Nutritious tissue in petals of annonaceae and its function in pollination by scarab beetles

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.