Are superior ovaries damaged by the bills of flower-visiting birds and does this preclude adaptation to bird pollinators?

Abstract

A biological trait may promote adaptation to particular pollinators, and this may be a major factor governing the variation of pollination systems among angiosperm taxa. For instance, one long-standing hypothesis is that compared with superior ovaries, inferior ovaries of angiosperm flowers may be protected from damage by visiting bird bills and, therefore, inferior ovaries may be associated more frequently with bird pollination. To test this hypothesis, we explored the pollination ecology of two Cerasus spp. (Rosaceae) with superior ovaries and investigated the potential damage to superior ovaries by bird bills, because such damage must be predicted by the hypothesis. To test whether there is a general relationship between ovary position and bird pollination, we examined published community-level studies involving bird pollination. Cerasus cerasoides is more inclined to bird pollination than C. conradinae in floral syndrome and pollination experiments, whereas damage to the ovaries or decline in fruit set after bird visitation was not detected in either species. The birds extended their tongues longer than the ovaries, demonstrating why the predicted damage was absent. Bird pollination was not less frequent in plants with superior ovaries in reviewed studies. Our findings did not support the prediction that superior ovaries are damaged by flower-visiting birds and overall the frequency of bird pollination varies with ovary position. These results highlight the complexity in predicting how floral traits affect plant adaptation to pollinators.