Résumé
Polyploidy can cause variation in plant functional traits and thereby
generate individuals that can adapt to fluctuating environments and
exploit new environments. However, few empirical studies have tested for
an association between ploidy level and climatic tolerance of invasive
cytotypes relative to conspecific native-range cytotypes. Here, we used an
invasive plant Solidago canadensis to test whether invasive populations
had a higher proportion of polyploids, greater height and stem-base
diameter, and occupied a wider range of climatic conditions than
conspecific native-range populations. We also tested whether the invasive
populations had overcome genetic founder effects. We sampled a total of 80
populations in parts of the invaded range in China and the native range in
North America for in situ measurements of plant height and stem-base
diameter in the field and for population genetic and cytotype analyses. To
examine climatic correlates, we augmented our field sampled data with
occurrence records obtained from the Global Biodiversity Information
Facility. All, except one, of the populations that we sampled in China
occurred in a humid subtropical climate. In contrast, the North American
populations occurred in humid continental, humid subtropical, and
semi-arid climatic zones. All populations of S. canadensis in
China were purely hexaploid while the North American populations were
diploid, tetraploid, and hexaploid. The invasive hexaploids were
significantly taller and had larger stem-base diameter than native
hexaploids. Native hexaploids were significantly taller and had larger
stem-base diameter than native diploids. Climatic correlate assessment
found that invasive and native populations occupied different climatic
envelopes, with invasive populations occurring in warmer and less seasonal
climates than native populations. However, there was no significant
correlation between ploidy level and climatic envelope of S. canadensis.
Molecular phylogeography data suggest reduced genetic founder effects in
the invaded range. Overall, these results suggest that polyploidy does not
influence S. canadensis climatic tolerance.