Bee boys and fly girls: Pollinator preferences for male and female umbels in protandrous parsnip, Trachymene incisa (Apiaceae).
Davila, Yvonne*,1, 2, Wardle, Glenda1, 1 The University of Sydney, Sydney, NSW, Australia2 Botanic Gardens Trust, Sydney, NSW, Australia
ABSTRACT- Trachymene incisa (Apiaceae) exhibits synchronous protandry, where the sexual phases of the whole umbel are separated in time. For successful pollination, pollinators must visit both male and female umbels during a foraging trip. Although protandry may increase outcrossing and prevent inbreeding, it also results in the presentation of umbels with different floral resources. The male phase umbels present pollen and nectar, whereas the female phase umbels only offer nectar. Therefore, we might expect pollen-collecting bees and flies to favour male umbels, whereas insects that only forage for nectar, such as butterflies, will favour female umbels. Previous observations of insects visiting T. incisa show that 82% of visits to umbels recorded in 2003 (n = 660) and 79% of visits in 2004 (n = 774) were to male umbels. However, male umbels out-number female umbels approximately 3:1 in the field, which may affect insect foraging. This study aimed to determine whether the insect visitors of T. incisa show a true preference for male or female umbels, which may reduce their effectiveness as pollinators. Artificial patches that contained an equal numbers of male and female umbels were arranged in the field. Native bees, flies, one butterfly species and one wasp species were recorded visiting the umbels. Visits to male and female umbels did not differ significantly for each insect type, even though the composition of the insect assemblages and total number of visits to experimental umbels varied among the three populations sampled. In addition, the mean foraging time did not differ significantly between male and female umbels for each insect type. Therefore, insect visitors visit male and female umbels of T. incisa equally despite differences in floral rewards
Key words: Apiaceae, floral reward, pollinator foraging, protandry
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