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Extraordinarily high fitness among early generation Louisiana Iris hybrids in a reciprocal transplant experiment.
Johnston, Jill*,1, Wesselingh, Renate2, Vogel, Jacob2, Donovan, Lisa1, Arnold, Michael1, 1 University of Georgia, Athens, GA2 Université catholique de Louvain, Louvain-la-Neuve, Belgium
ABSTRACT- It is commonly presumed that ecological distributions of hybrid zones are restricted to habitat intermediate to the parent species. Relative hybrid fitness represents the potential for new hybrid gene combinations to become integrated into the gene pool. Empirical studies of ecological niche breadth frequently confirm that hybrids have high relative fitness only in intermediate habitat. However, using experimental hybrids between Iris brevicaulis and I. fulva, we found that early generation hybrids can have high fitness throughout the range of both parent species and natural hybrid genotypes. We have collected three years of data on fitness components in a reciprocal transplant experiment, including seed germination, seedling survival, transplanted rhizome survival, and vegetative and sexual reproduction. Overall, seed and seedling fitness varied more due to habitat conditions than their species or hybrid identity. Among rhizome transplants, hybrid fitness was high in all habitats, indicating that hybrid success is not limited to intermediate habitat. Hybrid performance was highly variable, suggesting that few exceptional genotypes may have been responsible for much of the apparent hybrid success. In I. fulva habitat, hybrids were most fit, both in terms of survival and flowering. Thus, our data indicate that under natural conditions, early generation hybrids have the largest niche breadth in the Louisiana Iris species complex.
KEY WORDS: hybridization, hybrid zone, hybrid fitness, Iris