Salinity, not genetic incompatibilities, limits the establishment of the invasive hybrid cattail Typha × glauca in coastal wetlands

A single pair of co-existing species that can successfully hybridize may
produce many more hybrids in some 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 cattails Typha latifolia and T.
angustifolia seldom hybridize in some parts of their range, but in other
areas produce the dominant hybrid T. × glauca.  We used a
combination of field and greenhouse experiments to investigate why T. ×
glauca has invaded wetlands in the Laurentian Great Lakes region of
southern Ontario, Canada, but is much less common in the coastal wetlands
of NS in eastern Canada.  One potentially important environmental
difference between these two regions is salinity.  We therefore
tested three hypotheses: 1) T. latifolia and T. angustifolia in NS are
genetically incompatible; 2) the germination or growth of T. × glauca is
reduced by salinity; and 3) T. latifolia, a main competitor of T. ×
glauca, is locally adapted to saline conditions in NS.  Our
experiments showed that NS T. latifolia and T. angustifolia are
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 NS T. latifolia.  In addition, germination rates of
NS T. latifolia were higher than those of Ontario T. 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.