Differential effects of nectar robbing by the same bumble-bee species on three sympatric Corydalis species with varied mating systems.

Background and Aims Most research on the widespread phenomenon of nectar robbing has focused on the effect of the nectar robbers behaviour on host-plant fitness. However, attention also needs be paid to the characteristics of host plants, which can potentially influence the consequences of nectar robbing as well. A system of three sympatric Corydalis species sharing the same nectar-robbing bumble-bee was therefore studied over 3 years in order to investigate the effect of nectar robbing on host reproductive fitness. Methods Three perennial species of Corydalis were studied in the Shennongjia Mountain area, central China. Observations were conducted on visitor behaviour and visitation frequencies of nectar-robbers and legitimate pollinators. Key Results The results indicated that the effect of nectar robbing by Bombus pyrosoma varied among species, and the three species had different mating systems. Seed set was thus influenced differentially: there was no effect on seed set of the predominantly selfing C. tomentella; for the facultative outcrossing C. incisa, nectar robbing by B. pyrosoma had a positive effect; and nectar robbing had a significant negative effect on the seed set of outcrossing C. ternatifolia. Conclusions A hypothesis is proposed that the type of host-plant mating system could influence the consequences of nectar robbing on host reproductive fitness. [ABSTRACT FROM AUTHOR]