Abstract
Gene flow from plantations of nonlocal (genetically exotic) tree provenances into natural stands of the same species is probably a widespread phenomenon, but its effects remain largely unexamined. We investigated early fitness consequences of intraspecific exotic gene flow in the wild by assessing differences in survival among native, nonlocal, and F1 intraspecific hybrid seedlings naturally established within two native pine relicts (one of Pinus pinaster and the other of P.sylvestris) surrounded by nonlocal plantations. We obtained broad-scale temporally sequential genotypic samples of a cohort of recruits in each pine relict, from seeds before dispersal to established seedlings months after emergence, tracking temporal changes in the estimated proportion of each parental cross-type. Results show significant proportions of exotic male gametes before seed dispersal in the two pine relicts. Subsequently to seedling establishment, the frequency of exotic male gametes became nonsignificant in P.pinaster, and dropped by half in P.sylvestris. Exotic zygotic gene flow was significantly different from zero among early recruits for P.sylvestris, decreasing throughout seedling establishment. Seedling mortality resulted in small late sample sizes, and temporal differences in exotic gene flow estimates were not significant, so we could not reject the null hypothesis of invariant early viability across parental cross types in the wild.
Highlights
Global forest plantations total approximately 270Á106 ha, with annual planting rates of about 5Á106 ha in the early 21st century (FAO 2006)
We found significant proportions of exotic male gametes at the seed stage in the two studied relicts, which, subsequent to seed dispersal and seedling establishment, became nonsignificant in Pinus pinaster and dropped by half in P. sylvestris
Zygotic gene flow from the exotic plantations was absent in P. pinaster, while it was significant among early P. sylvestris recruits, decreasing throughout seedling establishment
Summary
Global forest plantations total approximately 270Á106 ha, with annual planting rates of about 5Á106 ha in the early 21st century (FAO 2006). The term ‘intraspecific exotic gene flow’ or ‘intraspecific exotic introgression’ is used here to refer to gene movement from nonlocal (genetically exotic) populations of a species into nearby natural populations of the same species, following Laikre et al (2010). The latter point out that genetic monitoring of this process within forestry research and management is urgent but remains virtually nonexistent, in contrast with decades-long studies in fisheries. As far as we know, we are the first to address, in forest trees, the empirical consequences of intraspecific gene flow from exotic plantations in the wild
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