Can conflicting selection from pollinators and nectar-robbing antagonists drive adaptive pollen limitation? A conceptual model and empirical test

Pollen limitation is widespread, despite predictions that it shouldn’t be. We propose a novel mechanism generating pollen limitation: conflicting selection by pollinators and antagonists on pollinator attraction traits. We introduce a heuristic model demonstrating antagonist-induced adaptive pollen limitation, and present a field study illustrating its occurrence in a wild population. 

For antagonist-induced adaptive pollen limitation to occur, four criteria must be met: 1) correlated attraction of pollinators and antagonists, 2) greater response by antagonists than pollinators to altered investment in attraction traits, 3) reduced investment in pollinator attraction leading to pollen limitation, and 4) higher fitness for plants with reduced investment in pollinator attraction.

We surveyed nectar robbery and reproductive output for 109 Odontonema cuspidatum (Acanthaceae) plants in a pollen-limited population over two years and used experimental floral arrays to evaluate how flower...