Pollination of Leuhea (Tiliaceae) In Costa Rican Deciduous Forest

Studies of the reproductive biology of three species of Luehae (Tiliaceae) conducted in Costa Rican deciduous forest demonstrated that all species produce hermaphroditic flowers exhibiting nocturnal anthesis, anther dehiscence, nectar secretion, and fragrances consistent with adaptation for nocturnal moth pollination. Luehea candida, flowering during the wet season, has self—incompatible flowers pollinated primarily by sphingid moths. Generalist diurnal visitors, including stingless bees, flies, and butterflies, were also common flower visitors, but experiments showed that they were ineffective pollinators. Luehea candida apparently rejects pollen from nearby conspecifics as a means of limiting inbreeding resulting from pollination by poor outcrossers such as stingless bees. The principal pollinators of L. seemannii, which flowers during the dry season, were determined to be the same types of diurnal visitors that contributed nothing to pollination success of L. candida. Nocturnal moths were low in abundance during the dry season and pollinated few flowers. Individuals of the deciduous forest population of L. seemannii ranged from partially to fully self—compatible, though an evergreen forest population was self—incompatible. The partial breakdown of incompatibility, diurnal pollinators, and nectar analysis of L. seemannii suggest an ongoing evolutionary shift to diurnal pollination resulting from the scarcity of nocturnal pollinators and selection by diurnal insects, especially stingless bees, in the deciduous forest. Luehea speciosa, with floral morphology and behavior nearly identical to L. candida, rarely attracted sphingids during its blooming period in the early dry season even though these moths were present in the habitat. Chemical analysis showed that nectar of L. speciosa is of a type preferred by bats rather than sphingids, but no evidence for bat pollination could be found. This species may also be pollinated largely by opportinistic diurnal visitors.