Data from: Climate and rapid local adaptation as drivers of germination and seed bank dynamics of Alliaria petiolata (garlic mustard) in North America

Local differences in climate conditions may facilitate rapid evolutionary
changes in introduced plants to optimize timing of germination or ability
to survive in seed banks, which may constitute beneficial demographic
adaptations during range expansions. Understanding differences in
germination requirements and emergence patterns across a species’ range is
critical for demographic modelling and potential invasive species control
efforts. We assessed germination responses of Alliaria petiolata using
seeds collected from 10 populations spanning much of the North American
distribution of the species. We compared germination responses under
different stratification regimes in a growth chamber over 2·5 years, and
evaluated seedling emergence in a common garden in Ithaca, New York over
13 years. We further evaluated how climate overlap between Ithaca and
original collection sites influenced emergence patterns. In the
laboratory, germination of all populations was similar and highest at 4 °C
stratification. Seeds exposed to sub-zero temperatures delayed germination
and population responses were variable. In the common garden, seedlings
from most populations emerged over 13 years, and emergence patterns were
strongly influenced by population. Annual emergence was positively
correlated with spring temperature and inversely correlated with number of
spring days with minimum temperature below freezing. Climate overlap
between the common garden and original collection location enhanced
germination, but common garden climate conditions over the course of the
13-year experiment and population identity had greater explanatory power.
Synthesis. Laboratory germination tests did not reflect seedling emergence
under field conditions. After 150 years of residence time in North
America, Alliaria petiolata populations have developed striking
differences in their responses to local climates and stratification
requirements suggesting that a complex interplay of pre-adaptation, rapid
evolutionary changes, and phenotypic plasticity result in locally adapted
populations.