Conservative flowering behaviors, such as flowering during long days in
summer or late flowering at a high leaf number, are often proposed to
protect against variable winter and spring temperatures which lead to
frost damage if premature flowering occurs. Yet, due the many factors in
natural environments relative to the number of individuals compared,
assessing which climate characteristics drive these flowering traits has
been difficult. We applied a multidisciplinary approach to ten
winter-annual Arabidopsis thaliana populations originating along a wide
climactic gradient in Norway. We paired a variable reduction strategy to
assess which of 100 climate descriptors from their home sites correlated
most to their behaviors when grown in common garden and assessed
sequence variation of 19 known environmental-response flowering genes.
We show that long-day sensitivity and late flowering may be driven not
by risk of spring frosts, but by growing season temperature and length
perhaps to opportunistically maximize growth.