Impacts of hybridization on native crabapple (Malus coronaria) by domestic apple (Malus domestica) in southern Ontario

Hybridization by introduced species can negatively influence native relatives in three ways: genetic assimilation, demographic swamping, and increased asexuality. Here, I tested the latter two effects of introduced domestic apple (Malus domestica) on native crabapple (M. coronaria). I applied four pollination treatments (open pollination, open + M. coronaria pollen, M. coronaria pollen, and M. domestica pollen) to M. coronaria trees and assessed the number and reproductive origins (sexual versus asexual) of resulting seeds using flow cytometry. There were no differences in fruit set or seed production among pollination treatments and no relationship between the number of heterospecific and conspecific seeds produced per fruit, suggesting no demographic swamping. The percentage of asexual seeds decreased with heterospecific pollination, but increased in seeds with tetraploid embryos. These results indicate that hybridization can influence native Malus in ways beyond the production of hybrids, with implications for sustainability of agricultural and natural ecosystems.