Hybridization as a Stimulus for the Evolution of Invasiveness in Plants
Culley, Theresa M. , Hardiman, Nicole .
The role of intraspecific hybridization in the evolution of invasiveness in the ornamental pear tree, Pyrus calleryana (Rosaceae).
MOST invasive plant species are examined only after they have begun to exert economic and ecological impacts, while species in early stages of invasion often go unnoticed. Such early invading species are of critical importance if we are to understand how invasiveness evolves and especially if hybridization is important in this process. We examined ecological and genetic factors affecting the initial spread of Pyrus calleryana, an ornamental tree from China that is commonly planted along roadways and in residential yards across the United States. The species is best known as the ‘Bradford’ cultivar, but genetically distinct cultivars of the same species have also been produced. Within the past decade, this self-incompatible species has begun to produce abundant fruit and is now appearing in disturbed habitats, primarily in the southern and eastern United States. Using molecular techniques and hand-pollinations, we discovered that fruit set only results from crosses between cultivars that differ by at least one self-incompatibility allele. Furthermore, parentage analysis using microsatellite markers of wild P. calleryana populations across the United States has revealed that wild individuals are usually F1 progeny resulting from various combinations of cultivars. More advanced hybrids were also detected in some locations and wild individuals have been observed producing fruit with viable seed, indicating that hybrids are fertile and have the potential for further spread. Thus, we suggest that P. calleryana may be in the early stages of becoming an invader and wild individuals result from intraspecific hybridization of populations, each composed of a genetically distinct cultivar.
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1 - University of Cincinnati, Department of Biological Sciences, 614 Rieveschl Hall, Cincinnati, Ohio, 45221, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Wednesday, August 2nd, 2006
Time: 11:30 AM