Nutrient intake simplified: correlations between pollen nutrients could enable rapid quality assessment by pollinators

Background and aimsThe (mutualistic) interaction between flowering plants and their insect pollinators has resulted in numerous co-adaptations in both plants and insects. It is still unclear, however, to what degree nutritional requirements of insects shaped the pollen nutrient profile of pollinator dependent plants. Pollen is chemically complex, and plants and pollinators have different demands for nutrients in pollen. The goal of our study was to assess how this conflict of interest over pollen chemistry may have affected pollen nutrient profiles.MethodsWe chemically analyzed and compared pollen nutrient profiles (i.e. amino acids, fatty acids and sterols) of 139 plant species. We investigated if nutrient profiles differed between plants with different levels of pollinator dependency. Here, we specifically focused on correlations between different nutrients. Such correlations indicate stable ratios between specific nutrients and would enable pollinators to rapidly obtain critical information on complex pollen nutrient profiles based on one or a few nutritional cues. Key resultsWe show that differences in pollen nutrient profiles, in particular protein content and the protein to lipid ratio, were better explained by the plants' pollinator dependence than phylogeny. We also revealed that e.g. correlations between amino acid were twice as common in insect pollinator dependent plants than in plants that do not depend on insect pollinators. ConclusionsOur findings suggest that plants depending on pollinators may not only invest more energy into producing pollen of higher protein content, but also ensure similar ratios between different nutrients to facilitate (rapid) assessment of pollen nutritional quality by their insect pollinators. Specific nutrient ratios have recently been shown to strongly affect pollinator foraging behavior and may therefore represent a good strategy for pollinator-dependent plants to increase pollinator visits and fidelity.