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Title: Hybridization and introgression between the exotic Siberian elm, Ulmus pumila, and the native Field elm, U. minor, in Italy

Author
item Brunet, Johanne
item Zalapa, Juan
item PECORI, FRANCESCO - National Research Council - Italy
item SANTINI, ALBERTO - National Research Council - Italy

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2013
Publication Date: 5/14/2013
Citation: Brunet, J., Zalapa, J.E., Pecori, F., Santini, A. 2013. Hybridization and introgression between the exotic Siberian elm, Ulmus pumila, and the native Field elm, U. minor, in Italy. Biological Invasions. Available: http://link.springer.com/article/10.1007%2Fs10530-013-0486-z.

Interpretive Summary: Uncontrolled invasive species can cause significant harm to agriculture and human health and are responsible for a high rate of species extinction and degradation of natural environments. Siberian elm, native to East Asia, was introduced in Italy in the 1930’s as a response to the first Dutch elm disease (DED) pandemic. Because of its high tolerance to DED, thousands of Siberian elms (Ulmus pumila L.) were distributed by authorities and nurseries throughout the whole Italian territory. Siberian elm is cross-compatible with Field elm (U. minor) and hybridization between these two species may increase genetic diversity and provide novel gene combinations which could facilitate rapid evolution and the potential evolution of invasiveness of U. pumila in Italy. The use of genetic markers indicated that hybridization between Siberian elm and Field elm was common. First-generation hybrids crossed with both U. pumila and U. minor to create backcross individuals. Overall, genetic diversity was greatest for the hybrids, followed by U. minor and lastly U. pumila. 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. This research provides critical information for ecologists and government officials to deem Siberian elm as a serious ecological concern.

Technical 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. We did not observe as strong a pattern of biased introgression towards U. pumila as was recorded in previous studies. The programs Structure and NewHybrids indicated the presence of first- (F1) and second- generation (F2) hybrids and of backcrosses (BC) in the hybrid population. The presence of healthy DED tolerant U. minor individuals combined with the self-compatibility of U. minor helped explain the presence of F2 individuals in Italy. The levels of heterozygosity were similar between U. minor and the hybrids and both groups had higher levels of heterozygosity relative to U. pumila. Although the levels of heterozygosity in the hybrids were lower than in previous studies, 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.