Hybridization and introgression between the exotic Siberian elm, Ulmus pumila , and the native Field elm, U. minor , in
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ORIGINAL PAPER
Hybridization and introgression between the exotic Siberian elm, Ulmus pumila, and the native Field elm, U. minor, in Italy Johanne Brunet • Juan E. Zalapa • Francesco Pecori • Alberto Santini
Received: 31 July 2012 / Accepted: 4 May 2013 / Published online: 14 May 2013 Ó Springer Science+Business Media Dordrecht (outside the USA) 2013
Abstract In response to the first Dutch elm disease (DED) pandemic, Siberian elm, Ulmus pumila, was planted to replace the native elm, U. minor, in Italy. The potential for hybridization between these two species is high and repeated hybridization could result in the genetic swamping of the native species and facilitate the evolution of invasiveness in the introduced species. We used genetic markers to examine the extent of hybridization between these two species and to determine the pattern of introgression. We quantified and compared the level of genetic diversity between the hybrids and the two parental species. Hybrids between U. pumila and U. minor were common. The pattern of introgression was not as strongly biased towards U. pumila as was previously observed for hybrids between U. rubra and U. pumila in the United States. The levels of heterozygosity were similar between U. minor and the hybrids and both
groups had higher levels of heterozygosity relative to U. pumila. The programs Structure and NewHybrids indicated the presence of first- (F1) and secondgeneration (F2) hybrids and of backcrosses in the hybrid population. The presence of healthy DED resistant U. minor individuals combined with the selfcompatibility of U. minor could help explain the presence of F2 individuals in Italy. The presence of F2 individuals, where most of the variability present in the hybrids will be released, could facilitate rapid evolution and the potential evolution of invasiveness of U. pumila in Italy.
J. Brunet (&) USDA-ARS, VCRU, Department of Entomology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706, USA e-mail: [email protected]; [email protected]
Introduction
J. E. Zalapa USDA-ARS, VCRU, Department of Horticulture, University of Wisconsin, 1575 Linden Drive, Madison, WI 53706, USA F. Pecori A. Santini Institute of Plant Protection, C.N.R., Via Madonna del Piano, 10, 50019 Sesto Fiorentino, Italy
Keywords Dutch elm disease Field elm Hybridization Introgression Microsatellites Siberian elm
The repeated introduction of exotic species by humans has accelerated the range expansion of many organisms (Crowl et al. 2008). While various species were inadvertently introduced, some introductions were intentional. For example, exotic trees have been planted as ornamental trees in urban areas or to replace native tree species decimated by a disease epidemic (Machon et al. 1997; Cogolludo-Agustin et al. 2000; Zalapa et al. 2010). The introduced species
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were often close congeners of the native species, which implied a high potential for hybridization between the native and introduced species. While the potential impact of hybridizatio
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