Intra- and interspecific hybridization in invasive Siberian elm

Authors: HIRSCH, HEIDI - Martin Luther University; Brunet, Johanne; Zalapa, Juan; VON WEHRDEN, HENRIK - Leuphana University; HARTMANN, MATTHIAS - Martin Luther University; SCHLAUTMAN, BRANDON - University Of Wisconsin; KOSMAN, EVSEY - Tel Aviv University; WESCHE, KARSTEN - Senckenberg German Entomological Institute; RENISON, DANIEL - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET); HENSEN, ISABELL - Martin Luther University

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2017
Publication Date: 3/16/2017
Publication URL: http://handle.nal.usda.gov/10113/5700674
Citation: Hirsch, H., Brunet, J., Zalapa, J.E., von Wehrden, H., Hartmann, M., Kleindienst, C., Schlautman, B., Kosman, E., Wesche, K., Renison, D., Hensen, I. 2017. Intra- and interspecific hybridization in invasive Siberian elm. Biological Invasions. 19(6):1889-1904. doi: 10.1007/s10530-017-1404-6.

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, Ulmus pumila, is native to East Asia and was introduced into different countries during the early- to mid-twentieth century. It has since naturalized and become invasive; in the United States alone Siberian elm has been declared an invasive in 41 States. Previous work indicated that hybridization with the native elm, either Red elm, U. rubra, in the midwestern parts of the United States, or Field elm, U. minor in Italy and Spain, occurred frequently and resulted in increased genetic diversity and could have facilitated the invasion of U. pumila in these regions. The current study examines whether hybridization occurs in areas where native elm species are not present and whether invasiveness could have evolved in the absence of interspecific hybridization. It also compares the environments inhabited by U. pumila in its native range relative to the invaded range in the western United States and Argentina. The results indicated that hybridization was not common in the western parts of the United States and in Argentina where no native elm species are present. These introduced elm populations maintained high levels of genetic diversity as a result of multiple introductions and the introduction of multiple individuals. Interspecific hybridization is not necessary before invasiveness can evolve in U. pumila. Moreover, populations in the non-native range (western United States and Argentina) tended to occur in warmer habitats and habitats with greater annual precipitation relative to populations of U. pumila in its native range. We also observed an increased level of genetic diversity associated with increasing temperature or water availability in U. pumila populations suggesting that genetic diversity may help the expansion to new habitats. This research provides critical information for ecologists and government officials dealing with invasive species about the factors that can affect the invasion process of a woody plant species.

Technical Abstract: Although numerous studies have examined the invasion history of herbaceous plants, few studies have investigated the invasion biology of woody plants. In this study, we determined whether inter-specific hybridization was necessary before invasiveness could evolve in the Siberian elm, Ulmus pumila. Previous studies of U. pumila in the midwestern United States and in Italy and Spain have revealed a high proportion of inter-specific hybrids in naturalized U. pumila populations. Such hybridization increased genetic diversity and could facilitate the expression of novel genotypes. In the current study, we examined whether inter-specific hybridization was present in U. pumila populations occurring in ranges where no native elm species occurred. Such hybridization would reflect the planting of hybrid individuals in these areas. We compared the climatic conditions under which U. pumila populations were found between the native and non-native ranges. We also examined potential correlations between increased temperature and water availability and the level of genetic diversity in these populations. We used microsatellite markers to genotype elm trees from 14 native populations from Asia and 30 non-native populations from the Western United States and 11 non-native populations from Argentina. To determine whether inter-specific hybridization was present, we used reference samples of U. pumila, U. rubra and U. minor in the analyses. Hybridization was uncommon in the non-native range in the Western United States and Argentina but the level of genetic diversity remained high within populations. We detected little differentiation among populations in Argentina or in the Western United States. Populations of U. pumila in the non-native range tended to occur in habitats with higher temperature and greater water availability relative to U. pumila populations in its native range. In addition, we observed an increase in the level of genetic diversity within populations as temperature or precipitation increased. Multiple introductions and/or introduction of multiple individuals could help explain the high level of genetic diversity observed in the non-native populations. The association between genetic diversity and higher temperature or precipitation supports a potential role of genetic diversity in range expansion. Our results indicate that different factors may be responsible for the maintenance of high genetic diversity in non-native populations and support the notion that genetic diversity may facilitate range expansion and the evolution of invasiveness.