EFFECTS OF POLLINIA REMOVAL AND INSERTION ON FLOWER LONGEVITY IN CHLORAEA-ALPINA (ORCHIDACEAE)

Although it is known that stigmatic pollen deposition may trigger earl y flower senescence, the existence of a similar plastic response of fl ower lifespan to pollen removal has been much less studied. Here we re port on a factorial, manipulative experiment in which all 2 x 2 flower combinations of pollinia removal and stigmatic pollinia insertion wer e performed in inflorescences of the Patagonian ground orchid Chloraea alpina. This experiment was conducted in the laboratory, in a populat ion of cut inflorescences and in the field. We hypothesized that if ex pected fitness gains, through both the male and female functions, were weighed against the costs of flower maintenance, then early flower se nescence should be triggered by either pollinia removal or insertion. The shortest flower lifespan would be expected in flowers where both p rocesses occurred. Results showed that flower longevity was very stron gly affected by pollinia insertion, reducing the flower lifespan by ap proximately 60%. The response of pollinia removal was much weaker. A s ignificant reduction in flower longevity caused by pollinia removal wa s only detected in unpollinated flowers (i.e. no pollinia inserted). W ithin the racemose inflorescences, flowers in basal positions lived lo nger than flowers in terminal ones, which might be evidence of the imp ortance of resource availability in determining maximum flower longevi ty. The observed responses of flower lifespan plasticity to pollinia m anipulation only partially supported our expectations based on fitness benefit-cost relationships. Other factors that might explain these di screpancies are the different fitness gains that may indeed accrue to the processes of pollinia removal and insertion as they occur in natur e, donor manipulation of the recipient flower lifespan associated with the evolution of pollen clustering into pollinia and physiological co nstraints in terms of the extent to which flower longevity may respond to pollen removal.