title: Fitness dynamics within a poplar hybrid zone: I. Prezygotic and postzygotic barriers impacting a native poplar hybrid stand.
abstract: Hybridization and introgression are pervasive evolutionary phenomena that provide insight into the selective forces that maintain species boundaries, permit gene flow, and control the direction of evolutionary change. Poplar trees (Populus L.) are well known for their ability to form viable hybrids and maintain their distinct species boundaries despite this interspecific gene flow. We sought to quantify the hybridization dynamics and postzygotic fitness within a hybrid stand of balsam poplar (Populus balsamifera L.), eastern cottonwood (P. deltoides Marsh.), and their natural hybrids to gain insight into the barriers maintaining this stable hybrid zone. We observed asymmetrical hybrid formation with P. deltoides acting as the seed parent, but with subsequent introgression biased toward P. balsamifera. Native hybrids expressed fitness traits intermediate to the parental species and were not universally unfit. That said, native hybrid seedlings were absent from the seedling population, which may indicate additional selective pressures controlling their recruitment. It is imperative that we understand the selective forces maintaining this native hybrid zone in order to quantify the impact of exotic poplar hybrids on this native system.
authors: Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Québec, Québec, Canada ; Natural Resources Canada, Canadian Forestry Centre, Great Lakes Forestry Centre Sault Ste. Marie, Ontario, Canada.
authors: Amanda D
authors: AD
authors: Roe
authors: Natural Resources Canada, Canadian Forestry Centre, Great Lakes Forestry Centre Sault Ste. Marie, Ontario, Canada.
authors: Chris J K
authors: CJ
authors: MacQuarrie
authors: Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Québec, Québec, Canada.
authors: Marie-Claude
authors: MC
authors: Gros-Louis
authors: Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre Fredericton, New Brunswick, Canada.
authors: J Dale
authors: JD
authors: Simpson
authors: Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Québec, Québec, Canada.
authors: Josyanne
authors: J
authors: Lamarche
authors: Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre Fredericton, New Brunswick, Canada.
authors: Tannis
authors: T
authors: Beardmore
authors: Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Québec, Québec, Canada ; Umeå University, Ecology and Environmental Sciences, Umeå Plant Science Centre Umeå, Sweden.
authors: Stacey L
authors: SL
authors: Thompson
authors: Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Québec, Québec, Canada.
authors: Philippe
authors: P
authors: Tanguay
authors: Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre Québec, Québec, Canada.
authors: Nathalie
authors: N
authors: Isabel
keywords: Hybrid fitness; SNPs; hybridization; introgression; postzygotic fitness; reproductive fitness