Floral movements in response to thunderstorms improve reproductive effort in the alpine species Gentiana algida (Gentianaceae)

Studies of floral movements in response to environmental change are rare in the literature, and information about possible adaptive benefits appears n onexistent. The closure of the upright, tubular flowers of alpine gentian ( Gentiana algida) were observed during the frequent afternoon thunderstorms characteristic of the central and southern Rocky Mountains (USA). Flowers c losed within minutes of an approaching thunderstorm and reopened after dire ct sunlight returned. Corolla opening widths decreased 10%/min prior to rai nfall, in close correspondence to declines in air and corolla temperatures. identical floral behavior was also induced experimentally in the field and laboratory by artificial changes in corolla temperature. Corolla closure d id not occur Juring experiments that simulated natural changes in solar irr adiance, wind, or absolute humidity during a thunderstorm. Furthermore indi vidual G. algida plants forced experimentally to remain open during rain ha d substantial losses of pollen after single rain events (up to 34%) and if forced to remain open for the entire flowering period (59%). Subsequent sea sonal reductions in female fitness (up to 73%) also occurred. including see d size and mass, number of ovules produced, number of viable seeds produced per ovule, and seed germination. Thus, corolla closing and opening in G. a lgida associated with frequent summer thunderstorms may be a behavioral ada ptation that improve both paternal and maternal reproductive effort.