The role of intraspecific hybridization in the evolution of invasiveness: a case study of the ornamental pear tree Pyrus calleryana

Abstract

Hybridization between genetically distinct populations of a single species can serve as an important stimulus for the evolution of invasiveness. Such intraspecific hybridization was examined in Pyrus calleryana, a Chinese tree species commonly planted as an ornamental in residential and commercial areas throughout the United States. This selfincompatible species is now escaping cultivation and appearing in disturbed habitats, where it has the potential to form dense thickets. Using genetic techniques incorporating nine microsatellite markers, we show that abundant fruit set on cultivated trees as well as the subsequent appearance of wild individuals result from crossing between genetically distinct horticultural cultivars of the same species that originated from different areas of China. We conclude that intraspecific hybridization can be a potent but little recognized process impacting the evolution of invasiveness in certain species.

Hybridization and the evolution of invasiveness in plants and other organisms

“…The genetic material to alleviate allelic incompatibility developed via interspecific hybridization in Spartina (Sloop et al 2008) and through intervarietal hybridization between graft and rootstock in abandoned orchards of Pyrus (Culley and Hardiman 2008). Senecio squalidis, a diploid, hybrid and self-incompatible species, is the parent to three additional species via hybridization with a native self-compatible species, S. vulgaris (Abbott et al 2008).…”

“…Despite the acknowledgement that many popular horticultural species readily hybridize with their native congeners, until very recently, there has been little regard for their genetic impact to native taxa or the invasive ability of their hybrid offspring. For example, hybridization is occurring between cultivars and their native counterparts within the genera Quercus, Pyrus, Acer, Malus, Platanus, and Cornus (Culley and Hardiman 2008;Coart et al 2003;Petit 2004). Ecological, genetic, and evolutionary study of such systems will provide baseline information about the generality of problems caused by hybridization between exotics and natives.…”

“…In a few cases, more thorough study has revealed that the hypothesis of hybrid origin is in error (e.g., Houghton-Thompson et al 2005;Burger et al 2006). In addition, there are a growing number of studies finding evidence of intra-taxon hybridization preceding the evolution of invasiveness (e.g., Culley and Hardiman 2008).…”

Introgression and Long-Term Naturalization of Archaeophytes into Native Plants - Underestimated Risk of Hybrids

“…This is perhaps the first case of a species of Pyrus being recognized as invasive. This sudden realization of invasion is explained as the overcoming of self-incompatibility owing to the planting of different cultivars and the Allee effect (Culley & Hardiman, 2009;Hardiman & Culley, 2010). However, since there are no native species of Pyrus in North America, negative genetic effects on native relatives would not occur.…”

Evaluation of seed viability of Callary pear (Pyrus calleryana) in Poznań

“…If the seeds are fertile they can sprout and establish wild stands. In the US where lots of different cultivars had been planted the species became a relatively new invasive that has only recently begun to spread across the country after intraspecific hybridization between cultivars (cuLLey & HArdimAn 2007, 2009, HArdimAn & cuLLey 2010, cuLLey et al 2011, merrit et al 2013.…”