Honeybees Enhance Reproduction without Affecting the Outcrossing Rate in Endemic Pedicularis densispica (Orobanchaceae)

Abstract

There has been substantial debate in recent years surrounding the impact of introduced honeybees on native biota. This study reports on an investigation of Pedicularis densispica, a subalpine annual herb endemic to Southwest China, in an attempt to determine the impact of introduced domestic honeybees on pollen dispersal and thus on their reproductive success and mating system. Honeybees were introduced into the study site in 2004, and a sudden seasonal pollinator shift from bumblebees to honeybees was observed. Intra- and inter-plant visits by different pollinators were recorded in the field in 2003 and 2004. Fruit and seed sets prior to and after the pollinator shift were measured. Experimental pollinations were performed to characterize the breeding system. Outcrossing rates at the seed stage were estimated for both years using RAPD markers. Our results indicated that honeybees foraged between plants more frequently than bumblebees did. Our results also revealed that the introduction of honeybees significantly enhanced reproductive success. However, no significant difference was detected between the outcrossing rates due to bumblebee and honeybee pollination. P. densispica was almost completely outcrossing ( T(m) = 0.956 and 0.967, respectively in 2003 and 2004) but partially self-compatible. This study presents the first report of the outcrossing rate in the genus pedicularis and reveals a limited influence of pollination on the mating system in P. densispica. The pollinator shift did not reduce reproductive success of the plants and honeybees may be used to augment pollinator services for nectariferous P. densispica.