Originally published as Genetics Published Articles Ahead of Print on January 16, 2006.

Genetics, Vol. 172, 2481-2489, April 2006, Copyright © 2006
doi:10.1534/genetics.105.053538

Detecting Adaptive Trait Introgression Between Iris fulva and I. brevicaulis in Highly Selective Field Conditions

* Department of Genetics, University of Georgia, Athens, Georgia 30602 and {dagger} Department of Biology, Duke University, Durham, North Carolina 27708

1 Corresponding author: Department of Genetics, Life Sciences Bldg., University of Georgia, Athens, GA 30602.
E-mail: nhmartin{at}uga.edu

The idea that natural hybridization has served as an important force in evolutionary and adaptive diversification has gained considerable momentum in recent years. By combining genome analyses with a highly selective field experiment, we provide evidence for adaptive trait introgression between two naturally hybridizing Louisiana Iris species, flood-tolerant Iris fulva and dry-adapted I. brevicaulis. We planted reciprocal backcross (BC1) hybrids along with pure-species plants into natural settings that, due to a flooding event, favored I. fulva. As expected, I. fulva plants survived at much higher rates than I. brevicaulis plants. Backcross hybrids toward I. fulva (BCIF) also survived at significantly higher rates than the reciprocal backcross toward I. brevicaulis (BCIB). Survivorship of BCIB hybrids was strongly influenced by the presence of a number of introgressed I. fulva alleles located throughout the genome, while survivorship in the reciprocal BCIF hybrids was heavily influenced by two epistatically acting QTL of opposite effects. These results demonstrate the potential for adaptive trait introgression between these two species and may help to explain patterns of genetic variation observed in naturally occurring hybrid zones.




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