduced. These traits were dominantly expressed in hybrids. Both species and the hybrids established shoot growth over 2 wk of complete submergence. Only in R. sylvestris was this not at the expense of root biomass, suggesting that R. sylvestris can photosynthesize underwater. Rorippa sylvestris also showed a hyponastic response. Hybrids were intermediate to the parents in this respect. This study shows that phenotypic expression of parental traits in F1 hybrids is mostly additive, but can also be dominant. This suggests that a large overlap in habitat use of parents and hybrids is likely. If such an overlap occurs, the main evolutionary consequences of hybridization in Rorippa will be the introgression of genes, as the hybrids are fully fertile.
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, Experimental Plant Systematics, Universiteit van Amsterdam, P.O. Box 94062, 1090 GB Amsterdam, the Netherlands.|Present address: Division of Environmental & Evolutionary Biology, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Marc
authors.initials: M
authors.lastname: Stift
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, Experimental Plant Systematics, Universiteit van Amsterdam, P.O. Box 94062, 1090 GB Amsterdam, the Netherlands.
authors.forename: Pieternella C
authors.initials: PC
authors.lastname: Luttikhuizen
authors.affiliation: Department of Experimental Plant Ecology, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, the Netherlands.
authors.forename: Eric J W
authors.initials: EJW
authors.lastname: Visser
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, Experimental Plant Systematics, Universiteit van Amsterdam, P.O. Box 94062, 1090 GB Amsterdam, the Netherlands.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Van Tienderen
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D003433:Crosses, Genetic; D006823:Hybrid Vigor; D006824:Hybridization, Genetic; D007101:Immersion; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology; D018517:Plant Roots / Q000254:growth & development / Q000502:physiology; D031225:Rorippa / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D014867:Water
chemical_list: D014867:Water