Effect of nectar guides on pollination efficiency in Alstroemeria aurea (Alstroemeriaceae)

Abstract

We evaluated the effect that nectar guides have on the efficiency in pollination of flowers in Alstroemeria aurea (Alstroemeriaceae), a herbaceous, xenogamous plant, which blooms in temperate forests of southern South America. The flowers were manipulated in situ and subjected to three treatments: flowers with nectar guides (FCG, not manipulated, control); flowers without nectar guides (FSG, flowers with
nectar guides that were obscured) and control-control (CC, flowers in which the nectariferous tepals were covered by other nectariferous tepals to test the possible effect of double petals). The efficiency of pollination was evaluated as a function of visitation frequency, quantity of pollen deposited on the stigmas of visited flowers and quantity of accumulated nectar. Our results show that the absence of nectar guides
significantly affected the efficiency of visits by pollinators (χ2 = 18.97, df: 2, p <<0.004) the quantity of pollen grains deposited on stigmas (F = 19.39 ; Gl: 2, p <<0.0001) and the accumulated volume of nectar (F = 12.87, df: 2, p <<0.005). The FSG were less visited, received fewer pollen grains per stigma and had a higher volume of accumulated nectar, unlike the FCG and CC. About 90% of all floral visits were accomplished by Bombus ruderathus (84.11%) and B.  dahlbomii (8.41 %), that possess well developed sensory perception (responding to nectar guide patterns in the flowers). We propose that the absence of nectar guides from the flowers of A. aurea, eliminated orientation patterns assisting visitors, indicating access to rewards, and consequently affected their pollination.