Salinity, not genetic incompatibilities, limits the establishment of the invasive hybrid cattailTypha x glaucain coastal wetlands

Hybrids of a single pair of parent species can be much more common in some geographical regions than in others. The reasons for this are not well understood, but could help explain processes such as species diversification or the range expansion of invasive hybrids. The widespread cattailsTypha latifoliaandT. angustifoliaseldom hybridize in some parts of their range, but in other areas produce the dominant hybridT. x glauca. We used a combination of field and greenhouse experiments to investigate whyT. x glaucahas invaded wetlands in the Laurentian Great Lakes region of southern Ontario, Canada, but is much less common in the coastal wetlands of Nova Scotia (NS) in eastern Canada. One potentially important environmental difference between these two regions is salinity. We therefore tested three hypotheses: (1)T. latifoliaandT. angustifoliain NS are genetically incompatible; (2) the germination or growth ofT. x glaucais reduced by salinity; and (3)T. latifolia,a main competitor ofT. x glauca, is locally adapted to saline conditions in NS. Our experiments showed that NST. latifoliaandT. angustifoliaare genetically compatible, and that saline conditions do not impede growth of hybrid plants. However, we also found that under conditions of high salinity, germination rates of hybrid seeds were substantially lower than those of NST. latifolia. In addition, germination rates of NST. latifoliawere higher than those of OntarioT. latifolia,suggesting local adaptation to salinity in coastal wetlands. This study adds to the growing body of literature which identifies the important roles that local habitat and adaptation can play in the distributions and characteristics of hybrid zones.