Genetic structure in hybrids and progenitors provides insight into processes underlying an invasive cattail (Typha x glauca) hybrid zone

Traditional models of hybrid zones have assumed relatively low hybrid
fitness, and thus focussed more on interspecific gene flow than on hybrid
dispersal.  Therefore, when hybrids have high fitness and the
potential for autonomous dispersal, we have limited understanding of
whether hybrid dispersal or repeated local hybrid formation is more
important for maintaining hybrid zones.  The invasive hybrid
cattail Typha × glauca occupies an extensive hybrid zone in northeastern
North America where it is sympatric with its progenitors T. latifolia and
T. angustifolia. We characterized genetic diversity and genetic structure
of the three taxa across a broad spatial scale, and tested the hypothesis
that the hybrid shows stronger evidence of gene flow than its progenitor
species, particularly among disturbed sites (ditches) compared to
established wetlands. Support for this hypothesis would suggest that
dispersal, rather than repeated local formation, is more important in
maintaining hybrid zones. Within each taxon, genetic differentiation among
ditches was comparable to that among wetlands, although clonal richness
was consistently greater in ditches suggesting more frequent seed
establishment. Genetic structure across sites was more pronounced in the
hybrid compared to either progenitor species.  Overall, our data
reflect relatively low gene flow in hybrids, and suggest that hybrids are
more likely to be created in situ than to be introduced from other sites.
Despite the high fitness of invasive T. × glauca and its potential for
autonomy, local processes appear more important than dispersal in
maintaining this hybrid zone.