Can introducing distant plants reduce the fitness of local plants?

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Long-distance transplantation of seed material in restoration programs has raised concerns that maladapted genotypes could hybridize with neighboring native plants of the same species and reduce local population fitness, a phenomenon called outbreeding depression.

Researchers studied the consequences of gene flow from foreign provenances into local populations of the common grassland species Plantago lanceolata (Plantaginaceae). They used controlled crossings between local plants and plants from geographically or environmentally distant populations to produce three generations of intraspecific hybrids: F1, F2, and backcrosses to local plants. In a field experiment, they compared the hybrids' performance with that of crosses within the same population.

Early growth was significantly reduced in some hybrids between populations, with a greater reduction in offspring of crosses with the local population from a different habitat than in those involving geographically distant populations. At the end of the growing season, most fitness-related traits of the hybrids between populations were close to the average of their parents. Consequently, crosses with low-performing foreign parents produced hybrids with lower fitness than local plants and diluted local adaptation. The researchers concluded that introducing maladapted populations from distant or ecologically distinct environments might decrease the fitness of neighboring local plants, at least temporarily.