Adaptation of floral traits and mating system to pollinator unpredictibility: the case of Disterigma stereophyllum (Ericaceae) in southwestern Colombia

The Neotropical group of Ericaceae offers a variety of floral displays. Here we present data on floral characteristics and breeding system of Disterigma stereophyllum, a Neotropical epiphyte Ericaceae abundant in semi-disturbed areas with pollinator unpredictability. Floral characteristics are intermediate between those typical of bee- and hummingbird-pollinated plants: the corolla is short, white, and urceolate, but the composition and amount of nectar are similar to those typically observed in hummingbird-pollinated species. Plants are capable of autonomously self-pollination, but manual outcrossing yielded more than twice as many fruits as self hand-pollination did. Moreover, outcross pollen grows more rapidly than self pollen down the style. Our results provide another example of a species with a mixed pollination syndrome which is cryptically self-incompatible and preferably attracts high-energy pollinators (hummingbirds), but which can also profit from small bee visitors and retains the ability to self-pollinate just in case. We hypothesize that interaction among several factors, including self pollinating possibility, and the capacity to attract a wide pollinator spectrum, may result in a lack of strong selection for a bee vs. a hummingbird floral morphology, thus allowing the persistence of mixed floral traits in these ericads. The maintenance of these traits may enhance the ability of this species to colonize semi-disturbed areas.