Spatial and temporal distribution of floral rewards within the capitula: the case of Hyalis argentea (Asteraceae)

Abstract

Background and aims: Differential resource allocation to attraction, reward, and sexual functions has been observed at capitula level of derived species of Asteraceae. Heterogamous capitula contain a combination of pistillate, staminate or sterile and perfect florets, thus rewarding and sexual functions are performed by different kinds of florets and at different times. Such spatial and temporal distribution of rewards within the capitula is not as clearly established in species with homogamous capitula, where all florets are perfect and produce pollen and nectar. We evaluated the spatial and temporal distribution of floral rewards in homogamous capitula of Hyalis argentea.
M&M: We compared the floral phenology, the number of pollen grains and nectar volume and concentration between ray and disk florets, and registered the foraging behaviour of floral visitors.
Results: Capitula have a centripetal and alternate flowering pattern and they were visited by bees, ants, butterflies, moths, beetles and thrips, but pollinated mainly by Apis mellifera. We did not find a temporal pattern in the offer of rewards within the capitula, but we do find a spatial pattern in nectar volume increasing from outer to inner florets.
Conclusions: This spatial variability in nectar quantity could impact pollinator behavior and thus enhance outcrossing likelihoods improving sexual reproduction in this self-incompatible species.