Sexual reproductive strategies of Puya nitida (Bromeliaceae) in a Colombian paramo, a tropical high-elevation ecosystem

The low availability of pollinators in high-elevation ecosystems can lead to flowering plants showing different adaptive responses in order to assure their reproductive success. Shifts toward autogamy and asexual reproductive rates (the reproductive assurance hypothesis) and the compensatory measures to maintain outcrossing such as flower longevity and more prolonged pistil receptivity (the increased pollination probability hypothesis) are some of these responses. Several studies have tested both hypotheses, but investigations of plants of tropical alpine environments such as paramos that support these assumptions are still scarce. Puya nitida, an endemic Colombian plant species distributed in the paramo and subparamo in the Eastern Cordillera of Cundinamarca department, was used as a case study to test its reproductive characteristics that assure its sexual reproduction. We analysed the species’ floral morphology and development, its phenological patterns and its plant mating-system. We found that Puya nitida showed floral characteristics that promote pollination by birds, herkogamy and dichogamy, flowers and receptive stigmas with 9 and 12 days of longevity, respectively and an index of self-incompatibility that shows that it is mostly self-incompatible. We found a synchronic phenological pattern with an annual frequency and an intermediate duration with a peak in the period of lowest rainfall. Our results suggested that longer floral development, prolonged stigma receptivity, herkogamy and dichogamy and self-incompatibility might assure reproductive success, since the cross-pollination might be favoured when few pollinators are in attendance. Overall, these reproductive mechanisms add evidence to the increased pollination probability hypothesis, specifically for a plant species of a tropical high-elevation ecosystem where pollinators are scarce.