Effect of Pollination Success on Floral Longevity in the Orchid Calypso bulbosa (Orchidaceae)

Abstract

The lifespan of an individual flower is often affected by pollination success. Species differ regarding whether male function (pollen removal), female function (pollen deposition), or both trigger floral senescence. We studied senescence in the singleflowered, deceptive orchid Calypso bulbosa by manipulating the degree of male and female reproductive success. We found that deposition of any amount of pollen resulted in dramatic changes in shape and color within 4 d, whereas unmanipulated flowers and those that had had pollinia removed remained unchanged for 8-11 d after treatment. Selection may favor the reproductive function that is less easily satisfied as the trigger for senescence, because a flower that senesces after accomplishment of this function is likely to have already succeeded at the more easily satisfied one. Deceptive (i.e., rewardless) flowers are more likely to satisfy male than female function since the latter requires that a pollinator be fooled twice, first to pick up pollen and second to deposit it. A survey of naturally pollinated Calypso showed that male function, pollinium removal, was more likely to occur than female function, deposition (95% vs. 66% of visited flowers); thus floral senescence in Calypso is triggered by achievement of the function less likely to succeed. Studies of senescence triggers in species in which female function is more likely to be achieved than male are necessary to further test this hypothesis.

The dynamics of pollen removal and deposition, and its effects on sexual phases in a protandrous plant: Glechoma longituba (Lamiaceae)

“…We also found that artificial removal of most pollen allready at flower opening led to an earlier onset of the female phase, which then started in the afternoon of flower anthesis (during which time pollination rate was low owing to few pollinators). The results support the hypothesis that floral longevity may be changed in response to pollen removal or pollen receipt (Devlin and Stephenson 1984, Proctor and Harder 1995, Ashman and Schoen 1996, Evanhoe and Galloway 2002, Ashman 2004, Giblin 2005, Castro et al 2008). Changes in floral longevity have been considered as strategies to optimize the balance between resource allocation and reproductive achievements (Schoen and Ashman 1995, Ashman and Schoen 1996, Ishii and Sakai 2001).…”

“…Because most flowers with pollen were in their male phase, A. plumipes displayed a preference for male phase flowers during this period, which caused the peak of pollen removal to coincide with this period. A second interpretation is that the species being a low herb, relative humidity around the flowers close to ground is higher in the morning (ca 80–90%) making it difficult for floral visitors to collect pollen, while drier air (ca 40–50%) in the afternoon makes it more conducive for visitors to forage for pollen (Wells and Lloyd 1991, Proctor and Harder 1995). It is likely that the latter situation is more probable.…”

Plasticity of flower longevity in Corydalis ambigua

“…In fact, flower longevity varies within a species. Pollination induces floral senescence (Halevy et al 1984; Ackerman 1989; Gregg 1991; Proctor & Harder 1995). Physical conditions such as the temperature also influence flower longevity (Michaud 1990).…”

Pollinator limitaton in a deceptive orchid, Pogonia japonica, on a floating peat mat

“…Much of the research on the pollination of orchids describes that the rate of pollinia removal is higher than the fruit set in deceptive orchids (Schemske 1980; Barrett & Helenurm 1987; Ackerman 1989; Ackerman & Montalvo 1990; Proctor & Harder 1995). However, for P. japonica in 1994, the fruit set (22.9%) exceeded pollinia removal (7.2%).…”