Abstract
ABSTRACT The feeding of pollinating dynastid-scarab beetles on nutritious tissue of Annonaceae flowers results in macroscopically visible gnawing marks on petals. In the present paper, we present and discuss examples of such gnawing marks on Annonaceae from the Cerrado and the Amazon Forest in Brazil. The localization of gnawing marks on the petals and the histochemistry of the nutritious tissues are emphasized. In some species, nutritious tissue is apparently distributed among all petals, while in other species it is more or less diffusely localized. There are also cases in which nutritious tissue occurs only on clearly localized regions of the inner petals. Petals of selected Amazon species were stained, and studied by light and scanning electron microscopy. The nutritious tissue consists of cells with mucilage-rich walls, which contain starch, lipids and/or tannins. Starch and lipids are not only energy-rich food for the beetles but are apparently also “fuel” for metabolic heating of the flowers, which is a further benefit for the pollinators inside the pollination chamber.
Highlights
The visiting of flowers by beetles usually is a long-lasting procedure
The nutritious tissue consists of cells with mucilagerich walls, which contain starch, lipids and/or tannins
When a larger number of beetles was visiting a flower, they ate on all petals of a flower and destroyed them (Fig. 1C), indicating that the entire corolla, viz. the outer and inner petals as a whole, consist of nutritious tissues appreciated by the pollinators
Summary
The visiting of flowers by beetles usually is a long-lasting procedure. It is not at all a short contact as it is for example by bees, butterflies, birds or bats, which rapidly collect nectar or pollen and leave the flowers afterwards. Beetles may remain on or in a flower or inflorescence for hours and days. The dominant specialist pollinator groups are beetles followed by flies. Since beetles and flies are both sedentary pollinators, which often remain for many hours on one flower or inflorescence, pollen transfer to the stigmas is most effective at their arrival and pollen-uptake shortly before they leave. Protogynous dichogamy probably was the answer of basal angiosperms for a successful cross-pollination by sedentary pollinators like beetles or flies (Gottsberger 2016a)
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