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Floral movements in response to thunderstorms improve reproductive effort in the alpine species Gentiana algida (Gentianaceae)¹

Department of Botany, University of Wyoming, Laramie, Wyoming 82071-3165 USA; and Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109-7325 USA

Studies of floral movements in response to environmental change are rare in the literature, and information about possible adaptive benefits appears nonexistent. 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 closed within minutes of an approaching thunderstorm and reopened after direct sunlight returned. Corolla opening widths decreased 10%/min prior to rainfall, 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 did not occur during experiments that simulated natural changes in solar irradiance, wind, or absolute humidity during a thunderstorm. Furthermore, individual G. algida plants forced experimentally to remain open during rain had substantial losses of pollen after single rain events (up to 34%) and if forced to remain open for the entire flowering period (59%). Subsequent seasonal reductions in female fitness (up to 73%) also occurred, including seed size and mass, number of ovules produced, number of viable seeds produced per ovule, and seed germination. Thus, corolla closing and opening in G. algida associated with frequent summer thunderstorms may be a behavioral adaptation that improves both paternal and maternal reproductive effort.

Key Words: alpine • floral movements • Gentiana • reproduction • temperature

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